Water-Soluble Vitamins Ch8 nut

signs

objective evidence of disease that are observed by healthcare professionals, such as a rash or abnormal blood tests.

Many of the B vitamins are interrelated and interdependent, in that the successful functioning of one B vitamin often depends on the successful functioning of other B vitamins. Likewise, deficiencies of B vitamins rarely occur in isolation, because several B vitamins will often occur together in the same types of foods. Chances are that a diet inadequate in one B vitamin will be low in others. However, a deficiency of a single B vitamin wreaked havoc in the not-too-distant past. A painful degenerative disease was sweeping East Asia in the closing decades of the 1800s, causing its victims to experience terrible muscle wasting and eventual heart failure. The disease was known as beriberi and was at one time fairly common among populations whose diet consisted largely of rice.

Beriberi patient on crutches. Beriberi is a disorder of the nervous system caused by a lack of vitamin B1 (thiamin) in the diet. It can cause weight loss, emotional disturbances, and weakness and pain in the limbs, among other symptoms.

CHARACTERISTICS OF THE WATER-SOLUBLE VITAMINS

CHARACTERISTICS OF THE WATER-SOLUBLE VITAMINS Water-soluble vitamins include eight B vitamins, vitamin C, and the vitamin-like nutrient choline. The B vitamins function primarily as coenzymes, chemical compounds that bind enzymes and are required by the enzymes to carry out their function or activity in the body's chemical processes. As coenzymes, B vitamins participate in chemical reactions that provide the body energy, as well as myriad other types of reactions. In addition to functioning as a coenzyme in several types of reactions, vitamin C also serves as an antioxidant, protecting cells from free-radical damage. (INFOGRAPHIC 8.1) INFOGRAPHIC 8.1 Properties of the Water-Soluble Vitamins Unlike fat-soluble vitamins, which leave the small intestine in chylomicrons via the lymph and are stored in the body like fat, water-soluble vitamins immediately enter the blood following absorption, where most circulate freely. Because the water-soluble vitamins are not stored in large quantities, we must consume adequate amounts of them consistently to maintain sufficient levels in our blood and cells to support critical body functions. In addition, foods must be handled with care to preserve vitamin content; some vitamins (both fat- and water-soluble) are unstable and can be destroyed by ultraviolet light, as well as by cooking and storage methods. When you boil foods that contain water-soluble vitamins, for instance, a percentage of the vitamins typically leach out into the cooking water. However, steps can be taken to help preserve vitamins in foods. (INFOGRAPHIC 8.2) INFOGRAPHIC 8.2 Preserving Vitamins in Foods STAY TUNED For more on the potential benefits and risks of dietary supplements, see Spotlight D. When we consume more of a water-soluble vitamin than is needed to meet daily requirements, our body typically eliminates the excess through our urine. Individuals are much less likely to experience toxic adverse effects due to overconsumption of water-soluble vitamins than they are if they consume too many fat-soluble vitamins. In fact, toxicity or adverse effects from high intake of the B vitamins from food sources alone has almost never been observed. However, the use of dietary supplements can push intake well above recommended intake levels. Tolerable Upper Intake Levels (ULs) have not been established for all of the water-soluble vitamins, but ULs exist for niacin, vitamin B6, folate, vitamin C, and choline. In the United States and countries with an adequate food supply, deficiencies of water-soluble vitamins are rare. However, there are circumstances when the risk of deficiency is higher—when calories are restricted, for example, or under conditions that affect absorption, such as diarrhea, intestinal disorders, and parasitic, bacterial, or viral gastrointestinal infections. Excessive alcohol use is a risk factor for several vitamin deficiencies as it can lead to decreased food intake, impaired absorption and utilization, and increased degradation and excretion of vitamins. (INFOGRAPHIC 8.3) In addition, the body's need for most water-soluble (and fat-soluble) vitamins is higher during certain life stages, such as in the elderly and during pregnancy and lactation (breastfeeding), increasing the risk of inadequate intake, potential deficiency, and the associated consequences. When we suffer from fevers or injuries and when we recover from surgery, we also need higher-than-normal amounts of water-soluble vitamins. INFOGRAPHIC 8.3 Possible Causes of Vitamin Deficiencies Although serious vitamin deficiencies are relatively uncommon in developed countries such as the United States, various factors can conspire to cause obvious signs and symptoms of deficiency in some individuals. In contrast, it is likely that a significant number of individuals in the United States have chronically low intake of one or more vitamins, resulting in subclinical deficiencies that cause no overt symptoms. What members of society do you think have the highest risk of vitamin deficiencies? In the early days of the 20th century, it wasn't easy to accept that a poor diet could cause pellagra's varied signs and symptoms, such as skin lesions, confusion, and diarrhea. Some suspected moldy corn or disease-carrying mosquitos caused the illness. Even after individuals in Goldberger's experiment regained their health when fed a varied and wholesome diet, many of his fellow doctors thought his ideas about pellagra were ridiculous. To prove them wrong, in a final jaw-dropping experiment conducted on April 26, 1916, Goldberger injected 5 ml of blood from someone suffering from pellagra into his assistant, Dr. George Wheeler. Wheeler did the same to Goldberger. They swabbed secretions from the noses and throats of pellagra sufferers and rubbed them in their own noses and on their own throats. They even swallowed pills containing scabs of pellagra rashes. If pellagra were caused by a germ, they reasoned, they would undoubtedly fall ill. They did not. Goldberger's uncouth experiments eventually convinced many doctors that pellagra was not an infectious disease, but Goldberger didn't live to figure out exactly what kind of nutritional deficiency caused pellagra. He died of cancer in 1929, leaving it up to someone else to track down the exact culprit.

