Food-seeking behavior is triggered by skin ultraviolet exposure in males | Hacker News Reader

Food-seeking behavior is triggered by skin ultraviolet exposure in males

nature.com

143 pointsakbarnama83 comments

>> A meta-analysis of several research studies has found differing results for the influence of seasonality on food intake23. We, therefore, analyzed data from a 3-year national nutrition survey of approximately 3,000 people. Using a generalized linear model adjusted for age, we found a significant interaction (P <0.001) between sex and season, revealing that men are markedly affected by solar radiation and its seasonal fluctuation compared to women ...

It's a correlation .. is "markedly affected by solar radiation" a reach when the same correlation exists for tempreture?

Is it the UV or is it that men eat more and more active in the summer than in winter?

Hmmm.

There is also some mouse experimental data

Sure .. does the effect correlate with both UV AND temp or have they ANOVA'd enough to say that that anything observed is predominently due to UV alone?

They work out the mechanism of UV induced orexia, then knockout the gene in the mouse thus abolishing the phenotype. They also work out why the effect is sexually dimorphic.

the mention that they controlled for age also directly says they didn't correct for anything else. e.g. if for whatever reason the male study population has a significant shift into any direction (income, physical characteristics like height, weight, etc.) bam you're entire data set is essentially useless.

and this is almost certainly going to be the case. it's nigh impossible to get similar averages for all metrics in a male between female comparison.

the data is very valuable on its own. but once again I have no idea how they think it remotely allows them to draw the specific conclusions regarding causality that they do.

Also vitamin D and testosterone production

This paper is not merely a meta-analysis.

It's both. The light-sensitive supraoptic part of your brain directly triggers your hypothalamums to release more or less corticotropin-releasing hormone. Which directly triggers adrenocorticotropic hormone+melanocyte [melanin cell] stimulating hormone.

In my view, guys who are overweight would be ill-advised to hide from the sun to lose weight. From their paper:

"Our study revealed that UVB exposure enhances food-seeking behavior in males via ghrelin and a process that is prevented in females. ... UV is a well-established carcinogen, but avoiding the sun rays adversely impacts human health, too. 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. Moreover, ghrelin enhances insulin sensitivity in metabolic syndrome patients and in animal models of type II diabetes. ... In addition to its function in regulating energy homeostasis and the functions mentioned above, ghrelin also mediates glucose homeostasis, muscular atrophy, bone metabolism, stress and anxiety, adipogenesis and the immune system."

I seem to recall also somewhere here on HN seeing a post about walking suppressing hunger? Ah, here it is;

https://news.ycombinator.com/item?id=31858063

So if you're outside guys, walk!

Personal anecdote inbound.

Sun exposure gives me a lot of energy (not excess exposure but I have a pretty high threshold). I don't want to eat much when it's sunny. I don't need it, and a full belly makes me less likely to engage in activities because I'm heavier and it's harder to breathe. I have very little food and usually light meals, like lots of salad, fruits and sea food, and mostly at night/evening.

Is that the Sun or the heat?

I eat normally (sometimes too much) when I'm in a heated space without sunlight.

So sunshine makes you hungry, but also cold makes you hungry. So a moderately warm but cloudy country should have very thin citizens, for example the UK...

oh wait

I assume this isn't meant too serious, but as far as I know cloud's do not necessarily block UV radiation. At least one can still get sunburned even on a cloudy day.

Clouds do very much attenuate UV radiation; how strongly they do so depends on their thickness/density. See ballpark figures here: https://www.epa.gov/sunsafety/calculating-uv-index-0

Clouds do not block junk food ads. They actually produce them :)

Food seeking behavior =/= thin males =/= thin citizens. Lot of weak linkages happening there.

An explanation why BBQs are the only time many men get interested in cooking. /s

I think that has more to do with being able to play with open fire

So does this mean that sunscreen helps with weight loss ?

Maybe, unless you use sunscreen that's also an endocrine disrupter, then all bets are off.

Pretty sure it does. Given how nasty it tastes, I lose all my appetite when I try to use it as condiment.

Sunscreen also has strong emetic and laxative properties as well.

I prefer to get my zinc supplement from cooking in galvanized containers.

https://youtu.be/jE35YUGtE9s

If you mean, is goopy and smells like a chemical factory, then yeah, I guess it'd turn off one's appetite a bit. Wouldn't want to hold food in the same hand I'd rubbed it on with.

Nah, I live in Europe so we have the good sunscreen, unlike the US [1].

1: https://www.theatlantic.com/technology/archive/2022/07/us-su...

If you use the old school white zinc oxide cream and keep it on your hands, you won’t eat anything out of disgust.

If you smear mayonnaise all over your skin like the people around here do, it's bound to cause problems with keeping food down.

I remember a recent study that claims skin exposure to the sun is necessary/needed to burn fat. I'll try to find it and update this comment.

