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).

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