Author
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Lukaski, Henry |
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Submitted to: Cell Biology and Toxicology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/1/2008 Publication Date: 9/1/2008 Citation: Lukaski, H.C. 2008. Mineral Losses During Extreme Environmental Conditions. Cell Biology and Toxicology. 24:466-470. Interpretive Summary: For more than 50 years, researchers have measured the concentrations of various minerals in the sweat of people exercising in the heat. Interpretation of the significance of the observed changes in the concentrations and losses of minerals has been complicated by a number of factors. Lack of standardization of measurement sites on the body, contamination of sweat, insensitive analytical methods, and variable temperature and exercise regimen contribute to the large variation in reported values. Nevertheless, some important conclusions are available. Use of regional sites for sweat collection over-estimates whole-body losses. Sweat collected at the abdomen, compared to the arm or back, yields greater concentrations of iron and zinc. The ambient temperature also affects mineral concentrations in sweat. For example, sweat concentrations are reduced in cool compared to hot temperatures but total mineral losses are similar because sweat rates are higher in hot conditions. Diminished sweat calcium, iron and zinc concentrations occur during repeated bouts of daily exercise or a prolonged exercise session. The nutritional significance of sweat loss of minerals is variable. Sweat losses of calcium, iron and zinc represents 10, 3 and 9%, respectively of recommended daily intakes. Although these findings suggest that sweat losses of calcium, iron and zinc can adversely affect mineral needs, refined and practical measurements of sweat losses that control for inter-regional variability and contamination must be developed and validated. Technical Abstract: Advisory groups that make recommendations for mineral intakes continue to identify accurate determinations of sweat mineral losses during physical activity as a critical void in their deliberations. Although estimates of sweat mineral concentrations are available, they are highly variable. Practical assessments use various sites on the body to collect sweat because of the difficulty to collect whole-body sweat during exercise. Iron and zinc concentrations in the sweat obtained from the abdomen and chest were more than twice as large as compared to the arm and back. However, use of regional sites overestimated whole-body loss of calcium more than 300%. Similarly, exercising in a cool compared to a hot environment resulted in decreased iron and zinc concentrations at the arm. Iron retention was significantly reduced in men consuming high (~35 mg) and usual (~18 mg/d) iron intakes and exercising in the heat when sweat losses of iron were included in the balance calculation. Also, inclusion of estimates of zinc loss in sweat of physically active men decreased zinc retention. A few studies reported that measured sweat losses of minerals during exercise were appreciable, and accounted for 10, 9 and 3% of recommended daily intakes of calcium and zinc, and iron, respectively. Further work using valid measurements of sweat losses of minerals is need. This information will be useful to dietetic and nutrition professionals who counsel physically active people. |
