Cold-induced thermogenesis, the energy expenditure increase above basal metabolic rate during cold exposure, could have a role in combating obesity. However, studies of cold-induced thermogenesis in older adults are sparse. We measured the capacity of cold-induced thermogenesis at the individualized coldest tolerable temperature before overt shivering in lean younger and older men.
During a 10-13 day inpatient study, we measured the energy expenditure of 12 younger (22.5±4.9 y) and 10 older men (61.0±4.9 y) of similar body mass index (23.1±1.6 kg/m2) and fat percentage (21.3±4.8%) at randomized, daily ambient temperatures from 16-31oC in a room calorimeter. Body composition was measured by dual-energy X-ray absorptiometry.
Compared to younger men, older men had a 0.37±0.09oC lower tympanic temperature over all ambient temperatures (p<0.001), but basal metabolic rate was not different after controlling for lean body mass (1579±149 kcal/d versus 1728±156 kcal/d for younger men, p=0.2). The temperature below which cold-induced thermogenesis begins, lower critical temperature, was 1.5oC warmer in older men (p=0.03), but the coldest tolerable temperatures were similar (21.3±1.3oC).The capacity of cold-induced thermogenesis in older men averaged 34.3±23.4% or 538±374 kcal/d above basal metabolism and was not different from that of younger men (17.1±11.2% or 300±218 kcal/d, p=0.1)
Despite a lower core temperature and warmer onset of cold-induced thermogenesis, older lean men demonstrated similar cold tolerance and cold-induced thermogenesis capacity to younger lean men. Further study is required to determine relative contribution to cold-induced thermogenesis from muscle and brown adipose tissue activation in younger and older men.