Vitamins
The RDA for vitamin B 12 is 2.4 micrograms for adults aged 19 to 50 years. 2 Older adults have the same requirement; however, many older individuals have a decreased ability to absorb B 12 . The synthetic form of B 12 can be absorbed more readily than food sources for these individuals; therefore, they should focus on incorporating fortified foods and supplements into their daily diet.
12 is critical for the health of the myelin sheath, so low intake causes the myelin sheath to swell and break down, leading to brain abnormalities and spinal cord degeneration. Pernicious anemia leads to altered red blood cell formation, producing megaloblasts and macrocytes, meaning large, irregular cells.
Adequate intakes of vitamin B 12 prevent the onset of pernicious anemia. Vitamin B 12 is also involved in preparing fatty acid chains to enter the citric acid cycle, thus facilitating energy production.
A health-related task of vitamin B 12 is the lowering of homocysteine and thus the prevention of heart disease. High levels of homocysteine have recently been accepted as a valid risk factor for cardiovascular disease. Homocysteine is converted to methionine with the coenzyme assistance of vitamin B 12 , thus lowering blood levels of homocysteine and the risk for disease.
For individuals who suffer from chronic diarrhea or sloughing of the brush border because of age, illness, or medications, vitamin B 12 absorption will be diminished. Absorption of vitamin B 12 is a complex process that involves many factors and sites in the GI tract. Defects in this process, especially a lack of intrinsic factor, impair absorption and can result in deficiency.
A healthy athlete consuming a balanced diet may not benefit from vitamin B 12 supplements. As mentioned previously, vegetarian or vegan athletes may need supplemental B 12 from fortified vegetarian foods, soy products, or multivitamins. Masters or elderly athletes may also need B 12 supplements if they have atrophic gastritis and/or low levels of intrinsic factor. Those with diagnosed pernicious anemia will have enhanced performance after consuming higher doses of B 12 .
The signs and symptoms of choline toxicity include low blood pressure, diarrhea, and a fishy body odor. Choline can be produced in the body from the amino acid methionine. Therefore, ingesting protein-rich foods, which provide methionine, can indirectly contribute to daily choline needs.
A study by Hongu and Sachan 25 reported that choline supplements given to healthy women promoted carnitine (A compound that transports fatty acids from the cytosol into the mitochondria, where they undergo beta-oxidation) conservation and favored incomplete oxidation of fatty acids and disposal of fatty acid carbons in the urine. Earlier studies suggest that this scenario, induced by the choline supplements, might reduce fat mass and increase fat oxidation during exercise.
Vitamin B 6 refers to all biologically active forms of vitamin B 6 , including pyridoxine, pyridoxal, pyridoxamine, pyridoxine phosphate, pyridoxal phosphate, and pyridoxamine phosphate. Pyridoxine, pyridoxal, and pyridoxamine are the forms most commonly found in foods.
B 6 is a component of more than 100 enzymes, which facilitate the breakdown of glycogen for energy as well as gluconeogenesis in the liver, synthesis of amino acids via transamination, conversion of tryptophan to niacin, formation of neurotransmitters, production of the red blood cells' hemoglobin ring, and the production of white blood cells.
Vitamin D is a unique fat-soluble vitamin because, in general, all of the body's needs for it can be met by synthesis within the body. It is in these cases that vitamin D, from food or supplemental sources, is essential and, as a result, is considered a vitamin. The primary role of vitamin D in the body is to control calcium levels in the blood, which, in turn, affects bone growth and development.
Calcitriol The active form of vitamin D in the body. It plays a vital role in calcium regulation and bone growth. In fact, vitamin D deficiency has been associated with increased risk for several chronic and autoimmune diseases, such as hypertension, cardiovascular disease, rheumatoid arthritis, depression, and certain cancers. The growing evidence regarding the importance of vitamin D and the fact that 77% of Americans are considered vitamin D insufficient has caused some nutrition professionals and researchers to question the current RDA for vitamin D as being too low.
