China News Service, Beijing, July 12 (Reporter Sun Zifa) Does sunlight affect appetite?
How?
Sunlight stimulates eating and weight gain in men, but not in women, through a hormone secreted by fat tissue in the skin, according to a new research paper published in Springer Nature's professional academic journal Nature-Metabolism.
This study sheds light on how sunlight affects eating behavior and whole-body energy balance, a process that is sorely overlooked.
According to the paper, the need to eat is largely controlled by communication between peripheral tissues and the brain.
Hormones released by multiple organs, such as the gut, adipose tissue, and liver, reach specific brain regions, such as the hypothalamus, to give instructions to eat or stop, depending on the current energy levels in the body.
Corresponding author Carmit Levy of Tel Aviv University in Israel, in collaboration with colleagues, analyzed epidemiological evidence from about 3,000 individuals in Israel over a three-year period and found that men, but not women, eat more in summer, Summer is also the period of the year when the solar radiation is the strongest.
This result is supported by research in male mice, which found that daily exposure to ultraviolet (UVB) light for 10 weeks stimulated the release of ghrelin from the fatty tissue of their skin.
When ghrelin reaches the hypothalamus, it turns on the male mice's appetite, which in turn promotes eating and weight gain.
However, this effect was not significant in female mice, because estrogen interferes with ghrelin released by fat cells in the skin.
Furthermore, in one experiment, human male skin samples increased ghrelin expression after 5 days of UV exposure, consistent with increased feeding behavior observed after sun exposure.
The authors concluded that their study identified skin fat as a possible mediator of feeding behavior through sunlight exposure, or adding a new adipose tissue subtype to the energy balance equation.
In a concurrently published "News & Views" article, international peer experts pointed out that the study undoubtedly lays the foundation for follow-up research into the role of the skin in energy and metabolic homeostasis.
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