Folate

Folate The vitamin folate and its synthetic form folic acid, used in supplements, acts as a coenzyme in the metabolism of certain amino acids and production of nucleic acids that are required for DNA and RNA synthesis. Therefore, the vitamin is essential for normal cell division and development. Furthermore, the nervous system requires folate to carry out a number of fundamental metabolic processes. In fact, research suggests that because nervous system function depends on folate, the vitamin may be among the most important in the early stages of pregnancy, when the nervous system develops in the fetus. STAY TUNED The role of nutrition in reducing risk of birth defects, including spina bifida, is discussed in Spotlight E Nutrition for Pregnancy, Breastfeeding, and Infancy. As related in Chapter 1's story on the Dutch Hunger Winter of 1940, babies conceived during that famine when mothers were unable to consume sufficient folate-rich foods were twice as likely to have birth defects as babies conceived before or after the famine. In large part because of the Dutch Hunger Winter, we know that expectant mothers who don't consume enough folate are at an increased risk of giving birth to children with abnormalities of the spinal cord and brain. These abnormalities, the most common of all birth defects in newborns, are known as neural tube defects. Historical records on the famine, which were pored over in a study that concluded in the 1970s, reveal that birth defect rates, specifically the spinal defect spina bifida, were higher than normal in the Netherlands during the famine. Data collected in the Dutch famine study and during the 50-some years since indicate that children who are deprived of folate during their fetal development are also more likely to develop schizophrenia, autism, attention problems, and language delays. The folate RDA for men and women older than 19 years is 400 mcg. It is recommended by the U.S. Centers for Disease Control and Prevention (CDC) that all women between the ages of 15 and 45 years consume at least this amount through a folate-rich diet or folic acid supplementation to reduce risk of folate deficiency and associated birth defects. To help women meet these requirements, in 1998, the FDA instituted a mandatory fortification program to common grain products (for example, flours, breads, cereals, and pasta). As a result of the fortification initiative, risk of folate deficiency in the United States has declined and helped prevent up to two-thirds of all cases of neural tube defects. Although many countries globally have not implemented mandatory fortification programs, a recent study among 58 nations found a 13.2% decline in neural tube-related birth defects when staple flours (wheat and maize) were fortified with folic acid. Once a woman becomes pregnant, the folate RDA goes up to 600 mcg to provide for increased demands of a developing fetus and to support the development of maternal tissues such as the placenta and the woman's expanding blood volume. Foods with plentiful naturally occurring folate include green leafy vegetables, avocado, mango, and beans. (INFOGRAPHIC 8.9)

