Section Four. Summary by Taylor & Francis Group, LLC

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1 Section Four Summary

2 21 Summary Vitamins and Trace Elements in Sports Nutrition Judy A. Driskell and Ira Wolinsky CONTENTS I. Introduction II. Water-Soluble Vitamins and Choline III. Fat-Soluble Vitamins IV. Trace Elements V. Conclusions and Implications References I. INTRODUCTION Vitamins and trace elements play many roles with regard to physical activity, including sports and exercise. All of the nutrients that function in energy metabolism, either directly or indirectly, also function in physical performance. Deficiencies of many of the nutrients are known to adversely affect exercise performance. In many early studies, the initial status of subjects with regard to the vitamin or mineral under investigation was not determined prior to initiation of supplementation. In most cases, the effects of supplementation are different in individuals deficient in the nutrient from those with adequate status. Some well controlled studies have been published that relate vitamin or trace mineral nutrition, including supplementation, to physical performance. The presence of nutrients in optimal quantities in the body maximizes exercise performance. Overall health, as well as physical and psychological well-being of all individuals, are affected by their nutrient intakes. The Institute of Medicine has established recommended dietary allowances (RDA) or adequate intakes (AI) for the various vitamins and trace minerals that healthy individuals should consume. This group sets nutrient intake recommendations for Americans (U.S.) and Canadians. Adequate intakes for nutrients were set when sufficient scientific evidence was not available to estimate an average requirement, from which the RDA is calculated. 1 This group has made a few recommendations with regard to suggested intakes of some of these vitamins and trace minerals for physically active adults. The RDAs/Als of adults, 19 y of age and above, for the vitamins and trace minerals discussed in this book are given in Table The U.S. Food and Drug Administration has established daily values (DV) for many nutrients that are used on food and supplement labels. The DVs for individuals 4 years of age and older for the vitamins and trace minerals 2 discussed in this volume are also given in Table Because many of the nutrients can be toxic, the Institute of Medicine also set tolerable upper intake levels (ULs) for these nutrients. The UL is the maximum intake by an individual that is unlikely to pose risks of adverse health effects in almost all (97 98%) individuals in a specified life-stage group, 1 and is sometimes referred to as the upper safe level. For most nutrients, the UL refers to total intakes from food, fortified food and nutrient supplements. The ULs of adults, 19 y of age and above, for the vitamins and trace minerals discussed in this 323

3 324 Sports Nutrition: Vitamins and Trace Elements TABLE 21.1 Recommended Dietary Allowances/Adequate Intakes a, Daily Values b and Tolerable Upper Intake Levels of Adults, a 19+ y of age, for Vitamins and Trace Minerals RDA/AI DV UL Nutrient Men Women 4+ y-old Men and Women Ascorbic Acid (mg/d) ,000 Thiamin (mg/d) ND c Riboflavin (mg/d) ND Niacin (mg/d) Vitamin B 6 (mg/d) 1.3/1.7 d 1.3/ Folate (µg/d) e 400 1,000 Vitamin B 12 (µg/d) 2.4 f 2.4 f 6.0 ND Pantothenic Acid (mg/d5) ND Biotin (µg/d) ND Choline (mg/d) ND 3,500 Vitamin A (µg/d) IU g 3,000 Vitamin D (µg/d) 5/10 d 5/10 d 400 IU h 50 Vitamin K (µg/d) ND Vitamin E (mg α-tocopherol/d) IU i 1,000 Iron (mg/d) 8 18/8 c Zinc (mg/d) Copper (µg/d) ,000 Iodine (µg/d) ,100 Chromium (µg/d) 35/30 d 25/20 d 120 ND Selenium (µg/d) Boron (mg/d) ND ND ND 20 Manganese (mg/d) j Molybdenum (µg/d) ,000 Nickel (mg/d) ND ND ND 1.0 Silicon (mg/d) ND ND ND ND Vanadium (mg/d) ND ND ND 1.8 a Values are from references 1, 7, 9 and 10. b DVs are used on food and supplement labels; the DVs given above are for individuals 4 y of age and older. Values are from reference 12. c ND = Not determinable. d Recommendations for y/51+ y. e All women capable of becoming pregnant should consume 400 µg from supplements or fortified foods in addition to intake from a varied diet. f It is advisable for those 51+ y to meet their RDA mainly from fortified foods or supplements. g See Chapter 11 for conversion factors. h 1 µg = 40 IU. i See Chapter 13 for conversion factors. j Represents intake from pharmacological agents only and does not include intake from food and water. book are given in Table Nutritionists, dietitians and other health professionals generally recommend that individuals have nutrient intakes somewhere between the RDAs/AIs and the ULs. These are recommendations for healthy individuals and do not relate to physician-prescribed nutrient supplements. A separate set of RDAs/AIs for athletes does not exist, however, some recommendations have been made specifically for athletes with regard to some of the nutrients.

