Transcript: Are Calcium Supplements Safe?
In 12 short years, government panels have gone from suggesting widespread calcium supplementation may be necessary to protect our bones to “Do Not Supplement”. What happened? It all started with a 2008 study in New Zealand. Short-term studies had showed that calcium supplementation may drop blood pressures by about a point. Though the effect appears to be transient, disappearing after a few months, it’s better than nothing. And excess calcium in the gut can cause fat malabsorption, by forming soap fat, reducing saturated fat absorption and increasing fecal saturated fat content. And, indeed, if you take a couple Tums along with your half bucket of KFC, up to twice as much fat would end up in your stool, and with less saturated fat absorbed in your system, your cholesterol might drop. So, the New Zealand researchers were expecting to lower heart attack rates by giving women calcium supplements. To their surprise, there appeared to be more heart attacks in the calcium supplement group.
Was this just a fluke? All eyes turned to the Women’s Health Initiative, the largest and longest randomized controlled trial of calcium supplementation. The name may sound familiar—that’s the study that uncovered how dangerous hormone replacement therapy was. Would it do the same for calcium supplements? The Women’s Health Initiative reported no adverse effects. However, the majority of the participants were already taking calcium supplements before the study started; so, effectively the study was just comparing higher versus lower dose calcium supplementation, not supplementation or no supplementation. But what if you go back and just see what happened to the women who started out not taking supplements and then were randomized to the supplement group? Those who started calcium supplements suffered significantly more heart attacks or strokes. Thus, high dose or low dose, any calcium supplementation seemed to increase cardiovascular disease risk.
Researchers went back, digging through other trial data for heart attack and stroke rates in women randomized to calcium supplements with or without vitamin D added, and confirmed the danger and most of the population studies agreed—users of calcium supplements tended to have increased rates of heart disease, stroke, and death.
The supplement industry was not happy, accusing researchers of relying in part on self-reported data—like they just ask if people had a heart attack or not rather than verifying it. And indeed long-term calcium supplementation caused all sorts of gastrointestinal distress including twice the risk of being hospitalized with acute symptoms that may have been confused with a heart attack. But no, the increased risk was seen consistently across the trials whether the heart attacks were verified or not.
OK, but why do calcium supplements increase heart attack risk, but not calcium you get in your diet? Perhaps because when you take calcium pills, you get a spike of calcium in your bloodstream that you don’t get just eating calcium rich foods. Within hours of taking supplemental calcium, the calcium levels in the blood shoot up and can stay up as long as eight hours. This evidently produces what’s called a hypercoagulable state, your blood clots more easily, which could increase the risk of clots in the heart or brain. And, indeed, higher calcium blood levels are tied to higher heart attack and stroke rates. So, the mechanism may be calcium supplements lead to unnaturally large, rapid, and sustained calcium levels in the blood, which can have a variety of potentially problematic effects.
Calcium supplements have been widely embraced on the grounds that they are a natural and, therefore, safe way of preventing osteoporotic fractures. But, it is now becoming clear that taking calcium in one or two daily doses is not natural, in that it does not reproduce the same metabolic effects as calcium in food. And furthermore, the evidence is also becoming steadily stronger that calcium supplementation may not be safe. That’s why most organizations providing advice regarding bone health now recommend that individuals should obtain their calcium requirement from diet in preference to supplements. But if we can’t reach it through diet alone, would the benefits to the bones outweigh the risks to the heart? We’ll find out, next.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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