NTDT 200 - Chapter 13: Major Minerals

potassium sources

found in a wide range of minimally processed foods, particularly fruits and vegetables.

minerals in acid-base balance

phosphorous, magnesium, potassium, and calcium.

phosphorus intake

phosphorus deficiency is rare, in part because the mineral is found in most protein rich foods, such as meats and diary, and because many food additives also contain phosphorus. In fact, there is some concern that Americans may be chronically over consuming phosphorus, a potential problem considering that increased blood levels of the mineral have been associated with cardiovascular and other types of chronic disease, particularly in people with kidney disease.

minerals in energy metabolism

phosphorus, magnesium, iron, and copper.

phosphorus functions

plays a critical role in bone health and is an essential component of bone and cartilage, phospholipids, DNA, and RNA. It is also involved in energy metabolism, and a multitude of enzymes and other proteins depend upon phosphorus to regulate their activity. Phosphorus is important in the maintenance of proper acid-base balance in the body.

osmosis

process that moves water from outside to inside cells and vice versa. The direction of water movement depends on the concentration of dissolved substances in intracellular and extracellular fluids called solutes. Some of the most important solutes are the electrolytes, sodium, potassium, and chloride. Water moves across a membrane toward areas where there is a greater concentration of solutes, and, therefore a lower concentration of water molecules.

processing foods and mineral content

processing and refining foods can sometimes boost, but more often reduce, mineral content. For instance, when cereal grains are refined and milled, they lose a portion of many important minerals and only iron is added back through enrichment. To maximize mineral intake then, individuals should emphasize eating whole, unprocessed foods. And although cooking itself does not degrade or break down minerals, boiling food can result in the leaching (or loss) of a varying amount of minerals into the cooking water - thus the recommendation to use cooking water in sauces or soups, whenever possible.

hypercalcemia

rare in healthy people; caused by excessive calcium intake that leads to excess calcium in the blood.

osteopenia

reduced bone mass, or bone density, along with reduced mineral content.

DASH diet servings

1. grains (6-8 daily servings): 1 slice of bread, 1/2 cup cooked rice/pasta/cereal, 1 oz dry cereal. 2. lean meats, poultry, and fish (6 or fewer daily servings): 1 oz cooked meat/poultry/fish, 1 egg. 3. fruits (4-5 daily servings): 1 medium fruit, 1/4 cup dried fruit. 1/2 cup fresh/frozen/canned fruit, 1/2 cup fruit juice. 4. nuts, seeds, and legumes (4-5 serving per week): 1/3 cup/ 1/2 oz nuts, 2 tbsp peanut butter, 2 tbsp or 1/2 oz seeds, 1/2 cup cooked legumes. 5. vegetables (4-5 daily servings): 1 cup raw leafy vegetables, 1/2 cup cut-up cooked/raw vegetables, 1/2 cup vegetable juice. 6. fats and oils (2-3 daily servings): 1 tsp soft margarine, 1 tsp vegetable oil, 1 tbsp mayonnaise, 2 tbsp salad dressing. 7. fat-free or low-fat milk products (2-3 daily servings): 1 cup milk/ yogurt, 1 1/2 oz cheese. 8. sweets and added sugars (5 or fewer servings per week): 1 tbsp sugar, 1 tbsp jelly/jam, 1/2 cup sorbet/gelatin, 1 cup lemonade.

roles of water in the body

1. it helps regulate body temperature within a very narrow range, which is important because even slight variations can affect body functions and damage organs. The temperature of water rises slowly, so, because there is so much water in your body, it provides an important "brake" for unwanted body temperature fluctuations. 2. water transports nutrients and oxygen to tissues in your body. It is also present in mucus and salivary juices of the digestive system, which help to move food through the digestive tract. 3. Water also lubricates joints and mucous membranes in our noses, eyes, and the GI tract. 4. since water can't be compressed, it helps to protect delicate tissues like the brain, eyes, and spinal cord against injury and shock. 5. water acts as a solvent. 6. water also helps to remove waste from the body via urination, perspiration, and bowel movements.

What is the current average US sodium consumption?

3,400 milligrams per day, but that number varies by age and sex. We get most of our sodium from processed and restaurant foods, with only about 10% coming from salt added at the table and another 10% coming from "fresh" unprocessed foods.

How much water do we lose through respiration?

