Seasonal changes in metabolic and temperature responses to cold air in humans

The metabolic and temperature response to mild cold were investigated in summer and winter in a moderate oceanic climate. Subjects were 10 women and 10 men, aged 19-36 years and BMI 17-32 kg/m(2). Metabolic rate (MR) and body temperatures were measured continuously in a climate chamber with an ambient temperature of 22 degreesC for I h and subsequently 3 h of 15 degreesC. The average metabolic response during cold exposure, measured as the increase in kJ/min over time, was significantly higher in winter (11.5%) compared to summer (7.0%, P < .05). The temperature response was comparable in both seasons. The metabolic response in winter was significantly related to the response in summer (r(2)=.47, P < .001). Total heat production during cold exposure was inversely related to the 2 temperature response in both seasons (summer, r(2)=.39, P < .01; winter r(2)=.32, P < .05). In conclusion, the observed higher metabolic response in winter compared to summer indicates cold adaptation. The magnitude of the cold response varies, but the relative contribution of metabolic and temperature response was subject specific and consistent throughout the seasons, which can have implications for energy balance and body composition. (C) 2004 Elsevier Inc. All rights reserved.