If Calcium Supplements Aren’t Safe, What About Calcium in Food?

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? I explore this in my Are Calcium Supplements Safe? video.

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 to be transient, disappearing after a few months, it’s better than nothing. Further, excess calcium in the gut can cause fat malabsorption by forming soap fat, reducing saturated fat absorption, and increasing fecal saturated fat content. Indeed, if you take a couple Tums along with your half bucket of KFC, up to twice as much fat could end up in your stool. With less saturated fat absorbed into your system, your cholesterol might drop. Given this, the New Zealand researchers were expecting to lower heart attack rates by giving women calcium supplements. To the researchers’ surprise, however, 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—it’s the same study that uncovered how dangerous hormone replacement therapy is. Would it uncover 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 doses of calcium supplementation rather than supplementation versus no supplementation. What if you go back and 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 they confirmed the danger. 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—that is, simply asking if people had had a heart attack or not, rather than verifying it. In fact, 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. However, the increased risk was seen consistently across the trials, regardless of whether the heart attacks were verified or not.

Okay, but why do calcium supplements increase heart attack risk, but the calcium you get in your diet doesn’t? Perhaps because when you take calcium pills, you get a spike of calcium in your bloodstream that you don’t get from just eating calcium-rich foods. Within hours of taking supplemental calcium, the calcium levels in the blood shoot up and can stay up for as long as eight hours. This evidently produces what’s called a hypercoagulable state. That is, your blood clots more easily, which could increase the risk of clots in the heart or brain. Indeed, higher calcium blood levels are tied to higher heart attack and stroke rates. So, the mechanism may be that 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.” However, 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,” the way nature intended. Furthermore, the evidence is also becoming steadily stronger that calcium supplementation may not be safe. This is why most organizations providing advice regarding bone health, now “recommend that individuals should obtain their calcium requirement from diet in preference to supplements.”


We actually evolved getting lots of calcium—from eating lots of green leafy weeds, not popping Tums. See Paleolithic Lessons for more on this. How else can we combat osteoporosis? See my videos Prunes for Osteoporosis and Almonds for Osteoporosis.

I’ve discussed whether calcium supplements are safe, but Are Calcium Supplements Effective?

For more on calcium and bone health, see my videos:

Calcium supplements aren’t alone in their lack of efficacy. It is a story consistent with disappointments surrounding many other supplements, which you can learn more about in the following videos:

And be sure to watch Should Pregnant Women Take Calcium Supplements to Lower Lead Levels? and Lead in Calcium Supplements

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Best Food for the Common Cold

It is well known that deficiencies in certain vitamins and minerals can lead to significant impairment of immune function and an increased susceptibility to infection that can be reversed by supplementation in deficient individuals. “However, it is unclear to what extent supplementation may aid in maintaining an optimal balance within the immune system in adequately nourished individuals.” As I discuss in my video, Kiwifruit for the Common Cold, researchers in New Zealand tried supplementing with whole kiwifruit. In a petri dish, gold kiwifruit puree appeared to boost natural killer cell activity in human blood and also boost the response to the tetanus vaccine. But, does the same thing that happens in a petri dish happen in people? In another study, researchers found that two immune-related sets of genes were upregulated by eating three kiwifruit a day. But, does that translate into actually helping us fight off infection? We didn’t know the answer until recently.

Researchers in New Zealand found that the consumption of gold kiwifruit reduces the severity and duration of certain upper respiratory tract infection symptoms. Why study gold kiwifruits? The study was funded by the company that owns the patent to gold kiwifruits.

In the study, a few dozen elderly individuals were randomized into one or two groups, eating either two bananas a day or four kiwifruit a day for a month, and then switching. The next month, the banana group ate kiwis, and the kiwi group ate bananas. The rationale for providing banana as the “placebo” was to provide an alternative fruit that had relatively similar calories, but lower nutritional value.

The study’s purpose was to determine whether regular consumption of gold kiwifruit reduces the incidence, duration, and severity of symptoms of upper respiratory tract infections, like the common cold, in comparison to bananas. They found no reduction in overall incidence, but those who did get sick during the kiwifruit phase had significantly reduced severity and duration of head congestion, as well as a reduced duration of sore throat. And not just by a little. The sick banana eaters suffered for five days with a sore throat and congestion, compared to the kiwifruit eaters, who felt better after just a day or two. That’s significant.

The reason the researchers studied older individuals is that they tend to be more susceptible to respiratory infections. Small children are another at-risk group, averaging twice as many upper respiratory tract infections as adults, four to six per year. So, in another study, 66 preschoolers were randomized into the same two groups, kiwifruit versus bananas. In the kiwi group, not only were there again significant improvements in the symptoms of those who got sick, fewer got sick in the first place—45% lower odds of a cold or flu-like illness, which means that the children eating kiwis had almost a 50% reduction in the chance of having a cold or flu.

This suggests that kiwifruit consumption may be a “daily prescription for health”; though about 1 in 150 children report being allergic to kiwifruit, which ranks them number three after milk and eggs, and above peanuts, in a survey of 3,500 kids, of the most common food allergies. So, kiwis are not for everybody.


The upside of the financial conflict of interest is that it offers a rare source of funding for fruit and vegetable research. For more on kiwis, see Kiwifruit for Irritable Bowel Syndrome, Kiwifruit and DNA Repair, and Kiwifruit for Insomnia.

What else can we do to lower our risk of pesky respiratory infections? Check out Can Gargling Prevent the Common Cold?, Preventing the Common Cold with Probiotics?, Nutritional Yeast to Prevent the Common Cold, and Using the Produce Aisle to Boost Immune Function.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: