Human whole body cold adaptation

Abstract

Reviews on whole body human cold adaptation generally do not distinguish between population studies and dedicated acclimation studies, leading to confusing results. Population studies show that indigenous black Africans have reduced shivering thermogenesis in the cold and poor cold induced vasodilation in fingers and toes compared to Caucasians and Inuit. About 40,000 y after humans left Africa, natives in cold terrestrial areas seems to have developed not only behavioral adaptations, but also physiological adaptations to cold. Dedicated studies show that repeated whole body exposure of individual volunteers, mainly Caucasians, to severe cold results in reduced cold sensation but no major physiological changes. Repeated cold water immersion seems to slightly reduce metabolic heat production, while repeated exposure to milder cold conditions shows some increase in metabolic heat production, in particular non-shivering thermogenesis. In conclusion, human cold adaptation in the form of increased metabolism and insulation seems to have occurred during recent evolution in populations, but cannot be developed during a lifetime in cold conditions as encountered in temperate and arctic regions. Therefore, we mainly depend on our behavioral skills to live in and survive the cold.

Keywords: acclimation; adaptation; brown fat; cold; cold induced vasodilation; cold water immersion; human; non-shivering thermogenesis; shivering.

Figure 1.

Heat balance in Watts for exposure to severe cold, mild cold, thermoneutrality and heat. Please note the contribution of non-shivering thermogenesis in mild cold and shivering and non-shivering thermogenesis in severe cold. Basal metabolic rate of 90 W is for young healthy males. Non-shivering thermogenesis is estimated at 27 W. Shivering thermogenesis (300 W) is based on work of Benzinger. Wet heat loss in cold/thermoneutrality is equal to ‘perspiratio insensibilis’ of about 10 W. In the heat, wet heat loss equals heat production since dry heat loss is negligible when skin temperature equals ambient temperature. The extra heat production of 30 W in the heat is based on recent measurements in Van Marken Lichtenbelt's lab, that will be submitted for publication. Dry heat loss in cold and thermoneutrality is equaled to the difference in the heat balance.