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> Vitamin D naturally occurs when people go outside and get exposed to the sun, ...

Not sure where you are living? If I go outside in winter (+2 months around) I need gloves, cap, scarf. Literally only a little portion of my face gets some sunlight until 5pm. Then it is dark!

I live in Germany!

So, this isn't an argument for a lot of people in cold countries or dark countries. Mostly both..

Exposing to the sun is very hard here around the year.

I had thought that it was possible to get vitamin D from moderate sun exposure in the winter and went looking for info to refute your post. Turns out you are right and I was wrong: https://www.nytimes.com/2022/12/06/well/live/vitamin-d-defic...

People living above the 37th parallel, basically the tropics, may not be getting enough in the winter, because the sun isn't strong enough to provide it.

Yes, thank you for this. I would additional repeat myself to say a very simple thing. If you have to wear clothes over your skin, because it is cold, no sun at all helps you out. I do not go out in a t-shirt when it is snowing..

BTW Inuit getting there vitamin D from fatty fish and other animals, not from the sun.

It’s brutal, I live near Toronto and not only is the winter sun quite weak but sunny days are quite uncommon. Almost every day is grey and overcast. Combine that with short daylight periods and winter becomes quite the gruelling challenge in terms of mental health especially.

Weeeellll :)

Toronto Harborfront Center is at 43.6397877,-79.3836877,17.12z according to Google. If I look for the southern most part of Germany, that seems to be Oberstdorf which is at 47.3997083,10.2805651,14.08z ;)

Or in other words, Germany in terms of natural sun light exposure in winter is way worse than Toronto. In fact, in Germany its dark much earlier and sun comes up much later for longer. I hear cloud cover is very comparable to the Toronto weather you describe so aptly.

One of the most populated areas of Germany is at around 51.5, if we wanted to "guess" where aldipower might be from. Going mostly straight up from Toronto, if you want to hit "civilization" at that level, that's Waskaganish, QC or Moosonee, ON a bit more south, right on our beautiful Hudson Bay.

I complain less and less about our beautiful country, the more I compare it w/ the world ;)

Wow, TIL. That’s kind of nuts, I just looked at latitude lines because I was sure you had to be wrong but it looks like where I live (which is actually Hamilton) is the same latitude as northern Italy. In fact, it’s almost exactly the same as Florence, where the forecasted highs over the next week are in mid- to high-teens (C). We have a blizzard and most days next week the high is 1 degree. I honestly didn’t realize how much climate is not strictly determined by latitude!

Wind and ocean currents make Western europe way warmer than Canada for a given latitude. Ottawa is only about 45 degrees north, same as Paris. Most of England is further North than that.

Minneapolis is also at 45 degrees; in fact there's a plaque in a public pathway that marks the exact spot. We just recently started getting sunlight at 5 PM again, but that will change soon once DST takes effect.

Europe is going to be in big trouble if the gulf current ever stops flowing.

Not just England, try Scotland and some of its Islands.

Not much chance of Vit D from sunlight for almost half the year.

Penzance 50.1 N London 51.5 N Berwick 55.8 N

Edinburgh 56.0 N Aberdeen 57.1 N Thurso 58.6 N

Kirkwall 59.0 N Lerwick 60.1 N Haroldswick 60.8 N

Cries in Nordic

I take 30 minutes longer lunch breaks in winter the days the sun is out, just to be able to get outside.

It's more or less impossible to get natural Vitamin D otherwise -- any spare time will be during the dark hours.

Paris is almost 49 degrees north. Even Ottawa is closer in latitude to Milan

You're welcome.

Also: Look up New York City ;)

And even then, Toronto gets about 2000 hours of annual sunshine, while London (a D swathes of Northern Europe) get about 1600 hours :(

For europeans - you'd have to go to southern Greece islands like Crete to get below 37th. Even Athens is 37.59 and northen Greece is 40 and above. So basically most of the Europe won't get enough during winter.

Yes, this is the reason people further from the tropics tend to have lighter skin and are more likely to have genetics allowing for lactose tolerance throughout life. They're natural adaptations by the body, in response to being in an environment which sunlight (and therefore vitamin D) is more scarce.

The lactose tolerance part doesn't really make sense because dairy products are not naturally high in vitamin D. Companies add the vitamin D to milk. Butter is an exception because it is nearly all fat, so it has a lot more vitamin D. But, because butter is nearly all fat, it also doesn't contain much lactose and is usually well tolerated by people with lactose intolerance.

I have read that the correlation of latitude and lactose tolerance has to do with the fact that milk was less prevalent in warmer climates because it did not store or travel well. So unless you grew up right around milk producing cattle, your gene pool had little exposure too it and thus little evolutionary pressure to continue to tolerate milk after infancy.

By contrast, Europe has a much colder climate and was well suited to dairy cows and storing and shipping dairy products.

So you're saying darker skin prevents the body from producing vitamin D? (Not saying it doesn't, I just didn't know.)

Also, what does lactose (in-)tolerance have to do with… anything? To my knowledge, the fact that lactose tolerance is that common among Europeans is largely a result of thousands of years of domesticating dairy animals. Not all light-skinned people in the world are automatically lactose-tolerant (or "are more likely to have genetics allowing for lactose tolerance throughout life" as you say).

Wikipedia agrees:

> Lactase persistence evolved in several populations independently, probably as an adaptation to the domestication of dairy animals around 10,000 years ago. Today the prevalence of lactose tolerance varies widely between regions and ethnic groups. The ability to digest lactose is most common in people of European descent, and to a lesser extent in some parts of the Middle East and Africa.

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

Also see the map on https://en.m.wikipedia.org/wiki/Lactase_persistence .

Seems like skin color is a trade off between protection from skin cancer and getting enough vitamin D. People in areas with abundant sunlight can get all the vitamin D they need from the sun with dark skin while being protected from cancer. People in areas with lower levels of sunlight don't need as much protection from skin cancer caused by the sun but their lighter skin does permit more vitamin D collection from that weaker sunlight.

Even if there is no sunlight for half the year (and this completely equalizes vitamin D levels in winter), various confounders of sun exposure will still affect a study on vitamin D levels, assuming the study collects some samples during the period when there is sunlight and vitamin D levels vary.

Also, the confounders of vitamin D supplementation I mentioned would apply even if you never get exposed to the sun.

I think your comment is assuming the vitamin D supplementation is effective, when that hasn’t really been established. We don’t even know that vitamin D has a direct effect on most of the correlated health measures.

Recommend to adults vitamin D intake of 4000 IU (100mcg) daily (or at least 2000 IU) in the absence of testing. 4000 IU is widely regarded as safe.

https://vitamindforall.org/letter.html

That is kind of beside the point. You would have to prove that people in cold countries never get any vitamin D from the sunlight throughout the entire year to eliminate it as a factor.

You would also have to be able to prove that people people with vitamin D Rich diets are identical to those without them.

Without a randomized controlled trial of vitamin D intervention, there is no way to say for sure that people with more or less vitamin D are seeing a benefit from the vitamin itself, and not some other hidden Factor.

Of course it is possible to give a randomized portion of subjects additional vitamin D and the rest a placebo and see if one portion is less likely to develop a disease than the other.

Of course, which is the point that I am making as well as the grandparent post.

Studies which have not done this should be taken with a grain of salt.

Our bodies can store enough to make it through the winter if you are replete at the beginning.

That, of course, assumes you don't wear sunscreen during the summer/fall, which I do