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Comment by pkaye | Hacker News Reader

Because of impaired kidney function, I get my vitamin D levels monitored every month. Yes supplements can take 2-3 months to increase the levels. The sun actually works pretty good if you can stay outside 15 minutes in noon sun. But that's difficult in the winter months.

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I've read varying reports of how much sun you need to generate a day's supply of vitamin D, but rarely do they mention how much skin needs to be exposed.

Face only? Face and arms? Entire upper body? Entire body?

Is there some online resource for this with time of year and latitude corrections? I imagine there's quite a difference between vitamin D production in noon sun in Fairbanks Alaska versus Miami Florida.

I did some searching...

"John Jacob Cannell, MD, executive director of The Vitamin D Council, notes that the skin makes 10,000 IU of vitamin D after 30 minutes of full-body sun exposure. He suggests that 10,000 IU of vitamin D is not toxic."

https://www.webmd.com/osteoporosis/features/the-truth-about-...

Except that 10000 IU is mostly localized in skin and released a bit slower.

For it, my face and arms are exposed. I walk in the bay area sun for 15 minutes after lunch. Doing this regularly over a month or two will boost my numbers from the mid 20s to mid 30s.

Not to mention it needs to be adjusted for skin tone. The whole reason that humans have a range of skin tones is that paler skin allows for better vitamin D absorption at higher latitudes.

Depends on a lot of things as you mentioned, but also especially on your pigmentation/levels of sunburn. I'm very dark skinned, so I need a lot longer for UV rays to penetrate.

Note that in the winter months even if you're naked outside in the UK you won't get any vitamin D, the sun is too low, the latitude (about same as Alaska) too high.

Would depend on how dark your skin is.

Another big challenge in winter months is that people are so covered with warm clothes, that even going out in Sun doesn't help much.

I wonder if glass windows would block out the benefits?

Yes it does block [1]. Coincidentally I was discussing this with a co-worker last week.

[1]: http://www.sciencefocus.com/qa/can-you-absorb-vitamin-d-thro...

Ordinary window glass blocks 90% of UV-B which is needed to produce VitD.

I do remember reading years ago about a sanitarium in the late 1800's - early 1900 where the windows in the sun rooms were quartz glass.

Anecdotally, a lot of window products have built in films, coatings, or dopants that reduce UV exposure and possibly other portions of the spectrum.

I would /guess/ that pure (greenhouse?) glass, maybe not even visibly transparent, would be effective.

Both could be worth studying if someone hasn't already.

Glass itself blocks a lot of UV. Even not doped.

There exist optically transparent plastics that do not.

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