Vitamin D is important for bone and muscle strength, but the belief that it significantly reduces the risk of heart disease, cancer and numerous other conditions is questionable. Although Vitamin D supplements are still widely used, well designed studies have established that the supplements are not needed by most people. Moderate sunshine and normal diets provide adequate vitamin D for most people.
Dr. JoAnn Manson led one of the largest and most cited randomized trials that contradicted the belief that vitamin D supplements are a cure-all. In this discussion she explains why there has been confusion about vitamin D. She also addresses the importance of the structure of scientific studies in determining the effects of medications and supplements.