4 Summary Vitamins and Trace Elements in Sports Nutrition 325 Dietary supplements containing vitamins and trace minerals are frequently taken by individuals of all ages, including the athletic population. Around one third to one half of adults in the U.S. take some form of vitamin-mineral supplement. 3 The Dietary Supplement Barometer Survey, a national poll of 1027 U.S. adults in summer 2001, commissioned by the Dietary Supplement Education Alliance, a coalition of industry stakeholders, found that 27% of those polled reported taking a multivitamin-multimineral daily and 21% took a single vitamin daily. 4 The leading supplements taken by the participants of the third National Health and Nutrition Survey (NHANES III) were: multivitamin-multimineral, multivitamins plus vitamin C, vitamin C as a single vitamin and vitamin E as a single vitamin. 5 Varsity athletes at the University of Nebraska were surveyed as to their usage of vitamin-mineral supplements. 6 Over half (56.7%) of the subjects reported taking vitamin-mineral supplements. The prevalence of taking supplements was higher, though nonsignificantly, for women (59.3%) than men (55.3%). The percentages of subjects reporting taking supplements ranged from 30.8 to 80.0% for women s varsity sports and 20.0 to 83.3 for men s (Table 21.2). The two most common reasons these varsity athletes gave for taking the vitaminmineral supplements were that they were recommended by family members or friends and to improve athletic performance. Many athletes apparently believe that supplementation with some of the vitamins and minerals is beneficial to them, particularly with regard to their physical performance. Evidence suggests that the taking of a multivitamin-multimineral supplement makes people feel better; hence, psychologically and perhaps, then, physiologically, vitamin and mineral supplementation may be beneficial to athletes. Unfortunately, the effect of vitamin-trace element supplementation on the athletes sense of well-being is seldom reported. Vitamins and essential trace elements are needed by all the cells of the human body. Deficiencies of most, if not all, vitamins and trace elements can decrease physical performance. Athletes who are most at risk of deficiencies of vitamins and trace elements are those who do not consume sufficient foods and who ingest mostly refined carbohydrates, overtrain and exercise in extreme manners or conditions. In the majority of individuals who do not have preexisting nutrient deficiencies, the consumption of multiple vitamin-mineral products containing more than the DVs of these nutrients does not enhance physical performance, at least those measures of physical performance that have been studied. However, individuals taking these supplements frequently have TABLE 21.2 Prevalence of Vitamin-Mineral Supplement Usage by University Athletes by Varsity Sport Female Sport n % Taking Supplements Male Sport n % Taking Supplements Cross-country 7 86 Tennis 6 83 Gymnastics Gymnastics Tennis 5 80 Track & field Swimming/Diving Baseball Golf Swimming/Diving Soccer Cross-country Volleyball 9 56 Football Yell squad/dance team Yell squad/dance team Track & field Wrestling 7 27 Softball Golf Basketball Basketball Source: adapted from Krumbach, C.J., Ellis, D.R. and Driskell, J.A., A report of vitamin and mineral supplement use among university athletes in a Division I institution. Int. J. Sport Nutr., 9, , 1999.

