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8
The Effect of Exercise and Heat on Vitamin Requirements

Priscilla M. Clarkson1

INTRODUCTION

Vitamins are essential nutrients that have a wide variety of functions. The fact that many vitamins play a critical role in energy production has captured the attention of those interested in ways to optimize exercise or work performance. Moreover, increased energy production during exercise could lead to an increased vitamin requirement for those individuals who participate in rigorous physical training.

Because vitamins are essential, generally cannot be manufactured by the body, and must be ingested on a regular basis, it has been tempting to suggest that if a little is good, more is better. This reasoning was perhaps the impetus for many studies that have assessed the effects of vitamin supplementation on physical performance (Robinson and Robinson, 1954). A review of early studies suggested that vitamins were lost to a significant degree in sweat (Robinson and Robinson, 1954). For this reason, exercise—especially in hot environments—was considered to result in vitamin deficiencies. Now it is generally agreed that the vitamin loss in sweat is negligible (Brotherhood, 1984; Mitchell and Edman, 1951; Robinson and Robinson, 1954) (Table 8-1). However, some vitamins have been implicated to have beneficial effects for those individuals living and working in a hot environment.

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Priscilla M. Clarkson, Department of Exercise Science, Boyden Building, University of Massachusetts at Amherst, Amherst, MA 01003



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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations 8 The Effect of Exercise and Heat on Vitamin Requirements Priscilla M. Clarkson1 INTRODUCTION Vitamins are essential nutrients that have a wide variety of functions. The fact that many vitamins play a critical role in energy production has captured the attention of those interested in ways to optimize exercise or work performance. Moreover, increased energy production during exercise could lead to an increased vitamin requirement for those individuals who participate in rigorous physical training. Because vitamins are essential, generally cannot be manufactured by the body, and must be ingested on a regular basis, it has been tempting to suggest that if a little is good, more is better. This reasoning was perhaps the impetus for many studies that have assessed the effects of vitamin supplementation on physical performance (Robinson and Robinson, 1954). A review of early studies suggested that vitamins were lost to a significant degree in sweat (Robinson and Robinson, 1954). For this reason, exercise—especially in hot environments—was considered to result in vitamin deficiencies. Now it is generally agreed that the vitamin loss in sweat is negligible (Brotherhood, 1984; Mitchell and Edman, 1951; Robinson and Robinson, 1954) (Table 8-1). However, some vitamins have been implicated to have beneficial effects for those individuals living and working in a hot environment. 1   Priscilla M. Clarkson, Department of Exercise Science, Boyden Building, University of Massachusetts at Amherst, Amherst, MA 01003

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations TABLE 8-1 Concentration of Vitamins Lost in Sweat Vitamin Concentration (µg per 100 ml) Thiamin 0–15 Riboflavin 0.5–12 Nicotinic acid (total) 8–14 Pantothenic acid 4–30 Ascorbic acid 0–50 Pyridoxine 7 Folic acid (plus metabolites) 0.26   SOURCE: Mitchell and Edman (1951). Data based on ranges reported from several studies completed in the 1940s. This chapter addresses whether those individuals who expend greater amounts of energy in exercise training or work require greater amounts of vitamins and whether vitamin supplementation will enhance exercise performance. Some of this information has also been covered in a previous paper (Clarkson, 1991). This chapter also examines whether exercise in a hot environment will lead to an increased requirement for certain vitamins and whether vitamin supplements will reduce heat stress. Vitamins are classified as either water soluble or fat soluble. Watersoluble vitamins are the B complex vitamins and vitamin C. These are stored in relatively small amounts in the body and cannot be retained for long periods. If blood levels of water-soluble vitamins exceed renal threshold, they are excreted into the urine. Most water-soluble vitamins serve major functions of either energy production or hematopoiesis. With the exception of vitamin K, fat-soluble vitamins are stored in greater amounts than the water-soluble vitamins. Fat-soluble vitamins are absorbed and transported in the body in close association with lipids and have roles that are largely independent of energy production. WATER-SOLUBLE VITAMINS Vitamin B complex consists of eight vitamins: vitamin B1 (thiamin), vitamin B2 (riboflavin), niacin, vitamin B6 (pyridoxine), vitamin B12 (cyanocobalamin), biotin, folic acid, and pantothenic acid. The quantity stored differs among the vitamins. For example, if an individual's diet is deficient in most of the B vitamins, clinical symptoms can sometimes occur in 3 to 7 days (Guyton, 1986). Vitamin B12 is an exception because it can be stored in the liver for a year or longer. The B vitamins, except B12 and folic acid, primarily serve as coenzymes in the metabolism of glucose and fatty

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations acids. Vitamin C serves many diverse functions in the body. A vitamin C-deficient diet can cause deficiency symptoms after a few weeks and can cause death from scurvy in 5 to 7 months (Guyton, 1986). In the following discussion, these topics will be addressed for each vitamin: its function, how an individual's status is determined, changes in status by chronic exercise, effects of restriction or supplementation on performance, and relationship to heat stress. Thiamin The importance of thiamin ingestion was noted in the late nineteenth century when it was found that adding meat and whole grain to sailors' diets aboard ship prevented the condition known as beriberi (Brown, 1990). Thiamin is absorbed from the small intestine, and some is phosphorylated to form pyrophosphate (the coenzyme form). Pyrophosphate and free thiamin are transported via the blood to tissues, with the highest concentrations occurring in the liver, kidney, and heart. Most thiamin is stored in the pyrophosphate form. Thiamin plays a role in carbohydrate metabolism. It functions specifically as a coenzyme in the conversion of pyruvate to acetyl coenzyme A (CoA) and alpha-ketoglutarate to succinyl CoA, as well as the transketolase reaction of the pentose phosphate pathway. A sensitive technique for assessing thiamin status is the use of an erythrocyte enzyme stimulation test performed on blood samples. Erythrocyte transketolase activity is assessed before and after addition of thiamin pyrophosphate (TPP). If a deficiency of TPP exists, then adding TPP to the blood will increase the activity of the enzyme. The level of erythrocyte TPP is also used to determine thiamin status. Sauberlich et al. (1979) reported that urinary excretion of thiamin was a reasonably reliable indicator of thiamin nutritional status, although its use has been questioned (Gubler, 1984). Whether physical exercise, because of the greater metabolic challenge, will increase the need for thiamin has not been fully established. The few studies that have assessed possible biochemical deficiencies of athletes have reported minimal evidence of thiamin deficiency compared with controls (Cohen et al., 1985; Guilland et al., 1989; Weight et al., 1988). Nijakowski (1966) found that blood levels of thiamin were lower in male athletes compared with a control group, however, it is possible that the lower levels were due to plasma volume expansion in athletes. Athletes were also tested after a 12-km skiing expedition, and thiamin levels showed a further decrease, which Nijakowski (1966) suggested was due to increased bodily requirements. The National Research Council (1989) recommended that thiamin intake be proportional to caloric intake such that 0.5 mg per 1000 kcal is

