Vitamin D is necessary for building bone. Older people often have low vitamin D levels through lack of exposure to sunlight and low dietary intake. Therefore, it has been suggested that taking additional vitamin D supplements may help to reduce the risk of hip and other fractures, which are very common in older people.
This review included 45 trials with 84,585 participants. The review found that taking vitamin D alone is unlikely to prevent fracture. Vitamin D taken with additional calcium supplements does appear to reduce risk of hip fractures in people living in institutional care. Although the risk of harmful effects from vitamin D and calcium is small, some people, particularly with kidney stones, kidney disease or high blood calcium, should seek medical advice before taking these supplements. —Cochrane April 2009