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Comment by aazaa | Hacker News Reader

> Vitamin D is a big deal. Recent studies have shown that patients with low Vitamin D levels are more likely to die from Covid-19 than their Vitamin D-rich counterparts,(1) and deficiency in the vitamin has been linked to seven of the ten leading causes of death in the U.S.(2)

1,500 or so words about Vitamin D, but not a single mention of UV?

Can the correlation between COVID-19 mortality and lack of Vitamin D be explained by lack of exercise and/or exposure to UV?

In other words, maybe Vitamin D levels have nothing to do with the disease. It's just a marker for inactivity, which is the real culprit.

If true, this explanation suggests that pumping people full of Vitamin D in the hope they'll fare better with certain diseases would be about as useful as force-relocating the homeless to Beverly Hills. Correlation, not causation.

The paper cited by the author (1) doesn't consider this possibility, either.

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The author has been cautioning against over-use of Vitamin D in this forum; this article raises the point about correlation specifically:

Using this study method, Vitamin D deficiency is correlated with many diseases. But correlation does not equal causation.

One of the mechanisms proposed in recent years to account for Vit D correlations, but not causations, is that Ultraviolet A (from sun exposure), also helps produce nitric oxide (NB, this is also a very good reason to be a nose breather, as this is a major source of your NO).

This won't account for everything either, but we're now fairly sure that the sun exposure -> VitD -> disease link is not as straight forward, and that VitD supps are not necessarily an answer to the low VitD correlations.

I believe the only VitD supplementation causative link we have strong evidence for is to preventing/treating rickets.

i was reading another thread where people were saying homeless and surfers, people who spend a lot of time outside, often have low vitamin D when they get tested. I have NO idea how true that is, but might be an interesting data point.

checkout the episode of RadioLab

A small study:

https://pubmed.ncbi.nlm.nih.gov/17426097/

I can't vouch for the veracity of this claim, but I once read somewhere that it takes a while for the vitamin D, which is apparently created in the upper layers of the skin, to work its way down into the bloodstream, and that if you spend a lot of time in the water, it doesn't make it through. Maybe because being wet a lot tends to dehydrate the skin? I don't know.

How much skin is exposed when wearing a wet suit? There's your answer. Just depends on whether the study took place in California (which has chilly water) or Hawaii (which doesn't).

Being outdoors isn't the same as sun exposure though. In particular, I can imagine that homeless people cover up more to prevent sunburn. Additionally, just being homeless might cause a depletion of vitamin D.

In general, I can imagine that people who spend a lot of time outdoors could get very little sun exposure since they would be more cognizant of the effects of the sun and more likely to wear sunscreen and protective clothing.

Can you explain why just being homeless might cause a depletion of vitamin D?

> they would be more cognizant of the effects of the sun and more likely to wear sunscreen and protective clothing.

That's easy. Crappy diet and alcoholism. Something like 68% of single adult homeless credit substance abuse with their homelessness[1], with alcohol being the most commonly abused substance. Alcoholism and vitamin D deficiency has definitely been linked.[2]

[1]http://www.ncdsv.org/images/USCM_Hunger-homelessness-Survey-...

[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5074581/

I sense you didn't read the 1500 words? Most of it is about the very item you raise, i.e correlation not causation.

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