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations required. Because of the increased energy demands of exercise, athletes ingest more food. However, many athletes are ingesting a greater proportion of carbohydrates, and it has been shown that some athletes have a high intake of refined carbohydrates with low vitamin content (Brouns and Saris 1989). Furthermore, carbohydrate loading regimens can result in low thiamin intakes. In the 1979 Tour de France, thiamin intakes were found to be too low (0.26 mg per 1000 kcal), which was attributed to the high carbohydrate meals. Van Erp-Baart et al. (1989) also pointed out that when energy intake is high, the amount of refined carbohydrate is high, and the nutrient density of thiamin drops. Because of the role of thiamin in energy metabolism, it would seem that thiamin deficiency would lead to decrements in exercise performance. However, although thiamin-deficient diets along with deficiencies in other B complex vitamins were shown to adversely affect performance (for review see Van der Beek, 1985), there is some controversy concerning whether thiamin deficiency alone will alter performance (Williams, 1976, 1989). Wood et al. (1980) in a well-controlled study found that performance was not affected by induced thiamin deficiency. They reported no significant difference in time to exhaustion during a cycle ergometry test between subjects who ingested a low-thiamin diet (500 ºg thiamin) for 4 to 5 weeks along with a placebo (without thiamin) and subjects who had ingested the same low-thiamin diet along with a thiamin supplement (5 mg thiamin). Few studies have assessed the effect of thiamin supplementation on exercise performance (see Keith, 1989). In two controlled studies, the effects of thiamin supplements of 5 mg per day for 1 week on an arm endurance task (Karpovich and Millman, 1942) and 0.1 mg daily for 10 to 12 weeks on grip strength and treadmill tests (aerobic and anaerobic work) (Keys et al., 1943) were examined. Both studies found that the supplement had no effect on any measure of work performance. Mills (1941) studied the effects of heat stress on young rats and found that optimal thiamin intake for growth was increased at high temperature (91°F), although these results were not confirmed by later studies (Edison et al., 1945). Based on his own findings, however, Mills (1941) suggested that thiamin supplements should make workers in boiler or furnace rooms or in other types of heat exposure more resistant to heat effects. Other studies found that an increase in environmental temperature resulted in a decreased thiamin requirement (Edison et al., 1945), and this decrease reflected the decrease in caloric requirements at elevated temperatures. However, the animals in that study were not exercising. It has been shown that exercise in the heat is more metabolically costly perhaps because of the extra energy costs of sweating, circulation, and respiratory mechanisms (Nielsen et al., 1990). If increased caloric intake is needed for those working in a hot environment, then thiamin intake should be increased proportionally.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Thiamin loss in sweat is considered to be around 10 µg per 100 ml (Table 8-1). Working in a hot environment can produce sweat losses of up to 10 liters per day. At this value, the amount of thiamin lost would be about 1.0 mg. Although a well-balanced diet could probably satisfy this need, there should be some concern if the diet is poor or if the thiamin requirement is not increased with an increase in energy intake (to meet the demands of work). Riboflavin The coenzyme forms of riboflavin are flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes function in cellular oxidation, specifically acting as hydrogen carriers in the mitochondrial electron transport system. Deficiencies in riboflavin are common in many Third World countries and occur invariably with deficiencies in the other water-soluble vitamins (McCormick, 1990). Riboflavin status can be assessed reliably from blood samples. A sensitive indicator is the measurement of erythrocyte glutathione reductase (EGR) activity (Cooperman and Lopez, 1984). When riboflavin stores are low, EGR loses its saturation with FAD, and its activity drops (Cooperman and Lopez, 1984). Whether chronic exercise alters riboflavin status is not certain. For the general U.S. population and most athlete groups studied, biochemical deficiencies of riboflavin are rare (Cohen et al., 1985; Guilland et al., 1989; Tremblay et al., 1984). However, one study found inadequate riboflavin status in 8 out of 18 athletes studied (Haralambie, 1976). It has been suggested that exercise training may increase the need for riboflavin. Belko et al. (1983) found that the need for riboflavin in healthy young women (based on an estimation of riboflavin intake required to achieve normal biochemical status) increased when they participated in jogging exercise for 20 to 50 minutes a day. Because biochemical deficiencies in athletes are rare, the increased need for riboflavin probably would be easily met by diet. Because of the importance of riboflavin to oxidative energy production, performance could be impaired by a riboflavin deficiency. Keys et al. (1944) placed six male students on a riboflavin-restricted diet (99 mg per day or 0.31 mg per 1000 kcal) for 84 days (n = 3) and 152 days (n = 3). Subjects performed an aerobic walking test (60 minutes) and an anaerobic test (60 seconds) on the treadmill and performed grip strength tests before, every 2 weeks during, and after the restricted-diet period. The low-riboflavin diet did not adversely alter the performance measures. Van der Beek (1985) reviewed other studies on riboflavin restriction and concluded that riboflavin depletion did not alter work performance on submaximal treadmill tests. Because studies have shown that riboflavin deficiency does not alter

