https://www.inverse.com/mind-body/are-you-wearing-gloves-a-mask-to-the-shops-you-might-be-doing-it-wrong/amp

From what I am hearing, vitamin D is generally helpful in limiting the widespreadness/severity of a lot of viruses. My question is regarding the correlation between the seasonal variations of 'flu-like infections and vitamin D production when sunshine is more prevalent. I feel sure it has been well researched, - enough for me to get the tablets, despite the sunny days we are experiencing. Lockdown means I am indoors much more. And dosage levels and toxicity are far apart with vitamin D, apparently. eg 15 µg cf 100 max safe recommended, though even that is not widely certain.

https://en.wikipedia.org/wiki/Vitamin_D#Immune_system