It's maddening. Over and over again we have ideas about how to treat a medical problem—ideas that are perfectly rational, that ought to work, and that even seem to work when we first try them out. And then, blam! We get slapped upside the head by science one more time. That happened last week, when the National Institutes of Health announced only modest benefits in preserving bone mass and preventing hip fractures among women who took calcium and vitamin D supplements in the course of NIH's long-running women's health study.
It seems perfectly reasonable to look for ways to increase the calcium content among older women to strengthen their bones and protect them from breaking. Bones are made of a rubbery protein matrix stuffed with crystals of a hard calcium mineral, hydroxyapatite. The protein, collagen, provides form and shape for the bone. The calcium mineral provides hardness, rigidity, and strength. With the help of vitamin D, specialized cells take up calcium dissolved in tissue fluids and incorporate it, as hydroxyapatite, into bone. But as we age, we lose calcium from our bones—women more than men, because the process is somehow related to falling levels of female hormones. As calcium loss makes the bones weak and fragile, old women become particularly at great risk from serious injuries caused by falls—especially hip, spine, and wrist fractures. Up to a point, giving supplemental calcium and vitamin D to young people whose diets may be calcium-deficient (not enough dairy products and leafy green vegetables) increases the calcium in their bones. Earlier studies hinted that the same might apply for the elderly, though less efficiently.
The Women's Health Initiative study sponsored by NIH involves more than 160,000 post-menopausal women and is projected to extend for almost 20 years. The calcium and vitamin D study involved more than 35,000 women aged from 50 to 79. They were divided into two groups. One group took a calcium-plus-vitamin-D supplement daily for seven years, and the other group took an identical-looking placebo. Researchers are supposed to remain neutral in their enthusiasm for the benefit of one treatment or another; practically speaking, however, it seems almost impossible for humans to be truly neutral. So the WHI studies are contrived in ways that conceal from the subject and the experimenter whether the treatment is an active one or a dummy (placebo). In other words, this study isn't just large—it's also very well done.
As reported in the last issue of the New England Journal of Medicine by Dr. Rebecca Johnson and her many colleagues, the results were not what the researchers expected. The hip bones of patients treated with extra calcium did become somewhat denser than comparable bones in the untreated group. But that increased density had no significant effect in preventing broken hips. Nor did the post-menopausal women who took calcium and vitamin D have a lower rate of wrist or spine fractures. In the seven years of this study, the only effect attributed to the daily treatment with calcium and vitamin D was a slightly increased risk of kidneys stones.
You'd think that this kind of evidence would be pretty persuasive—and that as a result, doctors would start telling women not to bother taking calcium and vitamin D. But years of habits and beliefs are hard to change. Calcium-plus-vitamin-D treatment is pretty cheap and low-risk. And with 300,000 U.S. hip fractures annually, the stakes for prevention are high. Maybe the study setup somehow obscured real benefits. My prediction is that, as with so many medical ideas, doctors (probably myself included) will long continue to recommend daily calcium supplements to elderly women. We'll just no longer have that self-satisfied feeling that comes from knowing that our advice has solid scientific support.