5 326 Sports Nutrition: Vitamins and Trace Elements perceived that the supplements were beneficial to them these supplements may thus have indirect effects on mental fitness, immune system function and prevention or recuperation from injury. Toxicity from multiple vitamin-mineral products is uncommon; however, ULs of safety exist for many of the individual vitamins and trace minerals. Vitamins are classified as being water-soluble or fat-soluble. The water-soluble vitamins include ascorbic acid, the B-complex vitamins (thiamin, riboflavin, niacin, vitamin B 6, folate, vitamin B 12, pantothenic acid and biotin) and perhaps choline. The fat-soluble vitamins include vitamin A, vitamin D, vitamin E and vitamin K. The essential trace elements/minerals are iron, zinc, copper, iodine, chromium, selenium, molybdenum and manganese. Evidence exists that the trace elements/ minerals boron, nickel, silicon and vanadium have beneficial roles in some species, though evidence of such roles in humans is limited. II. WATER-SOLUBLE VITAMINS AND CHOLINE Numerous researchers have investigated the ergogenic effects of ascorbic acid (vitamin C) and the results of these studies are mixed. Vitamin C deficiency or even marginal vitamin C status is known to adversely influence physical performance. Reports exist that up to 25% of athletes consumed less than the RDA for vitamin C. Several studies indicate that strenuous or prolonged exercise increases the need for vitamin C. For subjects having adequate vitamin C status prior to supplementation, research data do not appear to support a clear or consistent ergogenic effect of the vitamin. Most of the research has been done with runners; research is needed on other types of athletes, particularly of the strength-power variety. Keith, the author of Chapter 2 in this volume, suggests that athletes engaged in strenuous prolonged physical activity consume 100 to 1000 mg of vitamin C daily. The UL for vitamin C for adults is 2000 mg/day. 1 Thiamin (vitamin B 1 ) as a component of the coenzyme thiamin pyrophosphate (TPP), is important in energy metabolism. Thiamin is also needed for optimal neuromuscular functioning. Reportedly some athletes are marginally thiamin deficient. The need for thiamin is generally proportional to the caloric intake, especially when the diet is high in carbohydrates. Athletes may require more thiamin than sedentary individuals. Additional research is needed on the thiamin needs of physically active individuals. No UL exists for thiamin. 7 Riboflavin (vitamin B 2 ), as a component of the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), participates in many oxidation-reduction reactions in the body, particularly glycolysis, the tricarboxylic acid cycle and β-oxidation. Though physical activity may deplete riboflavin status, the riboflavin status of well-nourished athletes is similar to that of wellnourished nonathletic controls. There appears to be no advantage of riboflavin supplementation of athletes unless these individuals are deficient in the vitamin. No UL exists for riboflavin. 7 Niacin, as a component of the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), is needed for adenosine triphosphate (ATP) production from all the energy-yielding nutrients. Niacin deficiency impairs glycolysis and respiratory metabolism. Compromised niacin status in the athletic or general population does not seem to influence aerobic exercise performance. Supplementation with nicotinic acid reduces the availability of free fatty acids and potentiates the use of carbohydrates as sources of energy. The UL for niacin (as nicotinic acid) for adults is 35 mg/day. 7 Large doses of nicotinic acid are sometimes used to treat hyperlipidemia and more research on the athletic performance of individuals taking these doses would be interesting. Vitamin B 6, primarily as pyridoxal phosphate (PLP), functions in several metabolic pathways including some involving all the energy-yielding nutrients, but especially protein, during exercise. Vitamin B 6 deficiency may alter physical performance. Vitamin B 6 is involved in the protective effect of exercise on cardiovascular disease. The current thinking is that vitamin B 6 supplementation

