Going off of my friend circle here in Seattle, a city not exactly known for winning awards for exposure to sunlight, nobody I talked to has had bloodwork done that included vitamin deficiency panels in recent memory, so I don't know about "a large fraction of people in the developed world."
Huh, I had to ask specifically for it during my annual. Still salty about that since my insurance supposedly covers annual physicals but asking for the test meant that I was going beyond a routine physical and so they coded it as an office visit and billed me a not insignificant amount for it (for the visit, not the test itself, which was extra). Talking to the billing department and the insurance company got me nowhere.
I donate blood. The American Red Cross sometimes gives away small gifts ($5 Amazon Gift Card, windbreaker with ARC logo, etc.) to promote donation. The are now testing blood for COVID so I've had one free negative test so far.
There are different tests that you can get from places like LabCorp or Quest Diagnostics - doctors working for these places prescribe the test. Anyway, since ARC is testing your blood anyway, it seemed like a reasonable incentive would be to test your blood for Vitamin D deficiency. Or testosterone or cholesterol levels or whatever you wanted from a menu of choices.
That would be nice but blood tests aren't free and blood banks would have to pass that cost on to their customers. The main reason they tested for SARS-CoV-2 antibodies was to identify potential convalescent serum donors.
I agree, but I think there are a ton of people who take various multivitamins, apparently a slight majority of Americans and 70% of Americans over 65, so I think that plays a large role here.
You don't even need to do bloodwork. You just need to be aware that vitamin D deficiency may potentially cause COVID, and then increase your vitamin D intake.
So I don't believe that Vitamin D prevents COVID but I still increased my intake of Vitamin D because it seems like Vitamin D deficiency increased the severity of COVID. I wear a mask and practice social distancing to prevent COVID.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7385774/ is a UK study from July that doesn't come to any conclusions but they say "Our opinion is that if vitamin D does in fact reduce the severity of COVID-19 with regard to pneumonia/ARDS, inflammation, inflammatory cytokines, and thrombosis, then supplements would offer a relatively easy option to decrease the impact of the pandemic."
