The summer sun can make us feel hot, sweaty and a little burnt, but it can also make men more hungry, as it causes the release of a hormone that increases the appetite for fat reserves in the body. your skin, according to the data.
The study, published in the journal Nature Metabolism, adds to the growing evidence that the effects of sun exposure can be more complex than previously thought.
Excessive exposure is known to increase the risk of skin cancer, but recent studies have suggested that moderate exposure may increase life expectancy, on average, by helping to protect against cardiovascular disease and other causes of death. One possibility is that it lowers blood pressure by releasing nitric oxide from the skin, a process that causes blood vessels to relax. Other scientists have attributed the health benefits of sunlight to vitamin D production.
Wondering if food consumption could also provide some clues, Carmit Levy, a professor in the department of human molecular genetics and biochemistry at Tel Aviv University, and colleagues analyzed data from 3,000 participants who were enrolled. in a national nutrition survey. The researchers found that men, but not women, increased their food intake during the summer months. The effect was not great, equivalent to eating an extra 300 calories a day, but over time this might be enough to cause weight gain.
To investigate further, they exposed male and female volunteers to 25 minutes of noon sunlight on a clear day, and found that it caused an increase in ghrelin hormone levels that increased men’s appetite in the blood but not in the blood. of women.
Experiments with mice similarly found that when males were exposed to UVB rays, they ate more, were more motivated to look for food, and had an increase in ghrelin levels in their blood. This change was not observed in female mice.
The trigger for ghrelin release appeared to be DNA damage to skin cells. Estrogens blocked this effect, which is why sunlight did not affect women in the same way.
Levy explained that ghrelin, sometimes called the “hunger hormone,” had other effects on the body, in addition to regulating appetite: it also reduces inflammation and waste of the heart muscle, and narrows the arteries. [blood] pressure. “Ghrelin can be the mechanistic link between sun exposure and the reduction of cardiovascular disease,” he said.
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Carlos Diéguez and Rubén Nogueiras, professors at the University of Santiago de Compostela, Spain who did not participate in the study, described the results as “exciting”, adding that future studies evaluating the influence of age and ethnicity in relation to UVB exposure and food. the intake would be “eagerly awaited.” “This work will surely pave the way for further studies on the role of skin in energy and metabolic homeostasis. [balance]a field that had been largely overlooked, “they wrote in a news release and accompanying opinions in Nature Metabolism.
Dr. Duane Mellor, a dietitian and senior professor at Aston University, did not participate either, he was more cautious. “What it does show is the potential mechanism of how UVB can influence hormone metabolism and how this may be associated with an increase in the ghrelin appetite hormone, at least in mice,” he said.
“It is important to recognize that this paper does not state that exposure to sunlight and UVB leads to weight gain in humans. Instead, it provides some interesting insights into how moderate exposure to UVB might be related to health benefits, such as reduced cardiovascular risk and inflammation, as ghrelin has anti-inflammatory effects. “