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Can calcium supplements cause heart disease?

People taking calcium supplements to mitigate their risk of developing bone disease (osteoporosis) may be doing more harm to their health than good. That’s because a growing body of research shows the…

There’s no evidence suggesting that a calcium-rich diet causes heart problems. Rachel James

People taking calcium supplements to mitigate their risk of developing bone disease (osteoporosis) may be doing more harm to their health than good. That’s because a growing body of research shows the supplements confer little benefit and increase the risk of developing heart disease.

Calcium supplements have also traditionally been thought to reduce the risk of heart attacks because they produce small beneficial changes in both blood pressure and blood cholesterol levels. We set out to test this idea in a trial we had originally designed to check the effect of calcium supplements on fractures and bone density.

To our surprise, what we discovered was that heart attacks were actually more common in the (randomly selected) women who received calcium supplements than those who had randomly been given inactive tablets.

When we published this study in the British Medical Journal in 2008, it caused widespread surprise among doctors working in the area, as well as the general public. So to test whether this was the true effect of calcium supplements, we decided to do a meta-analysis of studies about taking them.

First, we contacted all the researchers who had carried out large trials of calcium supplements in the past to see whether they’d kept records of the medical problems that occurred in the course of the trials.

Data were available from 93% of trial subjects (almost 12,000 people) and these confirmed our finding that women who received calcium tablets in the studies had a 20% to 30% increase in heart attack risk.

We subsequently added to this database the results from other trials in which the intervention was calcium and vitamin D, rather than calcium alone. This showed the same effect – a 25% increase in the risk of heart attacks and a 15% increase in the risk of stroke.

These results were based on almost 29,000 people participating in research and so were much more reliable than the results we had published previously.

From these analyses, we were able to determine that the number of heart attacks and strokes apparently caused by calcium supplements was greater than the number of fractures that they appeared to prevent. Naturally, we concluded that the use of calcium tablets was likely to be doing more harm than good and should be discontinued.

It’s very important to note that none of our analyses included the effect of calcium-rich foods, and there’s really no evidence suggesting that a calcium-rich diet causes heart problems.

Matt Reinbold

The reason for the difference between tablet supplements and food remains uncertain, but it may be related to the increase in blood calcium level that’s seen for several hours following the large dose of calcium in tablet form. In contrast, calcium in food is absorbed more slowly and has very little impact on blood calcium levels.

Elevations of blood calcium levels have previously been shown to increase the risk of heart disease, possibly through producing calcium deposits in the walls of blood vessels and accelerated arterial disease.

A number of other researchers have now looked into these questions. This month, researchers from Germany reported that individuals taking calcium supplements appear to almost double the risk of heart attacks compared with people not taking supplements. And again, those who have high dietary calcium intakes tend toward lower risk of heart disease.

The German study didn’t randomly assign participants into groups taking calcium or placebo tablets, but simply reported events in individuals who had made the decision to take supplements independently. This is a less reliable way of determining the effects of an intervention than a randomised trial. Nonetheless, this observational study provides supportive evidence for the results of our trial analyses.

Last year, researchers in Sydney studied the effects of calcium supplements in a very elderly group of individuals living in hostels. One-third of the 600 people in the group died during follow up. Death rates increased by 47% in those randomised to calcium and death from heart disease was increased by 76%.

So the weight of evidence that calcium supplements are bad for the heart has steadily increased. What, then, should people do in the face of these findings?

Calcium supplements are mainly used to reduce the risk of fractures from osteoporosis (a bone disease that leads to increased likelihood of fracture). But there are other important measures that will also contribute to osteoporosis prevention, such as regular exercise, not smoking, maintaining a healthy body weight, regular sunlight exposure to maintain vitamin D levels, and removal of falls hazards in the home (such as loose rugs, power cords, and slippery floors).

A steady supply of calcium is important for bone health, but research clearly shows this should be derived from a balanced diet that includes several servings of dairy products, or other calcium sources, such as dark green vegetables or tofu.

Women in their 60s and men in their 70s should have their risk of osteoporotic fractures formally assessed. This usually involves bone density measurement.

People found to be at high risk of fractures should consider using one of the medicines proven to safely reduce fracture risk. This is likely to be more effective than relying on the weak anti-osteoporotic effects of calcium supplements, which come at an unacceptably high price – the increased risk of heart disease.

