Vitamin D supplementation to prevent acute respiratory tract infections (2017)
I can say from my own experience that the lack of vitamin D can have a significant impact on both mind and body.I suspect that essentially all people living at relatively northern latitudes have some sort of vitamin D deficiency. From what I know you need to have your face and arms exposed to direct sunshine for at least 15 minutes/day to keep healthy vitamin D levels in the body. Good luck with that in the European/Canadian/Northern US winter.