I know it seems funny, but aside from that situation, vitamin d deficiency can have quite serious implications to your health and is something that is often over looked.
Now if that gentleman is old and frail, stays indoors alot (care homes etc), then there could be a possibility of a Vit D deficiency. I'm not saying that would be responsible for covid, but it would affect his overall well-being and strength to fight off the virus.
I did wonder if it was this deficiency that was to blame for the increased risk to BAME. Don't forget also we have been restricting vulnerable people to staying home (ie indoors).
It's also not just a case of taking the vitamin to correct it for immediate recovery, it can take several months to get back to normal levels. Fatigue, tiredness and weakness are normally good indicators.
Worth noting this point is covered off by the NHS, under Coronavirus update;
https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
Coronavirus update
It's important to take vitamin D as you may have been indoors more than usual this year.
You should take 10 micrograms (400 IU) of vitamin D a day between October and early March to keep your bones and muscles healthy.
There have been some reports about vitamin D reducing the risk of coronavirus (COVID-19). But there is
currently not enough evidence to support taking vitamin D to prevent or treat coronavirus.
I highlight this, because it's about your overall well-being that is important, to aid in fighting off any illness.