Nitrogen Excretion in Sweat and Its Relation to Nitrogen Balance Requirements

The results of two experiments show that a considerable quantity of nitrogen is lost in sweat, under conditions that produce profuse sweating. These values average 149, 189 and 241 mg/hour during exposures to environmental temperatures of 70, 85 and 100°F, for men performing moderate daily physical activities. Men performing a daily minimum of physical activity at 100°F showed a decreased excretion of from 300 to approximately 200 mg/hour, after acclimatization. It has been observed that the nitrogen losses in sweat increased with an increase in physical activity and sweat rate. These observations are important since they show an additional nitrogen loss that has been ignored in many balance studies. Past studies where equilibrium was apparently attained should be reevaluated, with considerations for dermal nitrogen losses. The increased nitrogen losses in sweat, even after acclimatization, are not compensated by decreased nitrogen losses from the kidneys and alimentary tract. As a result, the protein requirements of 0.35 gm/kg body weight, should be increased by at least 13 to 14% to compensate for the nitrogen losses in sweat. The free amino acids excreted in sweat averaged more than 1 gm during a 7.5-hour exposure to 100°F temperatures. Data are also presented for other nitrogen compounds in sweat including urea nitrogen, ammonia, creatinine and uric acid.