FON241 Chapters 11 & 12

"Gla" Proteins

"Gla" proteins: Osteocalcin is a Gla protein that is secreted by osteoblasts and is associated with bone remodeling. Matrix Gla protein is located in the protein matrix of bone and is also found in cartilage, blood vessel walls, and other soft tissues. 18 The specific role of vitamin K in maintaining bone health is still under study, but there is growing evidence that vitamin K supplementation may increase bone density in people with osteoporosis and that diets rich in vitamin K are associated with reduced fracture rates.20 Matrix Gla protein also appears to play a role in preventing the calcification of arteries, which may reduce the risk for cardiovascular disease.

Trabecular Bone

(spongy or cancellous bone) A porous bone tissue that makes up only 20% of the skeleton and is found within the ends of the long bones, inside the spinal vertebrae, inside the flat bones (breastbone, ribs, and most bones of the skull), and inside the bones of the pelvis. makes up only 20% of the skeleton. It is found within the ends of the long bones (such as the bones of the arms and legs), and inside the spinal vertebrae, the breastbone, ribs, most bones of the skull, and the bones of the pelvis. Trabecular bone is sometimes referred to as spongy bone because to the naked eye it looks like a sponge, with no clear organization. The microscope reveals that trabecular bone is in fact aligned in a precise network of columns that protects the bone from stress. You can think of trabecular bone as the scaffolding of the inside of the bone that supports the outer cortical bone.

RDA for phosphorus

700 mg/day for adults in many foods and is found in high amounts in foods that contain protein. Milk, meats, and eggs are good sources Phosphorus is found in many processed foods as a food additive, where it enhances smoothness, binding, and moisture retention. In the form of phosphoric acid, it is also a major component of soft drinks. Phosphoric acid is added to soft drinks to give them a sharper, or more tart, flavor and to slow the growth of molds and bacteria

Gender and Genetics on Bone Health

80% of Americans with osteoporosis are women. There are three primary reasons for this: • Adult women have a lower absolute bone density than men. From birth through puberty, bone mass is the same in girls as in boys. But during puberty, bone mass increases more in boys, probably because of their prolonged period of accelerated growth. This means that when bone loss begins around age 40, women have less bone stored in their skeleton than men; thus, the loss of bone that occurs with aging causes osteoporosis sooner and to a greater extent in women than in men. • The hormonal changes that occur in men as they age do not have as dramatic an effect on bone density as those in women. • On average, women live longer than men, and because risk increases with age, more elderly women suffer from this disease. Secondary factors that are gender-specific include social pressure on girls to be thin. Extreme dieting is particularly harmful in adolescence, when bone mass is building and adequate consumption of calcium and other nutrients is critical. In many girls, weight loss causes both a loss of estrogen and reduced weight-bearing stress on the bones. In contrast, men experience pressure to "bulk up," typically by lifting weights. This puts healthful stress on the bones, resulting in increased density. Some individuals have a family history of osteoporosis, which increases their risk for this disease. Particularly at risk are Caucasian women of low body weight who have a firstdegree relative (mother or sister) with osteoporosis. Asian women are also at higher risk than other non-Caucasian groups.

T-Score

A comparison of an individual's bone density to the average peak bone density of a 30-year-old healthy adult. to assess the risk of fracture and determine whether or not the person has osteoporosis. If bone density is normal, the T-score will range between +1 and -1 of the value for a 30-year-old healthy adult. A negative T-score between -1 and -2.5 indicates low bone mass and an increased risk for fractures. If the T-score is more negative than -2.5, the person has osteoporosis

Calcium XU

A condition characterized by an abnormally low concentration of calcium in the blood A long-term repercussion of inadequate calcium intake is osteoporosis. But because other nutrients may be involved, we discuss this disease later in the chapter. Hypocalcemia is a term that describes an abnormally low level of calcium in the blood. Hypocalcemia does not result from consuming too little dietary calcium but is caused by various diseases. Some of the causes of hypocalcemia include kidney disease, vitamin D deficiency, and diseases that inhibit the production of PTH. Symptoms of hypocalcemia include muscle spasms and convulsions

Hypomagnesemia

A condition characterized by an abnormally low concentration of magnesium in the blood. results from magnesium deficiency. This condition may result from kidney disease, chronic diarrhea, or chronic alcohol abuse. Elderly people seem to be at particularly high risk of low dietary intakes of magnesium because they have a reduced appetite and blunted senses of taste and smell. In addition, the elderly face challenges related to shopping and preparing meals that contain foods high in magnesium, and their ability to absorb magnesium is reduced. Low blood calcium levels are a side effect of hypomagnesemia. Other symptoms of magnesium deficiency include muscle cramps, spasms or seizures, nausea, weakness, irritability, and confusion. Considering magnesium's role in bone formation, it is not surprising that long-term magnesium deficiency is associated with osteoporosis.Magnesium deficiency is also associated with many other chronic diseases, including heart disease, high blood pressure, and type 2 diabetes.

Calcium tetany

A condition in which muscles experience twitching and spasms due to inadequate blood calcium levels. assist in muscle contraction.Muscles are relaxed when calcium levels in the muscle are low. Contraction is stimulated by calcium flowing into the muscle cell; conversely,muscles relax when calcium is pumped back outside of the muscle cell. If calcium levels are inadequate, normal muscle contraction and relaxation is inhibited, and the person may suffer from twitching and spasms. This is referred to as calcium tetany

Hypercalcemia

A condition marked by an abnormally high concentration of calcium in the blood.

Hypermagnesemia

A condition marked by an abnormally high concentration of magnesium in the blood.

Cortical Bone

A dense bone tissue that makes up the outer surface of all bones, as well as the entirety of most small bones of the body. which is also called compact bone, is very dense. It comprises approximately 80% of the skeleton. The outer surface of all bones is cortical; plus many small bones of the body are made entirely of cortical bone

Osteoporosis

A disease characterized by low bone mass and deterioration of bone tissue, leading to increased bone fragility and fracture risk characterized by low bone mass and deterioration of bone tissue, leading to enhanced bone fragility and increase in fracture risk. The bone tissue of a person with osteoporosis is more porous and thinner than that of a person with healthy bone. These structural changes weaken the bone, leading to a significantly reduced ability of the bone to bear weight

Calcium Rigor

A failure of muscles to relax, which leads to a hardening or stiffening of the muscles; caused by high levels of blood calcium High levels of blood calcium can cause calcium rigor, which results in a failure of muscles to relax and leads to a hardening or stiffening of the muscles. These problems affect the function not only of skeletal muscles but also of heart muscle and can cause heart failure

Parathyroid Hormone

A hormone secreted by the parathyroid gland when blood calcium levels fall. It is also known as parathormone, and it increases blood calcium levels by stimulating the activation of vitamin D, increasing reabsorption of calcium from the kidneys, and stimulating osteoclasts to break down bone, which releases more calcium into the bloodstream. Also known as parathormone, PTH stimulates the activation of vitamin D. Together, PTH and vitamin D stimulate the kidneys to reabsorb calcium. They also stimulate osteoclasts to break down bone, releasing more calcium into the bloodstream. In addition, vitamin D increases the absorption of calcium from the intestines. Through these three mechanisms, blood calcium levels increase.