Intro

In 1914, an esteemed young doctor named Joseph Goldberger was asked by the U.S. Surgeon General to investigate a devastating and mysterious epidemic sweeping across the American South. Known at the time as mal de rosa, now more commonly referred to as pellagra, the condition was causing horrifying signs and symptoms among children and adults—scaly skin; mouth sores; diarrhea; confusion; and, ultimately, mental deterioration. (The signs of pellagra are sometimes known as the three Ds: dermatitis, diarrhea, and dementia.) Although statistics are hard to come by, in 1912, South Carolina alone reported 30,000 cases of this mysterious disease and 40% of those who developed it died. Dr. Goldberger is sitting at a table surrounded by hospital personnel and patients. At the time, most doctors believed that the mysterious condition was an infectious disease caused by an as-yet-unidentified microbe. But Goldberger wasn't convinced. He noticed that the condition tended to afflict poor people, not wealthy people, and that it would sicken prisoners in correction facilities but not the guards. A germ, he knew, wouldn't make such a sociological distinction. If not a germ, what was causing this terrible disease and how? Goldberger's idea, wildly controversial at the time, was that the devastating disease was caused by diet, as he had noticed that the people who were ill tended to eat nutrient-poor diets consisting of cornbread, molasses, and a little pork fat. Pellagra causes thickening, peeling, and discoloration of the skin. In 1915, in what would be considered a highly unethical experiment today, Goldberger experimented on 11 inmates in a Mississippi prison who had volunteered to participate in exchange for a pardon. Most of the inmates in this particular prison ate a well-balanced diet and did not suffer from pellagra. Goldberger fed his volunteers a much less nutritious corn-based diet and watched what happened. Within five months, six of the men showed signs of pellagra, whereas the other inmates in the prison, who ate the more balanced diet, did not. In another experiment, Goldberger supplemented the diets of those suffering from pellagra with fresh meat, milk, and vegetables, and they quickly recovered. The results of Goldberger's experiments seemed to implicate diet in the development of the disease, but the case was not closed. Today we understand that the foods we eat contain vitamins, organic micronutrients (compounds containing both carbon-carbon and carbon-hydrogen bonds) that are needed in small quantities for very specific functions, such as the maintenance of regulatory and metabolic (chemical) processes in the body. If we don't get enough of a vitamin or are unable to adequately use it, we may develop signs and symptoms characteristic of an insufficiency of that vitamin. The fat-soluble vitamins (A, D, E, and K) were the subject of Chapter 7. The vitamins that disperse easily in water-based solutions such as blood, called water-soluble vitamins, are discussed in this chapter.

Pellagra

a disease caused by niacin deficiency and characterized by the three Ds—dermatitis (skin inflammation), diarrhea, and dementia (mental decline).

Vitamin C

In the 18th and 19th centuries, as many as 2 million sailors were afflicted by a disease known as scurvy, a condition that causes anemia, bleeding gums, weakness, fatigue, joint pain, fragile bones, bruising, impaired wound healing, and immunity problems. In 1747, Scottish physician James Lind conducted a trial of six different treatments for 12 sailors with scurvy and found that only lemons and oranges were effective at curing the condition. These citrus fruits are rich in vitamin C; a deficiency of this water-soluble vitamin was the cause of the malady. Scurvy causes the subcutaneous bleeding (bleeding under the skin) visible on the legs of this person suffering from a vitamin C deficiency. Citrus fruits are an excellent source of vitamin C.