We lose about 350 mL (1 1/2 cups) of water each day through respiration. When we breathe, water evaporates from the lungs and the skin. How much water we lose while respiring depends on the air temperature and our body temperature, how active we are, how humid the air is, and how big our bodies are. The more we respire - for instance, when we exercise and breathe hard - the more water we lose.

hyponatremia

a condition in which sodium levels in the blood become low because of increased blood volume. The symptoms of hyponatremia sometimes mimic the symptoms of dehydration, or deficiency of water. To distinguish between hyponatremia and dehydration, some city marathons now test blood sodium concentrations in unwell athletes before deciding whether to treat for dehydration (which might involve saline) or for hyponatremia (which involves a hypertonic, or high-sodium solution). Other marathons have scales available so that runners can weigh themselves; weight gain from excess fluid during a marathon is a common sign of hyponatremia.

solvent

a liquid substance that is capable of dissolving another substance, and participates in the body's biochemical reactions. For instance, without water our bodies can't break down proteins, carbohydrates, or fats to extract energy.

sulfur

a mineral that occurs in our diet as a component of other compounds. It is present in the vitamins thiamin and biotin; and it is present in two of the amino acids (cysteine and methionine) that are found in our body's proteins, as well as those that we eat. When we need to synthesize sulfur-containing compounds, the ultimate source of that sulfur is almost invariantly one of those amino acids. Because sulfur is a component of proteins, deficiency is virtually unknown. Toxicity is also rare because the body can excrete excess sulfur in urine.

roles of calcium, phosphorus, and magnesium

accounting for 98% of the body's mineral content by weight, calcium, phosphorus, and magnesium play key roles in the development and maintenance of bone and other calcified tissues. The skeleton is not inert, it is an active organ, made up of tissue and cell in a continual state of activity; calcium and phosphate are the main components of this system. Magnesium contribute to the strength and firmness of bones and makes teeth harder; magnesium is essential of absorption and metabolism of calcium. Crystals of bone mineral are deposited on a matrix of protein which is comprised primarily of collagen.

calcium supplementation

although it is tempting to think that supplements are a "sure thing" to confirm that you are getting enough calcium, supplementation can potentially push intake to higher-than-recommended levels, especially when added to daily food sources that are fortified with calcium. Studies show that more than 60% of women older than 60 years take calcium supplements, which could push their intake close to the UL. High dietary intakes may cause constipation and can interfere with iron absorption.

magnesium and the adult body

an adult body contains about 25 g of magnesium, most of it - about 50-60% - is found in the bones; the rest is in the cells and fluids in the body.

functions of sodium

an essential nutrient, sodium is the primary electrolyte responsible for maintaining fluid balance between cells and throughout the body. It plays a crucial role in regulating blood pressure, and is the major positively charged ion in the active transport of a number of nutrients. For instance, sodium is required to move glucose and amino acids into cells. Its role in the active transport of a variety of compounds also means that it is indirectly needed to maintain the body's acid-base balance and a stable pH.

magnesium intake

approximately 60% of American adults do not consume the recommended intake level of magnesium, but outright deficiency symptoms are rare, because the kidneys limit excretion when intake is low and the body many absorb more. However, low intakes of magnesium are a risk factor for osteoporosis. Marginal or moderate magnesium deficiencies may also increase the risk of atherosclerosis, cancer, diabetes, and hypertension. There is ongoing research about the role of magnesium in preventing and managing these disorders. Excess consumption from the diet is also rare, but toxicity can occur from supplement misuse.

water and the human body

approximately 60-70% of our bodies are made up of water, but the ratio of water to other substances in our tissues varies, depending primarily on the ratio of fat mass to lean body mass (body composition), which is strongly influenced by age and sex. The body of an adult man is approximately 60% water, and an adult woman is about 55% water - with water composing about 75% of the mass of muscle, and 15% of adipose tissue mass. As people age, they typically lose muscle mass and gain fat, which will decrease the percent of body mass that is water. Organs have different water percentages too: the brain and heart are made of approximately 73% water, but bone is only about 10% water. Approximately 2/3 of the water in our bodies is intracellular, or found within cells; the rest is extracellular, found outside cells, primarily in the blood and the fluid that surround our cells (interstitial fluid).

How much of our body weight do minerals make up?

around 4%, with major minerals composing more and trace minerals composing less; however, both play equally critical roles in human health.

