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Comment by snemvalts | Hacker News Reader

Sunlight isn't enough in most northern hemisphere places for vitamin D. Or when you have darker skin.

Plus intense sunlight carries the risk of cancer.

> Plus intense sunlight carries the risk of cancer.

Not the whole truth. Broad spectrum sun exposure is correlated with a decreased risk of death from melanoma. The presence of solar elastosis (basically sun damaged skin) was associated with a 60% lower hazard ratio for death from melanoma, with a 0.009 P value in a 5 year study of 500+ women: https://pubmed.ncbi.nlm.nih.gov/15687362/ (cited almost 300 times)

On the flip side, avoiding sun exposure was found to double (!) the risk of all cause mortality in a 20 year (!) Swedish study of 29k people (!): https://doi.org/10.1111/joim.12251

Categorizing people from lowest to highest sun avoidance behavior (self reported), those who sought out sun exposure the most (sunbathing throughout the year) had a statistically significant 40-50% lower hazard ratio for all cause mortality.

I will still use sunscreen, but given that we evolved to be diurnal on a planet orbiting a sun, I would be more worried about not getting enough sun than getting too much sun.

You don't need a lot of minutes outside to get a sufficient amount of sunlight to produce Vitamin D. Maybe 15-20 min a day.

Where I live we had 14 hours of sunlight per entire January of last year. 14 hours. FOR ENTIRE MONTH. And sunrise is past 9 in the morning where entire population is already indoors working, sunset is about 3 in the afternoon.

So yeah, I maybe got 15 minutes of sun for entire January, but this is my generous guess.

Sounds like you live in Canada or Northern Norway or somewhere. I would get a UV lamp or something.

I play tennis in the Greek sun four hours a week (plus whatever other exposure) and I'm still deficient. I don't know who these levels were designed for, maybe my ancestors who were in the sun so often that they looked 50 in their thirties.

It's 0ºC here. The only exposed skin is the center of my face. I find it hard to believe 15 minutes of exposure are enough.

I regularly go outside with my shirt off at -10C, as long as there's no wind and the sun's beaming, I'm nice and warm. Got a bit of a suntan last week. Wife thinks I'm crazy :)

> The only exposed skin is the center of my face.

Me too. And I have a beard. Do I have to take that into account? Do bald men get more D-vitamin out of the sun? Studies never talk about hairiness.

Doesn't that vary with the skin color (aka melanin content in the skin)? I presume as a brown person I need more exposure for an equivalent dose compared to a Caucasian person.

It's a builtin feature of us white folks to think everyone else is also white. /s

Ha :)

Yes it does, darker skinned persons in northerly climes are at higher risk of lower vit D than we pale skins with the equal level of exposures to the sun.

How can this be explained from an evolutionary perspective? Weren't people more hairy in the not-so-recent past?

I can understand someone with a dark skin moving North gets problems, but otherwise, where do these issues come from?

Completely uneducated guess: Dark skin is an adjustment for areas that take on more sunlight, and even migrating a little north can mean that you are not getting enough sunlight (oh you already mentioned this but I missed it or was added later, anyway...)

For people who have light skin and still have deficiency: Office life probably means you must be proactively chasing sun in your free time, or get the damn supplements and be done with it :)

Evolution happens on time scales of many thousands of years. Our lifestyle has changed enormously in just the last couple hundred years.

Because for a lot of people just 15-20 minutes a day with bare arms and face is more than enough sunlight. Also the body stores vitamin D in fat cells as well, it's not like vitamin C that goes through you pretty quickly. On those nice sunny days you can build up your stores so to speak if you're out for a long time. However I can name plenty days I never even go outside during the sunlight. I prefer evening and night activities. I do take a supplement as a result of my doctor finding I had low vit-d level, now I take a 2000IU supplement every day.

I don't think pre-modern humans were prancing around naked in the midday sun. They probably stuck to the shade when sunlight was particularly intense, the same way many animals do. Given that we mostly evolved in pretty sunny areas, we would have gotten plenty of sun exposure even if we avoided direct sunlight for a large part of the day.

Given that we're prancing around naked in the midday sun on beaches for a large part of the year, I wouldn't doubt it. Even as late as a few decades ago, my grandparents were in the fields all day, and there's no shade there. Sure they took a midday break to eat, but that was probably only in the height of the summer.

More hairy, maybe, but less time indoors behind UV protective glass.

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