Calcitonin

A hormone secreted by the thyroid gland when blood calcium levels are too high.Calcitonin inhibits the actions of vitamin D, preventing reabsorption of calcium in the kidneys, limiting calcium absorption in the intestines, and inhibiting the osteoclasts from breaking down bone. When blood calcium levels are too high, the thyroid gland secretes a hormone called calcitonin, which inhibits the actions of vitamin D (Figure 11.5b). Thus, calcitonin prevents reabsorption of calcium in the kidneys, limits calcium absorption in the intestines, and inhibits the osteoclasts from breaking down bone.

Vitamin D XS

A person cannot get too much vitamin D from sun exposure, as the skin has the ability to limit its production. In addition, foods contain little natural vitamin D. Thus, the only way a person can consume too much vitamin D is through supplementation. Consuming too much vitamin D causes hypercalcemia, or high blood calcium concentrations. As discussed in the section on calcium, symptoms of hypercalcemia include weakness, loss of appetite, diarrhea, mental confusion, vomiting, excessive urine output, and extreme thirst.Hypercalcemia also leads to the formation of calcium deposits in soft tissues such as the kidney, liver, and heart. In addition, toxic levels of vitamin D lead to increased bone loss because calcium is then pulled from the bones and excreted more readily from the kidneys

Collagen

A protein that forms strong fibers in bone and connective tissue.

Milk Displacement effect study

A recent study of this problem tried to tease out which component of soft drinks may be detrimental to bone health.26 Four different carbonated soft drinks were tested: two that contained phosphoric acid and two that contained citric acid. Two of these drinks also contained caffeine and two did not. Calcium loss was measured as the amount of calcium excreted in the participants' urine. Interestingly, the results showed that the contents of soft drinks had little effect on calcium status. Although the two beverages that contained caffeine caused some loss of calcium during the 5-hour testing period, this effect of caffeine on calcium tends to taper off throughout the day and night, leading to no overall impact on calcium status over a 24-hour period. The researchers concluded that the most likely explanation for the link between soft drink consumption and poor bone health is the milk displacement effect; that is, soft drinks take the place of milk in our diets, depriving us of calcium and vitamin D.

Matrix Gla protein (MGP)

A vitamin K- dependent protein that is located in the protein matrix of bone and also found in cartilage, blood vessel walls, and other soft tissues

Osteocalcin

A vitamin K-dependent protein that is secreted by osteoblasts and is associated with bone turnover.

RDA and Good sources of Vitamin K

AI recommendations for adult men and adult women are 120 μg per day and 90 μg per day, respectively. No UL has been set. Only a few foods contribute substantially to our dietary intake of vitamin K. Green leafy vegetables including kale, spinach, collard greens, turnip greens, and lettuce are good sources, as are broccoli, Brussels sprouts, and cabbage.Vegetable oils, such as soybean oil and canola oil, are also good sources. The action of vitamin K is inhibited in laboratory animals given large doses of vitamin A and vitamin E; however, these vitamins do not appear to have the same effect on vitamin K in healthy humans

Describe the ages that our bones change

About 90% of a woman's bone density is built by 17 years of age, whereas the majority of a man's bone density is built during his twenties. However, male or female, before we reach the age of 30 years, our bodies have reached peak bone mass, and we can no longer significantly add to our bone density. In our thirties, our bone density remains relatively stable, but by age 40, it begins its irreversible decline. Although bones cannot increase in density after our twenties without medication, bone cells remain very active throughout adulthood, balancing the breakdown of older bone tissue and the formation of new bone In young healthy adults, the processes of bone resorption and formation are equal, so that just as much bone is broken down as is built, resulting in bone mass being maintained. Around 40 years of age, bone resorption begins to occur more rapidly than bone formation, and this imbalance results in an overall loss in bone density. Because this affects the vertebrae of the spine, people tend to lose height as they age. As discussed shortly, achieving a high peak bone mass through proper nutrition and exercise when one is young provides for a stronger skeleton before the loss of bone begins, and it can be protective against the debilitating effects of osteoporosis

RDA for Vitamin D

As with calcium, there is no RDA for vitamin D. Individuals living in very sunny climates relatively close to the Equator, such as the southern United States and Mexico, may synthesize enough vitamin D from the sun to meet their needs throughout the year—as long as they spend time outdoors. However, vitamin D synthesis from the sun is not possible during most of the winter months for people living in places located at a latitude of more than 40°N or more than 40°S. This is because at these latitudes, the sun never rises high enough in the sky during the winter to provide the direct sunlight needed. The 40°N latitude runs like a belt across the United States from northern Pennsylvania in the East to northern California in the West

Chapter 12

Blood and Immunity Blood transports to body cells virtually all the components necessary for life. No matter how much carbohydrate, fat, and protein we eat, we could not survive without healthy blood to transport these nutrients, and the oxygen to metabolize them, to our cells. In addition to transporting nutrients and oxygen, blood removes the waste products generated from metabolism so that they can be properly excreted. Our health and our ability to perform daily activities are compromised if the quantity and quality of our blood is diminished. Blood is actually a tissue, the only fluid tissue in the body. It is composed of four components (Figure 12.1). Erythrocytes, or red blood cells, are the cells that transport oxygen. Leukocytes, or white blood cells, are the key to our immune function and protect us from infection and illness. Platelets are cell fragments that assist in the formation of blood clots and help stop bleeding. Plasma is the fluid portion of the blood, and it is needed to maintain adequate blood volume so that blood can flow easily throughout the body. Certain micronutrients play important roles in the maintenance of blood health through their actions as coenzymes and cofactors and as regulators of oxygen transport. These nutrients are discussed in detail in the following section

Bone Growth

Bone growth and modeling begin during the early months of fetal life when the skeleton is forming and continue until early adulthood Bone remodeling predominates during adulthood; this process helps to maintain a healthy skeleton as one ages. bone growth, the size of bones increases. The first period of rapid bone growth is from birth to age 2, but growth continues in spurts throughout childhood and into adolescence.Most girls reach their adult height by age 14, and boys generally reach adult height by age 17.1 In the later decades of life, some loss in height usually occurs because of decreased bone density in the spine. Bone modeling is the process by which the shape of bones is determined, from the round "pebble" bones that make up the wrists, to the uniquely shaped bones of the face, to the long bones of the arms and legs. Even after bones stop growing in length, they can still increase in thickness if they are stressed by repetitive exercise such as weight training or by being overweight or obese Factors associated with a lower peak bone density include: late pubertal age in boys and late onset of menstruation in girls; inadequate calcium intake; low body weight; and physical inactivity during the pubertal years.

Functions Related to Metabolic Processes

Bone tissue acts as a storage reservoir for many minerals, including calcium, phosphorus, and fluoride. The body draws upon such deposits when these minerals are needed for various body processes; however, this can reduce bone mass. Most of the blood cells needed by our bodies are produced in the marrow of our bones.