How much water do you need?

because people vary so much in terms of how much water they need each day, there is not an established Recommended Daily Allowance (RDA) or Estimated Average Requirement (EAR) for water. However, in 2004, the Institute of Medicine set an AI value of 3.7 liters (about 15 1/2 cups) of total water intake per day for men living in temperate climates and 2.7 liters (about 11 1/2 cups) per day for women living in temperate climates.

Why is calcium tightly regulated?

because so many critical body functions depend on calcium, its concentration in the blood is tightly regulated so that it remains nearly constant regardless of dietary calcium intake. When calcium in blood falls even slightly, it will be released from bone to maintain steady blood calcium levels.

How does the body achieve water balance?

by attempting to ensure that the amount of water we consume in food and drinks and the amount we produce through metabolism equals the amount of water we excrete. The kidneys conserve water by reducing urine volume when necessary, and they excrete excess water by increasing the volume of urine and making it more dilute when we have excess fluid.

What is the best way to get essential minerals?

by eating an adequate, varied, and balanced diet.

How does the body maintain fluid balance?

by moving electrolytes to where more water is needed. However, the level of electrolytes in your body can become too low or too high. That can happen when the amount of water in your body changes, upsetting fluid balance and causing dehydration or even overhydration.

minerals in bone structure and health

calcium, magnesium, and phosphorus.

hypokalemia

caused by a serious potassium deficiency, such as when there is excessive fluid loss through vomiting, diarrhea, use of diuretics, or kidney disorder; a disorder characterized by fatigue, muscle weakness, abnormal heart rhythms, increased calcium excretion, and reduced insulin production.

consumption patterns for water

current consumption patterns indicate that fluids provide about 80% of our total water intake, with plain water making up about 45% of those fluids and other beverages making up the rest. Therefore, the AI for fluids is 3.0 liters for men and 2.2 liters for women. Both tap and bottled water are considered safe to drink; the EPA regulates the former, while the FDA regulates the latter, and they have similar standards. The body also produces a small amount of water as a byproduct of metabolic reactions, which also helps meet our total water needs.

dehydration

deficiency of water. There are a variety of symptoms associated with dehydration, including nausea, dizziness, elevated temperature, and concentrated urine. Dehydration is typically cause by excessive sweating, excessive urine output (because of diuretic use or uncontrolled diabetes), fever, vomiting, or diarrhea. It is also a widespread problem in developing countries, where safe, drinkable water can be hard to find. Although 70% of Earth is composed of water, only 3% of it is drinkable.

hypertension

defined as having blood pressure of at least 140/90 mmHg; increased risk comes from the overconsumption of sodium. On average, blood pressure rises progressively with intakes of sodium above 2,300 milligrams per day. Hypertension is a major risk factor for cardiovascular disease and stroke.

DASH diet

emphasizes "fruits, vegetables, whole grains, low-fat dairy products, poultry, fish, and nuts;" recommended by the American Heart Association and the American College of Cardiology to help Americans reach lower sodium goals as well as to boost the intake of potassium, calcium, and magnesium. The DASH eating plan has been found to be an effective approach in helping lower blood pressure and reduce the risk of heart disease.

potassium toxicity

extremely rare and would likely only result from dietary supplement misuse. However, despite the prevalence of low intake, multivitamin mineral supplements in the US contain only about 2% of the AI for potassium because of the risk of side effects, in particular low heart rate and abnormal heart rhythm. Potassium supplementation may sometimes be warranted, but should be prescribed and monitored by a healthcare provider because of potential side effects.

What does reducing sodium intake to the DGA do?

has been demonstrated to reduce the risk of hypertension in at-risk groups. However, there is currently no evidence that it actually reduces the risk of heart disease and stroke. In fact, there is some evidence that low sodium intake (less than 2,300 milligrams) may actually be associated with adverse health effects in some subgroups.

mineral absorption

humans absorb most minerals in the small intestine, and both active and passive processes transport them into the blood for distribution and use throughout the body.

risk factors for osteoporosis

include advanced age as well as a history of inactivity, smoking, excess alcohol consumption, and a family history of osteoporosis. To reduce their risk, individuals should maintain a healthy diet with adequate intake of calcium and vitamins D and K throughout life. Vitamin K is needed for the functioning of several proteins that are involve din regulating bone formation. Some studies have found that the risk of bone fractures decrease as intake of vitamin K increases. It is also important to participate in regular weight-bearing exercises, such as walking, running, or tennis, as well as perform resistance exercises to maintain bone health and reduce risk of osteoporosis.

cofactors

inorganic substances that facilitate and catalyze chemical reactions.

