Despite the findings, people still need to get enough calcium and vitamin D to reduce the risk of osteoporosis, or bone thinning, said Dr Mone Zaidi, an osteoporosis researcher at the Mount Sinai School of Medicine in New York, who was not involved in the study. It's like the four legs of the stool: vitamin D and calcium, exercise, medications if a person is losing bone, and the fourth leg is telling people how to prevent fractures, Zaidi said.