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations exercise performance, it would seem that supplementation should not enhance performance. Belko et al. (1983) studied the effects of riboflavin supplementation in two groups of overweight women who participated in a 12-week exercise program. One group ingested a total of 0.96 mg per 1000 kcal riboflavin per day, and the other group ingested 1.16 mg per 1000 kcal per day. The improvement in aerobic capacity did not differ between groups. Also no difference in exercise performance was found when elite swimmers were supplemented with 60 mg per day of riboflavin for 16 to 20 days (Tremblay et al., 1984). Tucker et al. (1960) studied the effects of exercise and heat stress on riboflavin excretion into the urine. In one experiment, men walked on a treadmill for 4 to 6 hours per day for six days with the temperature of the heat chamber at 49°C. The men spent a total of 10 hours per day at this temperature. Riboflavin excretion increased gradually over the course of the six days. The authors concluded that there could be a decreased requirement of riboflavin at high temperatures. The limited data available suggest that the riboflavin requirement may be increased by exercise. However, these needs must be easily met by athletes' diets because athletes have not been shown to have a riboflavin deficiency. The one study concerning exercise and heat stress suggests that there could be a decrease in riboflavin requirement. Further study is needed to confirm this. The amount of riboflavin lost in sweat is small (Table 8-1) and should not be a problem for those working in a hot environment and profusely sweating. The recommended intake of riboflavin is linked to caloric intake (0.6 mg per 1000 kcal), and to be safe, this recommendation should be followed by people living and working in a hot environment. Niacin Niacin is the term used to describe nicotinic acid (niacin) and nicotinamide (niacinamide). In the body, niacin is an essential component of two coenzymes: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). These coenzymes serve as electron carriers or hydrogen donors/acceptors in glycolysis, fatty acid oxidation, and the electron transport system. Severe niacin deficiency results in the condition known as pellagra (raw skin), which was common in the United States in the early 1900s but has virtually disappeared from industrialized countries (Swendseid and Swendseid, 1990). Two available studies of niacin nutriture of athletes suggest that athletes are not deficient in niacin (Cohen et al., 1985; Weight et al., 1988). These studies used nicotinic acid or niacin levels in the blood to determine status—a questionable assessment technique because niacin and niacin metabolites in the plasma are quite low (Hankes, 1984; Swendseid and Swendseid,

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations 1990). Erythrocyte NAD concentration or levels of 2-pyridone may be more sensitive indicators of niacin depletion (Swendseid and Swendseid, 1990). Some evidence suggests that exercise may increase the niacin requirement (Keith, 1989). Because most adult athletes have shown no evidence of niacin deficiency, the increased requirement probably is satisfied by the athlete's diet. Chronic ingestion of niacin above the recommended dietary allowance (RDA) (National Research Council, 1989) is not recommended, because large doses are often associated with undesirable side effects, such as flushing, liver damage, increased serum uric acid levels, skin problems, and elevated plasma glucose levels (Hunt and Groff, 1990). Niacinamide in large doses is not harmful. Acute ingestion of nicotinic acid (3 to 9 g per day) has also been shown to prevent the release of fatty acids (Keith, 1989; National Research Council, 1989), which may adversely affect endurance performance. In a double-blind placebo-controlled experiment, Hilsendager and Karpovich (1964) found that 75 mg of niacin had no effect on arm or leg endurance capacity. Bergstrom et al. (1969) compared the perception of a work load before and after subjects were given niacin, 1 g intravenously and 0.6 g perorally. After the supplementation, the subjects perceived the work load to be heavier. Niacin can decrease free fatty acid mobilization (Carlson and Oro, 1962; Williams, 1989), which may explain the negative effects of the niacin supplement. A decrease in free fatty acid mobilization would force the muscle to rely more on its muscle glycogen stores. In fact, Bergstrom et al. (1969) found that muscle glycogen content was lower in postexercise biopsy samples taken from subjects who had received the niacin supplements than with control subjects. The only information with regard to niacin requirements in a hot environment comes from an early study that found that nicotinic acid was lost in the sweat in significant amounts (100 µg per 100 ml; Mickelsen and Keys, 1943). However, later studies did not agree with this finding (Mitchell and Edman, 1951; Robinson and Robinson, 1954). Nicotinic acid is considered to be lost in concentrations of 20 µg or less per 100 ml of sweat (Mitchell and Edman, 1951). As with thiamin and riboflavin, niacin intake should be proportional to energy intake (6.6 mg niacin per 1000 kcal). If energy intake is increased to meet the demands of exercise or work in a hot environment, then niacin should be increased as well. Vitamin B6 (Pyridoxine) Vitamin B6 is composed of three natural compounds—pyridoxine, pyridoxamine, and pyridoxal (Merrill and Burnham, 1990)—that function in protein hemoglobin, myoglobin, and cytochromes. The coenzyme form of B6 is and amino acid metabolism; in gluconeogenesis; and in formation of

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations pyridoxal 5'-phosphate (PLP) and is used by over 60 enzymes. Glycogen phosphorylase, an enzyme involved in the breakdown of muscle glycogen, requires PLP as a coenzyme. Moreover, glycogen phosphorylase may serve as a reservoir for vitamin B6 storage (Merrill and Burnham, 1990) and release PLP into the circulation for use by other tissues. Vitamin B6 status in blood samples can be assessed in several ways (Driskell, 1984). The method of choice is to assess levels of PLP, the most active form of vitamin B6 (Driskell, 1984). Chronic exercise does not appear to result in a vitamin B6 deficiency. Although biochemical deficiencies for vitamin B6 were found in 17 to 35 percent of male college athletes, similar percentages were found for the control group (Guilland et al., 1989). However, the athletes had a greater intake of vitamin B6 compared with the control subjects. Adequate vitamin B6 levels were found from assessments of blood samples of other groups of athletes (Cohen et al., 1985; Weight et al., 1988). Although it seems that vitamin B6 status is not altered by chronic exercise, some studies have shown that acute exercise can alter the blood levels. Leklem and Shultz (1983) found that a 4500-m run substantially increased the blood levels of PLP in trained adolescent males. Hatcher et al. (1982) and Manore and Leklem (1988) reported an increase in blood levels of PLP after a 50-minute and after a 20-minute cycling exercise. PLP levels returned to baseline values after only 30 minutes rest (Manore and Leklem, 1988). It was suggested (Leklem and Shultz, 1983; Manore and Leklem, 1988) that PLP may be released from muscle glycogen phosphorylase during exercise so that PLP could be used as a cofactor for gluconeogenesis elsewhere in the body. Holmann et al. (1991) also found that prolonged treadmill running (2 hours at 60 to 65 percent of ) resulted in significant increases in blood levels of PLP that were independent of changes in plasma volume, blood glucose, blood free fatty acid levels, and blood enzyme levels. The authors suggested that the increase in plasma PLP could be due to a release of vitamin B6 from the liver to be used in skeletal muscle to fully saturate glycogen phosphorylase or be used for other critical PLP-dependent reactions (for example, aminotransaminase reactions). Another study found that 4-pyridoxic acid excretion in urine was significantly lower in trained athletes compared with controls after a vitamin B6 challenge (Dreon and Butterfield, 1986). The authors suggested that these results reflect a greater storage capacity in athletes so that 4-pyridoxic acid could be available for redistribution with increased need. Supplementation with vitamin B6 does not appear to enhance performance. Lawrence et al. (1975a) examined swimming performance of trained swimmers who ingested 51 mg of pyridoxine hydrochloride or a placebo