RECAP

Bones are organs that contain metabolically active tissues composed primarily of minerals and a fibrous protein called collagen.Of the two types of bone,cortical bone is more dense and trabecular bone is more porous.Trabecular bone is also more sensitive to hormonal and nutritional factors and turns over more rapidly than cortical bone.The three types of bone activity are growth, modeling, and remodeling. Bones reach their peak bone mass by the late teenage years into the twenties; bone mass begins to decline around age

Bones

Bones need to be both strong and flexible so they can resist the compression, stretching, and twisting that occur throughout our daily activities. Fortunately, the composition of bone is ideally suited for its complex job: About 65% of bone tissue is made up of an assortment of minerals (mostly calcium and phosphorus) that provide hardness, but the remaining 35% is a mixture of organic substances that provide strength, durability, and flexibility. The most important of these substances is a fibrous protein called collagen. You might be surprised to learn that collagen fibers are actually stronger than steel fibers of similar size.Within bones, the minerals form tiny crystals (called hydroxyapatite) that cluster around the collagen fibers. This design enables bones to bear weight while responding to demands for movement. Bone strength and flexibility are also affected by its structure. If you examine a bone very closely, you will notice two distinct types of tissue (Figure 11.1): cortical bone and trabecular bone.

Functions related to structure and Support

Bones provide physical support for our organs and body segments. Bones protect our vital organs; for example, the rib cage protects our lungs, the skull protects our brains, and the vertebrae in the spine protect the spinal cord. Bones provide support for muscles that allow movement—muscles attach to bones via tendons, and we are able to move all of our joints because of the connections between our muscles and our bones. it actually contains many microscopic openings that serve as passageways for blood vessels and nerves.

RECAP Calcium

Calcium is the most abundant mineral in the body and a significant component of bones. It is also necessary for normal nerve and muscle function. Blood calcium is maintained within a very narrow range, and bone calcium is used to maintain normal blood calcium if dietary intake is inadequate.The AI for calcium is 1,000 mg per day for adults aged 19 to 50; the AI increases to 1,200 mg per day for older adults and to 1,300 mg per day for adolescents.Dairy products, canned fish with bones, and some green leafy vegetables are good sources of calcium.The most common long-term effect of inadequate calcium consumption is osteoporosis.

What are the main minerals and vitamins that make strong bones

Calcium is the most recognized nutrient associated with bone health; however, vitamins D and K, phosphorus, magnesium, and fluoride are also essential for strong bones, and the roles of other vitamins, minerals, and phytochemicals

exercise bad for bone?

Can exercise ever be detrimental to bone health? Yes, when the body is not receiving the nutrients it needs to rebuild the hydroxyapatite and collagen broken down in response to physical activity. Thus, active people who are chronically malnourished, including people who are impoverished and those who suffer from eating disorders, are at increased fracture risk.

Osteoclasts

Cells that erode the surface of bones by secreting enzymes and acids that dig grooves into the bone matrix.

Osteoblasts

Cells that prompt the formation of new bone matrix by laying down the collagen-containing component of bone that is then mineralized. New bone is formed through the action of cells called osteoblasts, or "bone builders" (see Figure 11.3b). These cells work to synthesize new bone matrix by laying down the collagen-containing organic component of bone.Within this substance, the hydroxyapatite crystallizes and packs together to create new bone where it is needed. In young healthy adults, the processes of bone resorption and formation

Tobacco, ETOH and Caffeine & Osteoporosis

Cigarette smoking is known to decrease bone density because of its effects on hormones that influence bone formation and resorption; thus, cigarette smoking increases the risk for osteoporosis and resulting fractures. Chronic alcoholism is detrimental to bone health and is associated with high rates of fractures. In contrast, numerous research studies have shown that bone density is higher in people who are moderate drinkers.22, 36-39 Despite the fact that moderate alcohol intake may be protective for bone, the dangers of alcohol abuse on overall health warrant caution in making any dietary recommendations. As is consistent with the alcohol recommendations related to heart disease, it is recommended that people should not start drinking if they are nondrinkers, and people who do drink should do so in moderation. That means no more than two drinks per day for men and one drink per day for women. Some researchers consider excess caffeine consumption to be detrimental to bone health. Caffeine is known to increase calcium loss in the urine, at least over a brief period of time. Younger people are able to compensate for this calcium loss by increasing absorption of calcium from the intestine. However, older people are not always capable of compensating to the same degree. Although the findings have been inconsistent, recent research now indicates that the relative amounts of caffeine and calcium consumed are critical factors affecting bone health. In general, elderly women do not appear to be at risk for increased bone loss if they consume adequate amounts of calcium and moderate amounts of caffeine (equal to less than 2 cups of coffee, 4 cups of tea, or six 12-oz cans of caffeine-containing soft drinks per day).40 Elderly women who consume high levels of caffeine (more than 3 cups of coffee per day) have much higher rates of bone loss than women with low intakes.41 Thus, it appears important to bone health that we moderate our caffeine intake and ensure adequate consumption of calcium in the diet. The excretion of sodium and calcium by the kidneys are linked; thus, higher intakes of sodium are known to increase the excretion of calcium in the urine The effect of high dietary protein intake on bone health is controversial.Whereas it is well established that high protein intakes increase calcium loss, protein is a critical component of bone tissue and is necessary for bone health. High protein intakes have been shown to have both a negative and positive impact on bone health. Similar to caffeine, the key to this mystery appears to be adequate calcium intake. Elderly individuals taking calcium and vitamin D supplements and eating higher-protein diets were able to significantly increase bone mass over a 3-year period, whereas those eating more protein and not taking supplements lost bone mass over this same time period. Low protein intakes are also associated with bone loss and increased risk for osteoporosis and fractures in elderly people. Thus, there appears to be an interaction between dietary calcium and protein, in that adequate amounts of each nutrient are needed together to support bone health. Of the many nutrients that help maintain bone health, calcium and vitamin D have received the most attention for their role in the prevention of osteoporosis. Research studies conducted with older individuals have shown that these individuals reduce their bone loss and fracture risk by taking calcium and vitamin D supplements.We know that if people do not consume enough of these two nutrients over a prolonged period of time, their bone density is lower and they have a higher risk of bone fractures. Because bones reach peak density when people are young, it is very important that children and adolescents consume a high-quality diet that contains the proper balance of calcium, vitamin D, protein, and other nutrients to allow for optimal bone growth. Young adults also require a proper balance of these nutrients to maintain bone mass. In older adults, diets rich in calcium and vitamin D can help minimize bone loss. In addition to their role in reducing the risk for heart disease and cancer, diets high in fruits and vegetables are also associated with improved bone health. This is most likely due to the fact that fruits and vegetables are good sources of nutrients that play a role in bone and collagen health, including magnesium, vitamin C, and vitamin K.