Niacin

Recall that pellagra was sweeping the southern United States in the early part of the 20th century and that Dr. Goldberger had determined that eating a diet containing a variety of foods was curative. It wasn't until 1937, eight years after his death, that the specific curative compound in food was identified. An American biochemist gave a dose of nicotinic acid (niacin) to a dog suffering from a disease known as black tongue, the canine equivalent of pellagra. The dog was cured, and subsequent testing determined that niacin was also an effective treatment for humans with pellagra. Niacin plays an important role in the conversion of the macronutrients in food into energy, which is why the typical first symptom of pellagra is fatigue. Beyond energy metabolism, niacin is required for the synthesis of glucose, fatty acids, cholesterol, and steroid hormones and is critically important in DNA repair, cell signaling, and the regulation of gene expression. Therapeutically, doctors sometimes prescribe niacin in high doses to help lower "bad" LDL cholesterol and increase "good" HDL cholesterol. However, as with most vitamins, taking high doses of niacin can cause harmful side effects, and patients on a regimen of high-dose niacin must be monitored to ensure the potential benefits outweigh the risks. Niacin is rich in meats (especially poultry) and fish, as well as peanuts, mushrooms, and fortified cereals. It can also be synthesized in the body, albeit rather inefficiently, from the amino acid tryptophan found primarily in protein-rich foods. As a precursor to niacin, it takes about 60 mg of tryptophan in food to make 1 mg of niacin, so dietary recommendations are often given in niacin equivalents (NEs). NEs are used to describe the contribution to dietary intake of the preformed niacin and that which can be synthesized from the tryptophan provided by foods.

Riboflavin

Riboflavin The second B vitamin to be isolated was riboflavin, and its function is similar to that of niacin: Riboflavin is important for the metabolism of proteins, lipids, and carbohydrates. Milk and other dairy products are particularly good sources of riboflavin, and it is because riboflavin is destroyed by ultraviolet light that milk is kept in paper cartons or opaque plastic containers. A riboflavin deficiency (known as ariboflavinosis) is characterized by cracks and redness on the lips and corners of the mouth, swelling of tissues in the mouth, and a sore throat. Deficiency may be seen with chronic alcohol abuse or malabsorptive conditions. Seldom does riboflavin deficiency occur by itself; it typically is accompanied by deficiencies in other B vitamins. No toxicity with riboflavin consumption from food or supplements has been observed. (INFOGRAPHIC 8.7)

Technology of the time made it possible to refine white rice cheaply and efficiently. The hulls of the rice were removed and discarded to improve the storage life of the rice—brown rice would spoil faster than white rice. What the people didn't understand, however, was that removing the rice hull dramatically decreased the content of many essential nutrients from the rice.

Rice with and without hulls. The white "polished" rice on the right has been stripped of the nutrients found in the hulls.

symptoms

subjective evidence of disease that are experienced by the individual that only they can perceive, such as a stomachache or fatigue.

Choline

Choline is the most recent compound to be added to the list of essential nutrients. Although not a B vitamin, it is a water-soluble compound, and its function in the body is intertwined with that of folate and vitamin B12. In addition, it forms the critically important neurotransmitter acetylcholine, and it is part of two of the most abundant phospholipids in cell membranes. The primary sign of a choline deficiency is liver damage. Although we are capable of synthesizing choline, it is considered an essential nutrient because many people, particularly older men, require dietary sources to meet their needs. Excessive intake of choline, typically only through supplementation, causes a fishy body odor and a slight drop in blood pressure.

Animal foods such as meat, poultry, fish, and dairy are the only natural sources of vitamin B12; some grain and soy products are fortified with B12. Vegans (those who consume no animal products, including dairy and eggs) must either take B12 supplements or regularly consume food fortified with the vitamin to meet their RDA. (INFOGRAPHIC 8.12)

Gastric bypass patients are also at risk for B12 deficiency because less intrinsic factor is produced by the stomach after the surgery and less B12 is released in the stomach as much of the stomach is "bypassed." Other groups at risk for developing B12 deficiencies include those with pernicious anemia—a condition caused by the failure to produce intrinsic factor (as may often be the case in the elderly), resulting in vitamin B12 malabsorption and megaloblastic anemia. In these cases, treatment may require periodic injections of vitamin B12 or the oral administration of very high daily doses (generally 1 mg per day) of the vitamin. Very high doses can result in absorption by passive diffusion of a small amount in the absence of intrinsic factor.