Vitamin C is critical for the formation of collagen , which is a fibrous protein found in connective tissues of the body such as tendons, ligaments, cartilage, bones, and teeth. Collagen synthesis is also important in wound healing and the formation of scar tissue. Vitamin C plays a role in a healthy immune system and enhances iron absorption of nonheme iron, thus protecting the body against iron-deficiency anemia.
Cardiovascular research has indicated that vitamin C's role as an antioxidant seems to be protective against heart disease, especially by preventing the oxidation of LDL, which can lead to atherosclerosis. Vitamin C also aids in the formation of various hormones and in the production of neurotransmitters such as epinephrine.
Folate is the form of this vitamin found in whole foods, whereas folic acid is the most stable form or derivative of folate and is therefore used in supplements and fortified foods. Folate is critical for DNA synthesis and cell division, thus playing an important role in the growth and development of a fetus.
Folate helps to lower levels of homocysteine in the blood, thus potentially lowering the risk for heart disease. Folate also facilitates muscle tissue repair after strenuous exercise, aiding in recovery. Most neural-tube defects occur within the first month after conception. This discovery was the driving force behind the 1998 Food and Nutrition Board mandate to fortify grains in the United States with folic acid.
Vitamin A is found as retinol in animal foods and as beta-carotene and other carotenoids in plant foods. Units are IU to be consistent with DV definitions. Encouraging athletes to obtain vitamin A from food sources rather than supplements to avoid toxicity is recommended. This theory is reinforced by recent epidemiological studies that have suggested that increased intake of lutein lowers the risk for age-related macular degeneration.
Carotenoids are a unique category of plant-based substances that can positively affect overall health. Some functions, including improved immune function and antioxidant activity, may also be beneficial to athletic performance. Although no DRI has been set for these compounds, a diet rich in dark, colorful fruits and vegetables has been found to be advantageous to health and well-being. Although no DRIs are established for carotenoids, the Food and Nutrition Board recommends eating foods rich in carotenoids and avoiding supplementation.
The primary role of vitamin E in the body is as an antioxidant. Antioxidants protect the body from highly reactive molecules known as free radicals. The role vitamin E plays in protecting the skin and its underlying connective tissues is one reason why vitamin E has been advertised as the "anti-aging" vitamin. Vitamin E protects cell membranes by directly reacting with free radicals, thus preventing them from reacting with the fatty acids in the cell membranes.
Common signs of vitamin E deficiency take time to develop and are related to the breakdown of cell membranes. Muscle weakness and loss of motor coordination can result because of cell membrane damage to muscle and nerve tissue, respectively.
Niacin is a component of two coenzymes: nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+).
During aerobic exercise, NAD+ can accept a hydrogen ion and become NADH, carrying high-energy electrons to the electron transport chain for the production of ATP.
Specifically, pantothenic acid is a component of coenzyme A, a molecule critical for the passage of metabolic intermediates from fat, carbohydrate, and protein metabolism into the citric acid cycle. The citric acid cycle is one of the major metabolic pathways involved in the aerobic production of ATP. The key question is whether pantothenic acid supplementation will improve athletic performance. Limited research has been conducted to date; however, pantothenic acid supplementation has not been shown to be beneficial to athletes.
Fatigue, sleep disturbances, impaired coordination, nausea, hypoglycemia, and muscle cramps can signal low levels of pantothenic acid. However, deficiencies are very rare. In addition, the existing research does not provide enough information to warrant supplementation for enhanced athletic performance.
A study conducted by Herrmann et al. 21 found that 25% of study participants, all recreational athletes, had elevated homocysteine levels that were associated with low levels of both vitamin B 12 and folate. These efforts to prevent disease through exercise may be negated if daily nutrition and adequate intake of B 12 are neglected.
For elderly individuals, the parietal cells become less functional, producing less intrinsic factor, thus affecting vitamin B 12 absorption in the small intestine. Pancreatic enzymes cleave B 12 from the R-protein in the small intestine. B 12 then binds to intrinsic factor and travels to the ileum of the small intestine, where it binds to the brush border and is absorbed and transported throughout the body.
low intakes of B 6 , as well as folate and vitamin B 12 , have higher blood levels of homocysteine, which is a risk factor for heart disease. Many studies involving short-duration and moderate-intensity exercise have shown an increase in vitamin B 6 in the blood within minutes of the onset of exercise and throughout the exercise bout.