Edit: this seems to be the study https://www.nature.com/articles/s41598-017-16689-4 The gist of it is that sunlight shrinks fat cells, but I might be oversimplifying it

No. Not necessarily.

Also details and interactions matter. From paper:

Our study revealed that UVB exposure enhances food-seeking behavior in males via ghrelin and a process that is prevented in females. We found that p53 mediates transcription of ghrelin in skin adipocytes and that estrogen interferes with the p53-mediated transcriptional activity, thus blocking the positive effect of solar exposure on food-seeking behavior in females. ...

The increased hypothalamic expression of the orexigenic pathway indicates that ghrelin activated this pathway, which translated to increased food intake in males. As ghrelin serves as a peripheral satiety signal, its concentrations change in response to environmental cues and reach hypothalamic satiety centers.

However ...

A direct link between the skin and the brain was demonstrated in a study showing that UVB exposure induces the release of urocanic acid from the skin to the blood, which is converted to glutamate in brain neurons, leading to improvements in motor learning and object recognition in mice61. Ghrelin enhances learning and has anti-anxiety effects and neuroprotective functions32. It will be interesting to further study whether skin-mediated induction of ghrelin production directly improves brain function, such as memory and learning abilities and whether there are additional hormones released from the skin that modify human behavior.

UV is a well-established carcinogen, but avoiding the sun rays adversely impacts human health, too11. Since ghrelin has anti-inflammatory properties62, halts heart muscle wasting63 and decreases arterial pressure64, ghrelin may be the mechanistic link between solar exposure and cardiovascular disease reduction11. Moreover, ghrelin enhances insulin sensitivity in metabolic syndrome patients65 and in animal models of type II diabetes66. Patients who suffer from appetite loss, which affects their health and recovery rate, such as patients undergoing chemotherapy67 patients, should benefit from treatments that induce ghrelin production. Indeed, ghrelin administration during chemotherapy has been shown to increase food intake and appetite68. The ghrelin receptor is expressed in the brain69 and in peripheral tissues (that is spleen, myocardium, thyroid, pancreas, and adrenals)70. In addition to its function in regulating energy homeostasis32 and the functions mentioned above, ghrelin also mediates glucose homeostasis71, muscular atrophy72, bone metabolism73, stress and anxiety74, adipogenesis75 and the immune system76. Therefore, the various role of ghrelin, might be also observed upon UVB/solar exposure and will be interesting to investigate. Thus, our study suggest that the use of phototherapy might be extended.

Some melanocortin receptors drive appetite. We've known this for decades.

Melanocortin receptor 1 controls skin darkening and natural skin color. We've known this for decades.

Sunlight exposure triggers broad-spectrum melanocortin stimulating hormones. We've known this for decades.

*Specifically: alpha-melanocyte stimulating hormone, beta-melanocyte stimulating hormone, and gamma-melanocyte stimulating hormone. They're all byproducts of proopiomelanocortin. Adrenocorticotropic hormone is a coproduct of some melanocyte stimulating hormones, and can optionally be cleaved into more melanocyte stimulating hormones.

Hmm, I always get really hungry after going swimming, which I attributed to the exercise and extra calories burned to maintain body temperature because water conducts heat more efficiently. Maybe it’s also because it’s the only time a significant amount of my body is exposed to sunlight too.

Yeah, I've always been curious as to why I'm so hungry after swimming but it makes a lot of sense. You don't seek a tree canopy and you're out in the sun for potentially hours. Ripe for bringing out the ooga ooga to find food.

Swimming is extremely calorie intensive compared to exercise in the air :)

Interesting. How about post-menopause women?

Is there something biologically special about post-menopause women that makes you wonder if this applies to them?

Lower estrogen. The article says estrogen interferes with the effect in women.

Thanks, that makes sense.

To the other comments: I understand that a woman undergoes many changes when she goes through menopause. I was curious about which one in particular would be relevant here.

> Is there something biologically special about post-menopause women

Many things. Hormone levels alter dramatically, so the question you're replying to is very valid.

There are some risk factors that really change once women go through menopause. This is directly related to hormones. Basically, some risk factors that weren't issues in women pre-menopause start to mirror the risk factor that men face. The biggest one I can think of is heart health. Before menopause, less risk. Afterwards, the risk is more equal to men's risks.

And granted, I'm talking generally. I'm not a doctor, simply female and know these risks will change for me. And I also am simplifying here: Male/female is used in a general sense and I really don't know how hormones affect transfolks' risks (for example).

Apparently one of the side-effects of menopause can be weight gain. I was thinking of that with my original comment, that if less estrogen stopped the blocking of increased ghrelin promotion and caused an increase in appetite, it could explain (some part) of the effect.

Biologically there isn't much difference between a man and a post-menopausal woman. At that point the differences are almost entirely sociological.