DEXA

Currently the most accurate tool for measuring bone density. is considered the most accurate assessment tool for measuring bone density. This method can measure the density of the bone mass over the entire body. Special software is also available that provides an estimation of percentage of body fat. The DXA procedure is simple, painless, noninvasive, and considered to be of minimal risk to humans. It takes only 15 to 30 minutes to complete. The person participating in the test remains fully clothed but must remove all jewelry or other metal objects. The participant lies quietly on a table, and bone density is assessed through the use of a very low level of x-ray (Figure 11.4). DXA is a very important tool to determine a person's risk for osteoporosis. It generates a bone density score that is compared to the average peak bone density of a 30-year-old healthy adult DXA tests are generally recommended for postmenopausal women because they are at highest risk for osteoporosis and fracture. Men and younger women may also be recommended for a DXA test if they have significant risk factors for osteoporosis Other technologies have been developed to measure bone density. The quantitative ultrasound technique uses sound waves to measure the density of bone in the heel, shin, and kneecap. Peripheral dual energy x-ray absorptiometry, or pDXA, is a form of DXA that measures bone density in the peripheral regions of our bodies, including the wrist, heel, or finger. Single energy x-ray absorptiometry is a method that measures bone density at the wrist or heel. These technologies are frequently used at health fairs because the machines are portable and provide scores faster than the traditional DXA

Food sources of calcium

Dairy products are among the most common sources of calcium in the U.S. diet. Skim milk, low-fat cheeses, and nonfat yogurt are excellent sources of calcium, and they are low in fat and calories (Figure 11.6). Ice cream, regular cheese, and whole milk also contain a relatively high amount of calcium, but these foods should be eaten in moderation because of their high saturated fat and energy content. Cottage cheese is one dairy product that is a relatively poor source of calcium, as the processing of this food removes a great deal of the calcium. One cup of low-fat cottage cheese contains approximately 150 mg of calcium, whereas the same serving of low-fat milk contains almost 300 mg. However, calcium-fortified cottage cheese has recently become available. One cup of calcium-fortified cottage cheese contains 400 mg of calcium. Other good sources of calcium are green leafy vegetables such as kale, collard greens, turnip greens, broccoli, cauliflower, green cabbage, brussels sprouts, and Chinese cabbage (bok choy). The bioavailability of the calcium in these vegetables is relatively high compared with spinach, as they contain low levels of oxalates.Many packaged foods are now available fortified with calcium.

Calcium

Dietary calcium is absorbed in the intestines via active transport and passive diffusion across the intestinal mucosal membrane. The majority of calcium consumed in the diet is absorbed from the duodenum, as this area of the small intestine is slightly more acidic than the more distal regions, and calcium absorption is enhanced in an acidic environment. Active transport of calcium is dependent upon the active form of vitamin D, or 1,25- dihydroxyvitamin D; most of the absorption of calcium at low to moderate intake levels is accounted for by this vitamin D-enhanced active transport. Passive diffusion of calcium across the intestinal mucosal membrane is a function of the calcium concentration gradient in the intestines, and this mechanism becomes a more important means of calcium absorption at high calcium intakes.5 Calcium is by far the most abundant major mineral in the body, comprising about 2% of our entire body weight

RECAP

Dual energy x-ray absorptiometry (DXA or DEXA) is the gold-standard measurement of bone mass. It is a simple, painless, and minimal-risk procedure.The results of a DXA include a T-score, which is a comparison of the person's bone density with that of a 30-year-old healthy adult. A T-score between 1 and 1 is normal; a score between 1 and 2.5 indicates poor bone density; and a score more negative than 2.5 indicates osteoporosis. Quantitative ultrasound, peripheral dual energy x-ray absorptiometry, and single energy x-ray absorptiometry are additional methods that can be used to measure bone density.

RECAP FL-

Fluoride is a trace mineral whose primary function is to support the health of teeth and bones.The AI for fluoride is 4 and 3 mg per day for adult men and women,respectively. Primary sources of fluoride are fluoridated dental products and fluoridated water. Fluoride toxicity causes fluorosis of the teeth and skeleton,and fluoride deficiency causes an increase in tooth decay fluorosis: A condition marked by staining and pitting of the teeth; caused by an abnormally high intake of fluoride.

Vitamin K XS

Healthy individuals there is no known side effect with both food and supplemental supply. Synthetic forms of Vitamin K can cause liver damage but this for is no longer used

RECAP MG

Magnesium is a major mineral found in fresh foods, including spinach, nuts, seeds, whole grains, and meats. Magnesium is important for bone health, energy production, and muscle function. The RDA for magnesium is a function of age and gender. Hypermagnesemia can result in diarrhea, muscle cramps, and cardiac arrest. Hypomagnesemia causes hypocalcemia, muscle cramps, spasms, and weakness. Magnesium deficiencies are also associated with osteoporosis, heart disease, high blood pressure, and type 2 diabetes.

nonmodifiable risk factors

Older age (elderly) Caucasian or Asian race History of fractures as an adult Family history of osteoporosis Gender (female) History of amenorrhea (failure to menstruate) in women with no recognizable cause

Functions of Calcium

One of the primary roles of calcium is to provide structure to the bones and teeth. About 99% of the calcium found in the body is stored in the hydroxyapatite crystals built up on the collagen foundation of bone. As noted earlier, the combination of crystals and collagen provides both the characteristic hardness of bone and the flexibility needed to support various activities. The remaining 1% of calcium in the body is found in the blood and soft tissues. Calcium is alkaline, or basic, and plays a critical role in assisting with acid-base balance.We cannot survive for long if our blood calcium level rises above or falls below a very narrow range; therefore, the body maintains the appropriate blood calcium level at all costs

RECAP Osteoporosis

Osteoporosis is a major disease of concern for elderly men and women in the United States.Osteoporosis increases the risk for fractures and premature death from subsequent illness. Factors that increase the risk for osteoporosis include genetics,being female,being of the Caucasian or Asian race, low levels of estrogen, cigarette smoking, alcohol abuse, sedentary lifestyle, and diets low in calcium and vitamin D. Medications are available for the prevention and treatment of osteoporosis.

Factors that determine synthesis of Vitamin D

Other factors influencing vitamin D synthesis include time of day, skin color, age, and obesity status: • More vitamin D can be synthesized during the time of day when the sun's rays are strongest, generally between 9 AM and 3 PM.Vitamin D synthesis is severely limited or may be nonexistent on overcast days. • Darker skin contains more melanin pigment, which reduces the penetration of sunlight. Thus, people with dark skin have a more difficult time synthesizing vitamin D from the sun than do light-skinned people. • People 65 years of age or older experience a fourfold decrease in their capacity to synthesize vitamin D from the sun.12, 13 • Obesity is associated with lower levels of circulating vitamin D, possibly because of lower bioavailability of cholecalciferol from adipose tissue, decreased exposure to sunlight due to limited mobility or time spent outdoors with skin exposed, and alterations in vitamin D metabolism in the liver. Wearing protective clothing and sunscreen (with an SPF greater than 8) limits sun exposure, so it is suggested that we expose our hands, face, and arms to the sun two to three times per week for a period of time that is one-third to one-half of the amount needed to get sunburned.16 This means that if you normally sunburn in 1 hour, you should expose yourself to the sun for 20 to 30 minutes two to three times per week to synthesize adequate amounts of vitamin D. Again, this guideline does not apply to people living in more northern climates during the winter months; they can only get enough vitamin D by consuming it in their diet. Because not everyone is able to get adequate sun exposure throughout the year, an AI has been established for vitamin D. For men and women aged 19 to 50 years, the AI for vitamin D is 5 μg per day. The AI for vitamin D for men and women aged 50 to 70 years is 10 μg per day, and the AI increases to 15 μg per day for adults over the age of 70 years. The UL for vitamin D is 50 μg per day for all age groups. Recent evidence suggests that the current AI for vitamin D is not sufficient to maintain optimal bone health and reduce the risks for diseases such as cancer; the controversy surrounding the current recommendations for vitamin D intake are discussed in more detail in the Nutrition Debate at the end of this chapter. When reading labels, you will see the amount of vitamin D expressed on food and supplement labels in units of either μg or IU. For conversion purposes, 1 μg of vitamin D is equal to 40 IU of vitamin D.