Homocysteine and heart disease. Elevated homocysteine levels are linked to an increased risk of heart disease. Irreversible nerve damage can occur at levels of 1000-2000 milligrams per day of vitamin B6.
Niacin is obtained through the diet but can also be formed within the body from the amino acid tryptophan. Therefore, the RDA refers to niacin equivalents (NE), reflecting intake from niacin-rich foods as well as sources of tryptophan that can be converted into niacin.
Individuals taking niacin for its cholesterol-lowering effect must be under the supervision of a physician to monitor any potential complications and decrease the risk for liver damage.
A deficiency of vitamin K impairs blood clotting and can lead to substantial hemorrhaging. Thus, vitamin K is important to athletes, who are much more likely than the general population to receive cuts, tears, and abrasions as a result of their sport participation.
Individuals using antibiotics for a prolonged period may be at higher risk of deficiency because antibiotics may kill the naturally occurring bacteria in the gut that produce vitamin K. The best dietary sources of vitamin K are green leafy vegetables such as spinach and broccoli. Other foods such as milk, eggs, wheat cereals, and some fruits and vegetables contain small amounts of vitamin K.
There are hundreds of different carotenoids; however, the ones most identified as vital to health include alpha-and beta-carotene, lycopene, lutein, zeaxanthin, and cryptoxanthin. retinol activity equivalent (RAE) A unit of measure of the vitamin A content in foods. One RAE equals 1 microgram of retinol.
International Units (IU) An outdated system used to measure vitamin activity. Deficiency of vitamin A is rare in the United States, but it does exist in many countries where general malnutrition is found. Blindness is the most common and devastating result of deficiency. Night blindness is often an early symptom of vitamin A deficiency. Hyperkeratosis A clinical condition resulting from the overproduction of the skin protein known as keratin. Overproduction of keratin plugs skin follicles, thickens the skin surface, and causes skin to become bumpy and scaly. Vitamin A deficiency is related to hyperkeratosis.
The first signs of vitamin C deficiency are swollen gums and fatigue. If left untreated, the deficiency disease scurvy can develop, causing a degeneration of the skin, teeth, and blood vessels resulting from low collagen production. As a protective mechanism, the body stores several grams of vitamin C in case of short periods of low vitamin C intake. Long-term megadoses of vitamin C can also contribute to kidney stones, decrease the absorption of other nutrients, and may increase the risk for heart disease.
Supplements used to achieve higher doses of vitamin C should be consumed with caution. As mentioned previously, vitamin C aids in iron absorption. For athletes who are low in iron, this action can be beneficial; however, for those who are more susceptible to hemochromatosis, which is a disorder that results in the excessive absorption of iron, vitamin C supplementation is not recommended and may exacerbate symptoms. Another condition, known as rebound scurvy, can occur in athletes or individuals taking in high levels of vitamin C. It is called rebound scurvy because it results when the body "rebounds" from long-term exposure to high levels of vitamin C.
The two coenzymes flavin mononucleotide and flavin adenine dinucleotide contain riboflavin and are involved in the transport of electrons to the electron transport chain during aerobic energy production at rest and during exercise.
Riboflavin deficiency is recognized by symptoms such as red lips, cracks at the corners of the mouth, a sore throat, or an inflamed tongue.
Bios II, vitamin H, and coenzyme R—were all found to be beneficial to the body. With further investigation, it was recognized that all three compounds were the same nutrient—biotin. Biotin appears to be safe even at high levels, so no upper limit has been set.
Some documented signs and symptoms of biotin deficiency include fatigue, depression, nausea, dermatitis, and muscular pains. Raw egg whites will bind to biotin and may contribute to biotin deficiency if consumed on a regular basis.
