Submitted to: Medicine and Science in Sports and Exercise
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2007
Publication Date: 5/15/2008
Citation: Chinevere, T.D., Kenefick, R.W., Cheuvront, S.N., Lukaski, H.C., Sawka, M.N. 2008. Effect of Heat Acclimation on Sweat Minerals. Medicine and Science in Sports and Exercise. 40(5):886-891
Interpretive Summary: Loss of minerals in sweat increases when people exercise in a hot environment. Repeated days of physical activity in the heat increase the volume of sweat produced and decrease the concentrations of sodium and potassium in sweat. This study examined the effect of combined moderate-level exercise in a hot environment (~110 degrees Fahrenheit) for 10 days on concentrations of calcium, copper, iron, magnesium, and zinc in sweat collected from an arm. Compared to the first day of exercise in the heat, body sweat rates increased (6%). Concentrations of sodium, calcium, copper, and magnesium in sweat decreased significantly from 30 to 50%, whereas concentrations of iron and zinc in sweat decreased less. Compared to the first day of exercise in the heat, the estimated sweat loss of calcium (75 vs 55 mg/hr), copper (0.41 vs 0.22 mg/hr) and magnesium (8.36 vs 4.85 mg/hr) decreased significantly after acclimation. In contrast, sweat losses of iron (0.32 vs 0.08 mg/hr) and zinc (0.88 vs 0.74 mg/hr) did not change significantly. The finding confirm that initial exposures to exercise in the heat elicit appreciable losses of minerals in sweat (1 to 30% of recommended intakes for men), and decrease (1 to 15% of recommended intakes) after acclimation to exercise and heat. However, increases in sweat rate during prolonged periods of exercise in the heat may increase mineral losses in heat-acclimated individuals. This information will be useful to nutrition professionals who advise people on adaptations in diet during periods of increase physical activity in hot environments.
Technical Abstract: Purpose: This study examined the impact of 10-days of exercise-heat acclimation on sweat mineral concentrations. Methods: Eight male subjects walked on a treadmill at 1.56 m/sec, 4% grade for 100 continuous minutes or until rectal temperature reached 39.5°C on 10 consecutive days in an environmental chamber set at 45°C, 20% relative humidity. Arm sweat samples were collected during the first 30 minutes of exercise-heat stress on days 1 and 10 using a polyethylene arm glove. Results: Final core temperature and HR values were significantly lower (P<0.05) on day 10 versus day 1. Whole body sweating rates increased by ~6% (P=0.12). Sweat sodium concentration on day 10 (833 ± 166 mg/L) was significantly lower than day 1 (1253 ± 372 mg/L) (P<0.05). Sweat mineral concentrations of calcium (~29%), copper (~50%), and magnesium (~43%) were also significantly lower on day 10 versus day 1 of heat acclimation (P<0.05). A trend for lower sweat iron (~75%; P=0.07) and zinc (~23%; P=0.10) concentrations were observed from day 1 to day 10. The estimated hourly sweat mineral losses (arm concentration x whole-body sweat rate) were reduced for calcium (~27%), copper (~46%), magnesium (~42%) (P<0.05), but not iron (~75%) and zinc (~16%) (P>0.05) from day 1 to day 10. Conclusion: Exercise-heat acclimation conserves arm sweat mineral concentrations and possibly whole-body sweat losses of calcium, copper, and magnesium; and may reduce sweat iron and zinc concentrations.