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Comment by throwawaye3735 | Hacker News Reader

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.

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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/

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).

checkout the episode of RadioLab

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