Sunshine makes men hungry but does not have the same effect on women, according to a new study.
Ultraviolet (UV) rays from the sun activates a protein in men that boosts their appetite but does not affect women because it is blocked by oestrogen, say scientists at Tel Aviv University.
The academics say the finding demonstrates the first molecular connection between sunlight and eating habits.
Researchers suggest the new discovery is a biological legacy of UV hitting the skin to signal that winter is ending and mating season is soon to begin.
The team found that in men the sun activates protein p53 to repair DNA damage caused by its rays, leaving them consuming more in summer than winter while womens’ food intake stays relatively the same.
Activation of p53 tells the body to produce ghrelin – which stimulates hunger – but in women oestrogen blocks the protein’s interaction with ghrelin, preventing any increase in appetite.
The study, published in the journal Nature Metabolism, identifies the skin as the primary regulator for energy and appetite.
Professor Carmit Levy, a lead author, said: “We examined the differences between men and women after sun exposure and found that men eat more than women because their appetite has increased.
“Our study was the first gender-dependent medical study ever conducted on UV exposure, and for the first time, the molecular connection between UV exposure and appetite was deciphered.
“Gender-dependent medical studies are particularly complex, since twice the number of participants are required in order to find statistically significant differences.
“As humans, we have cast off our fur and consequently, our skin, the largest organ in our body, is exposed to signals from the environment.
“The protein p53, found in the skin, repairs damage to the DNA caused by sun exposure, but it does more than that. It signals to our bodies that winter is over, and we are out in the sun, possibly in preparation for the mating season.
“Our results provide an encouraging basis for more research, on both human metabolism and potential UV-based therapies for metabolic diseases and appetite disorders.”
The paper studied the eating habits of around 3,000 male and female Israelis for a year, some of whom spent time in the sun, and combined their results with their genetics studied in a lab.
