Why do men eat more and gain weight in the summer and women don’t?

The role of the sun in human health is complex and is not solely due to the production of vitamin D. Men and women have different hormonal responses to environmental cues such as the sun. New research has shown that UVB from the sun’s rays can trigger the release of hormones in men, which encourages foraging behavior and increases their food intake. The same reaction has not been observed in women, because estrogen blocks the hormonal pathway responsible for this behavior.

New scientific research has revealed that the sun may cause men to forage and increase their food intake, while similar results have not been seen in women. Published in the journal Nature Metabolism, this study highlights the association between UVB, one of the types of invisible ultraviolet rays coming from the sun, and elevated levels of ghrelin, the “hunger hormone”, in men.

Ghrelin is a hormone that stimulates appetite, increases food intake and promotes fat storage. It regulates energy, reduces nerve activity and prevents muscle wasting.

Sun, health and disease

The role of the sun and UVB exposure in human health is complex, but it is a recognized risk factor for the most serious form of skin cancer: melanoma, actinic keratoses, premature aging and cataracts. Yet the sun has also been shown to protect against heart disease, lower blood pressure, and release mood-enhancing endorphins. The beneficial effects of sunlight have often been attributed to vitamin D and its negative associations with UVB, but a recent study suggests the mechanisms may be more complex than that.

The new study, conducted by Tel Aviv University’s Department of Human Molecular Genetics and Biochemistry, showed skin had a major influence on energy levels and suggests this could “lead to therapeutic opportunities for gender-based treatments for endocrine-related diseases. »

Different reactions

The researchers analyzed dietary data from about 3,000 people aged 25 to 64 over a 12-month period, who participated in the National Health and Nutrition Survey (MABAT). According to participants’ average monthly energy consumption, men ate an average of 300 kcal more during the summer months, compared to women whose calorie intake remained more constant (1,507 kcal versus 1,475 kcal).

The researchers used a sun exposure experiment to understand this difference in more detail. Five men and five women aged 18 to 55 were exposed to UVB for 25 minutes. The researchers took blood before and after the exposure and then analyzed it. The study showed that the exposure changed proteins associated with metabolism and that men and women reacted differently.

The mechanism of weight gain

In another study, researchers used mice to study UVB exposure. For 10 weeks, 24 mice that had been partially shaved were exposed daily to low levels of UVB. Mice showed metabolic protein changes similar to humans; male mice increased their food intake and foraging behavior. The researchers noted that male mice showed increased release of the hormones ghrelin after UVB exposure, specifically released by fat cells in the skin.

These results have been confirmed in humans: the skin of males showed an increase in the expression of ghrelin after exposure to UVB for 5 days. According to research, DNA damage to skin cells was the trigger for the release of ghrelin via the p53 transcription pathway. Interestingly, the researchers found that this pathway was blocked by estrogen, which could explain the differences between men and women.

Gender differences are very common when it comes to hormones and metabolic changes. Men and women have different hormonal responses to many different types of triggers, and the underlying hormonal balance is also different.

Future research

If the study uncovered a potential mechanism for how UVB rays can influence hormone metabolism in both men and women, and how this may translate to increased ghrelin in mice, the researchers are far from sure. assert that sun exposure alone causes weight gain in humans.

This is because age, genetic predisposition, activity level, and co-occurring health conditions all affect hormone secretion. Much more research is needed to understand how we can use this information to help a person achieve and maintain a healthy weight. Nevertheless, this research clearly indicates that men and women react differently to seasonal changes, which can significantly alter their metabolism.