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21 Comments sorted by

  1. Colin Kline

    logged in via Facebook

    -
    Hokay, let's take the stats as stated in the article.

    But why the bloody hell wasn't there an hypothesis challenge mounted ?

    In the form of testing alternative double-blind groups of people who had :
    - taken day long slow release calcium, or equally,
    - micro-dose pils over the day ?

    Sheesh. Basic science / hypothesis selection !
    -

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    1. Mark Amey

      logged in via Facebook

      In reply to Colin Kline

      I think that this was an exploratory study, rather than an all out, double blinded RCT. Research involving foods and supplements is notoriously difficult to conduct, but, yes a proper RCT would be great. The may be looking for volunteers on the Conversation!

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  2. Geoff Russell

    Computer Programmer, Author

    On the contrary, there is plenty of evidence that diets high in calcium are dangerous where that calcium comes from full fat dairy products ... which is why the Harvard Healthy Eating plate has a glass of water next to it and not milk and recommends limiting dairy products to 1 to 2 servings per day. There may be multiple problems with too much dairy, but its high saturated fat content is the most clearly demonstrated problem ... hence our $1.2 billion dollar subsidy to the world's statin producers…

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    1. Fiona Lake

      logged in via Facebook

      In reply to Geoff Russell

      Geoff, just as the authors of Conversation articles disclose any background info that may influence their objectivity one way or another, you ought to be upfront and honest and make it clear when you post comments on these forums that you're actually an animal rights activist intent on shutting down livestock industries.

      Readers would then realise you're always going to find a way to say animal products should not be consumed, i.e. your comments can most politely be described as 'very subjective'.

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    2. Annarosa Berman

      logged in via Facebook

      In reply to Fiona Lake

      That's hardly fair. In the first place, there are scientific studies to back up what Geoff has said, including ones from Harvard. Are they subjective too?

      Moreover, according to this logic, someone who eats meat/dairy will always find reasons to prove that their dietary preferences are healthy, even when it is clear that there are areas of concern regarding consumption of animal products.

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    3. Geoff Russell

      Computer Programmer, Author

      In reply to Fiona Lake

      When I write articles, my association with AL is upfront. But I don't always point out that I have zero financial interest in these issues.

      I'd be happy if all The Conversation authors writing on food issues disclosed their dietary practices.

      We currently have the bizarre situation where people are meeting at Rio+20, being careful with all manner of environmental impacts for the conference itself but including the most environmentally costly food on the planet as part of the catering. We…

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    4. Geoff Russell

      Computer Programmer, Author

      In reply to Geoff Russell

      P.S. In April 2006, the CSIRO Board was told that diets high in red meat would raise bowel cancer risk but then allowed a book under the CSIRO banner which told the public the opposite. That misinformation is far more dangerous than merely hiding their financial interests. Financial interests can explain dangerous advice, but not hiding them doesn't necessarily stop the advice or people's taking notice of it.

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    5. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to Annarosa Berman

      I don't think this comparison ('according to this logic ... ') is valid.

      If Geoff wants to be vegetarian that's fine by me, I really has nothing to do with me.

      If I was trying to force meat-eating on everyone else and was selective in my use of literature that would be comparable to what AL is trying to do.

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    6. Annarosa Berman

      logged in via Facebook

      In reply to Murray Webster

      Bringing reputable research to people's attention does not amount to an attempt at "forcing" one's lifestyle on them. The meat and diary industries spend billions of dollars on advertising their products, without pointing out the risks associated with consuming those products. One could argue that they are forcing meat and dairy consumption on "everyone else", since voices of dissent do not have access to funding that would enable them to run similar campaings to promote opposing viewpoints.

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    7. Geoff Russell

      Computer Programmer, Author

      In reply to Annarosa Berman

      Yes, Annarosa. We don't have any money precisely because we don't have anything to sell. As for Murray's charge of "selective use" of literature, that's certainly not what I do. Not because I don't know how, but because it's a strategy with a poor future. e.g., I could point to studies where people eating chicken get more cancer, but I don't because they are easily countered. The World Cancer Research Fund went through mountains of stuff. Chicken
      meat should cause cancer because its full of carcinogens…

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  3. Murray Webster

    Forestry-Ecology Consultant/Contractor

    Well, not my area of expertise, though I have some experience with scientific method.