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations daily for 6 months. No significant difference was found between the groups on 100-yard swimming times. Because vitamin B6 is an integral part of the glycogen phosphorylase enzyme, several studies have examined the relationship between carbohydrate intake and vitamin B6. Hatcher et al. (1982) found that blood levels of PLP and vitamin B6 after exercise were lower in subjects who had consumed a low-carbohydrate diet compared with a moderate-or high-carbohydrate diet 3 days before the exercise. The authors suggested that on the low carbohydrate diet gluconeogenesis is accelerated, which increases the need for PLP as a cofactor. In another study from the same laboratory, de Vos et al. (1982) reported that vitamin B6 supplementation may cause a faster depletion of muscle glycogen stores during exercise after ingestion of a low-carbohydrate diet and may accentuate a depletion-loading manipulation used by athletes to increase glycogen stores (glycogen supercompensation). Manore and Leklem (1988) found that vitamin B6 supplementation, along with increased carbohydrate consumption, resulted in lower free fatty acids during exercise. The authors recommended that athletes who are on a highcarbohydrate diet should not supplement their diets with vitamin B6 above the RDA level. Presently there are no data regarding vitamin B6 requirements in a hot environment. The amount of vitamin B6 lost in sweat is considered insignificant (Mitchell and Edman, 1951). However, if food intake is increased, then the amount of vitamin B6 should be increased accordingly. It is recommended that 0.016 mg per g protein of vitamin B6 be ingested (vitamin B6 and protein occur together naturally in foods) (National Research Council, 1989). Pantothenic Acid Pantothenic acid acts as a structural component of coenzyme A (CoA), an acyl carrier protein. Pantothenic acid is important in transport of acyl groups to the Krebs cycle and in transport of fatty acyl groups across the mitochondrial membrane (Olson, 1990). Pantothenic acid is widely distributed in nature and found in all organisms. Therefore deficiencies are rare. However, during World War II, pantothenic acid deficiency was thought to be responsible for the burning foot syndrome among prisoners in Japan and the Philippines (Fox, 1984). It is not known whether exercise increases the requirement for pantothenic acid. Nijakowski (1966) found that athletes had higher levels of pantothenic acid in the blood compared to controls. Cycle ergometry exercise of short duration resulted in a decrease in pantothenic acid levels in the blood, but the levels were unchanged after a long-duration exercise of 4

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations hours. Because plasma volume was not corrected for, it is difficult to interpret these changes. The effect of pantothenic acid supplementation on exercise performance is equivocal. Compared with the placebo group, highly trained endurance runners who ingested 2-g doses of pantothenic acid per day for 2 weeks showed decreased exercise blood lactate levels and decreased oxygen consumption during prolonged exercise at 75 percent (Litoff et al., 1985). In contrast, Nice et al. (1984), using a controlled double-blind study, examined the effect of pantothenic acid supplementation (1 g per day for 2 weeks) or a placebo on run time to exhaustion in 18 highly trained distance runners. No significant differences were found between groups in run time or any of the standard blood parameters that were assessed (that is, cortisol, glucose, creatine phosphokinase, electrolytes). There are no data to suggest that the need for pantothenic acid would be increased by living and working in a hot environment. Pantothenic acid is not lost to a significant degree in sweat (Mitchell and Edman, 1951). Vitamin B12 (Cyanocobalamin) Vitamin B12 plays a role in the formation and function of red blood cells (Ellenbogen, 1984) and may also function in protein, fat, and carbohydrate metabolism (Van der Beek, 1985). The condition of pernicious anemia was first described in 1924, and in 1929 a factor in liver was found to act as an antipernicious factor. It was not until 1948 that vitamin B12 was isolated and used to treat pernicious anemia (Ellenbogen, 1984). No information is available on vitamin B12 status in athletes. However, it should be noted that athletes who are complete vegetarians may acquire a vitamin B12 deficiency because vitamin B12 is found mainly in animal products. Red cell vitamin B12 levels can indicate vitamin B12 status; however, low levels may also indicate a folate deficiency (Herbert, 1990). Several other tests are available to discern the two deficiencies; these are detailed elsewhere (Herbert, 1990). Existing evidence suggests that vitamin B12 supplementation has no effect on performance (Williams, 1976). Montoye et al. (1955), in a doubleblind study, placed 51 adolescent boys (ages 12 to 17) into either an experimental group that consumed 50 µg of vitamin B12 daily, a placebo group, or a control group. No significant difference was found after 7 weeks between the supplemented group or the placebo group in the time to run 0.5 mile or in the Harvard step-test score (Montoye et al., 1955). Tin-May-Than et al. (1978) studied performance capacity in 36 healthy male subjects before and after injection of 1 mg cyanocobalamin given 3 times a week for 6 weeks. They found no significant improvement in , grip strength, pull-ups, leg lifts, or standing broad jump performance.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations There is no information concerning the effects of heat stress on vitamin B12 status. Recent studies have shown that megadoses of vitamin C (500 mg) may detrimentally affect the availability of vitamin B12 from food (Herbert, 1990). Doses of vitamin C of 3 g per day may even result in vitamin B12 deficiency disease. How this occurs is still unclear, but Herbert (1990) states that nutritionists should advise persons taking megadoses of vitamin C to have their blood checked regularly for vitamin B12 status. These findings should be taken into account with regard to the use of vitamin C to reduce heat stress (see section on vitamin C). Folic Acid (Folate) and Biotin Folic acid (pteroylglutamic acid) and folate (pteroylglutamate) are involved with DNA synthesis and nucleotide and amino acid metabolism, and they are especially important in tissues undergoing rapid turnover, such as red blood cells. Folic acid deficiency has been suggested to be the most common vitamin deficiency in humans and can result in anemia (Keith, 1989). No studies have assessed the relationship of folic acid status and exercise performance or the effect of folic acid supplementation on performance. Biotin acts as a coenzyme for several carboxylase enzymes that are important in supplying intermediates for the Krebs cycle and for amino acid metabolism. It is also important in fatty acid and glycogen synthesis. Biotin deficiencies are rare in individuals consuming a nutritionally sound diet. One study found no difference in blood biotin levels in athletes compared with controls (Nijakowski, 1966). No studies have examined the effect of biotin supplementation on performance. B Complex Vitamins Many studies have shown that a deficiency of more than one of the B complex vitamins could lead to a decrease in physical performance capacity (for detailed reviews, see Van der Beek, 1985; Williams, 1989). Deficiency of a combination of several B vitamins produced subjective symptoms of fatigue, loss of ambition, irritability, and pain and loss of efficiency during normal work (see Van der Beek, 1985). Most of the studies that evaluated the effects of depletion of several B vitamins were done in the 1940s. More recently, Van der Beek et al. (1988) placed 12 men on a thiamin-, riboflavin-, vitamin C-, and vitamin B6-poor diet for 8 weeks. After 8 weeks, this diet caused borderline or moderately deficient blood levels of the four vitamins. These deficiencies were associated with a 9.8 percent decrease in and a 19.6 percent decrease in anaerobic threshold. Thus, a restricted diet of 21.3 to 32.5 percent of the Dutch RDA of these B vitamins

