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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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