Research Results Need Interpretation

Q:  I've been reading that women cannot reduce their risk of osteoporosis by increasing calcium intake, and that women cannot reduce their risk of heart disease with a low-fat diet.

What's going on? Whatever happened to "you are what you eat"?

A:  Several things are going on, and they all have to do with the interpretation and performance of clinical research.

Physician Joan Neuner, MD, MPH, an Assistant Professor of Internal Medicine at the Medical College of Wisconsin and an osteoporosis expert, uses the 2006 report from the large Women's Health Initiative clinical trial as an example: "The one-sentence conclusion of this trial is that supplementation with calcium and vitamin D does not reduce the risk of hip and spine fractures."

However, delving deeper, calcium plus vitamin D did increase the hip bone density, a marker of strong bones, and it reduced the risk of hip fracture in older women, the ones who are at highest risk for brittle bones and hip fracture. The trial would have been more powerful if the participants were primarily women already with some bone loss.

In other words, Neuner explains, it may take more than seven years of supplementation to measure a difference in bone health when most of the women start the trial with normal bones. This trial was not meant to challenge the truth that women with osteoporosis need to have extra calcium.

Another way the trial would have been more powerful is if the women who were randomized to take a placebo (instead of the calcium supplement) didn't consume any calcium on their own, either from dietary sources or supplements. Instead, the women assigned to placebo already had a daily calcium intake of more than 1,000 mg, close to the recommended 1,200 to 1,500 mg for postmenopausal women.

"It turns out that this trial studied the effect of 1,100 mg of calcium a day compared to 2,100 mg of calcium a day," Neuner says. While it would have been better to study the difference between 0 mg and 1,000 mg of daily calcium, it would have been impossible to ask women not to consume any calcium when it's known that calcium is an important nutrient."

So take heart - it's still important to eat carefully. When you hear about a single study that affects your health, you may wish to ask your doctor to put it in perspective.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices at the Froedtert & The Medical College of Wisconsin General Internal Medicine Clinic - East. Her column appears in the Milwaukee Journal-Sentinel.