During lipid peroxidation the double bond of an unsaturated fatty acid is broken, yielding intermediate compounds that can react with oxygen to form peroxide free radicals. A peroxide free radical has one unpaired electron, making it highly reactive with other fatty molecules within the cell membrane. To help decrease the cell membrane damage, vitamin E responds to the free radical by donating an electron, thus preventing it from reacting with other fatty acids in the cell membrane and causing further damage.
The bottom line is that so little is known about the effects of antioxidant supplementation on exercise that making recommendations to well-nourished athletes regarding antioxidant supplementation currently is neither necessary nor advisable. For now, the best nutrition advice is to incorporate more antioxidant-containing foods into the daily diet to ensure adequate intake of a variety of antioxidants and other nutrients.
Vitamin E is less likely than other fat-soluble vitamins, such as A and D, to become toxic to the body. However, high doses of vitamin E resulting from supplementation can affect vitamin K's blood-clotting functions, leading to excessive bleeding and easy bruising. The UL for adults is 1000 milligrams of alpha-tocopherol. Products made from vegetable oil, such as margarine, are among the best sources of vitamin E. Animal sources such as meat, poultry, and fish are at best moderate contributors to dietary vitamin E.
The primary role of vitamin K in the body is in blood clotting. When a laceration or an abrasion occurs, a series of activation reactions involving clotting factors is required to stop the bleeding. Vitamin K is essential in many of the steps of the clotting process. Without vitamin K, even a single cut could be life-threatening from the potential blood loss. Vitamin K is also important to bone health. It assists in the mineralization of bone with calcium, thus keeping bones dense and strong.
Choline is involved in the formation of the neurotransmitter acetylcholine, which is involved in muscle activation. In theory, higher intakes of choline would maintain higher blood levels of the nutrient and increased levels of acetylcholine in the nerve endings, thus preventing muscle fatigue and/or failure. More research is needed to evaluate this theory, however. Choline has also been shown to help maintain the structural integrity of cell membranes.
The risk for choline deficiency is low because it is found in a wide variety of foods. The human body also makes choline endogenously, further decreasing the risk for deficiency.
For example, if a B 12 deficiency is mistaken for a folate deficiency, higher levels of folate will repair the megaloblastic anemia, but other neurological problems will continue to develop as a result of the low vitamin B 12 intake. Low folate intake may also increase the risk for heart disease by allowing homocysteine levels to rise. Folate works with other water-soluble vitamins, B 6 and B 12 , to reduce homo-cysteine levels in the blood. Because athletes have an increased risk for vitamin B 12 deficiency, observing the UL of folate will help prevent misdiagnosis and resulting complications.
There have been no studies suggesting an increased exercise capacity by consuming extra folate.
The signs and symptoms of thiamin deficiency include decreased appetite, mental confusion, headaches, fatigue, muscle weakness, nerve degeneration, and pain in the calf muscles.
Thiamin deficiency is typically caused by an athlete consuming very few calories or having a diet composed mainly of processed foods.
The term phytochemicals comes from the Greek word phyto , meaning "plant"; they are so named because they are chemical substances found in plants. The phenols are a broad category of antioxidant compounds that work to prevent the oxidation of LDL cholesterol. The increased wine consumption in France may help protect against heart disease, and thus the "French paradox" was born. Consuming several cups of green or black tea daily will help athletes reap the potential disease prevention benefits of this beverage.
Vegetables including broccoli, brussels sprouts, cabbage, rutabaga, and cauliflower are part of the organosulfide group of phytochemicals. Therefore, athletes should avoid high-gas-producing vegetables within several hours before training. Consumption of these vegetables after workouts or competitions is the best practice to avoid uncomfortable gas production while reaping the health benefits.
Because of the profound effect vitamin D has on absorption of dietary calcium, vitamin D deficiency can have devastating effects on bone health. In children, vitamin D deficiency leads to rickets, which results in poorly formed, weak, and soft bones. In adults, deficiency of vitamin D increases the risk for osteoporosis. The fortification of milk with vitamin D was intended to address deficiency problems in children and adults in the United States. However, fortification of milk has not alleviated this problem. Therefore, adequate vitamin D intake in food or in supplement form is an essential part of developmental bone health, as well as prevention and treatment of osteoporosis in the aging population. Overdosing with vitamin D causes hypercalcemia , or high blood calcium. Hypercalcemia causes a depressed function of the nervous system, muscular weakness, heart arrhythmias, and calcium deposits in the kidneys (i.e., kidney stones), blood vessels, and other soft tissues.
