I don’t think that’s really the blocker here. Vitamin D supplementation is very low risk and the risks are well known. I’ve seen at least one study that I can recall saying exactly that—the correlation is there and vitamin D is safe and basically risk free so we should be supplementing it in at least the at-risk population immediately.

Vitamin D taken orally needs to bind with Calcium or Mg.

Sun Lamps may be a better option for the at risk group.

Are sun lamps sufficient to enhance Vitamin D production? They're mainly used for their psychological effects.

Elderly can't produce vitamin D.

Not particularly. They tend to have faulty liver more often though preventing them from producing enough cholesterol, and need more to handle the general cell damage, so less remains in the skin to synthesize vitamin D...

You can overdose on vitamin D and it can have significant side effects.

More or less anything that can have a positive effect on your health can have a negative effect if done wrong. If something has no possible negative effects it probably doesn’t do anything at all.

You can overdose on water but we still tell folks to drink several glasses a day, because most people don't get enough. That a tiny few are sensitive or go nuts with it shouldn't stop helping everyone else.

> But it's a "drug"

It is. It is not like other 'vitamins' and shouldn't even be called that way. It's a hormone. It is fat soluble, it will linger for quite a while.

> even though we know that it has effectively zero risk

Not true. https://www.health.harvard.edu/staying-healthy/taking-too-mu...

Most people don't consistently take it in high doses for it to become a serious problem. It doesn't mean it's without risks.

It's typically not treated as a "drug", but as a supplement, and widely recommended even outside covid.