I'm worried that Vitamin D is the new facemasks.

We have all of this suggestive evidence that Vit D might have a big impact on COVID19. An ordinary person hears this and thinks —

"We were already being told to take Vit D before the pandemic anyway... 1/

...if Vit D might help reduce the severity of COVID by any material amount, shouldn't we push hard to get everyone taking it?

Or give everyone a big dose when hospitalised?

The pandemic is so devastating even a small reduction is worth billions."

And yet despite that... 2/

I'm yet to hear any strong messaging by governments or public health folks advocating everyone take Vitamin D.

Here's a few possible explanations:

a. it's coming, just in the pipeline, these things take time 3/

b. experts have looked at the issue and rightly concluded that the evidence of impact is weaker than I think, so it's not a good use of limited public attention

c. people are overwhelmed and this just hasn't been raised as a top priority yet 4/

d. it hasn't been 'proven' to work by normal medical standards, so it has gotten stuck in the decision-making process somewhere.

In the past I would have thought d. was unlikely, but after seeing the UK/US performance on facemasks it seems all too possible. 5/

We aren't used to thinking of controlling pandemics with vitamins.

So it's natural for professionals in the system to be nervous about staking their reputations on advocating for a strange and 'speculative' approach that probably won't pan out. 6/

As a result it ends up having to jump an unreasonably high evidential bar.

To be clear there's a good chance that Vit D will turn out to be a red herring, but in disasters you need to move fast and play the odds.

If you wait for full info you'll already have lost the game. 7/

Does anyone understand the story here better? 8/