In the latest study to look at the effect of vitamin D on fracture risk, Swiss researchers found that taking more than 800 international units (IU) of vitamin D daily could reduce the risk of hip fractures in older women by 30 percent. “Vitamin D supplementation is effective in fracture reduction, including hip fractures,” said study author Dr. Heike Bischoff-Ferrari, from the Center on Aging and Mobility at the University of Zurich and Wald City Hospital, also in Zurich.