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Gey, G.O., K.H. Cooper, and R.A. Bottenberg 1970 Effect of ascorbic acid on endurance performance and athletic injury. J. Am. Med. Assoc. 211:105. Gleeson, M., J.D. Robertson, and R.J. Maughan 1987 Influence of exercise on ascorbic acid status in man. Clin. Sci. 73:501–505. Goldfarb, A.H., M.K. Todd, B.T. Boyer, H.M. Alessio, and R.G. Cutler 1989 Effect of vitamin E on lipid peroxidation at 80 percent max. Med. Sci. Sports Exerc. 21:S16 (abstract). Gubler, C.J. 1984 Thiamin. Pp. 245–297 in Handbook of Vitamins. Nutritional, Biochemical and Clinical Aspects, L.J. Machlin, ed. New York: Marcel Dekker. Guilland, J., T. Penaranda, C. Gallet, V. Boggio, F. Fuchs, and J. Klepping 1989 Vitamin status of young athletes including the effects of supplementation. Med. Sci. Sports Exerc. 21:441–449. Guyton, A.C. 1986 Textbook of Medical Physiology, 7th ed. Philadelphia: W.B. Saunders. Hankes, L.V. 1984 Nicotinic acid and Nicotinamide. Pp. 329–377 in Handbook of Vitamins. Nutritional, Biochemical and Clinical Aspects, L.J. Machlin, ed. New York: Marcel Dekker. Haralambie, G. 1976 Vitamin B2 status in athletes and the influence of riboflavin administration on neuromuscular irritability . Nutr. Metab. 20:1–8. Hatcher, L.F., J.E. Leklem, and D.E. Campbell 1982 Altered vitamin B6 metabolism during exercise in man: Effect of carbohydrate modified diets and vitamin B6 supplements. Med. Sci. Sports Exerc. 14:112 (abstract). Helgheim, I., O. Hetland, S. Nilsson, F. Ingjer, and S.B. Stromme 1979 The effects of vitamin E on serum enzyme levels following heavy exercise. Eur. J. Appl. Physiol. 40:283–289. Henschel, A., H.L. Taylor, O. Mickelsen, J.M. Brozek, and A. Keys 1944a The effect of high vitamin C and B intake on the ability of man to work in hot environments. Fed. Proc. 3:18. Henschel, A., H.L. Taylor, J. Brozek, O. Mickelsen, and A. Keys 1944b Vitamin C and ability to work in hot environments. Am. J. Trop. Med. Hyg. 24: 259–264. Herbert, V. 1990 Vitamin B-12. Pp. 170–178 in Present Knowledge in Nutrition, M. L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Hilsendager, D., and P. Karpovich 1964 Ergogenic effect of glycine and niacin separately and in combination. Res. Q. 35:389–392. Hindson, T.C. 1970 Ascorbic acid status of Europeans resident in the tropics. Br. J. Nutr. 24:801–802. Hofmann, A., R.D. Reynolds, B.L. Smoak, V.G. Villanueva, and P.A. Duester 1991 Plasma pyridoxal and pyridoxal 5'-phosphate concentrations in response to ingestion of water or glucose polymer during a 2-h run. Am. J. Clin. Nutr. 53:84–89. Holmes, H.N. 1942 Vitamin C in the war. Science 96:384–386. Howaid, H., B. Segesser, and W.F. Korner 1975 Ascorbic acid and athletic performance. Ann. N.Y. Acad. Sci. 258:458–463.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Hunt, S.M., and J.L. Groff 1990 Advanced Nutrition and Human Metabolism. St. Paul, Minn.: West Publishing. Jaffe, G.M. 1984 Vitamin C. Pp. 199–244 in Handbook of Vitamins. Nutritional, Biochemical and Clinical Aspects, L. J. Machlin, ed. New York: Marcel Dekker. Kagen, V.E., V.B. Spirichev, and A.N. Erin 1989 Vitamin E, physical exercise, and sport. Pp. 255–278 in Nutrition in Exercise and Sport, J.E. Hickson and I. Wolinsky, eds. Boca Raton, Florida: CRC Press. Kanter, M.M., G.R. Lesmes, L.A. Kaminsky, J. La Ham-Saeger, and N.D. Nequin 1988 Serum creatine kinase and lactate dehydrogenase changes following an eighty kilometer race. Eur. J. Appl. Physiol. 57:60–63. Karpovich, P.V., and N. Millman 1942 Vitamin B1 and endurance. N. Engl. J. Med. 226:881–882. Keith, R.E. 1989 Vitamins in sport and exercise. Pp. 233–253 in Nutrition in Exercise and Sport, J.E. Hickson and I. Wolinsky, eds. Boca Raton, Florida: CRC Press. Keith, R.E., and J.A. Driskell 1982 Lung function and treadmill performance of smoking and nonsmoking males receiving ascorbic acid supplements. Am. J. Clin. Nutr. 36:840–845. Keith, R.E., and E. Merrill 1983 The effects of vitamin C on maximal grip strength and muscular endurance. J. Sports Med. 23:253–256. Kendall, A.C. 1972 Rickets in the tropics and sub-tropics. Cent. Afr. J. Med. 18:47–49. Keren, G., and Y. Epstein 1980 The effect of high dosage vitamin C intake on aerobic and anaerobic capacity. J. Sports Med. 20:145–148. Keys, A., and A.F. Henschel 1941 High vitamin supplementation (B1, nicotinic acid and C) and the response to intensive exercise in U.S. Army infantrymen. Am. J. Physiol. 133:350–351. 1942 Vitamin supplementation of U.S. Army rations in relation to fatigue and the ability to do muscular work. J. Nutr. 23:259–269. Keys, A., A.F. Henschel, O. Mickelsen, and J. M. Brozek 1943 The performance of normal young men on controlled thiamine intaes. J. Nutr. 26:399–415. Keys, A., A.F. Henschel, O. Mickelsen, J.M. Brozek, and J.H. Crawford 1944 Physiological and biochemical functions in normal young men on a diet restricted in riboflavin. J. Nutr. 27:165–178. Kobayashi, Y. 1974 Effect of vitamin E on aerobic work performance in man during acute exposure to hypoxic hypoxia. Ph.D. dissertation. University of New Mexico, Albuquerque. Kotze, H.F., W.H. van der Wait, G.G. Rogers, and N.B. Strydom 1977 Effects of plasma ascorbic acid levels on heat acclimatization in man. J. Appl. Physiol. 42:711–716. Lawrence, J.D., J.L. Smith, R.C. Bower, and W.P. Riehl 1975a The effect of alpha-tocopherol (vitamin E) and pyridoxine HCI (vitamin B6) on the swimming endurance of trained swimmers. J. Am. Coil. Health Assoc. 23:219–222. Lawrence, J.D., R.C. Bower, W.P. Riehl, and J.L. Smith 1975b Effects of alpha-tocopherol acetate on the swimming endurance of trained swimmers. Am. J. Clin. Nutr. 28: 205–208.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Leklem, J.E., and T.D. Shultz 1983 Increased plasma pyridoxal 5'-phosphate and vitamin B6 in male adolescents after 4500-meter run. Am. J. Clin. Nutr. 38:541–548. Litoff, D., H. Scherzer, and J. Harrison 1985 Effects of pantothenic acid supplementation on human exercise. Med. Sci. Sports Exerc. 17:287 (abstract). Machlin, L.J. 1984 Vitamin E. Pp. 99–145 in Handbook of Vitamins. Nutritional, Biochemical and Clinical Aspects, L.J. Machlin, ed. New York: Marcel Dekker. Machlin, L.J., and A. Bendich 1987 Free radical tissue damage: Protective role of antioxidant nutrients. Fed. Am. Soc. Exp. Biol. J. 1:441–445. Manore, M.M., and J.E. Leklem 1988 Effect of carbohydrate and vitamin B6 on fuel substrates during exercise in women. Med. Sci. Sports Exerc. 20: 233–241. Maughan, R.J., A.E. Donnelly, M. Gleeson, P.H. Whiting, and K.A. Walker 1989 Delayed-onset muscle damage and lipid peroxidation in man after a downhill run. Muscle Nerve 12:332–336. Mayer, J., and B. Bullen 1960 Nutrition and athletic performance. Physiol. Rev. 40:369–397. McCormick, D.B. 1990 Riboflavin. Pp. 146–154 in Present Knowledge in Nutrition, M.L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Merrill, Jr., A.H., and F.S. Burnham 1990 Vitamin B-6. Pp. 155–162 in Present Knowledge in Nutrition, M. L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Mickelsen, O., and A. Keys 1943 The composition of sweat with special reference to the vitamins. J. Biol. Chem. 149: 479–490. Mills, C.A. 1941 Environmental temperatures and thiamine requirements. Am. J. Physiol. 133:525–532. Mitchell, H.H., and M. Edman 1951 Nutrition and Climatic Stress. Springfield, Ill.: Charles C. Thomas. Montoye, H.J., P.J. Spata, V. Pinckney, and L. Barron 1955 Effects of vitamin B12 supplementation on physical fitness and growth of young boys. J. Appl. Physiol. 7:589–592. Nagawa, T., H. Kita, J. Aoki, T. Maeshima, and K. Shiozawa 1968 The effect of vitamin E on endurance. Asian Med. J. 11:619–633. National Research Council 1989 Recommended Dietary Allowances, 10th ed. Washington, D.C.: National Academy Press. Nice, C., A.G. Reeves, T. Brinck-Johnsen, and W. Noll 1984 The effects of pantothenic acid on human exercise capacity. J. Sports Med. 24:26–29. Nielsen, B., G. Savard, E.A. Richter, M. Hargreaves, and B. Saltin 1990 Muscle blood flow and muscle metabolism during exercise and heat stress. J. Appl. Physiol. 