That’s because the general consensus is that higher levels of vitamin D are associated with rapid recovery or avoidance of Covid. Rational people would say that’s a good thing and support it.
IV vitamin D seemed to be beneficial in early COVID-19 patients in one randomized trial, which is the best evidence of a causal relationship we have between vitamin D and prevention of severe COVID. Attempts at giving oral vitamin D after diagnosis showed no benefit, but wouldn't really be expected to, either.
There's probably some protective effect, but it's also probably much smaller than most are estimating. That said, taking a small to moderate dose of vitamin D is likely to do more good than harm to people for other reasons, and may provide a small margin of protection against severe COVID. Further, it's cheap and easy to do.
Since March, I've been taking a multivitamin that includes a moderate amount of D.
Really eager downvotes on my comment, too, today.
Also, I'm not anonymous; my name is on the comment.
Or it could be Vitamin D, at least in part. To know the answer somebody has to actually do the science.
That said: the kind of aggregate mortality effect the (comparatively sparse) data on that site points to is absolutely miniscule compared to much more straightforward mitigations like wearing a mask and avoiding restaurants. And these are things that HN is wildly divided on. "Rational people" might wonder why that is.
I think wearing a mask is a relatively small benefit but small bends in exponential functions can have massive differences in aggregate outcomes.
[0] https://www.cdc.gov/coronavirus/2019-ncov/daily-life-coping/..., under "What makes activities safer?" they list "They are held in outdoor spaces. Indoor spaces with less ventilation where it might be harder to keep people apart are more risky."