Exposure to sunlight made men eat more and get fat

(ORDO NEWS) — Since the scientists did not reveal such a relationship for women, they concluded that the reaction to UV radiation depends on gender.

Scientists from Tel Aviv University, Max Stern College in the Jezreel Valley (Israel), Langon Medical Center at New York University and the Mortimer B. Zuckerman Behavior and Brain Institute at Columbia University (USA) found that exposure to sunlight is associated with more active food intake and weight gain in men, but not in women, thanks to a peptide hormone called ghrelin.

Appetite regulation is a complex process that affects health, in which the hormones ghrelin and leptin are actively involved . The first is responsible for responding to changes in energy homeostasis.

Its levels rise when the stomach is empty, so that the brain knows when to eat, and then decrease again after eating. The environmental factors that control the secretion of this hormone are sound, light, smell.

Ghrelin is the only known peripheral peptide that stimulates appetite, although there are many peripheral hormones that suppress it, including cholecystokinin, insulin, and leptin, the decrease in which provokes the development of obesity.

Previously, scientists came to the conclusion that the source of ghrelin secretion is not only the stomach, but also, most likely, the skin: the hormone is expressed in the epidermis, dermis and hypodermis, subcutaneous adipose tissue.

The authors of the new work tested the assumption that the skin is the main mediator of energy homeostasis. To do this, they analyzed data from a three-year national study on the nutrition of three thousand people.

“Using an age-adjusted generalized linear model, we found a significant relationship between gender and season, showing that men are more significantly affected by sunlight and its seasonal fluctuations than women,” the scientists write.

The researchers averaged monthly data on direct sunlight exposure. As it turned out, from March to September, men begin to eat more compared to the colder period (October-February): 2188 kilocalories versus 1875 kilocalories per day, respectively.

For women, nothing changed: 1475 kilocalories in March-September versus 1507 kilocalories in October-February. During the warm months, men also consumed more nutrients, including carbohydrates, proteins, fats, sodium, omega-3s, zinc, and iron. Some of them just stimulate the appetite.

To further test the response of both sexes to sun exposure, the authors asked volunteers (five males and five females aged 18-55) to spend approximately 25 minutes in the sun at noon, when the UV dose is 2,000 millijoules per centimeter squared. Blood samples taken before and after the experiment were subjected to mass spectral analysis.

“When exposed to the sun, men showed an increase in lipid and steroid metabolism. In addition, metabolic-related peptides were the most affected by sun exposure.

While in both sexes the response to environmental signals is enhanced, but the signaling through extracellular vesicles is weakened, from the point of view of the immune system and metabolism, men and women react differently, ”the researchers said.

The work didn’t stop there: for ten weeks, the scientists exposed mice – 12 rodents of each sex – to ultraviolet radiation daily (the dose was 50 millijoules per centimeter squared), which for a person is approximately equal to 20-30 minutes of exposure to the sun in the summer in Florida.

In both males and females, strong pigmentation of the ears was observed. Then the blood plasma proteins were sent for proteomic analysis. “Like in humans, after exposure to ultraviolet light, male mice showed more metabolic-related protein changes compared to female mice.

Taken together, our data show that males are more sensitive to sunlight and seasonal changes, and, like male mice, their metabolism is impaired,” the authors added.

So, daily UV radiation encouraged male rodents to actively search for food and eat more, as a result, they began to gain weight. Nothing of the sort was found in females. “To assess the effect of ultraviolet light on metabolism, we measured the maximum amount of oxygen consumed at the physiological level (VO2),” the authors write.

Both the control group and the rodents that survived long-term exposure to UV did not show a significant difference in VO2: therefore, the basal metabolic rate does not change under the influence of UV radiation.

According to the results of the study, it turned out that UV radiation forced males to search for food due to ghrelin. “Skin adipocytes produce and release ghrelin after UV exposure, which is caused by the activity of the p53 protein due to DNA damage.

Estrogen inhibited p53 activity in adipocytes, thereby blocking the increase in ghrelin levels in women. In mice lacking p53 in adipocytes, ghrelin levels failed to rise after exposure. These data show that the response to UV radiation depends on gender, ”the scientists concluded.

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