. "7. The Effect of Excercise and Heat on Mineral Metabolism and Requirements." Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press, 1993.
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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations
Consolazio et al. (1964) reported an average loss of 340 µg of selenium in sweat over an 8-hour period in men maintained at a temperature of 37.8°C. However, given the observation that typical selenium intakes are only on the order of 100 µg per day (Pennington et al., 1984), the loss reported by Consolazio seems excessive, and may reflect the technical difficulties involved in measuring this element. With the exception of the data by Consolazio, there are no current reports suggesting that selenium requirements are higher in hot environments compared to temperate regions.
Although the metabolic functions of chromium have not been clearly defined, chromium is known to be involved in the regulation of carbohydrate and lipid metabolism, presumably via a role in insulin action. Although not clearly defined in humans, signs associated with marginal chromium status in experimental animals include impaired glucose tolerance, elevated circulating insulin, elevated cholesterol and triglycerides, and increased incidence of aortic plaques (Campbell and Anderson, 1987). The dietary intake of chromium has been reported to be suboptimal for the general population based on dietary survey studies (Anderson and Kozlovsky, 1985). Recent research has indicated that chromium requirements may be influenced by strenuous exercise. Anderson et al. (1984) reported that serum chromium concentrations were increased in adult males immediately after a 6-mile run at near-maximal running capacity. This increase in serum chromium was still evident 2 hours after the completion of the run, and urinary chromium loss was elevated twofold on the run day compared to non-run days. Basal urinary chromium excretions have been shown to be lower in individuals routinely engaged in strenuous activity compared to sedentary controls (Anderson et al., 1988), which suggests either that chronic exercise results in a partial depletion of body chromium stores or that it induces metabolic changes that result in a reduction in urinary chromium excretion. Consistent with the latter idea, Vallerand et al. (1984) reported that, in rats, exercise training is associated with an increase in soft tissue chromium concentrations. In addition to exercise-induced increases in urinary chromium excretion, it would be expected that chromium losses would also be increased with excessive sweating. However, due to analytical difficulties in measuring this element, accurate data on sweat-associated losses of chromium are not currently available. Consolazio et al. (1964) reported that chromium loss in sweat over an 8-hour period averaged 60 µg in men maintained at 37.8°C, a value that would be double that of the typical dietary intake of the element. Studies aimed at better defining the amount of chromium lost in sweat at different amounts of sweat loss are clearly needed.
Chromium deficiency per se has not been accepted as a health problem in endurance athletes. However, it seems prudent, given the above findings, to monitor chromium status of individuals engaged in strenuous activity for prolonged periods of time, particularly if the activity is performed in a hot