Why is calcium from food better absorbed than calcium from supplements?

likely due to improved absorption with meals and the tendency of people to consume smaller amounts of calcium more frequently, which likely improves absorption efficiency.

functions of magnesium

magnesium is a cofactor in more than 300 chemical reactions in the body. Magnesium plays a role in the transport of ions across the cell membrane, a process that is important to muscle contraction, nerve impulse conduction, and maintaining the rhythm of the heart. Magnesium is involved in extracting energy carbohydrates, fats, and protein, as well as using that energy to perform work; and it plays a role in protein production. Magnesium is also necessary to convert vitamin D into its active form (calcitrol) to increase calcium absorption and thus plays and important role in bone health.

minerals in nerve and muscle function

magnesium, potassium, calcium, and sodium.

functions of minerals

many work in partnership with other minerals. They often function as parts of enzymes and hormones, participate in chemical reactions, transmit nerve impulses, maintain fluid balance, and support the immune system. They can also work with enzymes as cofactors. Like many of the B vitamins, minerals also play roles in energy metabolism, the chemical reactions that release the energy from food. Minerals also help build and maintain structural components in the body such as bones, teeth, cell membranes, and connective tissue.

potassium deficiency

milder forms, which are common in the US as most Americans only get about half the potassium they should, can increase the risk of hypertension, stroke, heart attacks, and other health problems.

calcium-rich food

milk, yogurt, cheese, some legumes, and certain dark-green leafy vegetables (Chinese cabbage, kale, and broccoli). Because these vegetables are low in oxalates the bioavailability of calcium is high: about 50% is absorbed. In contrast, through spinach is high in calcium, it is also high in oxalates that bind to calcium and inhibit its absorption. Consequently, the bioavailability of calcium in spinach is low: only about 5% is absorbed. Calcium is also added to some grains, juices, tofu, and cereals. Milk, an excellent source of calcium, is usually also fortified with vitamin D, which works with calcium to promote bone health.

mineral absorption and bioavailability

mineral absorption is influenced by their bioavailability, the ability of nutrients to be absorbed and utilized in the body, which itself is affected by various factors. One such factor is nutritional status. When a person is deficient in a mineral or the needs for that mineral have increased, the absorption and bioavailability of that mineral tends to increase. For instance, during pregnancy, a woman's body absorbs calcium more efficiently than usual. Likewise, people absorb less of minerals if they already get enough. It is important to note, however, that although absorption of minerals slows during overconsumption, it doesn't stop - so it is still possible to consume excess, or even toxic, amounts of minerals. When mineral levels in the body increase, the excess is typically excreted in the urine. Minerals can also complete with each other for absorption; for example, excess iron consumption from supplements can interfere with zinc absorption. Finally, the presence of certain vitamins can also affect bioavailability; vitamin D, for instance, actually boosts absorption of calcium and phosphorus.

minerals in plants

minerals in plants reflect the mineral content of the soil in which they are grown. Because of this, mineral content can vary dramatically depending on the region in which the plants are grown and farming practices used to grow them. Animal foods are typically a better source of minerals, in part because animals eat plants and concentrate their nutrients. As a result, vegans and vegetarians may be at a higher risk for deficiencies in the minerals that are typically concentrated in animal foods, such as calcium, iron, and zinc.

bone remodeling

necessary not only to maintain blood calcium levels, but it is also required during bone growth in the young, to allow bone to adapt to strain, and to repair the microscopic damage that occurs daily.

Can minerals be synthesized by the body?

no, they cannot; they must be ingested through the diet. They have a narrow range of safe intake, so there's often a fine line between getting too little and too much of a mineral. Intake of minerals above the recommended levels can also have other adverse effects including gastrointestinal problems. With the possible exception of sodium, we are at greatest risk of consuming too much of a particular mineral when we take dietary supplements, as overconsumption rarely occurs through food alone.

