Yes, I've been told that by my doctor and confirmed to my satisfaction with a little research -- most of us are deficient in Vitamin D, and magnesium. I take both regularly. I've read that the "15 min of sun" really only works at noon, in the summer, or at the equator, with most of the skin exposed.... which is far different than the conditions most of us get in sun exposure. Therefore we need to supplement with Vit D. Good news is you don't have to take it every day. Once a week works fine, but take with dinner (fat soluble). I'm not a medical person, this is just my current understanding.