4 ms·

The point is that being outside naked at noon every day for 15 minutes wouldn't hurt you. Therefore, a daily dose of 20,000 IU / day won't hurt you. Therefore

The point is that being outside naked at noon every day for 15 minutes wouldn't hurt you. Therefore, a daily dose of 20,000 IU / day won't hurt you. Therefore, a 5000 IU supplement every day won't hurt you either.

elric 6y ago
One does not follow the other. Maybe taking 5000 IU orally has a vastly different effect to letting it acculumate through skin? That's purely speculation on my part though, just trying to illustrate that these two are not necessarily equivalent.
- trevorkoob 6y ago
  It is certainly a different mechanism. There are inactive isomers of pre-Vitamin D (tachysterol and lumisterol) that prevent over-production of Vitamin D from continued UV exposure. I list these numbers to give a general idea of the levels of Vitamin D that people experience without oral supplementation. My conclusion was that too many studies were being done to determine the correct or safe amount to supplement rather than testing regularly to determine a safe/optimal blood concentration. Very excited for good prospective studies of Vitamin D.
Barrin92 6y ago
is this just an extrapolation or does my body actually constantly produce the same amount of vitamin D if i sit in the sun even if I don't have a deficit? Because usually phisiological processes are in some kind of equilibrium and regulated, so it's not straightforward to compare it to supplements.
- disgruntledphd2 6y ago
  The article goes into some detail on this, my understanding is that Vitamin D is produced in inactive form with sunlight exposure and then this is more-slowly released as needed (over winter apparently, but nobody's quite sure apparently).
- trevorkoob 6y ago
  7-dehydrocholesterol is photolyzed by UV to previtamin D. There is then spontaneous isomerization between this previtamin D, vitamin D and 2 inactive isomers. As vitamin D is used by the body, and the inactive isomers remain in the skin, there is an equilibrium - as vitamin D is used by the body it is drawn from the skin, leading to more conversion of inactive isomers to active vitamin D.
perl4ever 6y ago
Why do we think that the various effects of sun exposure are caused by vitamin D, rather than vitamin D just being one of the effects?
DarthGhandi 6y ago
That's a bold assumption to be making, especially regarding a fat soluble vitamin that builds up in the body. A bag of carrots wont hurt you yet an equivalent dose of betacarotene (vit A) supplement definitely will and is strongly associated with increasing certain cancers. There's a reason you won't see those on the shelf apart from miniscule amounts in multivitamins. Nothing in nutrition exists in a vacuum.

elric 6y ago

One does not follow the other. Maybe taking 5000 IU orally has a vastly different effect to letting it acculumate through skin? That's purely speculation on my part though, just trying to illustrate that these two are not necessarily equivalent.

trevorkoob 6y ago
It is certainly a different mechanism. There are inactive isomers of pre-Vitamin D (tachysterol and lumisterol) that prevent over-production of Vitamin D from continued UV exposure. I list these numbers to give a general idea of the levels of Vitamin D that people experience without oral supplementation. My conclusion was that too many studies were being done to determine the correct or safe amount to supplement rather than testing regularly to determine a safe/optimal blood concentration. Very excited for good prospective studies of Vitamin D.

Barrin92 6y ago

is this just an extrapolation or does my body actually constantly produce the same amount of vitamin D if i sit in the sun even if I don't have a deficit? Because usually phisiological processes are in some kind of equilibrium and regulated, so it's not straightforward to compare it to supplements.

disgruntledphd2 6y ago
The article goes into some detail on this, my understanding is that Vitamin D is produced in inactive form with sunlight exposure and then this is more-slowly released as needed (over winter apparently, but nobody's quite sure apparently).
trevorkoob 6y ago
7-dehydrocholesterol is photolyzed by UV to previtamin D. There is then spontaneous isomerization between this previtamin D, vitamin D and 2 inactive isomers. As vitamin D is used by the body, and the inactive isomers remain in the skin, there is an equilibrium - as vitamin D is used by the body it is drawn from the skin, leading to more conversion of inactive isomers to active vitamin D.

perl4ever 6y ago

Why do we think that the various effects of sun exposure are caused by vitamin D, rather than vitamin D just being one of the effects?

DarthGhandi 6y ago

That's a bold assumption to be making, especially regarding a fat soluble vitamin that builds up in the body. A bag of carrots wont hurt you yet an equivalent dose of betacarotene (vit A) supplement definitely will and is strongly associated with increasing certain cancers. There's a reason you won't see those on the shelf apart from miniscule amounts in multivitamins. Nothing in nutrition exists in a vacuum.