Long periods without sunshine can play a role in a surprising variety of physical and mental disorders
It's a good discussion of vitamin D and infection control.
But don't forget that orexin production is stimulated by sunlight on the retinas. And orexin deficiency also leads to immune problems.
I think this shift is actually an adaptation to northern latitudes but it's not really advantageous if you don't stay inside and drink all winter. It's a Viking thing, it does not seem to be helpful if you have to work year-round.
Don't just take supplements. Go outside. Get sun on your face. It will help heal your guts and skin.
Wear warm clothes, but breathe cold air. It stimulates the lungs to fight infection and increases brown fat production.