Why do we need to drink fluids?

one of the reasons we need to drink fluids is because we lose water throughout the day and our bodies can't store extra to fill the void.

minerals in fluid balance

sodium, chloride, and potassium.

major minerals

sometimes called "macro" minerals; have a daily requirement of 100 milligrams or more. Include sodium (100g), potassium (120g), chloride (82g), calcium (1,200g), magnesium (25g), phosphorus (630g), and sulfur (140g). Only calcium and phosphorous, which are found predominantly in our bones and teeth, are present in our body in amounts that exceed a pound.

trace minerals

sometimes called "micro" minerals; have a daily requirement of less than 100 milligrams. Include iron, zinc, copper, iodine, selenium, molybdenum, fluoride, manganese, and chromium.

minerals that are components of body proteins

sulfur.

tap water and essential minerals

tap water can be a source of some essential minerals: "hard" water, which is more commonly found in the US typically contains more calcium and magnesium, whereas "soft" water contains more sodium, which is added in proportion to the "hardness" of the water source. Mineral content in tap water, whether hard or soft, can vary regionally and according to treatment methods. Tap water may contribute as little as 6% of overall intake of calcium or magnesium, but can add around 30% with consumption of approximately two liters a day in some areas. Consuming two liters of "soft" tap water generally contributes rather insignificant amounts of sodium to overall intake, but in some areas it can add up to almost half of the total daily sodium recommendations. To find what minerals are present in significant amounts in your water, refer to the annual municipal water report for the area in which you live.

calcium intake

the Institute of Medicine has set the AI for calcium at 1,000 milligrams per day for men and women aged 19-50 years; the Tolerable Upper Level (UL) is set at 2,500 milligrams.

sodium intake recommendations

the Institute of Medicine has set the AI level for sodium at 1,500 milligrams per day for men and women aged 19 to 50 years, noting that needs can be increased in endurance athletes who perspire a lot and people who work in hot and humid conditions. The UL for adults 19 years and older is 2,300 milligrams per day. The DGAs recommend limiting sodium intake to 2,300 milligrams per day but advise all adults 51 years and older, all African Americans older than two years, and all individuals with diabetes, high blood pressure, or chronic kidney disease, to consume no more than 1,500 milligrams per day. This high-risk group comprises more than half of the US population.

antidiuretic hormone (ADH)

the hypothalamus in the brain detects increased concentrations of solutes in blood; it also receives signals when blood volume drops. In response, the hypothalamus stimulates the pituitary to release ADH into the blood. ADH tells the kidneys to conserve water to bring more water back into the bloodstream, which will also lower the concentration of solutes. When the brain detects that water volume has increased again, it decreases the production of ADH so that the kidneys stop conserving water. Without ADH, urine becomes very dilute.

calcium homeostasis

the mechanism by which the body maintain calcium levels. When blood calcium levels fall, the parathyroid gland releases parathyroid hormone (PTH), which stimulates the production of the active form of vitamin D (calcitrol) and thereby increases calcium absorption from the intestine. PTH and activated vitamin D work together to mobilize calcium from the bone and decrease calcium excretion from the kidneys.

electrolytes

the minerals sodium, potassium, and chloride maintain fluid balance in the body, transmit nerve impulses, and help muscles contract; electrically charged minerals that are fully dissolved in bodily fluids (such as the blood and urine and the fluids inside and outside of cells). Maintaining the right balance of electrolytes is necessary for the transport of nutrients, muscle contractions, and other processes. With the help of the kidneys, electrolytes balance the fluid outside the cells with the fluid inside the cells. Sodium and chloride are primarily found outside cells and potassium is typically found inside.

calcium

the most abundant mineral in the body, with 99% found in bones and teeth, where it provides an essential structural component for their formation. Bones provide a reservoir of calcium that can be tapped to supply calcium to body fluids when its concentration in blood decreases. The other 1% is located in the body cells and fluids, where it is necessary for many essential functions such as blood clotting, hormone secretion, muscle contraction, and nerve transmission.

binders

the presence of dietary elements called binders can also influence mineral absorption. Binders such as phytates, found in whole cereal grains; oxalates, found in spinach and some vegetables; and polyphenols, present in coffee and tea, can limit bioavailability by chemically binding to minerals.

potassium function

the primary electrolyte within cells; works together with sodium (and chloride) to maintain fluid balance. Potassium may also help relax blood vessel walls, which can also lower blood pressure. Potassium also functions as a cofactor for certain enzymes, helps nerves transmit and muscles contract, plays a role in nutrient transport, and helps to maintain the electrical activity of the heart to sustain a steady heartbeat.

