According to an Israeli study, sunlight can make men hungry by stimulating the secretion of appetite-stimulating hormones.
Researchers from Tel Aviv University were looking at the effect of weather on food intake. They analyzed dietary data on nearly 3,000 people who were participating in nutritional studies for the research.
They found that men increased their caloric intake by about 300 calories a day during the summer, while women did not.
The scientists then asked male and female volunteers to go outside on bright, sunny days for further investigation. With participants wearing sleeveless shirts and shorts, researchers theorize that the effect is related to the amount of skin exposed to the sun.
They found that sunlight induced the release of the hormone ghrelin in the blood of men, but not women. Ghrelin, known as the “hunger hormone,” increases appetite, among other effects.
The researchers found the same process in mice. Male mice had more ghrelin in their bloodstream and ate more after being exposed to UVB light rays, a type of sunlight, but female mice did not.
Researchers said the differences between men and women may be related to the way testosterone and estrogen UVB interact with sunlight, which damages the skin.
Ultraviolet sunlight is a well-known carcinogen, but avoiding sunlight can also harm health, the study authors said, noting that ghrelin is anti-inflammatory.
Moderate solar exposure seems to reduce heart disease, and he said ghrelin may play a role.
The hormone also affects the body in many other ways that the researchers said should be studied more.
The research was published in the peer-reviewed science journal nature metabolism on Monday.