6 Summary Vitamins and Trace Elements in Sports Nutrition 327 of individuals with adequate status of the vitamin has no beneficial effect on physical performance measurements. The UL of vitamin B 6 for adults is 100 mg/day. 7 Folate functions in nucleic acid synthesis and is a component of several enzymes involved in amino acid metabolism. Folate deficiency is primarily manifested as megaloblastic anemia. Any type of anemia can influence physical performance, particularly in endurance athletes. No measurable increase in athletic performance has been observed in athletes who consumed amounts of folate higher than that recommended for the general population. Folate can lower plasma homocysteine concentrations. Research is needed on the relationships between exercise and hyperhomocysteinemia, if any. The UL for folate for adults is 1000 µg/day from fortified foods or supplements, but not other foods. 7 Vitamin B 12, cobalamin, is crucial for the synthesis of DNA and is needed for erythrocyte synthesis. Hematopoietic defects, especially megaloblastic anemia and neurological damage, are seen in vitamin B 12 deficiency. The most common cause of vitamin B 12 deficiency is an inadequacy of intrinsic factor secretion. In the athlete with normal or marginal B 12 status, with no accompanying signs of deficiency, no evidence exists that increased quantities of the vitamin will enhance athletic performance. No UL exists for vitamin B Pantothenic acid functions in cells as a component of coenzyme A, which plays a central role in intermediary metabolism. Biotin functions as a coenzyme for carboxylases as well as having a role in chromatin structure and cell signaling. These two B-vitamins are ubiquitous in human diets and deficiencies are rare. Pharmacologic doses of pantothenic acid appear not to enhance physical performance. Studies on biotin and physical performance have not been published. No UL exists for either pantothenic acid or biotin. 7 Uncertainities exist with regard to the safety of pharmacological doses of either pantothenic acid or biotin and gene expression and cell signaling. Choline was classified as an essential nutrient by the Institute of Medicine, National Academy of Sciences in 1998 and AIs were established for this nutrient. 7 Choline, a lipotropic agent, functions in the maintenance of membrane integrity, neurotransmission, as a precursor for compounds serving in cell signaling and as a methyl donor. Only recently has a listing of the choline concentrations in common foods been developed. Decreased plasma choline concentrations have been reported in marathon runners and cyclists. Deuster and Cooper, the authors of Chapter 10 in this volume, listed the following possible roles for choline in physical activity: a component of acetylcholine, a neurotransmitter having neuromuscular functions, the hemoconcentration of choline, a lipotropic agent, a substance playing a role in creatine synthesis. The UL of choline for adults is 3500 mg/day. 7 III. FAT-SOLUBLE VITAMINS Vitamin A in the body can come from preformed vitamin A or from provitamin A carotenoids, the most abundant of which are β-carotene, α-carotene and β-cryptoxanthin. An optimal intake of vitamin A is needed for general health, physical performance and recovery from strenuous exercise. Athletes in developed countries reportedly have adequate vitamin A status. Many studies that have estimated vitamin A intakes have methodological problems inaccurate reporting by subjects, the changing vitamin A activity conversion factors for carotenoids in plant foods and the habit of reporting vitamin A from all sources together without specifying the proportion from animal sources, vitamin A-fortified foods and vitamin A supplements vs. the various provitamin A carotenoids. The functioning of carotenoids in physical activity has been recently reviewed. 8 Some athletes take too much vitamin A, which can be harmful and potentially toxic. The UL for vitamin A for adults is 3000 µg/day. 9

7 328 Sports Nutrition: Vitamins and Trace Elements Individuals can obtain vitamin D from the diet (including vitamin D-fortified foods), vitamin D supplements or exposure to sunlight. A few studies have been conducted with regard to vitamin D and physical performance. Vitamin D does not appear to be involved in athletic performance, though blood levels of the vitamin have been associated with musculoskeletal function in the elderly. Individuals sometimes take too much vitamin D, which can be harmful and potentially toxic. The UL for vitamin D for adults is 50 µg/day. 10 Vitamin K may come from dietary sources and synthesis by the intestinal microflora. Vitamin K is needed for proper blood clotting. Osteocalcin, a vitamin K-dependent protein, functions in bone formation. Low intakes of vitamin K, along with antibiotic therapy, may produce deficiency symptoms. To date, no evidence indicates that vitamin K has an ergogenic effect. There is not a UL for vitamin K. 9 Evidence indicates that exercise