Metabolism: Sunlight stimulates food intake in males

Exposure to sunlight stimulates food intake and weight gain in males, but not females, via a hormone secreted by fat tissue within the skin. The study, published in Nature Metabolism, reveals how sunlight may affect eating behaviour and whole-body energy balance, a process that has largely been overlooked.

The need to consume food is mainly controlled by communication between peripheral tissues and the brain. Hormones that are released from several organs (for example, the gut, fat tissue and the liver) reach specific brain regions, such as the hypothalamus, which then dictates the need to eat or stop eating, depending on the current amount of energy available in the body.

Examining epidemiological evidence from approximately 3,000 individuals in Israel over the course of three years, Carmit Levy and colleagues reveal that males, but not females increased their food intake during the summer, a time when solar radiation is at its peak. The finding was supported by studies in male mice whereby daily ultraviolet (UVB) exposure for ten weeks stimulated the release of the hunger hormone ghrelin from the skin’s fat tissue. Upon reaching the hypothalamus, ghrelin increased appetite in these male mice, thus promoting food intake and weight gain. However, this effect was blunted in female mice because the sex hormone estrogen interfered with the release of ghrelin from the fat cells within the skin. Additionally, in an experimental setup, male human skin samples exposed to UVB over five days led to increased expression of ghrelin, which is in line with the increased food-seeking behaviour observed after solar exposure.

The authors conclude that this work identifies skin fat as a possible mediator of feeding behaviour through exposure to sunlight, potentially adding a new subtype of fat tissue to the energy balance equation. In an associated News & Views, Carlos Dieguez and Ruben Nogueiras highlight that “this work will surely pave the way for further studies on the role of the skin in energy and metabolic homeostasis”.