Biology This article is more than 1 year oldSunlight may trigger hormone that makes men hungrier, study suggests
This article is more than 1 year oldScientists find ghrelin levels rose in men’s blood after sun exposure, but oestrogen appears to block increase in women
Summer sunshine can leave us feeling hot, sweaty and a bit burnt – but it may also make men hungrier, by triggering the release of an appetite-boosting hormone from fat stores in their skin, data suggests.
The study, which was published in the journal Nature Metabolism, adds to growing evidence that the effects of sun exposure may be more complex than first thought.
Excessive exposure is well known to increase the risk of skin cancer, but recent studies have suggested 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 through the release of 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 whether food consumption could also provide some clues, Carmit Levy, a professor at Tel Aviv University’s department of human molecular genetics and biochemistry, and his colleagues analysed data from 3,000 participants who were enrolled in a national nutrition survey. The researchers found men but not women increased their food intake during the summer months. The effect was not huge – equivalent to eating an extra 300 calories a day – but over time this could be enough to cause weight gain.
To investigate further, they exposed male and female volunteers to 25 minutes of midday sunlight on a clear day, and found it triggered an increase in levels of the appetite-boosting hormone ghrelin in the men’s blood but not in women’s.
Experiments in mice similarly found that when males were exposed to UVB rays, they ate more, were more motivated to search for food and had increased levels of ghrelin in their blood. No such change was seen in female mice.
The trigger for ghrelin release appeared to be DNA damage in skin cells. Oestrogen blocked this effect, which may be why sunlight did not affect females in the same way.
Levy explained that ghrelin, sometimes called the ‘“hunger hormone”, had other effects on the body, besides appetite regulation: it also reduces inflammation and heart muscle wasting, and decreases arterial [blood] pressure. “Ghrelin may be the mechanistic link between solar exposure and cardiovascular disease reduction,” she said.
Carlos Diéguez and Rubén Nogueiras, professors at the University of Santiago de Compostela, Spain who were not involved in the study, described the results as “exciting”, adding that future studies assessing the influence of age and ethnicity in relation to UVB exposure and food intake would be “eagerly awaited”. “This work will surely pave the way for further studies on the role of the skin in energy and metabolic homeostasis [balance], a field that had largely been overlooked,” they wrote in an accompanying news and views in Nature Metabolism.
Dr Duane Mellor, a dietitian and senior teaching fellow at Aston University also not involved, 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 appetite hormone ghrelin, at least in mice,” he said.
“It is important to recognise this paper does not claim that sunlight and UVB exposure will lead to weight gain in human males. Instead it provides some interesting insights in how moderate UVB exposure could be linked to health benefits including reduced cardiovascular risk and inflammation, as ghrelin has anti-inflammatory effects.”
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