Can sunlight make you hungrier?

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ISLAMABAD (Online): New scientific research has found that sunshine can cause men to seek food and increase their food intake, while similar findings were not observed in women.
Published in the Journal Nature MetabolismTrusted Source, the study highlights the association between UVB—one of the types of invisible ultraviolet rays that come from the sun—and elevated levels of ghrelin “the hunger hormone” in men.

GhrelinTrusted Source is a hormone that stimulates appetite, increases food intake, and promotes fat storage. It has also been found to regulate energy, reduce nerve activity and prevent muscle wastage.

Sunshine, health, and disease
The role of sunshine 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 cataractsTrusted Source.

Yet sunshine has also been shown to protect against heart diseaseTrusted Source, reduce blood pressureTrusted Source, and release mood-improving endorphins. The sun’s beneficial effects have often been attributed to vitamin D and its negative associations with UVB, but a recent study suggests the mechanisms could be more complex than that.

The new study, led by Dr. Carmit Levy, associate professor at the Department of Human Molecular Genetics and Biochemistry at Tel Aviv University, has shown the skin to have a major influence on energy levels and suggests that this may “lead to therapeutic opportunities for sex-based treatments of endocrine-related diseases.”

Different reactions
Researchers analyzed dietary data from around 3,000 people ages 25–64 over a period of 12 months who were taking part in the National Health and Nutrition (MABAT)Trusted Source survey.

According to the participants’ average monthly energy consumption, men eat an average of 300 kcal more over summer months, compared to women whose calorie intake remained more constant (1,507 kcal vs 1,475 kcal).

The researchers used a solar exposure experiment to understand the difference in more detail. Five men and five women ages 18–55 years were exposed to UVB for 25 minutes, with researchers sampling blood before and after exposure and then analyzing it.
The study showed that the exposure altered metabolism-associated proteins and that men and women reacted differently.

The mechanism
In another study, the researchers used mice to investigate UVB exposure. Over 10 weeks, 24 mice that had been partly shaved were exposed daily to low levels of UVB. The mice showed similar gender metabolic protein changes to humans; male mice increased their food intake and food-seeking behavior.

The researchers noted that male mice demonstrated an increased release in the ghrelin hormones after UVB exposure, specifically released from skin fat cells.
These findings were confirmed in human skin—male skin showed an increase in ghrelin expression after UVB exposure for 5 days.

According to the research, DNA damage to the skin cells was the trigger for the release of ghrelin via the p53 transcriptional pathway. Interestingly, the researchers found that this pathway was blocked by estrogen, which could explain the differences between men and women.

Dr. Mir Ali, bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center, CA, who was not involved in the study, spoke to Medical News Today about the findings.

“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,” he said.
Future research

While the study has found a potential mechanism behind how UVB rays can influence hormone metabolism in men and women, and how this may translate into an increase in ghrelin in mice, researchers are far from claiming that sunlight exposure will lead to weight gain in humans.
Dr. Ali cautioned that “Age, genetic predisposition, activity level and concurrent health conditions all affect hormonal secretion” and advised that “Much more research is necessary to understand how we can use this information to help someone attain and maintain a healthy weight.”
Nevertheless, this research clearly indicates that men and women respond differently to seasonal changes which can significantly alter their metabolism.