 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 have shown that calcium supplementation may drop blood pressures by about a point, though the effect appears transient, disappearing after a few months, but 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 of tons, along with your half bucket of KFC, up to twice as much fat could end up in your stool. And with less saturated fat absorbed into 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 might 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 participants were already taking calcium supplements before the study started. So effectively, the study was just comparing higher versus lower dose calcium supplementation, not calcium supplements versus no calcium supplements. But 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. Researchers who started calcium supplements suffered significantly more heart attacks or strokes. Thus, high dose or low dose anti-calcium supplementation seems to increase cardiovascular disease risk. So 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 the researchers of relying in part on self-reported data, like they just asked people if they had a heart attack or not, rather than verifying it. Indeed, long-term calcium supplementation causes 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 and brain. And indeed, higher calcium blood levels are tied to higher heart attack and stroke rates, so the mechanism may be calcium supplements leading 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's now become clear that taking calcium in one or two daily doses is not natural, and that it does not reproduce the same metabolic effects as calcium in food, the way nature intended. 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.