Q. If you sit in front of a window with sunlight coming through, will your body produce vitamin D or do you have to be outdoors with direct sunlight?
A. The process by which your skin naturally makes vitamin D when exposed to sunlight uses short-wave ultraviolet-B rays (as opposed to long-wave ultraviolet-A rays). According to Bess Dawson-Hughes, MD, director of Tufts' HNRCA Bone Metabolism Laboratory, however, typical car, home and office windows block most UVB rays. So the sunlight coming through a window will not usually make vitamin D.