Yeah, that's very likely actually, since the biggest risk group, the elderly, are also one of the groups with the highest levels of vitamin D deficiency.
In this study here 84% of the elderly had some amount of vitamin D deficiency (Figure 3).
There must be very well controlled groups of elderly people who after some blood test have been taking supplements and checking their vitamine D levels. I wonder how the virus is affecting this group compared with the general population of the same age. If this group were doing well, I think it would be quite conclusive, since it would show that people under treatment (and therefore with some previous health problem) are doing better than supposedly healthy people with low vitamine D values.
I do the same. Getting enough sunlight is hard during wintertime.
Vitamin D deficiency has been linked to compromised immune systems, depression, rickets and several other things. More research is needed within several of those areas, but I believe it to be safe to assume that supplementing with vitamin D is good for you if you're deficient. If not, well, it's not like it's going to hurt you unless you overdo it.
In this study here 84% of the elderly had some amount of vitamin D deficiency (Figure 3).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6178567/#:~:tex....
I do take Vitamin D supplements since they're cheap and available, just in case there is something to it, but I wouldn't bet on it.