Thiamin

-also known as vitamin B1; it is needed to provide energy from the breakdown of glucose, fatty acids, and some amino acids, as well as the production of sugars needed for the synthesis of RNA and DNA. -Funk named his first vitamin B1; today, it's commonly known as thiamin. The coenzyme form of thiamin is needed to provide energy from the breakdown of glucose, fatty acids, and some amino acids—where it participates in reactions that release carbon dioxide (CO2). It is also required for the production of sugars needed for the synthesis of RNA and DNA. Good food sources of thiamin include pork and fortified grain products. (INFOGRAPHIC 8.5) - The disruptions in metabolism that occur with a thiamin deficiency alter the production of several neurotransmitters, chemical messengers released by nerve cells to send signals to other cells of the nervous system. Disrupting the balance of neurotransmitters leads to mental disturbances such as apathy, irritability, and confusion. Other deficiency symptoms include fatigue and muscle weakness. STAY TUNED Chapter 13 Nutrition During the College Years discusses alcohol use, abuse, and metabolism. Although beriberi is not common in the United States today, another thiamin deficiency, called Wernicke-Korsakoff syndrome, can be found in many developed nations. Alcohol abuse is the leading cause of Wernicke-Korsakoff syndrome, with as many as 80% of chronic alcohol abusers showing signs of deficiency, often resulting in severe neurological disturbances. Individuals who regularly consume excess alcohol are at high risk of thiamin deficiency because alcohol consumption displaces the intake of nutrient-rich foods, decreases thiamin absorption, increases its excretion in urine, decreases its storage in the liver, and decreases conversion of thiamin into its coenzyme. In fact, chronic alcohol abuse increases the risk of deficiency for most of the water-soluble vitamins through several of these mechanisms.

Pantothenic Acid

Another B vitamin, pantothenic acid, has critical functions in energy metabolism and is required for the synthesis of fatty acids, cholesterol, steroid hormones, and two neurotransmitters. Named for the Greek word pantothen, meaning "from all sides," deficiencies of pantothenic acid are rare because of its widespread occurrence in virtually all foods.

Vitamin C, also known as ascorbic acid, acts as a coenzyme in biological reactions and aids in hormone production. It's also involved in the synthesis of collagen, which is used to build bone, teeth, scar tissue, and arterial walls, and it enhances iron absorption. The majority of the signs associated with scurvy are caused by the inability to synthesize collagen appropriately, which causes blood vessels to leak, wounds to heal poorly, and gums to bleed. In addition, vitamin C functions as an antioxidant, a substance that prevents damage to cells by inhibiting the oxidation caused by free radicals, which can damage DNA and tissues. Despite the old wives' tales, vitamin C is not a cure for the common cold: A 2013 evaluation of published research on vitamin C concluded that "no consistent effect of vitamin C was seen on the duration or severity of colds in the therapeutic trials," meaning that there is likely little benefit to taking vitamin C supplements once the symptoms of a cold are detected. In contrast, regular vitamin C supplementation may result in a very slight decrease in the duration of a cold by about 8% in children and 14% in adults. In individuals experiencing short-term physical stress, such as running a marathon, regular vitamin C supplementation can reduce the incidence of colds by as much as 50%. As with some of the B vitamins, vitamin C may have a role in reducing the risk of heart disease. Vitamin C is found naturally in citrus fruits, tomatoes, tomato juice, potatoes, Brussels sprouts, cauliflower, broccoli, strawberries, cabbage, and squash (INFOGRAPHIC 8.13). However, it is readily destroyed by storage and cooking. Potatoes and apples lose about 50% of their vitamin C content after four to five months of storage.

Consumption of vitamin C in excess of the UL, set at 2000 mg for both men and women, may cause diarrhea and bloating, and it may increase the risk of kidney stones in people with kidney disease. The RDA is 90 mg for men 19 and older and 75 mg for women 19 and older. Because smokers are exposed to greater oxidative stress and they have lower concentrations of vitamin C in the body, they are advised to increase their intake by another 35 mg over the RDA.