results in oxidative damage. Quoting Mastaloudis and Traber, the authors of Chapter 13, Vitamin E supplementation appears to be effective in attenuating lipid peroxidation induced by aerobic/endurance type exercise, but not strength training. The findings of various researchers on this topic seem to be influenced by the amount and duration of vitamin E or antioxidant mixture supplementation, the type, intensity and duration of the exercise, as well as how oxidative damage and athletic performance were measured. Additional well designed research is needed. Maras et al. 11 estimated the vitamin E intakes of U.S. adults in the Continuing Survey of Food Intakes by Individuals (CSFII) using α-tocopherol content values from Release 15 of U.S. Department of Agriculture s National Nutrient Database for Standard Reference and found that the vast majority of the adults included in the CSFII consumed less than the current RDA of vitamin E. Endurance athletes, as well as elderly individuals not on coumarin drugs, may benefit from taking vitamin E supplements. Vitamin E has an adverse effect on the functioning of the coumarin drugs. The UL for vitamin E for adults is 1,000 mg/d of any form of supplementary α-tocopherol. 1 IV. TRACE ELEMENTS Iron deficiency, the most prevalent single nutrient deficiency worldwide, reduces the amount of oxygen available for aerobic metabolism, thus limiting an individual s endurance. In anemia, caused by iron deficiency among other nutrient deficiencies and pathological conditions, the amount of oxygen transported by hemoglobin in blood is low. In the deficiency, a decrease in myoglobin is also observed that contributes to decreased muscular aerobic capacity. Lower concentrations of cytochromes and other iron-containing enzymes are also evident in the deficiency. Iron supplements given to individuals who are deficient or marginally deficient in iron has been shown to be beneficial with regard to aerobic work performance measurements. Athletes at the greatest risk of developing altered body iron status are female athletes, distance runners and vegetarian athletes. Iron deficiency without anemia is observed with high prevalence in female athletes and it may also be a problem in other athletic populations. Body iron may be redistributed in athletes. Iron supplements are widely used by athletes. Women athletes frequently do not meet their RDA of 18 mg/day and they may benefit from taking supplements containing iron. Male athletes generally easily meet their RDA of 8 mg/day. Several studies have been conducted on women athletes with adequate iron status who were given iron supplements. The majority of these studies found no improved performance with regard to various exercise measurements. However, a few studies have reported that the supplementation seemed to positively influence blood lactic acid concentrations after heavy exercise. Many studies have not indicated whether their subjects had adequate iron status prior to iron supplementation, a factor that would certainly influence their research findings. Iron at high doses can be toxic and people have overdosed on iron supplements. The UL of iron for adults is 45 mg/day. 9 Zinc plays many roles in carbohydrate, lipid and protein metabolism and thus is needed for optimal performance. Exercise induces increased excretion of zinc as compared with non-exercise conditions. However, the body tends to adapt by selectively adjusting absorption and endogenous

8 Summary Vitamins and Trace Elements in Sports Nutrition 329 excretion of the zinc, and generally the losses of zinc due to strenuous exercise are compensated. Recent evidence indicates that restricted zinc intake decreases muscle strength and endurance and impairs cardiorespiratory function. Data from the third National Health and Nutrition Survey (NHANES III), , indicate that the mean zinc intake of the U.S. population is less than half the recommended amount. 