The requirement for B vitamins does not seem to be increased by living and working in a hot environment. Although loss of these vitamins in sweat is minimal, a deficiency could occur over time from profuse sweating coupled with an insufficient dietary intake. Because thiamin, riboflavin, niacin, and vitamin B6 are important to energy metabolism, the level of vitamin intake should be related to the amount of food consumed. Thus, for adults, 0.5 mg of thiamin per 1000-kcal diet, 0.6 mg of riboflavin per 1000-kcal diet, 0.016 mg of vitamin B6 per g protein, and 6.6 mg of niacin per 1000-kcal diet are recommended (National Research Council, 1989). If calorie intake is not sufficient to meet the demands of exercise in the heat, then the vitamin intake will be compromised as well.
Folic acid and vitamin B12 are not linked to energy production, and their intake should be that of the 1989 RDA. There is no information to suggest that exposure to a hot environment would increase their need above levels recommended by the National Research Council.
Since World War I, vitamin C has received popular attention as a nutrient that can reduce heat stress. More recent studies have generally confirmed the anecdotal studies. Increased vitamin intake of 250 mg seems to have a positive effect on reducing heat stress during acclimatization in those individuals with adequate but low vitamin C levels. Some data have shown that vitamin C status may be compromised by long-term exposure to a hot environment. Thus, vitamin C supplements may be useful for those individuals who live and work in a hot environment. However, intakes of greater than 250 mg per day are not recommended because high doses of vitamin C can adversely affect the absorption of vitamin B12.
The one study (Bell et al., 1988) suggesting that vitamin D may be related to muscle building induced by strenuous resistance exercise is interesting and warrants further attention. However, at this time, there is no reason to recommend vitamin D supplements for people who work in the heat. Exposure to sunlight probably is sufficient for adequate vitamin D status.
Vitamins A, C, and E are antioxidants and may be useful in the reduction of lipid peroxidation induced by exercise stress. However, there have been no studies to examine whether lipid peroxidation is exacerbated by exercise in a hot environment. Further studies on whether these vitamins will be important as antioxidants for people living and working in a hot environment are warranted.
The following recommendations are made:
Thiamin, riboflavin, vitamin B6, and niacin should be linked to changes in food consumption as recommended by the RDAs (National Research Council, 1989). Insufficient data exist to recommend otherwise.