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Comment by plorg | Hacker News Reader

The same wiki article says there is a limit to the capacity of synthesis by UVB due to the quantity of reagent 7-dehydrocholesterol produced in the skin, but I don't know the math on what amount of exposure would be required to hit that limit - presumably it (or something like it) is covered in the article above.

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Some napkin math, then. About 25–50 μg 7-DHC / cm2 skin (Wiki). About 1.5 m^2 human skin area (google AI summary). About 35% skin exposed (R. Kift, linked earlier). 1.5 * 100 * 100 * 25 * .35 = 131250 μg. Need 50-250 μg of colecalciferol (2000-10000 IU). Anyone would likely get sunburn before running out of 7-DHC (excepting a low 7-DHC condition, or me getting the wrong numbers).

https://en.wikipedia.org/wiki/7-Dehydrocholesterol

This study says "Findings include that small UV doses on a regular basis are more efficient for vitamin D synthesis than larger sub-erythemal doses", using a logarithmic model for blood calcifediol as a function of exposure.

https://pmc.ncbi.nlm.nih.gov/articles/PMC8558903/

But it doesn't address colecalciferol production and storage. Fat stores colecalciferol, and I don't know of any way to measure that directly. I would guess that further UVB exposure linearly produces colecalciferol (with linear DNA damage, minus DNA repair with time), but the liver and kidneys logarithmically produce calcifediol and calcitriol. Just a guess. Still more questions :)

All i know is that i feel miserable if i dont get sunlight for extended periods (months) and i feel fantastic (again) after 20-30 minutes of shirt-less sun exposure. It's not the heat, it lasts for days.

The cold doesnt bother me, i sunbath in the winter too. This obviously isnt for everyone.

Even if it is bad for me i dont need anyones help. Let them go shut down Burger King and Jack Daniels and whatever enjoyable bad things people do.

That said, thanks for the science.

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