Thus, the supplements were more effective when heat stress was relatively high and blood levels of vitamin C had not reached the saturation point.
Although vitamin C status was adequate for the subjects in both of the studies cited above, the status was probably lower than in the normal healthy population, and the vitamin C supplementation raised blood levels of vitamin C to that found in healthy, well-fed individuals. However, blood levels of 0.43 to 0.60 mg per 100 ml may not be uncharacteristic of many lower socioeconomic groups, especially those who have poor diets, do not take supplements, and are smokers. In fact, Woteki et al. (1986) reported that in a 1976–1980 survey, about 5 percent of young adult American males were found to have blood vitamin C levels below 0.25 mg per 100 ml. Thus it could be expected that a sizable proportion of those individuals rapidly mobilized into military service may have suboptimal vitamin C status (between 0.43 and 0.60 mg per 100 ml).
Some data show that vitamin C status may be compromised by living and working in a hot environment for an extended period of time (see Scott, 1975). Visagie et al. (1974) found among mine workers in South Africa a high incidence of vitamin C deficiency during the first 3 months of employment. This deficiency occurred despite diets adequate in vitamin C.
Hindson (1970) examined vitamin C levels in the white blood cells of apparently healthy Europeans living in the tropics, a subject population consisting of British forces and their families living in Singapore. Anyone taking vitamin C supplements was excluded. Results showed a significant drop in vitamin C levels for the men but only a modest fall for the women. Although vitamin C is not lost in sweat to a significant degree in acclimatized individuals, vitamin C is needed in increased quantities for the process of sweating. Hindson (1970) concluded that vitamin C supplements should be taken by men who are working in the tropics. Also, vitamin C has been shown to be beneficial in treating prickly heat, a common disease of sweat glands for those living in the tropics (Hindson, 1970).
Recently, Chen et al. (1990) developed a sports drink especially for athletes training in hot environments. Made from Actinidia sinensis Planch (ASP; also known as kiwifruit), the drink contained several minerals and 48 mg per 100 ml vitamin C (Chen et al., 1990). During the summer of 1982, elite Chinese soccer and track athletes were tested at their training site. Environmental temperatures were 26.6° to 31.5°C. Athletes drank 500 to 1200 ml of ASP 10 minutes prior to a 1.5-to 2.7-hour normal training session and again halfway through the training session. On a separate occasion (training session), subjects drank an equivalent volume of a placebo drink. Vitamin C content in the athletes' urine averaged 132 mg per day when ingesting the ASP drink and 44 mg per day when ingesting the placebo. The authors concluded that vitamin C status of athletes ingesting the