69:1040–1046. Nijakowski, F. 1966 Assays of some vitamins of the B complex group in human blood in relation to muscular effort. Acta Physiol. Pol. 17:397–404.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Norman, A.W. 1990 Vitamin D. Pp. 108–116 in Present Knowledge in Nutrition, M. L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Olson, J.A. 1984 Vitamin A. Pp. 1–43 in Handbook of Vitamins. Nutritional, Biochemical and Clinical Aspects, L. J. Machlin, ed. New York: Marcel Dekker. 1990 Vitamin A. Pp. 96–107 in Present Knowledge in Nutrition, M. L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Olson, R.E. 1990 Pantothenic acid. Pp. 208–211 in Present Knowledge in Nutrition, M. L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Pike, R.L., and M.L. Brown 1984 Nutrition, An Integrated Approach, 3rd ed. New York: Macmillan. Pincemail, J., C. Deby, G. Camus, F. Pirnay, R. Bouchez, L. Massaux, and R. Goutier 1988 Tocopherol mobilization during intensive exercise. Eur. J. Appl. Physiol. 57:189–191. Poda, G.A. 1979 Vitamin C for heat symptoms? Ann. Intern. Med. 91(4):657. Read, M.H., and S.L. McGuffin 1983 The effect of B-complex supplementation on endurance performance. J. Sports Med. 23:178–184. Robinson, S., and A.H. Robinson 1954 Chemical composition of sweat. Physiol. Rev. 34:202–220. Sauberlich, H.E. 1990 Ascorbic acid. Pp. 132–141 in Present Knowledge in Nutrition, M.L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Sauberlich, H.E., Y.F. Herman, C.O. Stevens, and R.H. Herman 1979 Thiamin requirement of the adult human. Am. J. Clin. Nutr. 32:2237–2248. Scott, M.L. 1975 Environmental influences on ascorbic acid requirements in animals. Ann. N.Y. Acad. Sci. 258:151–155. Sharman, I.M., M.G. Down, and R.N. Sen 1971 The effects of vitamin E and training on physiological function and athletic performance in adolescent swimmers. Br. J. Nutr. 26:265–276. Sharman, I.M., M.G. Down, and N.G. Norgan 1976 The effects of vitamin E on physiological function and athletic performance of trained swimmers. J. Sports Med. 16:215–225. Shephard, R.J., R. Campbell, P. Pimm, D. Stuart, and G.R. Wright 1974 Vitamin E, exercise, and the recovery from physical activity. Eur. J. Appl. Physiol. 33:119–126. Simon-Schnass, I., and H. Pabst 1988 Influence of vitamin E on physical performance. Internat. J. Vit. Nutr. Res. 58:49–54. Staton, W.M. 1952 The influence of ascorbic acid in minimizing post-exercise muscle soreness in young men. Res. Q. 23:356–360. Strydom, N.B., H.F. Kotze, W.H. Van der Wait, and G.G. Rogers 1976 Effect of ascorbic acid on rate of heat acclimatization. J. Appl. Physiol. 41:202–205. Sumida, S., K. Tanaka, H. Kitao, and F. Nakadomo 1989 Exercise-induced lipid peroxidation and leakage of enzymes before and after vitamin E supplementation. Int. J. Biochem. 21:835–838.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Swendseid, J., and M.E. Swendseid 1990 Niacin. Pp. 163–169 in Present Knowledge in Nutrition, M. L. Brown, ed. Washington, D.C.: International Life Sciences Institute. Talbot, D., and J. Jamieson 1977 An examination of the effect of vitamin E on the performance of highly trained swimmers. Can. J. Appl. Sport Sci. 2:67–69. Tin-May-Than, Ma-Win-May, Khin-Sann-Aung, and M. Mya-Tu 1978 The effect of vitamin B12 on physical performance capacity. Br. J. Nutr. 40:269–273. Tremblay, A., B. Boilard, M.F. Breton, H. Bessette, and A.G. Roberge 1984 The effects of riboflavin supplementation on the nutritional status and performance of elite swimmers. Nutr. Res. 4:201–208. Tucker, R.G., O. Mickelsen, and A. Keys 1960 The influence of sleep, work, diuresis, heat, acute starvation, thiamine intake and bed rest on human riboflavin excretion. J. Nutr. 72:251–261. Van der Beek, E.J. 1985 Vitamins and endurance training: Food for running or faddish claims? Sports Med. 2:175–197. Van der Beek, E.J., W. van Dokkum, J. Schrijver, M. Wedel, A.W.K. Gaillard, A. Wesstra, H. van de Weerd, and R.J.J. Hermus 1988 Thiamin, riboflavin, and vitamins B-6 and C: Impact of combined restricted intake on functional performance in man . Am. J. Clin. Nutr. 48:1451–1462. Van der Beek, E.J., W. van Dokkum, J. Schrijver, A. Wesstra, C. Kistemaker and R.J.J. Hermus 1990 Controlled vitamin C restriction and physical performance in volunteers. J. Am. Coil. Nutr. 9:332–339. Van Erp-Baart, A.M.J., W.M.H. Saris, R.A. Binkhorst, J.A. Vos, and J.W.H. Elvers 1989 Nationwide survey on nutritional habits in elite athletes. Part 2. Mineral and vitamin intake. Int. J. Sports Med. 10:S11–16. Viguie, C.A., L. Packer, and G.A. Brooks 1989 Antioxidant supplementation affects indices of muscle trauma and oxidant stress in human blood during exercise. Med. Sci. Sports Exerc. 21:S16 (abstract). Visagie, M.E., J.P. Du Plessis, G. Groothof, A. Alberts, and N.F. Laubscher 1974 Changes in vitamin A and C levels in Black mine workers. S. African Med. J. 48:2502–2506. Wald, G., L. Brouha, and R.E. Johnson 1942 Experimental human vitamin A deficiency and the ability to perform muscular exercise . Am. J. Physiol. 137:551–556. Watt, T., T. T. Romet, I. McFarlane, D. McGuey, C. Allen, and R.C. Goode 1974 Vitamin E and oxygen consumption. Lancet 2:354–355 (abstract). Weight, L.M., T.D. Noakes, D. Labadarios, J. Graves, P. Jacobs, and P.A. Berman 1988 Vitamin and mineral status of trained athletes including the effects of supplementation. Am. J. Clin. Nutr. 47:186–191. Williams, M. H. 1976 Nutritional Aspects of Human Physical and Athletic Performance. Springfield, Ill.: Charles C. Thomas. 1989 Vitamin supplementation and athletic performance, an overview. Int. J. Vitam. Nutr. Res. 30:161–191. Wood, B., A. Gijsbers, A. Goode, S. Davis, J. Mulholland, and K. Breen 1980 A study of partial thiamin restriction in human volunteers. Am. J. Clin. Nutr. 33:848–861.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Woteki, C., C. Johnson, and R. Murphy 1986 Nutritional status of the U.S. population: Iron, vitamin C, and zinc. Pp. 21–39 in What is America Eating? Proceedings of a Symposium, Food and Nutrition Board, National Research Council. Washington, D.C.: National Academy Press. Young, A.J. 1990 Energy substrate utilization during exercise in extreme environments. Pp. 65–117 in Exercise and Sport Sciences Reviews, vol. 18, K. E. Pandolf, ed. Baltimore, Md.: Williams & Wilkins. DISCUSSION DR. NESHEIM: Thank you, Dr. Clarkson. We have a few minutes for questions or comments. DR. EVANS: Well, we have one paper that we published in January and two more that are about to be published in which we have looked at the effects of vitamin E supplementations on skeletal muscle damage, circulating and skeletal muscle cytokine (CK) levels, and neutrophil generation. And it appears that vitamin E has a profound effect in subjects that are over 60 in terms of altering all of their responses so that they look like young people in terms of CK release and neutrophil generation and monocyte function. But it has very little effect in young people in all of those things and it may well be that membrane function is very different in old people as compared to young people. But the other thing that vitamin E does is that it causes almost a total suppression of interleukin-1 (IL-1) production which may also have some very interesting effects. If IL-1 is necessary for adaptation to increased use, vitamin E may have some not such great effects. PARTICIPANT: Dr. Clarkson, I was particularly interested in how you arrived at the quantitative figure of 250 milligrams (mg) for vitamin C. DR. CLARKSON: That is what Strydom (Strydom et al., 1976) actually used in his paper. He used 250 milligrams as a supplement as well as 500 mg. PARTICIPANT: Did he titrate the dose or was that just something that he chose? DR. CLARKSON: I believe he based it on the Henshel et al. earlier study, (Henschel et al., 1944b) and it was no different. That graph depicting the 250 mg and the 500 mg dose showed no difference between the two doses. So 250 mg seems to be sufficient. PARTICIPANT: You know it seems to be striking that all of the potential