I'm pretty sure most men have higher testosterone than post-menopausal women.

Biologically, there is a huge difference between a man and a post-menopausal woman. At best, you could say that hormonally they are more similar, though even that is not entirely true. But hormones have many long term effects that menopause doesn't and can't erase (for example, post-menopausal women's gonads do not typically descend from their abdomens into a pouch, as they tend to do in males under the effects of testosterone; post-menopausal women also have significantly higher rates of uterine cancers than men do).

Thanks ... you made my day!

I find this sort of stuff quite interesting even if I don't understand the science at all.

I was wondering the other day why I find calorie restriction incredibly easy in winter (and at night, generally), yet quite difficult in summer, so this jumped out at me! I can go 6pm-10am without a pang of hunger, yet my wife can't even get to sleep if she's hungry.

So can low and high frequency EMFs trigger this same ghrelin response?

Serious question since light is also an EMF.

https://www.researchgate.net/profile/Tea-Museliani/publicati...

So... evolutionary legacy from the cave dwelling era when the gender roles were more rigid?

introducing: the dark diet.

The challenge: stay in a dark room for a long time

How much weight will YOU lose?

Mice study, should be in title?

It says right there in the paper

“ In both mice and human males”

It’s become a meme to point out studies are done on just mice (to contextualize how sensationalist science media can be), but it’s had the effect of making commenting contests where the first one to point it out gets many upvotes.

So people seek it out without reading the full paper

They missed a chance to say "in males both Of Mice and Men"

Although mice are mentioned in the abstract, it seems like they tested mice and humans, and put both sets of results in one paper:

"In both mice and human males, increased appetite is correlated with elevated levels of circulating ghrelin."

Oh, whoops, read too fast, my bad.

No, they also have human participants:

> To further explore the difference between the response of men and women to solar exposure, we asked volunteers (n = 5 men and n = 5 women; age 18–55 years) to expose, for about 25 min, to the sun on a bright sunny midday (2,000 mJ/cm2 UVB). [...] Our data demonstrate that, while both sexes increase their response to environmental cues and decrease their extracellular vesicle pathways, in terms of the immune system and metabolism, men and women react in the distinct manner

Hmm; n=5? Is that enough? Was this study so difficult to perform with higher n? (Didn’t read beyond the abstract)

That was only the experimental part of the study, which they did to explore what had been suggested by observational results[0] on a much larger group:

> A meta-analysis of several research studies has found differing results for the influence of seasonality on food intake[23]. We, therefore, analyzed data from a 3-year national nutrition survey of approximately 3,000 people. Using a generalized linear model adjusted for age, we found a significant interaction (P <0.001) between sex and season, revealing that men are markedly affected by solar radiation and its seasonal fluctuation compared to women (Fig. [1a]). Additionally, we averaged the monthly direct solar radiation data (KJ/m2) (Fig. [1a]) and found that men significantly increase energy consumption during the summer (March to September) as compared to winter (October to February) (2,188 Kcal versus 1,875 Kcal, respectively; p <0.001), while energy consumption in women remains the same (1,475 Kcal versus 1,507 Kcal, respectively; p = 0.79) (Fig. [1b] and Extended Data Fig. [1a]). Notably, since we found a significant increase in nutrients including: carbohydrates, proteins, fat, sodium, omega-3, zinc and iron in men during the summer (Extended Data Fig. [1a]), it is possible that the increase in men’s energy intake is due to an increase in appetite-stimulating nutrients such as sodium.

[0] https://www.nature.com/articles/s42255-022-00587-9#Sec2

[23] https://www.nature.com/articles/s42255-022-00587-9#ref-CR23

[1a, 1b] https://www.nature.com/articles/s42255-022-00587-9#Fig1

The conclusions drawn from that 3-year longitudinal nutrition survey are questionable. There does not appear to be any attempt to correct for seasonal energy expenditure changes. Ideally, you'd like to see some questions regarding activity level by season as well as energy intake. It's a perfectly reasonable alternative hypothesis that men are eating more in the sunnier seasons because they're doing more outdoor work. It's also possible the people answering these surveys are not accurately weighing and logging their meals, as those numbers in all cases are suspiciously low, but that wouldn't necessarily affect the relative changes as long as they're equally wrong in all seasons.

If they can see a significant effect is a small number of participants, that is good - it means they didn't need to search for the effect of UV light, it was obvious. The reason to have a big sample is usually to control for side-effects in drug testing. Often, the big sample size will mean that even very, very small effects are statistically significant.

Spent the minute it takes to parse the abstract and learn it is not just about mice.

The paper describes observations of both mice and humans.

This is covered everytime a study comes out, mice are similar to humans

https://www.yourgenome.org/facts/why-use-the-mouse-in-resear...