Phosphorus XU

Phosphorus deficiencies are rare but can occur in people who abuse alcohol, in premature infants, and in elderly people with poor diets. People with vitamin D deficiency, hyperparathyroidism (oversecretion of parathyroid hormone), and those who overuse antacids that bind with phosphorus may also have low blood phosphorus levels

RECAP PHOSPHORUS

Phosphorus is the major negatively charged electrolyte inside of the cell. It helps maintain fluid balance and bone health. It also assists in regulating chemical reactions, and it is a primary component of ATP, DNA, and RNA. Phosphorus is commonly found in high-protein foods. Excess phosphorus can lead to muscle spasms and convulsion, whereas phosphorus deficiencies are rare.

RDA for Mg

RDA for magnesium changes across age groups and genders. For adult men 19 to 30 years of age, the RDA for magnesium is 400 mg per day; the RDA increases to 420 mg per day for men 31 years of age and older. For adult women 19 to 30 years of age, the RDA for magnesium is 310 mg per day; this value increases to 320 mg per day for women 31 years of age and older. There is no UL for magnesium for food and water; the UL for magnesium from pharmacologic sources is 350 mg per day

Exercise and Bone Density

Regular exercise is highly protective against bone loss and osteoporosis. Athletes are consistently shown to have more dense bones than nonathletes, and regular participation in weight-bearing exercises such as walking, jogging, tennis, and strength training can help increase and maintain bone mass.When we exercise, our muscles contract and pull on our bones; this stresses bone tissue in a healthful way that stimulates increases in bone density. In addition, carrying weight during activities such as walking and jogging stresses the bones of the legs, hips, and lower back, resulting in a healthier bone mass in these areas. It appears that people of all ages can improve and maintain bone health by consistent physical activity.

Factors that enhance Vitamin D

Season—Most vitamin D is produced during summer months, particularly June and July Latitude—Locations closer to the Equator get more sunlight throughout the year Time of Day—Generally the hours between 9:00 AM and 3:00 PM (depending on latitude and time of year) Age—Younger Limited or no use of sunscreen Sunny weather Exposed skin Lighter skin pigmentation

Factors that inhibit Vitamin D

Season—Winter months (October through February) result in little or no vitamin D production Latitude—Regions that are north of 40°N and south of 40°S get inadequate sun Time of Day—Early morning, late afternoon, and evening hours Age—Older, due to reduced skin thickness with age Use of sunscreen with SPF 8 or greater Cloudy weather Protective clothing Darker skin pigmentation Glass and plastics—Windows or other barriers made of glass or plastic (such as Plexiglas) block the sun's rays Obesity—May negatively affect metabolism and storage of vitamin D

Modifiable Risk Factors

Smoking Low body weight Low calcium intake Low sun exposure Alcohol abuse History of amenorrhea (failure to menstruate) in women with inadequate nutrition Estrogen deficiency (females) Testosterone deficiency (males) Repeated falls Sedentary lifestyle

What is "hard" water?

The "harder" the water, the higher its content of magnesium. This large variability in the magnesium content of water makes it impossible to estimate how much our drinking water may contribute to the magnesium content of our diets

Bone Density

The degree of compactness of bone tissue, reflecting the strength of the bones. Peak bone density is the point at which a bone is strongest. the shape and size of bones do not significantly change after puberty, bone density, or the compactness of bones, continues to develop into early adulthood. Peak bone density is the point at which bones are strongest because they are at their highest density. Factors associated with a lower peak bone density include: late pubertal age in boys and late onset of menstruation in girls; inadequate calcium intake; low body weight; and physical inactivity during the pubertal years.2-4 About 90% of a woman's bone density is built by 17 years of age, whereas the majority of a man's bone density is built during his twenties. However, male or female, before we reach the age of 30 years, our bodies have reached peak bone mass, and we can no longer significantly add to our bone density. In our thirties, our bone density remains relatively stable, but by age 40, it begins its irreversible decline.

Bioavailability

The degree to which our bodies can absorb and utilize any given nutrient. refers to the degree to which the body can absorb and utilize any given nutrient. The bioavailability of calcium depends in part on a person's age and his or her need for calcium. For example, infants, children, and adolescents can absorb more than 60% of the calcium they consume, as calcium needs are very high during these stages of life. In addition, pregnant and lactating women can absorb about 50% of dietary calcium. In contrast, healthy young adults only absorb about 30% of the calcium consumed in the diet.When calcium needs are high, the body can generally increase its absorption of calcium from the small intestine. Although older adults have a high need for calcium, their ability to absorb calcium from the small intestine diminishes with age and can be as low as 25%. These variations in bioavailability and absorption capacity were taken into account when calcium recommendations were determined. The bioavailability of calcium also depends on how much calcium is consumed throughout the day or at any one time.When diets are generally high in calcium, absorption of calcium is reduced. In addition, the body cannot absorb more than 500 mg of calcium at any one time, and as the amount of calcium in a single meal or supplement goes up, the fraction that is absorbed goes down. This explains why it is critical to consume calcium-rich foods throughout the day rather than relying on a single high-dose supplement. Conversely, when dietary intake of calcium is low, the absorption of calcium is increased. Dietary factors can also affect the absorption of calcium. Binding factors such as phytates and oxalates occur naturally in some calcium-rich seeds, nuts, grains, and vegetables such as spinach and Swiss chard. Such factors bind to the calcium in these foods and prevent its absorption from the intestine. Additionally, consuming calcium at the same time as iron, zinc, magnesium, or phosphorus has the potential to interfere with the absorption and utilization of all of these minerals. Despite these potential interactions, the Institute of Medicine concluded that at the present time, there is not sufficient evidence to suggest that these interactions cause deficiencies of calcium or other minerals in healthy individuals people who are vulnerable to mineral deficiencies, such as the elderly or people consuming very low mineral intakes, and more research needs to be done in these populations to determine the health risks associated with interactions between calcium and other minerals. Finally, because vitamin D is necessary for the absorption of calcium, lack of vitamin D severely limits the bioavailability of calcium.We discuss this and other contributions of vitamin D to bone health shortly.

Phylloquinone

The form of vitamin K found in plants. absorption of phylloquinone occurs in the jejunum and ileum of the small intestine, and its absorption is dependent upon the normal flow of bile and pancreatic juice. Dietary fat enhances its absorption. The absorption of phylloquinone has been reported to be as low as 10% from boiled spinach eaten with butter to as high as 80% when given in its free form.18 It is transported through the lymph as a component of chylomicrons, and it circulates to the liver, where most of the vitamin K in the body is stored. Small amounts of vitamin K are also stored in adipose tissue and bone.1

menaquinone

The form of vitamin K produced by bacteria in the large intestine. absorption of menaquinone is not well understood, and its contribution to the maintenance of vitamin K status has been difficult to assess

Calcitriol

The primary active form of vitamin D in the body.

