[abecedarius]

Another data point: 5000 IU of D3 daily for years, after testing initially at around 20 ng/dL (iir the units c); this spring my level from a blood test was >90 in the first test since then. It seems like taking 10000 IU instead would've been overkill for me.

I supplement K2 and Mg also (plus a few unrelated things). I also get sick less, though I made enough other changes I can't tell whether to credit the supplements. (The K2 definitely helped a skin issue -- I could reliably bring it back by stopping taking the K2. That's probably a pretty idiosyncratic problem of mine, but it's an example of a supplement clearly helping.)

Chris Masterjohn has suggested that high levels of vitamin D could make you more susceptible to the virus, because some papers suggest that D upregulates ACE2 expression. He thinks it's best to aim for a blood level in the 30-35 range. I don't know how seriously to take this suggestion. For now I reduced my supplement to 1000IU/day.

[Daishiman]

What skin condition was helped? I have a skin condition that is anecdotally helped by supplementation but I see few or no controlled trials.

[abecedarius]

It looks like psoriasis on my heels, but I haven't sought a diagnosis. A regular bit of collagen also helps against it. I suspect I have some gut malabsorption issue and that's why supplements can make an especially clear difference in my case, though this is guessing on top of guessing.