Please excuse a white person posting - and I hope the answer is that you know all this already, but just in case you havent read it elsewhere
Vitamin D may be protective against Covid. Dept Health recommendation is for everyone to take a small supplement in winter anyway. But they dont shout it from the rooftops.
Some groups - including those with darker skin, the elderly and anyone who is indoors a lot or covers their skin when outdoors - are advised to consider a supplement all year.
Here are a couple of the studies suggesting this is important for Covid.
www.ncbi.nlm.nih.gov/pmc/articles/PMC7456194/ and
journals.plos.org/plosone/article?id=10.1371/journal.pone.0239252#pone-0239252-g002