I have to take Vitamin D all year. I got really sick a year and a half ago due to low levels and wound up with some other issues that it triggered. Turns out, I have MS and the low vitamin D probably helped trigger a flare.

I literally cannot get enough Vitamin D in the winter: The days are short here in Norway and the sun isn't enough. Theoretically, I might be able to get it in the summer, but I really need to wear strong sunscreen since a medicine increases my skin cancer risk. The neurologist doesn't really want me to not take the supplements anyway.

My diet isn't bad. Mostly vegetarian, though I try to eat fish once a week and not otherwise completely devoid of animal products (dairy, for example). The rest of my bloodwork turns out OK.