Brown adipose tissue thermogenesis among young adults in northeastern Siberia and Midwest United States and its relationship with other biological adaptations to cold climates.

OBJECTIVES: Recent research suggests that brown adipose tissue (BAT) plays a functional role in non-shivering thermogenesis; however, few studies have examined population variation in BAT or its relationship with other mechanisms of adaptation to cold stress. This study characterized BAT thermogenesis and other adaptive responses to low temperatures among Indigenous Siberian young adults and young adults living near Chicago, IL. MATERIALS AND METHODS: We recruited 72 Yakut participants (42 females; 30 males) and 54 participants in Evanston, IL (40 females; 14 males). Anthropometric dimensions and resting metabolic rate (RMR) were measured, and we calculated percent divergence in RMR from expected values (divRMR). We also quantified change in supraclavicular temperature, sternum temperature, and energy expenditure after a mild cooling condition. RESULTS: Participants in Yakutia were less likely to shiver during the cooling condition (p < .05) and exhibited significantly greater evidence of BAT thermogenesis, warmer sternum temperatures, and higher divRMR than participants in Evanston (p < .05). Additionally, the relationship between change in supraclavicular temperature and energy expenditure differed between the two samples. CONCLUSIONS: Yakut young adults displayed greater evidence of BAT thermogenesis in response to mild cooling compared with young adults living near Chicago, IL. Furthermore, the relationship between BAT thermogenesis and change in energy expenditure appears to be stronger among Yakut adults. Adults that exhibited greater metabolic response to cold stress, such as higher BAT thermogenesis and divRMR, maintained warmer sternum temperatures. These results highlight the degree to which adaptation to cold climates involves multiple integrated biological pathways.

Evidence for a sensitive period of plasticity in brown adipose tissue during early childhood among indigenous Siberians.

OBJECTIVES: Evolutionary theorists have debated the adaptive significance of developmental plasticity in organisms with long lifespans such as humans. This debate in part stems from uncertainty regarding the timing of sensitive periods. Does sensitivity to environmental signals fluctuate across development or does it steadily decline? We investigated developmental plasticity in brown adipose tissue (BAT) among indigenous Siberians in order to explore the timing of phenotypic sensitivity to cold stress. METHODS: BAT thermogenesis was quantified using infrared thermal imaging in 78 adults (25 men; 33 women). Cold exposure during gestation, infancy, early childhood, middle childhood, and adolescence was quantified using: (1) the average ambient temperature across each period; (2) the number of times daily temperature dropped below -40°F during each period. We also assessed past cold exposure with a retrospective survey of participation in outdoor activities. RESULTS: Adult BAT thermogenesis was significantly associated with the average temperature (p = 0.021), the number of times it was below -40°F (p = 0.026), and participation in winter outdoor activities (p = 0.037) during early childhood. CONCLUSIONS: Our results suggest that early childhood represents an important stage for developmental plasticity, and that culture may play a critical role in shaping the timing of environmental signals. The findings highlight a new pathway through which the local consequences of global climate change may influence human biology, and they suggest that ambient temperature may represent an understudied component of the developmental origins of health and disease.