Taking larger doses of vitamin D may reduce the risk of hip fractures in older women by 30%, a new study finds. The study combined the results of 11 prior studies. They included a total of 31,022 people. More than 90% were women. All were 65 or older. People were randomly assigned to take vitamin D pills or placebo (fake) pills. The new analysis found that the risk of hip fracture was 10% lower for those assigned to receive the real vitamin D pills. That difference was so small it could have been caused by chance. But the researchers also looked at measurements of how much vitamin D people actually took. This included extra vitamin D that people took on their own. Hip fracture risk was 30% lower in those who took at least 800 international units a day. The New England Journal of Medicine published the study. HealthDay News wrote about it July 4.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Have you heard the news about vitamin D? It's hard to ignore! Sure, it plays an important role in maintaining bone health. But in recent years studies have also found potential links between low vitamin D and:

• An impaired immune system
• Dementia
• An unhealthy body weight
• Worsened symptoms of asthma
• A higher risk of rheumatoid arthritis
• A higher risk of cancer

What's not clear is how important these findings are. That's because we don't know whether vitamin D deficiency actually causes all of these problems. It's also uncertain whether taking extra vitamin D can treat or prevent them.

For example, suppose a study finds that a group of people with cancer have lower vitamin D levels than people without cancer. That doesn't mean low vitamin D causes cancer. It also doesn't prove that taking vitamin D pills will prevent it. It's possible that people who have a high risk of cancer for other reasons tend to consume less vitamin D than people with lower cancer risk.

A new study tries to clear up the role of taking vitamin D pills in preventing bone fractures. The new study combines the results of 11 previous trials. They included more than 31,000 people and nearly 5,000 fractures. Here's what the researchers found:

• Overall, being assigned to receive vitamin D in the studies had a minor impact (at best) on fracture risk.
• People who took the most vitamin D (800 international units a day or more) had a 30% lower rate of hip fracture. They had a 14% lower rate of any non-spine fracture, such as a wrist fracture. The analysis did not include spine fractures.
• The findings were similar regardless of how much calcium people took in or their blood vitamin D level at the start of the study. (Many of the studies did not include this information, however.)

An editorial published with this research points out a flaw in past studies, including some that were part of this new analysis. These studies did not determine whether people started out with low blood vitamin D levels. Other studies did not say whether the pill dosage people took was high enough to raise low levels to normal.

For these reasons, this new analysis might underestimate the impact of vitamin D. Taking vitamin D pills might be more effective for people whose blood vitamin D levels are low.

What Changes Can I Make Now?

You can make changes now to improve your bone health. Reducing factors that increase your risk of weak bones is the first step. One risk factor, family history, can't be changed. But others can be. They include:

• Lack of exercise
• Not consuming enough calcium
• Not getting enough vitamin D or sun exposure
• Smoking
• Drinking excessive alcohol
• Taking certain medicines, especially corticosteroids, that can weaken bones. Don't change your medicines without your doctor's approval.
• Having an overactive thyroid or taking too much thyroid hormone

Ask your doctor whether you should be tested for osteoporosis. This is a condition that causes weak, easily broken bones. If your doctor has recommended a medicine to prevent or treat osteoporosis, take it as prescribed. If you have side effects or other concerns about it, talk to your doctor.

As this study shows, vitamin D pills can improve bone health. But it may take a higher dose than commonly found in multivitamins. Talk to your doctor about any symptoms (such as bone pain) that might suggest you have low vitamin D. Ask whether you should have a blood test to find out. Make sure the test measures 25-OH-vitamin D. Other forms in the blood may not be a reliable reflection of whether you have enough.

If there is any concern you might be vitamin D deficient, review ways you can get more vitamin D from your diet. Talking to a nutritionist may be a good idea.

Consider taking 800 to 1,000 international units of vitamin D each day. Be sure to get your doctor's approval first. Avoid the use of mega-doses of vitamin D (or any other vitamin). This can be hazardous.

What Can I Expect Looking to the Future?

In the future, you can expect researchers to find out:

• Whether low vitamin D actually causes the diseases with which it has been linked
• Who should be screened for low vitamin D
• The ideal blood level of vitamin D and the ideal dosage in pills

Taking extra vitamins does not always improve health. But, if you're deficient in a vitamin, you should change your diet or take enough in a pill to return your levels to normal. It sounds so simple. Yet many people who should take supplements don't do it. Many others take vitamins they don’t need. That's why we need more research like this new study.