Individual variation in the relation between body temperature and energy expenditure in response to elevated ambient temperature

The question we address here is whether a mild increase in environmental te mperature affects body temperature and energy expenditure, focusing on the individual variation in the relation between energy expenditure and body te mperature. We studied eight normal weight healthy females, 48 h at an ambie nt temperature of 22 degreesC, and 48 h at 27 degreesC. Energy expenditure GEE) was measured in a respiration chamber. Subjects' skin temperature was measured continuously from 8:00 a.m. until 12:00 p.m.: forehead, infraclavi cular zone, thigh, hand, and foot. Core temperature was determined tympanic ally. Body composition was determined by under water weighing. Exposure to 27 degreesC caused a significant increase in body temperature (both skin an d core), a decrease in temperature gradients, and a decrease in energy expe nditure. At 27 degreesC 24 h EE, adjusted for body composition, was signifi cantly related to body tympanic temperature. The decrease in 24 h EE, at 27 0C ambient temperature, was significantly negatively related to the increas e in T-tym, indicating individual responses in adaptation to elevated ambie nt temperature. Changes in temperature gradient (comparing 27 degreesC with 22 degreesC) were negatively related to changes in EE. This shows that ind ividuals differ in their response to an increase in environmental temperatu re regarding the relative contribution of insulative or metabolic adjustmen ts. (C) 2001 Elsevier Science Inc. All rights reserved.