12 Evidence that zinc supplementation of individuals with adequate zinc status is beneficial with regard to physical performance is lacking. Excessive intakes of zinc may induce copper deficiency. The UL of zinc for adults is 40 mg/day. 9 Copper functions as a component of the body s antioxidant system, yet it can be toxic by causing the generation of free radicals. Copper is involved with oxygen consumption and stress. Evidence exists that athletes may have blood copper concentrations outside the normal range and increased losses of copper in urine and sweat during exercise. Surveys indicate that athletes, like others, frequently consume less than recommended intakes of copper. There is no evidence that the copper requirement for athletes is different from that of the general population. The UL of copper for adults is 10,000 µg/day. 9 Iodine is a component of the thyroid hormones that function in normal growth and metabolism, including metabolic energy production. Iodine deficiency, the most common cause of goiter, is prevalent in many developing countries. Little research has been published on the relationship between iodine and physical performance. Strenuous exercise does result in some changes in thyroid metabolism, though it is unclear whether these changes are temporary or permanent or even of biological significance. Iodine is present in sweat, and iodine losses can be substantial in extended exercise under hot conditions; this issue needs to be further investigated. Excessive intakes of iodine are potentially harmful. The UL of iodine for adults is 1,100 µg/day. 9 Chromium functions in the maintenance of blood glucose levels by potentiating the activity of insulin. Chromium excretion is influenced by the stress of exercise as well as diets high in monoand disaccharides. Athletes should consume enough chromium in their diets to meet recommendations. Early reports suggested that chromium picolinate supplementation would favorably increase the loss of body fat. However, these studies had flaws. Subsequent well controlled studies indicated that no basis exists for claims of chromium picolinate as a weight- or fat-loss agent in humans. Excessive intakes of chromium picolinate can have deleterious effects. No UL exists for chromium, as toxicity for that present in foods has not been observed. 9 Selenium, a constituent of glutathione peroxidase, functions as an antioxidant and may protect tissues from the oxidative stress induced by exercise. Selenium and vitamin E function as synergistic antioxidants; the same is true for selenium and ascorbic acid. No differences in pre- and 120-h post-race glutathione peroxidase activities were observed in trained athletes; however, erythrocytes were more susceptible to hydrogen peroxide-induced peroxidation after the race than before. Athletes given 100 to 240 µg selenium daily had decreased oxidative damage after exercise according to several studies; however, another study indicated that time to exhaustion on a treadmill was not influenced by the supplementation. Virtually no research has been conducted comparing the effects of the various forms of selenium on exercise measurements; some of the forms of selenium are less toxic than others. Selenium supplementation is not recommended at levels much above the RDAs because of the toxicities that have been observed at relatively low intake levels. The UL of selenium for adults is 400 µg/day. 1 RDAs exist for molybdenum and AIs for manganese. There is evidence that boron, nickel, silicon and vanadium have beneficial roles in some physiological processes in some species, though the evidence of such a role in humans is limited. Large intakes of these trace elements, possibly excluding silicon, can be toxic. 9 Suggestions have been made that several of these trace elements may be of benefit to individuals performing physical activity: boron may facilitate anabolic steroid activity; manganese, boron, silicon, nickel and vanadium may enhance bone strength and joint health; manganese, boron, nickel and vanadium may enhance energy utilization and endurance; and boron, manganese and molybdenum may help overcome the oxidative stress induced by vigorous exercise. Consumption of diets containing all the food groups likely provides sufficient amounts of

9 330 Sports Nutrition: Vitamins and Trace Elements these trace elements for optimal athletic performance. The ULs of adults for molybdenum is 2,000 µg/day; for manganese, 11 mg/day (represents intake from pharmacological agents only and does not include intake from food and water); boron, 20 mg/day; nickel, 1.0 mg/day; and vandanium, 1.8 mg/day. 9 A UL does not exist for silicon. 