A look at the trials

The review, published in the New England Journal of Medicine, looked at data from 11 trials that included a combined total of more than 31,000 people. These trials compared vitamin D to placebo in people who were at least 65 years old and monitored participants for fractures over time. Vitamin D was given daily, weekly, or every four months, and in some of the trials, vitamin D was combined with calcium. The people in the trials were monitored for hip and non-vertebral (that is, not involving the spine) fractures.

It only helps if you take it

After analyzing the combined data from all of the studies, the reviewers found the following:

• Pretrial vitamin D levels were generally low, with 30% of participants having clear deficiencies and 88% having levels considered to be suboptimal.
• People whose actual intake of vitamin D was 792 to 2,000 IU per day had a significant, 30% reduction in hip fractures, and a 14% reduction in all non-vertebral fractures.
• There was no reduction in any fracture risk in people whose actual intake was less than 792 IU per day.
• Among people with the highest actual vitamin D intake, those who also received 1,000 mg per day or more of calcium had a higher risk of fracture than people who took less than 1,000 mg per day.

One key finding was that only actual intake mattered. When the reviewers looked at people assigned to vitamin D groups, they did not see a statistically significant difference in fracture risk. This may mean that some people in vitamin D groups do not take their supplements, or that some people in placebo groups were inadvertently taking vitamin D. According to the authors of the current review, previous reviews that compared people in vitamin D groups to people in placebo groups and found no effect may not have considered actual intake.

Take enough and take it often

"The findings suggest that only a high intake of vitamin D leads to a significant reduction in the risk of fracture," the reviewers said. "Furthermore, our data suggest that at the highest actual intake level of vitamin D, a smaller amount of calcium supplementation (less than 1,000 mg per day), as compared with a larger amount (1,000 mg per day or more), may be more beneficial in reducing the risk of fracture."

The reviewers noted that taking vitamin D appeared to be just as effective when given weekly as when given daily. Taking vitamin D every four months may also be effective, but only one study in this review used such a schedule. Taking a large amount of vitamin D once per year has not been shown to reduce fracture risk.

Reduce your fracture risk

Based on the findings of this review, older people can protect their bones by taking 800 to 2,000 IU per day of vitamin D. Here are some other things you can do to prevent fractures:

• Don't smoke. Cigarette smoking is strongly linked to osteoporosis and bone fracture.
• Limit alcohol. Although some studies have found that having one alcoholic drink per day may be good for your bones, drinking too much causes calcium and bone loss and increases fracture risk.
• Maintain a healthy weight. When it comes to bones, being underweight is the main concern. Try to keep your weight normal for your height.
• Exercise regularly. Weight-bearing exercises like walking, jogging, and playing team sports can help keep bones strong.
• Stay balanced. Tai chi, qigong, and gentle styles of yoga can improve balance, preventing falls that could result in fractures.

(N Engl J Med 2012;367:40-9)