UV rays have been shown to stimulate the release of ghrelin, the “hunger hormone” in skin tissue, but only in men
There are many reasons why our appetite is triggered. Being on an empty stomach is the most obvious, but we can also get hungry because we are thirsty (often confused with one thing for the other), because we are nervous or sad or, in this case, because of the sunlight.
Researchers at Tel Aviv University in Israel found that sunlight stimulates appetite in men by increasing the production of the hormone ghrelin in skin tissue. This amazing light effect was discovered by researchers during a three-year longitudinal study with 3,000 participantswhich was published in the journal Nature Metabolism.
The men studied consumed more than 300 kilocalories a day between March and September than in the colder months. Blood tests in another experiment showed increased levels of ghrelin, known as the “hunger hormone”, after just half an hour in the sun. This hormone also increases the metabolism of fat stores. However, the effect does not occur in women.
Sunlight has very different and also contradictory effects on the body. On the one hand, it has a beneficial effect on health, 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 this research show that sunlight also influences metabolism, but in a gender-specific way.
To further investigate how UV radiation affects feelings of hunger, the researchers repeated similar experiments in mice. They exposed the rodents to artificial daylight for 10 weeks. Male mice exposed to light also ate more than females and had higher levels of ghrelin. Surprisingly, ghrelin circulating in the blood was not related to the secretion of ghrelin in the stomach, where it is mainly produced, but to its expression in the fat cells of the skin.
In other experiments with human skin grafts, scientists found that sunlight activates the p53 protein, which induces the release of ghrelin. Until now, the protein was primarily known as an “antioncogene” because it inhibits the growth of cancer cells. Genetically modified male mice lacking p53 in skin fat cells did not eat more after UV irradiation than rodents without light treatment.
This cell experiment also served to explain why this does not occur in females. The female sex hormone estrogen prevents the p53 protein from giving its signal to release ghrelin.
The study paves the way for a new field of research dealing with the skin’s influence on metabolism and energy balance. Meanwhile, light therapy can already help people suffering from loss of appetite, such as chemotherapy patients. The link between UV radiation and ghrelin production is also suspected to explain other health-promoting effects of sunlight, such as its anti-inflammatory properties, preventing heart muscle atrophy, and lowering blood pressure.
REFERENCE
Food-seeking behavior is triggered by ultraviolet skin exposure in men