Skip to main content
ARS Home » Plains Area » Grand Forks, North Dakota » Grand Forks Human Nutrition Research Center » Healthy Body Weight Research » Research » Publications at this Location » Publication #209970
Title: Sweat mineral element responses during 7 h of exercise-heat stress

Author
item MONTAIN, SCOTT - USARIEM
item CHEUVRONT, SAMUEL - USARIEM
item Lukaski, Henry

Submitted to: International Journal of Sport Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2007
Publication Date: 12/15/2007
Citation: Montain, S.J., Cheuvront, S.N., Lukaski, H.C. 2007. Sweat mineral element responses during 7 h of exercise-heat stress. International Journal of Sport Nutrition. 17(6):574-582.

Interpretive Summary: Environmental conditions and physical activity affect the loss of minerals for the body surface. With increased emphasis on increasing physical activity, particularly exercise, to promote health, there is a need to examine the impact of controlled exercise on the loss of minerals in sweat. Healthy military personnel, who were adapted to a hot and humid environment, participated in a trial in which sweat was collected from the upper back during exposure to hot-dry and hot-dry environmental conditions while walking. Sweat was collected during five consecutive 60-minute periods. At 27 degrees Celsius, sweat sodium, potassium, calcium, magnesium, and copper concentrations did not change significantly during the 300 min exposure. In contrast, zinc concentration declined significantly during the trial. Similar results were found during the 30 degree Celsius exposure despite the doubling of the rate of sweating. The key finding is that sweat concentration, and hence loss, of zinc decreases during prolonged bouts of exercise in hot environments. Although the reason for this apparent conservation of zinc is not known, it may be explained by a loss of skin cells during the initial heat-exercise exposure. Zinc is located in cells in greater concentrations than in blood. These findings are important because they provide new evidence that sweat loss of minerals is appreciable and can significantly contribute to reducing body stores of minerals during physical activity in hot and humid environments. This information will be useful to dietitians and nutritional professionals who advise physically active people.

Technical Abstract: Uncertainty exists regarding the effect of sustained sweating on sweat mineral element composition. This study determined the effect of multiple hours of exercise-heat stress on sweat mineral concentrations. Seven heat acclimated subjects (6 males, 1 female) completed 5 consecutive 60 min bouts of treadmill exercise (1.56 m/s, 2% grade) with 20 min rest between each exercise period in two weather conditions (27°C, 40% relative humidity and 35°C, 30% relative humidity at a constant air flow of 1 m/s). Sweat was collected from a sweat collection pouch attached to the upper back during exercise bouts 1, 3 and 5. Mineral elements were determined by using inductively coupled plasma emission spectrography. In 27°C condition, sweat sodium (863 [563] ug/ml; mean [sd]), potassium (222 [48] ug/ml), calcium (16 [7]) ug/ml), magnesium (1265 [566] ng/ml), and copper (80 [56] ng/ml) remained similar to baseline over 7 h of exercise-heat stress, whereas sweat zinc declined 42-45% after the initial hour of exercise-heat stress (Ex1=655 [362], Ex3=382 [168], Ex5=355 [288] ng/ml, p<0.05). Similar outcomes were observed for sweat zinc in 35°C when sweat rate was ~2x greater. Sweating rate had no effect on sweat trace element composition. Sweat sodium, potassium and calcium losses during multiple hours of sustained sweating, can be predicted from initial sweat composition. Estimates of sweat zinc losses, however, will be overestimated if sweat zinc conservation is not accounted for in sweat zinc loss estimates.