Resorption

The process by which the surface of bone is broken down by cells called osteoclasts. Bone is broken down through a process referred to as resorption (Figure 11.3a). During resorption, cells called osteoclasts erode the bone surface by secreting enzymes and acids that dig grooves into the bone matrix. Their ruffled surface also acts somewhat like a scrubbing brush to assist in the erosion process. One of the primary reasons the body regularly breaks down bone is to release calcium into the bloodstream The body also breaks down bone that is fractured and needs to be repaired. Resorption at the injury site smooths the rough edges created by the break. Bone may also be broken down in areas away from the fracture site to obtain the minerals that are needed to repair the damage. Regardless of the reason, once bone is broken down, the resulting products are transported into the bloodstream and utilized for various body functions.

Remodeling

The two-step process by which bone tissue is recycled; includes the breakdown of existing bone and the formation of new bone.

Food Sources of Vitamin D

There are many forms of vitamin D, but only two are active in the body. These two forms are vitamin D2, also called ergocalciferol, and vitamin D3, or cholecalciferol. Vitamin D2 is found exclusively in plant foods and may also be used in vitamin D supplements, whereas vitamin D3 is found in animal foods and is also the form of vitamin D we synthesize from the sun. Most foods naturally contain very little vitamin D, and those foods that do, such as cod liver oil and canned mackerel, are not typically consumed in the American diet. Thus, the primary source of vitamin D in the diet is from fortified foods such as milk (Figure 11.10). In the United States, milk is fortified with 10 μg of vitamin D per quart. Because earlier studies examining the actual vitamin D content of fortified milk found that the amount of vitamin D varied widely, the USDA now monitors dairies to make sure they meet the mandated vitamin D fortification guidelines. Other foods that contain high amounts of vitamin D include cod liver oil, fatty fish (such as salmon, mackerel, and sardines), and certain fortified cereals. Eggs, butter, some margarines, and liver contain small amounts of vitamin D, but one would have to eat very large amounts of these foods to consume enough vitamin D. In addition, because plants contain very little vitamin D, vegetarians who consume no dairy products need to obtain their vitamin D from sun exposure, fortified soy or cereal products, or supplements.

RDA for Calcium

There are no RDA values for calcium. The Adequate Intake (AI) value for adult men and women aged 19 to 50 years is 1,000 mg of calcium per day. For men and women older than 50 years of age, the AI increases to 1,200 mg of calcium per day. At 1,300 mg per day, the AI for boys and girls aged 15 to 18 years is even higher, reflecting their developing bone mass. The Upper Limit (UL) for calcium is 2,500 mg for all age groups.

RDA for Fl-

There is no RDA for fluoride. The AI for children aged 4 to 8 years is 1 mg per day; this value increases to 2 mg per day for boys and girls aged 9 to 13 years. The AI for boys and girls aged 14 to 18 years is 3 mg per day. The AI for adults is 4 mg per day for adult men and 3 mg per day for adult women. The UL for fluoride is 2.2 mg per day for children aged 4 to 8 years; the UL for everyone older than 8 years of age is 10 mg per day. tea is a good source of fluoride: one 8-oz cup provides about 20% to 25% of the AI.

RECAP Vitamin D

Vitamin D is a fat-soluble vitamin and a hormone. It can be made in the skin using energy from sunlight. Vitamin D regulates blood calcium levels and maintains bone health.The AI for vitamin D is 5 μg per day for adult men and women aged 19 to 50 years; the AI increases to 15 μg per day for adults over the age of 70 years.Foods contain little vitamin D, with fortified milk being the primary source. Vitamin D toxicity causes hypercalcemia.Vitamin D deficiency can result in osteoporosis; rickets is vitamin D deficiency in children,whereas osteomalacia describes vitamin D deficiency in adults.

RECAP VITAMIN K

Vitamin K is a fat-soluble vitamin and coenzyme that is important for blood clotting and bone metabolism.We obtain vitamin K largely from bacteria in the large intestine. The AIs for adult men and adult women are 120 μg per day and 90 μg per day, respectively. Green leafy vegetables and vegetable oils contain vitamin K.There are no known toxicity symptoms for vitamin K in healthy individuals.Vitamin K deficiency is rare and may lead to excessive bleeding.

Do we absorb all the mg of calcium into our diets

When you are selecting foods that are good sources of calcium, it is important to remember that we do not absorb 100% of the calcium contained in our foods.8 For example, although a serving of milk contains approximately 300 mg of calcium, we do not actually absorb this entire amount into our bodies

Absorption of Mag

ability of the small intestine to absorb magnesium is reduced when one consumes a diet that is extremely high in fiber and phytates, because these substances bind with magnesium. Even though seeds and nuts are relatively high in fiber, they are excellent sources of absorbable magnesium. Overall, our absorption of magnesium should be sufficient if we consume the recommended amount of fiber each day (20 to 35 g per day). In contrast, higher dietary protein intakes enhance the absorption and retention of magnesium

bone density as we age

bone density declines with age, low bone mass and osteoporosis are significant health concerns for both older men and women. The prevalence of osteoporosis and low bone mass are predicted to increase in the United States during the next 20 years, primarily because of increased longevity; as the U.S. population ages, more people will live long enough to suffer from osteoporosis. Hormonal changes that occur with aging have a significant impact on bone loss. Average bone loss approximates 0.3% to 0.5% per year after 30 years of age; however, during menopause in women, levels of the hormone estrogen decrease dramatically and cause bone loss to increase to about 3% per year during the first 5 years of menopause. Both estrogen and testosterone play important roles in promoting the deposition of new bone and limiting the activity of osteoclasts. Thus, men can also suffer from osteoporosis caused by age-related decreases in testosterone. In addition, reduced levels of physical activity in older people and a decreased ability to metabolize vitamin D with age exacerbate the hormone related bone loss.

Cholicalciferol/D3

cholecalciferol Vitamin D3, a form of vitamin D found in animal foods and the form we synthesize from the sun

Does Phosphoric Acid reduce bone growth/density?

consuming soft drinks is associated with reduced bone mass or an increased risk of fractures in both youth and adults. • consuming soft drinks in place of calcium-containing beverages, such as milk, leads to a deficient intake of calcium; • the acidic properties and high phosphorus content of soft drinks cause an increased loss of calcium because calcium is drawn from bone into the blood to neutralize the excess acid; and • the caffeine found in many soft drinks causes increased calcium loss through the urine.

Ergocalciferol (Vitamin D2)

ergocalciferol Vitamin D2, a form of vitamin D found exclusively in plant foods

Calcium in XS

excess calcium is simply excreted in feces. one concern with consuming too much calcium is that it can lead to various mineral imbalances because calcium interferes with the absorption of other minerals, including iron, zinc, and magnesium interference may only be of major concern in individuals vulnerable to mineral imbalance, such as the elderly and people who consume very low amounts of minerals in their diets. In some people, the formation of kidney stones is associated with high intakes of calcium, oxalates, protein, and vegetable fiber. Various diseases and metabolic disorders can alter the body's ability to regulate blood calcium. Hypercalcemia is a condition in which blood calcium levels reach abnormally high concentrations. Hypercalcemia can be caused by cancer and also by the overproduction of PTH Symptoms of hypercalcemia include fatigue, loss of appetite, constipation, and mental confusion and can lead to coma and possibly death. Hypercalcemia can also lead to an accumulation of calcium deposits in the soft tissues such as the liver and kidneys, causing failure of these organs.