Your comment that 'you're not a mouse so this doesn't apply' is an overly simplistic conclusion based solely on a visual observation that is repeated on Hackernews so often there needs to be a bot that replies

It's about as good a phrase as 'correlation does not imply causation'. Obviously it's wrong for any correlation that's the result of causation, but it's true enough to be a frustratingly good criticism despite its dumb simplicity. So it is with mice models which have repeatedly failed to transfer findings to humans. The list of reasons in your link is mainly about how easy they are to work with, and the 'similarities' is glossed over, but obviously there are vastly superior animal models which are dramatically closer to humans to test on than mice. It's just not done nearly as much due to how difficult it is, and arguably how horribly unethical it is to test on non-human apes.

Saying my source glosses over something doesn't mean the assertion is wrong, it only means it doesn't go into detail.

Here's a tad more complex paper with examples https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3987984/

The similarities and ethical concerns are why mice are used. However my original comment was because the post implied the research was wrong because they "don't look like mouse".

Which I said was overy simplistic and arrogant. As if then a researcher reading that comment would suddenly realize "wait..were not mice, this and all other studies are worthless. I used mice for no reason but couldn't think of a reason not to or how they are different"

Yes, just like 'correlation does not imply causation' requires an actual alternative explanation to be proposed, so does 'it's just mice'. We don't really disagree on that.

I don't know how the study was set up because i haven't looked yet, i will be looking to see if being awake vs asleep is a confounding variable.

sun exposure makes me sleepy

That's the first I've heard that solar radiation protects against cancer. That's enough evidence for me to stop supplementing vitamin D and go outside. Next time hesitate before telling us the thing responsible for life on earth is bad. Really great experts we have who also got the food pyramid and multivitamins wrong. The scientific method isn't working too well if it's consistently churning out peer reviewed false conclusions.

Everything in moderation. Fresh water is bad for you if it prevents you from breathing.

Or cause hyponatremia

Even if you can breathe fine, drinking way too much water can be fatal!

https://en.m.wikipedia.org/wiki/Water_intoxication

There's more than one kind of cancer... specifically here it seems the effect of interest is on colon cancer. So you might be trading off the risk of skin cancer vs colon.

And for higher latitudes vitamin D supplementation is generally a winter issue, when people are unlikely to get enough sunlight on their skin for either sunburn or vitamin D production.

Unless you're actually following "the experts" directly yourself (and I certainly don't) what you're really reading is journalism based on press releases based on abstracts of papers. So before seeking to overthrow the scientific method, see if you could get a better source of advice based upon it.

I'll take skin cancer over colon cancer any day, given it's generally the least severe.

Skin cancer is associated with good health, because to get it you need a healthy lifestyle where you're outside a lot, and you're probably older, and most kinds of it are benign.

There is some evidence that sunscreen is bad for you.

https://news.ycombinator.com/item?id=23086211

And of course, it gives your kids autism if you're a mother living too far north.

...because to get it you need a healthy lifestyle where you're outside a lot, and you're probably older, and most kinds of it are benign.

This simply isn't true. You can get lots of sun exposure simply by sitting in your backyard or balcony. You can get it sitting at sports games. Or lying on the beach. Or being a delivery driver. Folks with limited mobility can still get plenty of sun. Sun exposure doesn't mean you are active at all.

Skin cancer is simply more common in older folks, but lots of younger folks get it. IIRC, skin cancer is the most common type of cancer in young folks, especially women.

I'm pretty sure that sunscreen has not been proven to cause autism. I do live pretty far north, and absolutely no one is being warned about such a thing. I cannot imagine Norway allowing sunscreen sales if they honestly thought it caused autism - they'd at least tell pregnant folks to avoid sun for a few months. Also, many people here are fair skinned and not having sunscreen would mean that sunburns would be more severe.

Did you read the article I linked?

> I'm pretty sure that sunscreen has not been proven to cause autism.

Is joke.

But - low Vitamin D in Swedish immigrant mothers is associated with autism in their children: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4396835/

For some people, even being exposed to sunlight won't push vitamin D to safe levels.

People with darker skin tones, for instance, have a natural protection against Sun light and have a harder time synthesizing vitamin D.

Just because something provides the conditions necessary for life doesn't mean that all aspects of it are healthy. The world isn't so black and white, but instead, it is full of nuance and shades of grey. In this case: Sure, we'd die without the sun but it doesn't mean that we need a lot of it shining directly on our skin.

Salt is similar: Sure, you need some to live. That doesn't mean that drinking salt water is healthy nor is licking a salt block regularly.

You have missed the point. Scientists were the ones making it black and white. The consensus was the sun was bad for your health. They said stay out of the sun and supplement with vitamin D. As for salt, scientists got that wrong as well. Read The Salt Fix [1] for more on that.

[1] https://www.amazon.ca/Salt-Fix-Experts-Wrong-Eating-ebook/dp...

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