Cold-induced thermogenesis in humans.

A basic property of endothermic thermoregulation is the ability to generate heat by increasing metabolism in response to cold ambient temperatures to maintain a stable core body temperature. This process, known as cold-induced thermogenesis (CIT), has been measured in humans as early as 1780 by Antoine Lavoisier, but has found renewed interest because of the recent 'rediscovery' of thermogenic, cold-activated brown adipose tissue (BAT) in adult humans. In this review, we summarize some of the key findings of the work involving CIT over the past two centuries and highlight some of the seminal studies focused on this topic. There has been a substantial range of variability in the reported CIT in these studies, from 0 to 280% above basal metabolism. We identify and discuss several potential sources of this variability, including both methodological (measurement device, cold exposure temperature and duration) and biological (age and body composition of subject population) discrepancies. These factors should be considered when measuring CIT going forward to better assess whether BAT or other thermogenic organs are viable targets to combat chronic positive energy balance based on their relative capacities to elevate human metabolism.