Can consuming calcium and vitamin D help prevent bone fractures?

Although calcium is clearly important for sturdy bones, evidence that a high calcium intake can prevent fractures isn't as strong you might think. For example, results from the Physicians' Health Study and Nurses' Health Study showed that people who drank no more than one glass of milk per week weren't any more likely to break a hip or forearm than were those who drank two or more glasses per week. And a meta-analysis of prospective trials found no association between calcium intake and fracture risk. What's more, the combined results of randomized trials that compared calcium supplements with a placebo showed that calcium supplements did not protect against fractures of the hip or other bones.

Because many people are low in vitamin D, which is crucial for calcium absorption, studies that look at the two nutrients together may be a fairer test. A trial of 36,000 healthy postmenopausal women (conducted as part of the Women's Health Initiative) found that taking calcium and vitamin D supplements cut hip fracture rates by only 12% overall. Yet when researchers analyzed the impact on particular subsets of women, they found greater benefits for two groups. Women of any age in the study who consistently took the supplements (as opposed to those who tended to miss doses) had a 29% reduction. The best supplement for strong bones, however, is regular exercise.