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations effects on vitamin supplementation have been measured just using a gross measure in a . Maybe you can comment on that. It seems to me that there are so many other potentially more sensitive measurements that we can make of metabolic responses to exercise that have been ignored for the most part because is easy to measure. DR. CLARKSON: I agree. Many studies that we find have used but there are also several studies that used submaximal exercise and studies that used strength. These are easy to measure. I think that is why they are used. Also, except for vitamin C where I only showed you three representative studies, mostly all the studies that are available were presented here. So it is not that there are a hundred other studies out there. I think that more people should be involved in looking at the effects of vitamins on performance. I think one of the problems why people aren't involved in looking at vitamins is that it is hard to measure in the blood and therefore difficult to determine initial status. PARTICIPANT: My question is specifically in terms of looking at measurements as opposed to plasma or sweat loss. What about some other measure—urine or something else. DR. CLARKSON: Well, urine levels are hard to interpret because what happens is, as soon as you reach a threshold level the nutrient spills over, so you are not quite sure what urinary secretion means. Does increased excretion mean you need less? Perhaps for a nonexercising person this is true. I am not ready to really believe that for an exercising person. In this case when you get an increased excretion it is not clear what this really means. If I gave a sedentary individual large doses of a particular vitamin and it increases in the urine, then we would say, yes, the status is adequate and the person does not need a supplement. However, when you add stressors like heat and exercise, I am not really sure what an increase in urinary levels of vitamins means. PARTICIPANT: I just wanted to follow up one comment you had made on niacin. There are two papers—certainly submitted—in those studies Evelyn Stephasson(?) had administered niacin supplementation to individuals and had them exposed to heat and attempted exercise. She found a very profound dilation and increased incidence of syncopy. So niacin supplementation in heat could actually reduce performance. DR. CLARKSON: Yes, I mentioned the flushing. PARTICIPANT: In the Strydom (Strydom et al., 1976) paper, do you hap-

