Re: vitamin D?

Yes, I mean any terrain.
Eat only locally grown organic produce wherever possible, including chlorella and other foods which will detox heavy metals. This coupled with periodic water-only-fasting and pathogens/harmful bacteria will be unable to survive or thrive.
Whether anyone chooses to supplement with D3 is an individual choice but where direct sunlight exposure is minimal, D3 supplementation would seem to be a prudent option.

Chrisb1.