Roles of Brown Adipose Tissue in Seasonal Variations of Thermogenesis in Men

Abstract

ObjectiveBrown adipose tissue (BAT), a site of non‐shivering thermogenesis, plays a role in body temperature regulation during cold exposure. The incidence and activity of human BAT show seasonal variations, being low in summer and high in winter. In the present study, we examined a possible role of BAT to seasonal variations in whole‐body energy expenditure (EE) and thermoregulation.Methods and ResultsForty‐five healthy male volunteers underwent FDG‐PET/CT after 2‐h cold exposure at 19ºC in winter to estimate their maximal BAT activity, and were divided into high (n=30) and low (n=15) activity groups. Cold‐induced thermogenesis (CIT), the difference in EE at 27 and 19ºC, of the high activity group was higher in winter than summer (185.6 kcal/d v.s. 18.3 kcal/d, P < 0.001) whereas that of the low activity group unchanged (90.6 kcal/d, ‐46.5 kcal/d). The temperature of the eardrum (Tear) and the skin (Tskin) in the supraclavicular region close to BAT during cold exposure dropped more in the low activity group than the high activity group in winter, but not in summer. In contrast, the Tskin response in the other two regions distant from BAT was similar in the two groups in either season.ConclusionsCIT increased from summer to winter in a BAT‐dependent manner, in parallel with cold‐induced changes in Tear/Tskin, indicating a significant role of BAT in the seasonal changes in EE and thermal response to cold exposure.