Vegetarians need to rely on the endogenous production of vitamin D from sun exposure or the consumption of fortified foods and the use of supplements. Athletes who train extensively indoors or who consume lower or inadequate amounts of calories or whose food choices do not include vitamin D-rich sources daily may need and benefit from supplementation.
Retinol is transported in the blood to the retina in the eye, where it is converted to retinal. Retinal combines with the protein opsin to form the pigment rhodopsin, which allows humans to see black-and-white images. Iodopsin, another pigment that involves retinal, allows humans to see color images. Light entering the eye stimulates a process of separating retinal from the opsin and iodopsin, causing the proteins to change shape. The change in protein shape stimulates optical receptors in the retina that send electrical impulses to the brain, which, in turn, enables sight. When vitamin A is deficient, blindness can occur.
Vitamin A and the visual cycle. Rhodopsin is the combination of the protein opsin and vitamin A (retinal). When stimulated by light, opsin changes shape, and vitamin A changes from its bent cis form to a straighter trans form. This sends a signal to the brain, allowing images to be seen in black and white. A similar process using a different protein called iodopsin provides color.
Adequate vitamin A is essential for athletes to help repair those tissues that may be injured during sporting events. Vitamin A has shown some promise as an antioxidant that may help prevent cancer and certain chronic diseases. The maintenance of epithelial tissues in preventing infection is so important that vitamin A has been labeled as the "anti-infection" vitamin.
Vitamin A can be consumed in the diet from animal sources as retinoids or from plant sources as carotenoids. Choosing more colorful vegetables and fruits, including reds, yellows, blues, and purples. Carotenoids are less biologically active than are retinoids, and therefore greater amounts need to be consumed to meet daily requirements. This standard is the retinol activity equivalent (RAE) . One RAE is the amount of a given form of vitamin A equal to the activity of 1 microgram of retinol. Although carotenoids may be slightly lacking in their ability to convert to vitamin A, their overall contribution to physical health is expansive.
Vitamins, A (including the carotenoids) and E, and the water-soluble vitamin C all have powerful antioxidant properties in the body. Free radicals basically cause molecules to give up electrons in a process known as oxidation so that they can match any unpaired electrons and become more stable. Undesirable free radical oxidation may damage DNA, lipids, proteins, and other molecules and thus may be involved in the development of cancer, cardiovascular disease, and possibly nerve degenerative diseases. Reactive oxidative species (ROS) Free radical molecules that contain oxygen in their molecular formula and that are formed during aerobic metabolism. Commonly occurring reactive oxidative species in the human include superoxidases, hydroxyl radicals, and peroxyl radicals.
Vitamins A (including the carotenoids), E, and C. These nonenzymatic antioxidants either directly interact with free radicals (see FIGURE 6.18 ) or work as coenzymes. In summary, the body's antioxidants, whether enzymatic or nonenzymatic, are crucial to helping the body protect itself from free radicals.
Enrichment adds niacin as well as thiamin, riboflavin, folic acid, and iron to processed grains.
recent research reviews have concluded that well-nourished athletes do not benefit from niacin supplements. Signs and symptoms of niacin deficiency include loss of appetite, skin rashes, mental confusion, lack of energy, and muscle weakness. If the deficiency is left untreated, the deficiency disease pellagra develops. Pellagra is characterized by the three "Ds": dementia (mental confusion), diarrhea, and dermatitis (skin rashes). If pellagra is left untreated, there is a fourth "D," death.
Thiamine is important in athletes because it plays a major role in energy production and is also important for developing and maintaining a healthy nervous system.
thiamin is a component of the coenzyme thiamin pyrophosphate that converts pyruvate into acetyl CoA, which then enters into the Krebs cycle during aerobic energy production