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Comment by shajznnckfke | Hacker News Reader

Humans in Northern Europe have adapted to those conditions with very light skin that maximizes sunlight exposure.

> And how do you that for a fact? It's nutrition science. It's not reliable. These numbers of how much we need has been changing for as long as I can remember.

The changing numbers are why I gave such a wide range. Regardless of who you believe, it’s completely impractical to get the vitamin D you need from meat. It’s not even in the right order of magnitude. What is your proposed required daily value of vitamin D? If you’re going to go around claiming it’s possible to get your needed vitamin D from foods, you ought to have done some math to back up this claim.

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The only relevant math I need is that humans have done fine with animal fats for thousands of years. The value I need is what I can get naturally.

And BTW, I have dark skin, I live in one of the Northest parts of the world humans live, haven't taken vitamin D supplements in years and my vitamin D levels have been great (upper middle of whatever acceptable range they use) when I got tested several times over the past years. I don't even care anymore. I will continue to eat what humans are supposed to eat and I'll be fine.

Even if your numbers are not good, you should not be eating these chemicals in isolation. We don't need nutrients, we need food.

Nutrient-nutrient interaction is very difficult to study, but it has been found to be crucial every time they've managed to do it.

> The only relevant math I need is that humans have done fine with animal fats for thousands of years.

That's true, however, humans have been spending days mostly inside, both living and working, for much, much less time than that, which dramatically affects how much natural D they are getting from the sun.

I'd love to see some research on the overall exposure to sunlight, on average, a person has received over the last century. My guess is that in very recent decades, especially the last couple, as working remotely and not needing to leave the house even to commute, sunlight exposure has plummeted.

Also, the risks of sun exposure have been widely reported over recent decades and advances in powerful sunblock have made even those who do spend time outdoors less likely to absorb the sun's rays.

So to place it in the context of how humans have lived for thousands of years ignores the realities of modern times.

Again, nutrition science is very misleading.

Sunlight doesn't have vitamins. What supposedly happens is that when you get exposed to sunlight, some of the cholesterol in your blood gets converted to Vitamin D. What part of sunlight, you might wonder. Is it the visible spectrum? No, it's infrared, you know the thing that you get from your radiator.

So, two factors determine how much vitamin D you're going to get:

- cholesterol levels in your blood

- how much heat you're exposed to (i.e. how warm your room is)

I'm sure we need sunlight for other things... like our sleep cycles or whatever... but we definitely don't need it for vitamin D.

Another commenter pointed out the factual error about vitamin D coming from IR vs. UV, but there’s another misconception in this post.

The amount of IR you get exposed to is not the same thing as how warm your room is. If you touch a hot pan, or get hot because you’re hanging out where the air temperature is high, that heat isn’t being transferred to you by IR. It’s being transferred by thermal conduction: https://en.m.wikipedia.org/wiki/Thermal_conduction

So even if vitamin D was created by IR, you wouldn’t get any from sitting in a hot room.

No, it's ultraviolet. The opposite side.

Perhaps you’re eating some food that has been supplemented with vitamin D. For example, one cup of milk fortified with vitamin D might have 100 UI (as much as six steaks).

I don't drink milk, lactose intolerant.

And even in Northern Europe, people were outside all the time. Nowadays we sit in the dark offices in the artificial lighting.

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