    I congratulate Professor Reid on writing an article that is easy to read and understand for most people. The majority of articles written by academics for public consumption, include so much technical jargon that they are not understood by most readers.

    It seems to me that there is much debate about the risks associated with saturated fat and I conclude that the science is not settled, probably because it is very complex and variable. Personally I went from a low-fat diet to a protein/fibre (moderate fat) based diet ten years ago and my blood test are coming back healthy. The Dr did not even ask about my diet, just said "keep doing what you are doing", so dairy products and the calcium it provides will be staying in my diet.

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  4. Michael Macdonald

    Chemist

    In the recent german study, a large proportion of participants in the supplement group were taking NSAIDs (double almost), which are known to increase the risk of MI. Would this difference account for some of the increased risk in the calcium supplement group?

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  5. Ronson Dalby

    logged in via Twitter

    Well, I'm not taking any chances: my 'Cenovis MegaCalcium +D' just went into the bin.

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  6. Annarosa Berman

    logged in via Facebook

    The link between dairy intake and bone fractures is not clear, as these Harvard articles show:

    http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/calcium-full-story/

    “Currently, there's no good evidence that consuming more than one serving of milk per day in addition to a reasonable diet (which typically provides about 300 milligrams of calcium per day from nondairy sources) will reduce fracture risk. Because of unresolved concerns about the risk of ovarian and prostate cancer…

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    1. Michael Macdonald

      Chemist

      In reply to Annarosa Berman

      All those two studies show is that added calcium is of no benefit in those particular groups of people, they do not say that no calcium is need as you seem to have implied.

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    2. Annarosa Berman

      logged in via Facebook

      In reply to Michael Macdonald

      It was not my intention to imply that we don't need calcium; clearly we do. I tried to point out that the link between dairy consumption and bone health is not clear, as especially the second study illustrates.

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  7. Fiona Lake

    logged in via Facebook

    Ian re. this sentence: "From these analyses, we were able to determine that the number of heart attacks and strokes apparently caused by calcium supplements was greater than the number of fractures that they appeared to prevent" - the increase in heart attacks and strokes was how much greater than the number of fractures apparently prevented? I.E. only a few percentages greater, or a lot? This is information required to assess the comparative risks, when deciding whether to continue taking prescribed calcium & vitamin D supplements to maintain bone density measured as being less than average.

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  8. Carole Hubbard

    conservationist

    Modern medicine is pretty backwards when it comes to nutrients and the reason I say this is because I've been taking mineral cellsalts now for many years to treat many conditions with great success. It is considered that modern science is pretty cutting edge and at the forefront of all that is happening, but in reality it is merely a front for pushing pharmaceutical drugs. So it is no surprise to me that this latest finding that calcium tablets are worse than no calcium tablets in some respect. The…

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  9. Edward John Fearn

    Hypnotherapist and Naturopath

    In light of this information,magnesium supplementation may play a greater role in increasing bone density in high risk groups. Especially as a causal relationship between arrhythmias and magnesium deficiency in CHF has been proposed by some researchers.(1)

    "Among other things, magnesium regulates active calcium transport. As a result, there has been a growing interest in the role of magnesium (Mg) in bone metabolism. A group of menopausal women were given magnesium hydroxide to assess the effects of magnesium on bone density. At the end of the 2-year study, magnesium therapy appears to have prevented fractures and resulted in a significant increase in bone density". (2)

    (1) Hypomagnesemia in heart failure with ventricular arrhythmias. Beneficial effects of magnesium supplementation L. Ceremużyński, J. Gębalska, R. Wołk, E. MakowskaJournal of Internal Medicine Volume 247, Issue 1, pages 78–86, January 2000

    (2) Nutrition Reviews Volume 53, Issue 3, pages 71–74, March 1995

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    1. Fiona Lake

      logged in via Facebook

      In reply to Edward John Fearn

      Thanks for the useful & factual info Edward. I've noticed that when I take a magnesium & zinc supplement that my fingernails are less brittle, have no idea whether this is in anyway indicative of what may also be good for bone density, but I'm sticking with it.

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