Dark, chilly days may be the culprit for an ailment besides seasonal affective disorder: back pain. Since the winter sun is too far for UVB rays to significantly reach most of the Northern Hemisphere, we don't end up making enough vitamin D, which helps maintain strong bones for healthy backs. Stewart B. Leavitt, Ph.D., executive director of Pain Treatment Topics, reports that back-pain sufferers given 2000 IU of vitamin D3 supplements—double the typical RDA—may feel relief after three months. Intrigued? Check out the patient brochure on pain-topics.org and consult with your doctor (though we personally prefer frequent winter pilgrimages to the Caribbean).