8 V. CONCLUSIONS AND IMPLICATIONS Generally, existing data do not suggest an effect of vitamins and trace elements on physical activity, exercise and sport as long as individuals are consuming adequate amounts of these nutrients, but the data are skimpy. Additional well designed research is needed on vitamins and trace minerals in relation to exercise and sport performance. Few double-blind, crossover, placebo-controlled studies have been conducted on humans and even fewer of these have been long-term. The initial vitamin or trace mineral status of the subjects has to be ascertained and only subjects having adequate status should be used in supplementation studies. Individuals having higher than normal status indices of the vitamin or trace mineral also should not be used as subjects in supplementation studies, because these individuals probably have previously taken rather large doses of the nutrient under study for several months. Initial baseline exercise parameter measurements of subjects should be determined prior to supplementation, as much individual variation exists among persons of all ages with regard to the values for the various exercise parameters. Exercise may affect the form of the vitamin in the plasma and in the body as a whole. Exercise may affect the distributions of the vitamins and trace minerals in the various body tissues. Vitamins and trace minerals may be effective at some dosage levels but not others. Studies should be of sufficient duration for effects, if any, to be observed. Some gender and age differences might exist. The efficacy of supplementation with the various vitamins and trace minerals may vary with regard to different forms of physical activity and different performance measurements. Does supplementation affect the performance variables on a short-term or long-term basis? How well do subjects adapt to supplementation and training? Are there mood changes that could affect performance? Large or excessive intakes of some of the vitamins and trace minerals may be detrimental to health. Many, but not all, of the nutrients are better utilized by the body if they are consumed as a component of food. Unfortunately, many people do not consume nutritionally adequate diets and these individuals would benefit from taking vitamin-mineral supplements. It appears prudent for all adults to take vitamin supplements, according to a scientific review and clinical applications paper published in 2002 in the Journal of the American Medical Association. 13 Athletes are encouraged to consume a nutritionally adequate diet and should consider, based on their dietary intakes and general state of health, whether they should take a multivitamin-multimineral supplement. Some evidence, though not conclusive, exists that the needs of athletes for antioxidant vitamins may be higher than of the typical population. REFERENCES 1. Institute of Medicine, National Academy of Sciences, Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids, National Academy Press, Washington, DC, U.S. Food and Drug Administration, A food labeling guide: Reference values for nutrition labeling, [Online] accessed January 27, Federation of American Societies for Experimental Biology, Life Sciences Research Office. Third Report on Nutrition Monitoring in the United States, vol. 2, U. S. Government Printing Office, Washington, DC, Dietary Supplement Information Bureau, Exploring consumer attitudes about Dietary Supplement Barometer Survey. [Online] accessed January 27, 2005.

10 Summary Vitamins and Trace Elements in Sports Nutrition Ervin, R.B., Wright, M.P.H. and Reed-Gillette, D., Prevalence of Leading Types of Dietary Supplements Used in the Third National Health and Nutrition Examination Survey, [Advance Data from Vital and Health Statistics, no. 349], National Center for Health Statistics, Hyattsville, MD, Krumbach, C.J., Ellis, D.R. and Driskell, J.A., A report of vitamin and mineral supplement use among university athletes in a Division I institution. Int. J. Sports Nutr. 9, , Institute of Medicine, National Academy of Sciences, Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B 6, Folate, Vitamin B 12, Pantothenic Acid, Biotin, and Choline, National Academy Press, Washington, DC, Stacewicz-Sapuntzakis, M. and Diwadkar-Navsariwla, V., Carotenoids, in Nutritional Ergogenic Aids, Wolinsky, I. and Driskell, J.A., Eds., CRC Press, Boca Raton, FL, Institute of Medicine, National Academy of Sciences, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc, National Academy Press, Washington, DC, Institute of Medicine, National Academy of Sciences, Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride, National Academy Press, Washington, DC, Maras, J.E., Bermudez, O.I., Qiao, N., Bakun, P.J., Boody-Alter, E.L. and Tucker, K.L., Intake of α- tocopherol is limited among U.S. adults. J. Am. Diet. Assoc. 104, , Briefel, R.R., Bialostosky, K., Kennedy-Stephenson, J., McDowell, M.A., Ervin, R.B., and Wright, J.D., Zinc intake of the U.S. population: Findings from the third National Health and Nutrition Examination Survey, J. Nutr. 130, 1367S 1373S, Fletcher, R.H. and Fairfield, K.M., Vitamins for chronic disease prevention in adults. J. Am. Med. Assoc. 287, , 2002.