Nothing a few pounds of ivermectin can't fix.
/s
https://www.reddit.com/r/interestingasfuck/comments/8iflwh/c...
I dont think it is ever ok to justify hurting the kids because we don't like the parents.
Because UVB scatters more than UVA (Rayleigh scattering), shade increases the UVB:UVA ratio from 1:1 to about 0.52:0.35 under a shade umbrella, or 0.53:0.37 under a tree. See Table 1 (paywalled, sorry) https://doi.org/10.1016/j.jsbmb.2005.04.039
of course, most that go to a tanning booth care more about looks than health
UVB shouldnt just be legal, it should be mandatory.
But yes, one can have too much of a good thing in this regard.
The paper says you can produce enough vitamin d to maintain healthy levels from a specific amount of sunlight per day, depending on latitude and skin color.
The original comment suggests that there’s some (very short!) limit beyond which the body is unable to produce more vitamin d, which is very different. I’d be very curious to see sources for that.
UVB synthesizes cholecalciferol (vitamin D3) in the skin, which the liver converts into calcifediol (what blood tests usually measure), which the kidneys convert to calcitriol (the active hormone). Wiki claims the kidneys have a negative feedback loop, converting excess calcifediol into inactive 24,25-dihydroxycholecalciferol. I wish I had better sources (for my vitamin D pdf folder).
https://en.wikipedia.org/wiki/Vitamin_D#Excess
But just knowing that, I don't immediately see anything limiting cholecalciferol or calcifediol amount and storage.
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 :)