Vitamin K

fat-soluble vitamin stored primarily in the liver, is actually a family of compounds known as quinones. Phylloquinone, which is the primary dietary form of vitamin K, is also the form found in plants; menaquinone is the animal form of vitamin K produced by bacteria in the large intestine

Vitamin D

fat-soluble vitamins in that excess amounts are stored in the liver and adipose tissue. But vitamin D is different from other nutrients in two ways. First, vitamin D does not always need to come from the diet. This is because the body can synthesize vitamin D using energy from exposure to sunlight. However, when we do not get enough sunlight, we must consume vitamin D in our diet. Second, in addition to being a nutrient, vitamin D is considered a hormone because it is made in one part of the body, yet regulates various activities in other parts of the body When the ultraviolet rays of the sun hit the skin, they react with 7-dehydrocholesterol. This cholesterol compound is converted into a precursor of vitamin D, cholecalciferol, which is also called provitamin D3. This inactive form is then converted to calcidiol in the liver, where it is stored.When needed, calcidiol travels to the kidneys where it is converted into calcitriol, which is considered the primary active form of vitamin D in the body. Calcitriol then circulates to various parts of the body, performing its many functions. Excess calcitriol can also be stored in adipose tissue for later use.

Female Athlete Triad

female athlete triad A condition characterized by the coexistence of three disorders in some athletic females: an eating disorder, amenorrhea, a condition characterized by the coexistence of three (or a triad of) clinical conditions in some physically active females: low energy availability (with or without eating disorders), amenorrhea, and osteoporosis. In the female athlete triad, inadequate food intake and regular strenuous exercise together result in a state of severe energy drain that causes a multitude of hormonal changes, including a reduction in estrogen production. These hormonal changes can result in the complete loss of menstrual function, called amenorrhea. Estrogen is important to maintaining healthy bone in women, so the loss of estrogen leads to osteoporosis in young women.and osteoporosis

Food sources of Mg

found in green leafy vegetables such as spinach. It is also found in wholegrains, seeds, and nuts. Other good food sources of magnesium include seafood, beans, and some dairy products. Refined and processed foods are low in magnesium. Trail Mix is a good source of Mag.

Fluoride XS

increases the protein content of tooth enamel, resulting in a condition called fluorosis. Because increased protein makes the enamel more porous, the teeth become stained and pitted (Figure 11.15). Teeth seem to be at highest risk for fluorosis during the first 8 years of life, when the permanent teeth are developing. To reduce the risk of fluorosis, children should not swallow oral care products that are meant for topical use only, and children under the age of 6 years should be supervised while using fluoridecontaining products. Mild fluorosis generally causes white patches on the teeth, and it has no effect on tooth function. Although moderate and severe fluorosis causes greater discoloration of the teeth, there appears to be no adverse effect on tooth function. Excess consumption of fluoride can also cause fluorosis of the skeleton.Mild skeletal fluorosis results in an increased bone mass and stiffness and pain in the joints.Moderate and severe skeletal fluorosis can be crippling

Tx for osteoporosis

individuals with osteoporosis are encouraged to consume adequate calcium and vitamin D and to exercise regularly. Studies have shown that the most effective exercise programs include weight-bearing exercises such as jogging, stair climbing, and resistance training. In addition, several medications are available: • Bisphosphonates, such as alendronate (brand name Fosamax), which decrease bone loss and can increase bone density and reduce the risk of spinal and nonspinal fractures • Selective estrogen receptor modulators, such as raloxifene (brand name Evista), which have an estrogen-like effect on bone tissue, slowing the rate of bone loss and prompting some increase in bone mass • Calcitonin (brand name Calcimar or Miacalcin), a pharmacologic preparation of the same thyroid hormone mentioned earlier, which can reduce the rate of bone loss • Hormone replacement therapy (HRT), which combines estrogen with a hormone called progestin, and can reduce bone loss, increase bone density, and reduce the risk of hip and spinal fractures

Fluoride

ionic form of the element fluorine, and it is also a trace mineral. About 99% of the fluoride in the body is stored in teeth and bones assists in the development and maintenance of teeth and bones. During the development of both baby teeth and permanent teeth, fluoride combines with calcium and phosphorus to form fluorohydroxyapatite, which is more resistant to destruction by acids and bacteria than hydroxyapatite. Even after all of our permanent teeth are in, treating them with fluoride, whether at the dentist's office or by using fluoridated toothpaste, gives them more protection against dental caries (cavities) than teeth that have not been treated. That's because fluoride enhances tooth mineralization, decreases and reverses tooth demineralization, and inhibits the metabolism of acid-producing bacteria that cause tooth decay. fluorohydroxyapatite: A mineral compound in human teeth that contains fluoride, calcium, and phosphorus and is more resistant to destruction by acids and bacteria than hydroxyapatite stimulates new bone growth, and it is currently being researched as a potential treatment for osteoporosis both alone and in combination with other medications.29-31While early results are promising, more research needs to be conducted to determine if fluoride is an effective treatment for osteoporosis.

Magnesium

major mineral. Approximately 50% of dietary magnesium is absorbed via both passive and active transport mechanisms; maximal absorption of magnesium occurs in the distal jejunum and ileum of the small intestine. The absorption of magnesium decreases with higher dietary intakes. The kidneys are responsible for the regulation of blood magnesium levels. Two forms of vitamin D, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, can enhance the intestinal absorption of magnesium to a limited extent. Excessive alcohol intake can cause magnesium depletion, and some diuretic medications can lead to increased excretion of magnesium in the urine. Dietary fiber and phytates decrease intestinal absorption of magnesium. Total body magnesium content is approximately 25 g. About 50% to 60% of the magnesium in the body is found in bones, with the rest located in soft tissues

What are poor sources of calcium

meats and fish are not good sources of calcium. An exception is canned fish with bones (for example, sardines or salmon), providing you eat the bones. Fruits (except dried figs) and nonfortified grain products are also poor sources of calcium

Magnesium XS

no known toxicity symptoms related to consuming excess magnesium in the diet. The toxicity symptoms that result from pharmacologic use of magnesium include diarrhea, nausea, and abdominal cramps. In extreme cases, large doses can result in acid-base imbalances, massive dehydration, cardiac arrest, and death. High blood magnesium, or hypermagnesemia, occurs in individuals with impaired kidney function who consume large amounts of nondietary magnesium, such as antacids. Side effects include impairment of nerve,muscle, and heart function.

Function of Mg

one of the minerals that make up the structure of bone. It is also important in the regulation of bone and mineral status. Specifically, magnesium influences the formation of hydroxyapatite crystals through its regulation of calcium balance and its interactions with vitamin D and parathyroid hormone. Magnesium is a critical cofactor for more than 300 enzyme systems.Magnesium is necessary for the production of ATP, and it plays an important role in DNA and protein synthesis and repair.Magnesium supplementation has been shown to improve insulin sensitivity, and there is epidemiological evidence that a high magnesium intake is associated with a decrease in the risk for colorectal cancer.27, 28 Magnesium supports normal vitamin D metabolism and action and is necessary for normal muscle contraction and blood clotting.

Osteomalacia

osteomalacia Vitamin D-deficiency disease in adults, in which bones become weak and prone to fractures

Phosphorus XS

people with kidney disease and those who take too many vitamin D supplements or too many phosphorus-containing antacids can suffer from high blood phosphorus levels; severely high levels of blood phosphorus can cause muscle spasms and convulsions.

