Sunlight may make men hungry by stimulating the release of a hormone that boosts appetite, according to a peer-reviewed Israeli study.
Researchers from Tel Aviv University were looking into the effect of seasonality on food intake. They analyzed dietary data on around 3,000 people who were participating in a nutritional study for the research.
They found that men increased their caloric intake by about 300 calories a day during the summer, while women did not.
To investigate further, the scientists then had men and women volunteers go out on bright, sunny days. The participants wore sleeveless shirts and shorts, with the researchers theorizing that the effect is correlated with the amount of skin exposed to the sun.
They found that the sunshine induced the release of the hormone ghrelin into the men’s blood, but not the women’s. Ghrelin, known as a “hunger hormone,” boosts appetite, among other effects.
The researchers found the same process in mice. Male mice had more ghrelin in their bloodstream and ate more after exposure to UVB light rays, a type of sunlight, but female mice did not.
The differences between men and women may be related to the ways testosterone and estrogen interact with UVB sunlight, which damages the skin, the researchers said.
The study’s authors said ultraviolet sunlight is a well-known carcinogen, but avoiding sunshine can also harm health, noting that ghrelin is anti-inflammatory.
Moderate solar exposure reduces cardiovascular disease, and they said ghrelin might play a part.
The hormone also affects the body in a variety of other ways that the researchers said should be studied more.
The research was published in the peer-reviewed science journal Nature Metabolism on Monday.