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tale from World War II, I had him take 100 mg of vitamin C (ascorbic acid) three times daily during the summer months. Even though temperatures stayed at 32°C and higher (up to 40.6°C), he was able to drive his non-air-conditioned car and function. If he forgot to take his vitamin C, he got "sick."

In an early study, Henschel et al. (1944b) studied men who (a) were on a rigidly controlled vitamin C-restricted diet or on a vitamin C-supplemented (500 mg per day) diet for 4 to 7 days and who (b) were exercising in the heat for 2 hours per day for 4 days. The criterion measures were pulse rate at rest, pulse rate during exercise, and rectal temperature. No differences were found between the restricted and the supplemented conditions. Heat exhaustion occurred with equal frequency in each condition.

Strydom et al. (1976) reevaluated the Henschel et al. (1944b) study and noted that the authors had acknowledged that the vitamin C-supplemented condition showed a slight advantage with regard to rectal temperature. Furthermore, Henschel et al. (1944b) had studied only 4 days of heat stress, which may not have been sufficient to determine the effects of vitamin C supplementation. Therefore, Strydom et al. (1976) decided to further investigate whether vitamin C ingestion would affect the rate and degree of acclimatization to heat stress. In a study done in South Africa, they placed 60 mining recruits into three groups and administered a placebo, vitamin C (250 mg per day), or vitamin C (500 mg per day) for 10 days. During the supplementation period, the subjects were exposed to temperatures of 33.9°C for 4 hours per day while working at an intensity of 35 watts. Measurement of rectal temperature showed that vitamin C supplementation enhanced the rate and degree of acclimatization, with no difference between the two levels of supplementation. No effect of the supplement was found on sweat rates or heart rate response to the work. The initial blood levels of vitamin C for the three groups were 0.48 mg per 100 ml (placebo group), 0.60 mg per 100 ml (250-mg ascorbic acid group), and 0.43 mg per 100 ml (500-mg ascorbic acid group). These levels are considered adequate (Hunt and Groff, 1990), but at the low end of normal (Strydom et al., 1976).

In a subsequent study from the same laboratory (Kotze et al., 1977), a similar experiment was performed, but blood ascorbic acid levels were also assessed daily during the 10 days of heat stress. Resting blood ascorbic acid levels increased by the same amount in subjects receiving either the 250-mg or the 500-mg vitamin C supplement, and blood levels reached the saturation point between the third and the fifth day. The increase in blood ascorbic acid levels was associated with a reduction in rectal temperature and a reduction in total sweat output (which was independent of the reduction in rectal temperature). The maximum beneficial effect of the supplements in reducing rectal temperature occurred over the first 3 days of heat stress.

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