Brown adipose tissue (BAT) is a specialized tissue for non-shivering thermogenesis (NST) after cold exposure. Although BAT research has long been limited mostly in small rodents, the rediscovery of metabolically active BAT in adult humans has dramatically promoted the translational studies on BAT in health and diseases. In recent years, it has become clear that BAT cross-talks with some peripheral tissues and controls their functions and systemic homeostasis of energy and metabolic substrates. Moreover, it has been found that BAT contributes to NST after nutrient intake as well as cold exposure. Thus, BAT is a metabolic regulator beyond thermogenesis and a target against obesity and metabolic syndrome. This is supported by discovering that various paracrine and endocrine factors are secreted from BAT, called as BATkines. However, there is still few information about the genetic and environmental factors that determine the activity and amount of human BAT. Here, we review our current understanding on the pathophysiology of human BAT, including its seasonal and diurnal variations.
