Rethinking Calcium Supplements
This week I discovered how painful it can be to change a habit. Not because it means admitting I was doing the wrong thing, but because it means analyzing how feeble my reasons were for the habit in the first place.
Ever since I started practice I’ve been recommending calcium supplements to post-menopausal women. Why? Mostly out of habit. There’s not a shred of evidence that calcium supplements prevent fractures, but some suggestion that they may help bone density. But what’s the harm? Calcium supplements are safe and wholesome and natural, right?
Last week the journal BMJ published a meta-analysis of randomized trials which compared calcium supplement against placebo. (Expand your geeky medical literature vocabulary! A meta-analysis is a study that systematically reviews already published studies on a particular topic and statistically pools together the results of all these studies. The goal of a meta-analysis is to reach a more definitive conclusion than the individual studies did.) It’s important to note that these trials were not studying the effects of calcium supplement on heart attacks. They were each looking at the effect of calcium on different outcomes – bone density, fractures, colon cancer, whatever. The investigators looked through the original study data and (where the data was available) counted the numbers of heart attacks in patients taking calcium supplements and in those taking placebo.
For the studies in which data was available on individual patients, about 3.5% had heart attacks on calcium while about 2.7% had a heart attack on placebo over an average follow up of 3.6 years. That may not seem like a big difference but it means that for every 69 patients on calcium rather than placebo for 5 years there was one extra heart attack. Some media reports characterized this as a small increased risk of heart attacks, but it’s not. It’s in the same numerical ballpark as the decrease in heart attacks from treating high blood pressure.
Even if this harm was numerically small, remember, we have to weigh it against a completely unproven benefit. Doctors have been recommending calcium supplements on the assumption that they prevent fractures, an assumption that has not been demonstrated in trials. The study calculates that, even taking optimistic estimates for fracture reduction from calcium supplements, treating 1,000 people with calcium supplements for five years would cause an additional 14 heart attacks and prevent 26 fractures. That’s a terrible tradeoff.
So calcium supplements seem to be a bad idea. But there are some important additional points. First, the authors were careful to state that dietary calcium (calcium in your food, not in supplements) has never been implicated in heart attack risk and is presumably safe. So we should be getting our calcium in our diets, not in supplements. Second, this study did not address vitamin D, which has many proven benefits that calcium does not. So keep taking your vitamin D supplements. Finally, patients with osteoporosis who are taking medications that rebuild bone need excellent calcium intake for the medication to be effective. In these patients, who are at high risk for fracture, the benefit of calcium supplements may be greater than the risk.
An editorial in the same issue of BMJ concluded that “given the uncertain benefits of calcium supplements, any level of risk is unwarranted,” and that calcium supplements “should not be given without concomitant treatment for osteoporosis.”
So as painful as it is to change my mind about something I thought was completely benign two weeks ago, for my patients who do not have osteoporosis, I recommend stopping calcium supplements. Obviously, if you have questions about your unique situation, ask your doctor.
Maybe next week I’ll find out that smelling roses causes seizures.