Key ideas

KEY IDEAS The essential water-soluble vitamins disperse easily in water-based solutions and include the B vitamins, vitamin C, and the vitamin-like nutrient choline. Water-soluble vitamins are not stored in large quantities in the body and must be consumed consistently in adequate amounts to meet the body's needs and prevent deficiencies. Dietary deficiency diseases of a water-soluble vitamin result from inadequate intake or conditions that decrease absorption with subsequent low levels of the vitamin in blood. Although deficiencies of many of the B vitamins may have similar signs and symptoms and often occur simultaneously, unique deficiency diseases have been identified for many of the B vitamins and vitamin C. Although water-soluble vitamins rarely reach toxicity levels from food alone, excess intake through dietary supplements and/or fortified foods may exceed the established Tolerable Upper Intake Level (UL) for some vitamins. The B vitamins include thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), cobalamin (B12), and folate (B9). The B vitamins function primarily as coenzymes, chemical compounds that bind enzymes and are required for those enzymes' functions or activities. As coenzymes, they participate in energy metabolism—transforming carbohydrate, protein, and fat into energy—as well as a myriad of other types of reactions. Fortification and enrichment refer to the addition of vitamins, minerals, and/or protein to a food product such that it contains at least 10% more of the Daily Value of the nutrient than the same food that is not enriched. Megaloblastic anemia—characterized by large, immature, and sometimes irregularly shaped red blood cells—results from folate deficiency but is also seen with vitamin B12 deficiency. Choline, the most recently identified essential nutrient, is a water-soluble compound frequently grouped with the B vitamins because of its intertwined role with folate and vitamin B12. Vitamin C is a water-soluble vitamin that functions as a coenzyme in biological reactions, aids in hormone production, serves as an antioxidant, and is involved in the synthesis of collagen.

As chance would have it, a Dutch researcher named Christiaan Eijkman noticed that chickens fed a diet of white rice became ill, so ill they would stumble in a drunken manner and collapse on their sides. When the brown rice hulls were added to their diet, the chickens recovered. Eijkman surmised incorrectly that there were illness-causing compounds in the white rice and that something in the rice hulls cured it. Many years later, Polish-born American biochemist Casimir Funk was attempting to isolate and identify the exact anti-beriberi factor present in the hulls of brown rice. Funk called the factor vitamine (from vital and amine), and the term was later shortened to vitamin. In fact, in 1912, Funk was the first to propose that the diseases beriberi, scurvy, rickets, and pellagra were caused by deficiencies of specific vitamin(e)s.

Polish-born American biochemist Dr. Casimir Funk, who coined the term vitamin is shown in New York City, January 20, 1953.

Biotin

Present in a wide variety of foods, biotin is required as a coenzyme for only five human enzymes, each of which adds a carbon dioxide to the starting chemical compound. These reactions participate in the breakdown of some amino acids and the synthesis of fatty acids and glucose. Deficiency is rare, although mild forms have been reported in pregnant women and may occur, as with many of the B vitamins, as a result of chronic alcohol abuse. Interestingly, frequent ingestion of raw eggs can result in a biotin deficiency as the protein avidin in raw egg whites binds to biotin, making it unavailable for absorption. And although true biotin deficiency can result in hair loss, skin rashes, and brittle nails, there is no significant evidence that biotin supplementation in healthy individuals results in hair or nail growth.

Consumption of vitamin C in excess of the UL, set at 2000 mg for both men and women, may cause diarrhea and bloating, and it may increase the risk of kidney stones in people with kidney disease. The RDA is 90 mg for men 19 and older and 75 mg for women 19 and older. Because smokers are exposed to greater oxidative stress and they have lower concentrations of vitamin C in the body, they are advised to increase their intake by another 35 mg over the RDA. INFOGRAPHIC 8.14 shows a list of all of the water-soluble vitamins and their functions.

Scurvy, beriberi, and pellagra are diseases largely of the past, because of the work of the physicians, physiologists, and chemists who were pioneers in vitamin research. Although our understanding of vitamins and other nutrients in foods is ever growing, micronutrient deficiency still haunts people in developing nations, people in war-torn regions, and refugees from conflict. Relief organizations do their best to find ways to distribute food and supplementary nutrients to support those populations. However, as we will see in Chapter 9, iron, iodine, and zinc deficiencies are still common.

