Mercola: Sunshine [UVA] Can Destroy Vitamin D

UVB generates vitamin D. If we are exposed to little UVB but a lot of UVA, UVA could destroy vitamin D, according to Mercola.

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Re: Mercola: Sunshine Can Destroy Vitamin D

Just thinking aloud, since UVA penetrates materials more easily, maybe sun exposure during a cloudy day could result in higher UVA exposure relative to UVB.

Re: Mercola: Sunshine Can Destroy Vitamin D

Lol.. want me to take this serious? Without a single link and:

So, How Exactly Does Sunshine Lower Your Vitamin D Levels?

It’s important to realize that vitamin D3 is formed from exposure to UVB rays, whereas UVA radiation actually destroys vitamin D.

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You call this exact? And washing off vitamin D? Where is the evidence vitamin D collects on the skin?

Sorry... but why should I believe this? because Mercola is saying?

This is exact the reason why I adore Peat. Peat has mostly everything based on sience that you can track yourself. Got sick and tired of nonsense being spread by people who don't know how it really works.. I am not saying this is he wrong, but pff.. get me some more decent information please, for example about photo decomposition of vitamin D if there is (didn't try google).

Re: Mercola: Sunshine Can Destroy Vitamin D

I didn't mean to post it as evidence or implying that it's real, because I don't have evidence. I posted more with a "this is an interesting view" attitude.

Re: Mercola: Sunshine Can Destroy Vitamin D

Suikerbuik said:

And washing off vitamin D? Where is the evidence vitamin D collects on the skin?

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I think that should be the topic of a different thread.

Re: Mercola: Sunshine Can Destroy Vitamin D

There have been many observations that UVA destroys Vitamin D. No consensus. Here is some of the science. http://vitamindwiki.com/tiki-index.php?page_id=788

Re: Mercola: Sunshine Can Destroy Vitamin D

Welcome hiahore! That was an interesting link. It makes me think I should probably get my vitamin D levels tested again, it's been awhile.

Re: Mercola: Sunshine Can Destroy Vitamin D

If it were true, it would be a hit to the idea that one should preferably not sunbathe at noon, and that one should use a glass, if the goal were to increase vitamin D.

Re: Mercola: Sunshine Can Destroy Vitamin D

j. said:

If it were true, it would be a hit to the idea that one should preferably not sunbathe at noon, and that one should use a glass, if the goal were to increase vitamin D.

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I interpreted it as meaning overexposure prevented proper absorption and utilisation. I have no idea if it's right or wrong but as a city dweller over 30 with freckles it probably wouldn't hurt to see where my levels are at currently especially after a winter with no sun.

Re: Mercola: Sunshine Can Destroy Vitamin D

Hi hlahore thank you, If there's so many observations why is it so hard to find HOW they have measured this? Most searches lead me to the paper you posted however.

See reference 34 ; Webb AR, B.R. deCosta, M.F. Holick. Sunlight regulates the cutaneous production of vitamin D3 by causing its photodegradation. J Clin Endocr Metab 1989;68:882–7. ; have you got a link to the full paper? I can't find it, only the abstract:

Abstract
Exposure to sunlight initiates the formation of vitamin D3 in skin as the UV B radiation in the solar spectrum causes the photoconversion of 7-dehydrocholesterol to previtamin D3. A heat-induced isomerization then converts previtamin D3 to vitamin D3 over a period of days. A number of irradiation products of vitamin D3 are known to form upon irradiation with high intensity UV radiation, but the effect of subsequent exposures to sunlight on the vitamin D3 formed in skin is not known. To investigate this phenomenon, human skin containing vitamin D3 was exposed to sunlight in Boston. A model system of [3H]vitamin D3 in methanol was also used to study the effects of sunlight on vitamin D3 throughout the year. Vitamin D3 proved to be exquisitely sensitive to sunlight, and once formed in the skin, exposure to sunlight resulted in its rapid photodegradation to a variety of photoproducts, including 5,6-transvitamin D3, suprasterol I, and suprasterol II.
http://www.ncbi.nlm.nih.gov/pubmed/2541158

I have no doubt that UVA breaks down D3, just want to know how they have measured this? with what kind of cells/ tissue or in vivo?, exposure duration? etc, etc.