"Nature Metabolism": Basking in the sun will make men fat! Scientists have found that ultraviolet exposure causes increased ghrelin levels, increased appetite, and weight gain in men

*For medical professionals only

p53, the famous cancer-related genes, we can often see it appear in bowel cancer, lung cancer, liver cancer and other related literature, cancer inhibition and cancer promotion form at will, scientists behind it painstakingly pursue, a good escape he chased it wings are difficult to fly

But if, I mean if, p53 appears in a story where sun protection and weight loss are the protagonists

Professor Carmit Levy of Tel Aviv University and his research team found that ultraviolet exposure induces elevated ghrelin levels, making people hungry easily, eating more, and ultimately causing weight gain

The results were published in Nature metabolism

The history of human research on ultraviolet rays is not short

UV intensity is closely related to

Men's food intake is affected by the season

Is it possible that how much you eat is also related to the intensity of ultraviolet rays? Is there even such a big gender difference?

With these questions in mind, Professor Carmit Levy officially began his exploration

First, verify that UV rays really have an effect on
appetite.

The researchers recruited 32 dermatological patients who received phototherapy with UV exposures (0.
1-2.
5J/cm²) 2 or 3 times a week for a total of 10-12 sessions
.

Through the Disease-Related Appetite Questionnaire (DRAQ), the researchers found that men became more likely to have a stronger appetite after receiving light therapy, felt hungrier more frequently, and consumed a larger
amount of food per meal.

Women do not have these changes
after receiving light therapy.

This suggests that UV exposure does alter a man's appetite and food intake
.

So, will male mice have the same response?

In order to increase the exposure in ultraviolet light, the mice were shaved off their back hair, so that the exposure area reached about
50%-60% of the whole body area.

Mice received 50 mJ/cm² of ultraviolet radiation for 10 weeks
.

Under such conditions, male mice showed obvious changes in foraging behavior, the number of meals increased, and the amount also became larger, but the foraging behavior of female mice did not change
.

UV exposure had no effect on the metabolic levels of the mice, but the male mice gained weight

The researchers also found that the mice's metabolic levels did not rise or decrease
as a result of UV exposure.

That, male mice increase food intake, metabolic levels do not change, do not exercise, the end result, of course, is weight gain
.

By comparing changes in hormone and peptide levels in the plasma of mice before and after UV exposure, the researchers found that ghrelin levels in the plasma of male mice increased, ghrelin levels in female mice remained unchanged, and other hormones that played a key role in appetite regulation, such as insulin concentrations, did not see significant changes
in both male and female mice.

So this ghrelin is the key to increased appetite?

Ghrelin, as the name suggests, is produced mainly by the stomach and increases
in levels when hungry.

But if the stomach is removed, the level of ghrelin in the blood is reduced by only 65%, that is, there are other tissues involved in the secretion
of ghrelin.

As incredible as it sounds, a series of studies have shown that skin tissue is indeed involved in the secretion of multiple hormones, and subcutaneous fat cells are another source of expression for gastric ghrecin [2].

As for the increase in ghrelin levels caused by ultraviolet exposure, how to think that the "suspicion" of subcutaneous fat cells is heavier
.

The researchers simulated ultraviolet exposure using ex vivo human skin and found that ghrelin peaked at 8 h of exposure in men's subcutaneous fat cells, while ghrelin expression in women was not affected
.

Next, the researchers used ghreferin receptor antagonists on the mice, and after UV exposure, the experimental mice ate as usual, but the food intake was much lower than before the drug, indicating that it was indeed ghreferin that mediated the increase in
food intake in male mice caused by ultraviolet exposure.

The researchers compared promoter sequences with differences in expression before and after UV exposure, got some possible transcription factor binding sites, and found, ah, p53, how are you here?

Ultraviolet rays induce an increase in the level of p53 in ex vivo skin tissue in men

The researchers constructed a p53-deficient mouse model of subcutaneous fat cells and found that ultraviolet exposure at this time could no longer induce an increase in ghrelin levels in male mice, and naturally there were no changes in appetite and food intake, and there was no weight gain
.

So why were female mice not affected by UV exposure? The researchers found through the data that although no clear mechanism was found, there was indeed some association between ghrelin and sex hormones
.

Ghrelin in men was positively correlated with testosterone levels, while estradiol hormone in women was associated
with inhibition of ghrexin synthesis.

During ex vivo skin tissue culture, researchers also found that female estrogen and receptor levels were significantly higher than those in men
.

The researchers stimulated UV-exposed fat cells with dihydrotestosterone and β-estradiol, respectively, and found that dihydrotestosterone induced elevated ghrelin levels, while β-estradiol inhibited UV-induced elevated
ghrelin levels.

If the ovaries of female mice are removed, UV-induced changes
in appetite and food intake can also be observed.

UV exposure test in volunteers

The UV exposure that was previously simulated in the laboratory, how effective is the UV exposure from nature (the sun)? The researchers recruited 27 volunteers, 13 men and 14 women, aged 18-55, to bask in the sun for 25 minutes wearing sleeveless tops and shorts (UV exposure is about 2000 mJ/cm²), collected blood samples the day before and the day after sunbathing, and were asked appetite-related questions
by a professional counselor.

Men felt hungrier than normal, women did not report significant differences in hunger levels, and ghrelin levels showed similar changes
.

However, don't think of this as a simple study
of "weight loss" and "fat gain".

Ghrelin has anti-inflammatory properties, inhibits myocardial atrophy, lowers arterial pressure, and may be associated
with the cardiac benefits of "sunbathing.
"
In addition, ghrelin also has the functions of enhancing learning ability, anti-anxiety and neuroprotective.


Or if we look a little longer, is there still an area between skin fat and brain function that we haven't explored?

Among many scenarios, the researchers chose a seemingly simplest one as the end of the article, "the scope of light therapy may be expanded
as a result.
"

Friends who have purchased courses,

Directly enter the mini program to listen to the addition of food Oh ~

References:

[1] Parikh S, Parikh R, Michael K, et al.
Food-seeking behavior is triggered by skin ultraviolet exposure in males[J].
Nature metabolism, 2022, 4(7): 883-900.

[2] Knerr I, Herzog D, Rauh M, et al.
Leptin and ghrelin expression in adipose tissues and serum levels in gastric banding patients[J].
European journal of clinical investigation, 2006, 36(6): 389-394.

The author of this article Wang Xuening