respiration

the process of transporting oxygen from the air to the cells within tissues (inhalation) and, conversely, transporting carbon dioxide to the air (exhalation).

phosphorus

the second most abundant mineral in the body and is present in every cell of the body.

bones

the structural component of the body that shield our brain and organs from injury and make it possible to move. Minerals make up approximately 2/3 of the mass of the skeletal system and are involved in growth and maintenance of cellular membranes and connective tissues. Three major minerals of particular importance for bone formation and maintenance are calcium, phosphorus, and magnesium; with crystal of primarily calcium and phosphorus laid down on a matrix of proteins (predominantly collagen, a structural protein found in connective tissue) during bone formation.

chloride

the third electrolyte involved in fluid balance. Like sodium, it is primarily found in extracellular fluids such as blood. Since chloride composes half of the mineral composition of table salt (NaCl), our chloride intake correlates directly to our sodium intake. In addition to its role in fluid balance, chloride also forms half of hydrochloric acid (HCl), found in the stomach's gastric juices. Because sodium is abundant in the American diet, chloride deficiencies are extremely rare. Overconsumption of chloride, like sodium, increases blood pressure.

Does high calcium intake promote the formation of kidney stones?

there is little evidence that supports this.

What are minerals?

they are ions, elements with a positive or negative charge due to their unequal numbers of electrons and protons. The charges of mineral ions, whether positive or negative, allow them to participate in chemical reactions and bond with other molecules.

thirst

typically a powerful and rapid barometer that tells us when we need to drink (and conversely, lack of thirst tells us we don't need to drink). The same factors (an increase in solutes in the blood or a drop in blood volume) that stimulate the release of ADH also stimulate the brain to generate the sensation of thirst. So, in the end, ADH and thirst work in concert to increase body fluids and decrease the concentration of solutes in blood. However, in those over 65, the thirst sensation is diminished when they become dehydrated or experience increased solute concentration in blood, which slows the restoration of fluid balance.

How much water do we lose through bowel movements?

we lose 140-150 mL (2/3 cups) of water through our bowel movements; the amount is small because most of the water in our stools is reabsorbed into the body before the stool is eliminated. Diarrhea, however, can dramatically increase water loss, which can be dangerous: diarrhea-associated dehydration is a major cause of child death in areas of the world that do not have access to clean water, as contaminated water can cause diarrheal illnesses. When we suffer diarrhea, we lose from 3,300-7,300 mL of water a day - as much as 70 times what we would lose through normal bowel movements.

Why do our water needs fluctuate?

we need more water when we are ill, because we respire more with a fever, and our body perspires to cool itself; vomiting also increases water loss. We also need more water when we eat high-protein diets, in part because water is necessary to remove the byproducts of protein metabolism that accumulate in the blood. High-fiber diets increase our water needs too, because fiber increases the water content of our stools, making it easier for us to pass them. Water needs are increased when we drink alcohol, take certain medications, and spend time at high altitudes.

osteoporosis

when osteopenia becomes severe, and bone loss worsens to cause bones to be fragile and porous; the risk of bone fractures is dramatically increased. Osteoporosis afflicts more than 10 million Americans; approximately 1/2 of all women an 1/4 of all men older than 50 years of age experience osteoporosis-related bone fracture. This is particularly worrisome as the risk of mortality increases by as much as 4x in the first 4 months following an osteoporosis-related fracture.

sources of sodium

widely consumed as table salt, which is otherwise known as sodium chloride (NaCl). Sodium is used extensively in food processing and is often added to foods during cooking and at mealtimes to improve taste. The sodium content of packaged foods is a mandatory component of the Nutrition Facts Panel on the food label.

calcium and bone health

with age, the balance of calcium release and deposition in bone changes. During years of growth, such as childhood, more calcium is added to bone in relation to the amount lost, but as we get older, bone breakdown often exceeds formation. Peak bone mass is established at around age 30, so it is important, during the formative years of bone development, to consume adequate amounts of calcium and vitamin D. If intake is low or absorption is impaired, bone loss occurs because the body uses the calcium in bone to maintain blood levels and support calcium-dependent bodily functions. Bone loss accelerates in postmenopausal women because of low levels of the hormone estrogen.