Sunlight Might Make Men Hungrier Through Hormonal Changes, Study Suggests

A study published Monday in Nature Metabolism seeks to dissect this strange discrepancy. Researchers at Tel Aviv University were conducting a separate nutrition survey when they noticed that men increased their food intake during the summer months. Suspecting that environmental cues may be at play, the researchers had participants from a group of approximately 3,000 mixed-gender volunteers expose themselves to 25 minutes of direct sunlight per day. Men experienced an increase in the appetite-boosting hormone ghrelin, while women did not.

Ghrelin resides in the gut and is integral to metabolic homeostasis. It’s responsible for sending hunger signals to the brain, thus prompting one to seek out nutrition. Ghrelin production is also triggered by DNA damage within skin cells exposed to UVB radiation, which is where midday sunlight comes in. The researchers found that increased sun exposure prompted men to consume up to 300 more calories per day. Meanwhile, estrogen appeared to “block” the biological interactions responsible for ghrelin’s appetite boosts, which kept womens’ appetites stable.

The team at Tel Aviv University were able to duplicate these results in mice. Males exposed to UVB radiation increased their food intake, while females that underwent identical exposure did not. As predicted, the males’ blood contained higher ghrelin levels post-exposure than it did pre-exposure.

Simply knowing that ghrelin might have an effect on hunger might not reveal any immediate medical epiphanies. But beyond regulating one’s appetite, ghrelin has a number of physiological benefits. The hormone helps to reduce inflammation, blood pressure, and cardiac muscle deterioration, which are all key to recovery after a heart attack. Ghrelin also “enhances insulin sensitivity in metabolic syndrome patients and in animal models of type II diabetes,” according to the research paper. The authors suggest that treatments involving increased ghrelin could prove beneficial for male chemotherapy patients and others experiencing illness-related appetite loss. Ghrelin might even have an impact on one’s perception of stress and anxiety, including in cases of PTSD.

The researchers acknowledge that excessive UV exposure has its risks, most notably skin cancer. “But avoiding the sun rays adversely impacts human health, too,” write the study’s authors. “Since ghrelin has anti-inflammatory properties, halts heart muscle wasting, and decreases arterial pressure, ghrelin may be the mechanistic link between solar exposure and cardiovascular disease reduction.”

Note: For the sake of efficiency, the term “men” is used to refer to those with bodies assigned male at birth.