Vitamin b12

Vitamin B12 is unique among the vitamins for several reasons: It has the largest and most complex structure, and it contains the mineral cobalt, which is why the vitamin is also known as cobalamin. Unlike other water-soluble vitamins, vitamin B12 is stored in significant quantities in the liver. Because vitamin B12 found naturally in foods is bound to food proteins, gastric acid from the stomach is required for it to be released from those proteins. It must then bind to a protein produced in the stomach called intrinsic factor. The cobalamin-intrinsic factor complex is then absorbed in the small intestine. STAY TUNED For more on the nutritional considerations in the aging adult, see Spotlight G. B12 acts as a coenzyme in only two reactions—one of which is important in deriving energy from several amino acids and the other is the aforementioned reaction involving folate and the conversion of homocysteine to methionine. This last reaction is also indispensable for activating folate; therefore, without B12, folate becomes trapped in an unusable form. For this reason, B12 is also required for DNA synthesis and cell division. Because the metabolism of folate and vitamin B12 are closely linked, a deficiency in B12 produces the same megaloblastic anemia that is seen with a folate deficiency, causing increased fatigue during physical activity. As a B12 deficiency continues, it often causes a tingling or lack of sensation in the legs and arms and may progress to include cognitive impairment and problems with motor control. The risk of developing a deficiency of vitamin B12 increases as we age. Diminished or compromised food intake, sometimes seen in the aging population, decreases the amount of B12 available through the diet. In addition, between 10% and 30% of older people don't properly absorb the B12 that is found naturally in food because of a common condition that reduces the production of both gastric acid and intrinsic factor by the stomach. For this reason, individuals older than 50 years are advised to meet their B12 RDA mainly by consuming foods fortified with vitamin B12 or by taking supplements containing B12, because fortification and supplement forms of B12 are not bound to food proteins and therefore do not rely on gastric acid for absorption. A 2013 study noted that new diagnostic tests have revealed a "surprisingly high prevalence" of a subtle form of subclinical B12 deficiency among the elderly. Low vitamin B12 status is associated with more rapid cognitive decline as we age, adding more importance to adequate B12 intake. Get your vitamin B12. Some people don't consume enough vitamin B12 to meet their needs, whereas others can't absorb enough no matter how much they take in. As a result, vitamin B12 deficiency is relatively common, especially among older people.

Vitamin B6 (pyridoxine)

Vitamin B6—often referred to by one of its chemical names pyridoxine—functions as a coenzyme in the release of glucose from stored glycogen and in amino acid metabolism. It is required for the conversion of the amino acid tryptophan to niacin. The body also uses vitamin B6 for the production of some neurotransmitters and hemoglobin (the iron-containing protein found in red blood cells that transports oxygen throughout the body). Good food sources include pork and other meats, bananas, and potatoes. Deficiency in vitamin B6 can cause various signs and symptoms, including anemia, impaired immune function, weakness, dermatitis, and neurological disorders such as confusion and convulsions. Poor vitamin B6 status has also been associated with an increased risk of cardiovascular disease. Adverse and sometimes irreversible neurological effects such as pain and numbness in the extremities can occur in people who take vitamin B6 supplements in doses above the UL. (INFOGRAPHIC 8.8)

The B vitamins

You might wonder why there are so many B vitamins. Initially, the B vitamins were thought to be a single large B vitamin complex, but once the structures and functions were better understood, researchers realized they were actually separate vitamins with distinct functions. To better distinguish the compounds, they retained the title B vitamin but gave each vitamin a number and, later, a name. So the B vitamins include thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), cobalamin (B12), and folate (B9). Some are commonly called by their chemical name, whereas others are identified by their numerical designation, particularly when there are multiple chemical forms of the vitamin. All B vitamins function as coenzymes, with most playing critical roles in energy metabolism. Energy metabolism refers to the chemical reactions that are involved in storing fuels (such as glycogen and triglycerides) or breaking them down to provide the energy necessary to drive a variety of chemical reactions and other body processes (such as active transport and muscle contractions). Coenzymes are not actually part of the enzyme structure; rather, they assist enzymes in carrying out their reactions, often by directly interacting with the reaction substrate (a molecule upon which an enzyme acts). In other words, the B vitamins do not provide energy to the cells, but they play a critical role in energy transformation. (INFOGRAPHIC 8.4) B vitamins are also required for amino acid, drug, and free-radical metabolism as well as the synthesis of hundreds of compounds necessary to support life, such as steroid hormones, nucleic acids for DNA synthesis and cell division, and the oxygen-carrying heme group that is part of hemoglobin.