Sunlight makes men hungry


Sunbeams stimulate appetite in men by promoting the production of the hormone ghrelin in skin tissue. Researchers from Tel Aviv University discovered this surprising effect of light during a three-year longitudinal study with 3000 participants. As Shivang Parikh’s working group reports in the journal Nature Metabolism, men consumed over 300 calories more per day between March and September than in the colder months. Blood analyzes in a separate experiment showed increased levels of ghrelin, known as the “hunger hormone,” after just half an hour in the sun; in addition, men metabolized fats more. The effect does not occur in women.

Sunlight has very different and also contradictory effects on the organism. On the one hand, it has a health-promoting effect, for example by stimulating the formation of vitamin D. On the other hand, UV rays are the main cause of skin cancer. The results of Parikh and his colleagues now show that sunlight also affects metabolism – but in a gender-specific way.

In order to examine in more detail how UV radiation affects the perception of hunger, the researchers repeated similar experiments in mice. They exposed the rodents to artificial daylight for 10 weeks. Male, light-exposed mice also ate more than females and recorded an increased ghrelin level. “Surprisingly, circulating ghrelin was not correlated with the expression of ghrelin in the stomach, where ghrelin is primarily produced, but with its expression in dermal fat cells,” write physiologists Carlos Dieguez and Ruben Nogueiras in a companion article.

In further experiments with human skin transplants, the scientists found that sunlight activates the protein p53, which triggers the release of ghrelin. The protein was previously known primarily as an “anti-oncogene” because it inhibits the growth of cancer cells. After UV irradiation, genetically modified male mice without p53 in the skin fat cells ate no more than rodents without light treatment. Cell experiments also showed the reason why this doesn’t happen in women. The female sex hormone estrogen prevents the protein p53 from giving its signal to release ghrelin.



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