my pcp told me to take a vit D supplement. My blood level was low. He told me most Americans have a D deficit, and I asked him if it was because we don't go outside much (Vit D is "the sunshine vitamin" after all), and he said no. I'm suspicious; I think our indoor lives do have something to do with our deficit, as well as reduced consumption of vit D-fortified food products like cows' milk.
I'm glad it's helping you, and I wish it would help me.