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Comment by awolf | Hacker News Reader

There are many different types of vitamin D synthesized in our bodies which require sunlight to form. The many varieties of D are used in an enormous amount of different chemical processes in our bodies- many of which are quite complex and not fully understood.

Vitamin D supplements consist of (mostly) one type of Vitamin D. People are typically deficient in that specific type so mild supplementation is a reasonable option. Just don't kid yourself into thinking that taking Vitamin D is a replacement for spending adequate time outdoors. Compared to the first 100 million years of our species existence, hiding indoors all day is a relatively new invention. It will be a while before science produces a silver bullet in gelcap form.

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Could you provide some references? I'm really interested to learn more

EDIT: I'm looking for backup to the claim that sunlight provides something that you don't get in a vitamin D3 supplement. It seems reasonable but has a big impact on the solution.

[5] forms (vitamers) of vitamin D exist (see table). The two major forms are vitamin D2 or ergocalciferol, and vitamin D3 or cholecalciferol, vitamin D without a subscript refers to either D2 or D3 or both. These are known collectively as calciferol....Vitamin D3 (cholecalciferol) is produced by ultraviolet irradiation (UV) of its precursor 7-dehydrocholesterol. This molecule occurs naturally in the skin of animals and in milk. Vitamin D3 can be made by exposure of the skin to UV, or by exposing milk directly to UV (one commercial method).

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Vitamin D3 (cholecalciferol) is produced industrially by exposing 7-dehydrocholesterol to UVB light, followed by purification.[143] The 7-dehydrocholesterol is a natural substance in wool grease (lanolin) from sheep or other woolly animals. Vitamin D2 (ergocalciferol) is produced in a similar way using ergosterol from yeast or mushrooms as a starting material.[143]

Tl;dr of 5 types & only D2 and D3 are commercial avail

--Wikipedia: http://en.wikipedia.org/wiki/Vitamin_D

It looks to me like the supplement is D3 and the one you get from UV exposure is D3, so no, spending time outdoors doesn't give you any better Vitamin D than the supplement. Of course, exercise has other benefits.

I would amend that to no proven benefits. The body is a complex system. D3 generated by the body via natural pathways may be more effective than ingested D3 in some way we don't understand yet.

Leaving aside any other ill-understood benefits of sun exposure.

That simply lists precursors to calcitriol, which you can get but isn't recommended because it is hard to dose.

There are other reasons to sunbathe (e.g. NO release) but there is only one active form of D.

Also, Vitamin D is just one particular aspect our bodies depend on the sun. You also need sun exposition to improve the immune system, avoid depression and insomnia. Not to mention all the other biochemical processes and health benefits we still might not know.

The obvious fact is that we evolved to live under at least some sun exposition (depending on your genetic background), trying to replace that entirely with pills is backwards.

The above Factors are mostly regarding Vitamin D production or exposure onto your retinas. Nobody is claiming you need to replace it entirely. The right strategy depends on the context and esp. at which ends of the normal distribution curve you are (regarding sun exposure).

It's very seductive to argue from an evolutionary advantage perspective. It can be used to generate Hypotheses that need testing. But one shouldn't give health advice based on it. After all we brush teeth, wear clothes and benefit massively from machines and modern medicine.

> It's very seductive to argue from an evolutionary advantage perspective. It can be used to generate Hypotheses that need testing. But one shouldn't give health advice based on it. After all we brush teeth, wear clothes and benefit massively from machines and modern medicine.

It's about sane defaults. The effort to validate every reasonable hypothesis is extraordinary, and sometimes impossible. We can't afford to live our lives based only on what conclusions science has been able to come to so far. Making some choices based on ancestral norms is perfectly acceptable and better than many alternatives.

Doesn't seam to be such a good heuristic, honestly. Why not look first at what seem to work for (a large sample of) other people?

Then you don't have to follow that complicated evolutionary logic style thinking. (I know it's very trendy right not) In the end Nature isn't smart and can't think.

Vitamin D supplements are generally D3 by design because that's the form most readily absorbed by the body.

That said you're probably better off getting it from catfish or salmon (which also contain omega fatty acids, a "good" fat which you might otherwise consider supplementing if you aren't getting enough in your diet)

And of course it's not a dichotomy, you can supplement D3 daily and also try to eat a lot of fish!

Nitpicking, but I don't think we as a species have been here for 100 million years. I doubt we've been even as hairless as we are now for more than a few hundred thousand, so we may not have gotten as much sunlight due to that. But your point still stands.

I always wondered why the dogs always like to lay out in the sun and furred animals get their Vitamin D. Wikipedia: "In some animals, the presence of fur or feathers blocks the UV rays from reaching the skin. In birds and fur-bearing mammals, vitamin D is generated from the oily secretions of the skin deposited onto the feathers or fur and is obtained orally during grooming.[97]" http://en.wikipedia.org/wiki/Vitamin_D

from personal experience, my computing sessions with reduced to no sunlight sessions for days in my room led to vitamin deficit, i did learn a lot of things though, but the results of the deficit are still apparent to me.

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