Heatwaves can cause men to gain weight, according to a new study. It revealed that UV sunlight triggers “ food -seeking behaviour and food intake” in men, but not women.
The study, published on Monday, tracked the habits of 3,000 people over one year, between 1999 and 2001. Researchers at Tel Aviv University, Israel, found that of those studied and exposed to UV light, only the men saw an increase in the number of calories they consumed and how frequently. The women were not affected in the same way.
The cause of this change in eating habits in men was said to be due to the production of a hunger hormone, ghrelin, which was released when UVB light on the skin activated the p53 gene. The same effect was found in male mice.
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Ghrenlin, known as the hunger hormone, stimulates the appetite and increases food intake. It is produced mainly in the stomach.
The findings were published in Nature Metabolism on Monday, July 11. Researchers concluded: “In both mice and human males, increased appetite is correlated with elevated levels of circulating ghrelin.”
The researchers found that UVB light was responsible for activating a gene (p53) that triggers the secretion of the hormone ghrelin from the skin’s fat cells, adipocytes. However, mice that had that gene inhibited by the scientists did not experience an increase in food-seeking behaviour or weight gain.
The study states: “Specifically, UVB irradiation leads to p53 transcriptional activation of ghrelin in skin adipocytes, while a conditional p53-knockout in mice abolishes UVB-induced ghrelin expression and food-seeking behaviour.”
This was especially true for males in the summer period who ate more and sought out food more regularly when solar UV was at its highest, Professor Carmit Levy and her team found. Increased exposure to UV light led to weight gain in male mice over a 10-week period, but not the female mice.
However, the same effect was not seen in the women participating due to the female hormone oestrogen. The study found: “In females, oestrogen interferes with the p53–chromatin interaction on the ghrelin promoter, thus blocking ghrelin and food-seeking behaviour in response to UVB exposure.”
The results of the study could explain why you may be more inclined to grab an ice cream in the sun if you’re a man. But the findings could also help clinicians to adapt “for sex-based treatments of endocrine-related diseases”.
The study concluded that: “Men are significantly affected by solar radiation and its seasonal fluctuation compared to women, resulting in a more pronounced energy intake during summer.
“Further, we found that daily low-levels of UVB exposure enhance the food intake and food-seeking behaviour of male mice, but not of female mice, a sex difference we observed also in human patients undergoing phototherapy. Appetite enhancement was correlated with elevated levels of circulating ghrelin, in both mouse and human males.”
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