Phosphorus

phosphorus is the major intracellular negatively charged electrolyte. In the body, phosphorus is most commonly found combined with oxygen in the form of phosphate (or PO4 3-. Phosphorus is an essential constituent of all cells and is found in both plants and animals

Function of Phosphorus

plays a critical role in bone formation, as it is a part of the mineral complex of bone. As discussed earlier in this chapter, calcium and phosphorus crystallize to form hydroxyapatite crystals, which provide the hardness of bone. About 85% of the body's phosphorus is stored in bones, with the rest stored in soft tissues such as muscles and organs. phosphorus in maintaining proper fluid balance was discussed in detail in Chapter 9. Phosphorus is also a primary component of several energy molecules including adenosine triphosphate (ATP). It helps activate and deactivate enzymes, is a component of the genetic material in the nuclei of the cells (including both DNA and RNA), and is a component of cell membranes and lipoproteins.

Vitamin D XU

primary deficiency associated with inadequate vitamin D is loss of bone mass. In fact, when vitamin D levels are inadequate, the intestines can only absorb 10% to 15% of the calcium consumed.Vitamin D deficiencies occur most often in individuals who have diseases that cause intestinal malabsorption of fat and thus the fat-soluble vitamins. People with liver disease, kidney disease, Crohn's disease, celiac disease, cystic fibrosis, or Whipple disease suffer from vitamin D deficiencies and require supplements. Vitamin D-deficiency disease in children, called rickets, results in inadequate mineralization or demineralization of the skeleton. The symptoms of rickets include deformities of the skeleton such as bowed legs, knocked knees, and an enlarged head and rib cage (Figure 11.11). Rickets is not common in the United States because of fortification of milk products with vitamin D, but children with illnesses that cause fat malabsorption or who drink no milk and get limited sun exposure are at increased risk. A recent review of reported cases of rickets among children in the United States found that approximately 83% of children with rickets were African American, and 96% were breast-fed.17 Breast milk contains very little vitamin D, and fewer than 5% of the breast-fed children were reported to have received vitamin D supplementation. Thus, rickets appears to occur more commonly in children with darker skin, as their need for adequate sun exposure is higher than that for light-skinned children, and in breast-fed children who do not receive adequate vitamin D supplementation. In addition, rickets is still a significant nutritional problem for children outside of the United States. Vitamin D-deficiency disease in adults is called osteomalacia, a term meaning "soft bones."With osteomalacia, bones become weak and prone to malformations and fractures. Osteoporosis, discussed in detail later in this chapter, can also result from a vitamin D deficiency. Vitamin D deficiencies have recently been found to be more common among American adults than previously thought. This may be partly due to jobs and lifestyle choices that keep people indoors for most of the day. Not surprisingly, the population at greatest risk is older institutionalized individuals who get little or no sun exposure. Various medications can also alter the metabolism and activity of vitamin D. For instance, glucocorticoids, which are medications used to reduce inflammation, can cause bone loss by inhibiting the ability to absorb calcium through the actions of vitamin D. Antiseizure medications such as phenobarbital and Dilantin alter vitamin D metabolism. Thus, people who are taking such medications may need to increase their vitamin D intake.

Primary Function of Vitamin K

primary function of vitamin K is to serve as a coenzyme during the production of specific proteins that play important roles in the coagulation of blood and in bone metabolism.

Fl XU

primary result of fluoride deficiency is dental caries. Adequate fluoride intake appears necessary at an early age and throughout adult life to reduce the risk for tooth decay. Inadequate fluoride intake may also be associated with lower bone density, but there is not enough research currently available to support the widespread use of fluoride to prevent osteoporosis.

Vitamin K XU

reduced ability to form blood clots, leading to excessive bleeding; however, primary vitamin K deficiency is rare in humans. People with diseases that cause malabsorption of fat, such as celiac disease, Crohn's disease, and cystic fibrosis, can suffer secondarily from a deficiency of vitamin K. Long-term use of antibiotics, which typically reduce bacterial populations in the colon, combined with limited dietary intake of vitamin K-rich food sources can also lead to vitamin K deficiency. Newborns are typically given an injection of vitamin K at birth, as they lack the intestinal bacteria necessary to produce this nutrient. The impact of vitamin K deficiency on bone health is controversial. A recent study of vitamin K intake and risk of hip fractures found that women who consumed the least amount of vitamin K had a higher risk of bone fractures than women who consumed relatively more vitamin K.2

Rickets

rickets Vitamin D-deficiency disease in children. Symptoms include deformities of the skeleton such as bowed legs and knocked knees.

What are the other roles of calcium

roles of calcium include the maintenance of healthy blood pressure, the initiation of blood clotting, and the regulation of various hormones and enzymes.

The range of Calcium

the body must maintain blood calcium levels within a very narrow range. Thus, when an individual does not consume or absorb enough calcium from the diet, osteoclasts erode bone so that calcium can be released into the blood. To maintain healthy bone density, we need to consume and absorb enough calcium to balance the calcium taken from our bones. Calcium is also critical for the normal transmission of nerve impulses. Calcium flows into nerve cells and stimulates the release of molecules called neurotransmitters, which transfer the nerve impulses from one nerve cell (neuron) to another.Without adequate calcium, the nerves' ability to transmit messages is inhibited. Not surprisingly, when blood calcium levels fall dangerously low, a person can experience convulsions.

Where to fractures take place the most?

the hip and the vertebrae of the spinal column are common sites of osteoporosis; thus, it is not surprising that osteoporosis is the single most important cause of fractures of the hip and spine in older adults 20% of older adults who suffer a hip fracture die within 1 year after the fracture occurs, and death rates are higher for men than for women. Osteoporosis of the spine also causes a generalized loss of height and can be disfiguring: Gradual compression fractures in the vertebrae of the upper back lead to a shortening and hunching of the spine called kyphosis, commonly referred to as dowager's hump. one in three women and one in five men over the age of 50 are affected, and in the United States, more than 10 million people have been diagnosed. Factors that influence the risk for osteoporosis include age, gender, genetics, nutrition, and physical activity

Functions of Vitamin D

vitamin D, PTH, and calcitonin all work together continuously to regulate blood calcium levels, which in turn maintains bone health. They do this by regulating the absorption of calcium and phosphorus from the small intestine, causing more to be absorbed when the need for them is higher and less when the need is lower. They also decrease or increase blood calcium levels by signaling the kidneys to excrete more or less calcium in the urine. Finally, vitamin D works with PTH to stimulate osteoclasts to break down bone when calcium is needed elsewhere in the body. Vitamin D is also necessary for the normal calcification of bone; this means it assists the process by which minerals such as calcium and phosphorus are crystallized play a role in decreasing the formation of some cancerous tumors, as it can prevent certain types of cells from growing out of control. Similar to vitamin A, vitamin D appears to play a role in cell differentiation in various tissues.

Bone Modeling

• Determines bone shape • Begins in the womb • Continues until early adulthood

Bone Growth

• Determines bone size • Begins in the womb • Continues until early adulthood

Bone Remodeling

• Maintains integrity of bone• Replaces old bone with new bone to maintain mineral balance • Involves bone resorption and formation • Occurs predominantly during adulthood Remodeling is also used to repair fractures and to strengthen bone regions that are exposed to higher physical stress. The process of remodeling involves two steps: resorption and formation.