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations pen to recall whether he assessed what the vitamin C status was before he did the supplementation? DR. CLARKSON: No, on the second paper they did check vitamin C levels. PARTICIPANT: And they were adequate before this? DR. CLARKSON: Yes, but low. PARTICIPANT: Based on plasma concentrations? DR. CLARKSON: Yes. PARTICIPANT: I just want to make a comment. I don't know if anyone noticed, about a week or two ago in Science magazine, there was just a short note on Dr. Linus Pauling who is still at age 90 consuming 18 grams per day of vitamin C. I don't know what type of effects that would have on absorption and interference that you talk about. And the other thing, I was also interested in the work in the South Africans on vitamin C apparently accelerating the acquisition of acclimation. Do you know of any other papers that have followed that up? That was mid-1970s; correct? DR. CLARKSON: Yes, and that is it. I found that one. PARTICIPANT: I could offer a technical comment. My thesis was on vitamin B12 chemistry and I did study some of the interactions of vitamin C and B12 and so has Victor Herbert (RDA, ninth edition). And a lot of these effects are an artifact of the analytical techniques. I don't take that too seriously. It turns out that vitamin C plus certain forms of B12 will be generating singlet oxygen and will destroy the chromophore in the test tube. So if you don't prevent this artifact—it is a pro-oxidant when you add it to iron usually. So a lot of the studies are flawed because they didn't prevent this. You have high C levels carried over in your serum when you are doing analysis in B12. DR. CLARKSON: In his (Herbert, 1990) recent review of literature on vitamin B12, Herbert suggests that vitamin C does have an effect on absorption of vitamin B12. PARTICIPANT: Just a comment on vitamin B12. I would think it would be rather unlikely that you would see a B12 deficiency if you were to put adults on a low intake for a period of time. It is going to take a long long time to get a deficiency.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations Actually, I did my thesis work on B12 requirements in baby pigs and the only way we could ever produce a B12 requirement in those pigs was to put the dams on a low or almost no B12 intake and then take the pigs away from the dam almost immediately after birth and put them on a vitamin B12-free diet and then we could produce a deficiency and, as a matter of fact, we produced it very quickly. But if we let them have the colostrum milk for even four or five days, it just went a long time to ever produce a B12 deficiency. PARTICIPANT: I would like to comment that there is some data that I think has appeared in the literature now by Doris Calloway and colleagues who were involved in a three-country study—Mexico, Kenya, and Egypt—and were looking at growth and other performance parameters in children. They appeared to be finding an impact of animal protein intake per day in terms of the growth and development of these young children and they are looking very hard at trying to get data on the actual B12 content of these diets. It is a possibility, since these populations tend to be very much on a vegetarian type of program—very little meat in these poorer populations—that you are seeing some of it (vitamin B12 deficiency) in the military. But then again, I think it is highly unlikely that we would see a B12 deficiency as it relates to that. PARTICIPANT: Just maybe one other comment. Haven't there been some reported vitamin D deficiencies in Middle Eastern countries in which women, in fact, have very little skin exposure to the sun? I mean, it is a complicating factor. In a desert environment, many people have kind of an ironic effect of D deficiency because their skin doesn't see the sun. PARTICIPANT: I seem to recall reading some comments to that but I don't know of any specific literature. DR. EVANS: We are in the process of conducting some studies in vitamin D deficiencies in older people but vitamin D deficiency is very present. They don't drink milk and they don't see the sun very much and it may be associated with a profound muscle weakness due to a calcium metabolism problem. DR. CLARKSON: There might also be vitamin D deficiencies in some athlete groups like dancers who don't drink milk, because quite a few of them do have a low consumption of milk and they do not spend much time in the sunlight. PARTICIPANT: I was going to ask a question, and this relates to the microorganisms in the GI tract and the vitamin C. I wonder, has anyone

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations done any studies and looked at the types of microbes that are in the GI tract, the possibility of infection (subclinical infections) that occur in long-distance runners? Has anyone ever done that type of work? PARTICIPANT: If anything, there was one paper that suggested that too much vitamin C might contribute to some of the lesions that have been observed in the GI tract in athletes. PARTICIPANT: You would have to take in a large amount, wouldn't you? DR. EVANS: With some athletes, apparently they do take in quite a bit. DR. NESHEIM: Thank you very much for your interesting comments.

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