Millions of men and women swallow a big calcium pill every day because they have been told it is good for their bones. That advice may be misguided, especially in light of research suggesting that high doses of supplemental calcium could pose risks for the cardiovascular system.
What Is the Evidence on Calcium Supplements?
One study suggesting that calcium supplements might have unexpected risks was published in JAMA Internal Medicine (online, april 22, 2013). Between 1995 and 1996 nearly 400,000 men and women were recruited into the National Institutes of Health-AARP Diet and Health Study. Their calcium intake was assessed with a very thorough questionnaire. They were then followed for 12 years. Men who consumed more than 1500 mg of calcium daily were at increased risk for cardiovascular disease death. The researchers did not find an elevated risk in women who took calcium supplements.
The authors concluded:
“We found a significant interaction by sex. Elevated CVD [cardiovascular disease] mortality with increasing supplemental calcium in-take was observed only in men; however, we cannot rule out the possibility that supplemental calcium intake may be associated with cardiovascular mortality in women.”
Some women took heart from these results, as women seemingly avoided the problem of cardiovascular mortality despite taking calcium supplements. That finding was probably misleading, however.
More Research Shows Women Are Also Vulnerable:
Other research suggests that women may not be immune to this problem. A study in 2012 involving nearly 24,000 German adults found that those taking calcium supplements were more likely to have heart attacks during the 11 years of follow-up (Heart, online May 23, 2012).
The researchers speculated that excess calcium circulating in the body might lead to calcification in blood vessels. Few people realize that the plaque that clogs coronary arteries is made up predominantly of calcium.
Another study involving women only also suggested that large doses of supplemental calcium might lead to heart complications. In this research (BMJ, online, April 19, 2011), more than 16,000 women over the age of 40 were randomized to take both calcium and vitamin D or placebo. Those taking the supplements had about 20 percent more heart attacks and other vascular problems.
A Pattern in the Findings:
Results from 13 other studies of calcium with or without vitamin D were consistent: those taking supplements were slightly more likely than those on placebo to suffer a heart attack or stroke. The researchers estimated that if 1,000 people took calcium for five years, six of them would have a heart attack or stroke and only three fractures would be prevented. Such a risk/benefit ratio is not favorable.
An editorial titled “Calcium Supplements: Bad for the Heart?” in the journal Heart [June, 2012] reviews the medical literature on this controversial topic. Here is the executive summary from the editorial: calcium supplements have been linked to kidney stones, constipation and other more serious digestive complaints, coronary artery calcification, heart attacks and strokes. After considering all the data that has accumulated over the last several years, the authors conclude:
“Thus, the consistent evidence is that calcium supplements do more harm than good and that other interventions are preferable for reducing the risk of osteoporotic fractures…We should return to seeing calcium as an important component of a balanced diet and not as a low-cost panacea to the universal problem of postmenopausal bone loss.”
The Fallacy of Taking Too Much:
Many people figure that if a little calcium is necessary for strong bones (as it is), then a lot would work even better. It is estimated that one of two older men in the U.S. takes a calcium pill and nearly three out of four older women do so. Many health care practitioners have reinforced this attitude and even encouraged older men and women to take around 1500 mg of calcium a day in pill form. The evidence, however, seems to suggest that such large doses of calcium are linked to kidney stones, constipation, coronary artery calcification, heart attacks and strokes (Heart, June, 2012).
In the study published in JAMA Internal Medicine the authors propose a mechanism to explain how too much calcium creates complications:
“One plausible biological mechanism through which calcium may exert a harmful effect on cardiovascular health is vascular calcification–the deposit of calcium phosphate in cardiovascular structures…Emerging evidence has linked calcification of coronary arteries with increased atherosclerotic plaque burden, risk of coronary heart disease and mortality.”
The authors also point out that excess calcium might increase blood coagulation and lead to “stiffness” in the arterial wall.
A more recent study has confirmed that people taking calcium supplements were more likely to have calcification in their coronary arteries (Journal of the American Heart Association, October 11, 2016). In the MESA study (Multi-Ethnic Study of Atherosclerosis), those taking calcium supplements had the highest calcification scores. People getting the most calcium from their diets, however, had the cleanest arteries. You can read more about this study here.
But What About Taking Calcium Supplements for Strong Bones?
Although we have been repeatedly told that calcium supplements will be good for bones, if one really looks at the research, and there is an amazing amount of it, you will discover that the data demonstrating that calcium can be helpful in preventing fractures are exceptionally weak. Over the years more than 140 studies have examined the effects of calcium on fracture risk. About one third suggest benefit. Over half show no reduced risk. The rest were inconclusive.
Let’s take a look at epidemiology. In countries where people consume a LOT of milk, dairy products AND calcium supplements (Scandinavia, the United States and the UK), hip fractures are very common. In countries where milk and dairy consumption is low and calcium pills are rare (Africa, China, New Guinea and Iran), the hip fracture rate is much lower.
What about vitamin D?
Many people believe that if you just add vitamin D to calcium, the problem is solved. The meta-analysis of various studies only analyzed the research that has been completed. Most of the big studies were done with calcium alone. The doses of calcium that were employed in the various studies ranged from 500 mg of calcium carbonate to 1,400 mg of calcium citrate and 2,000 mg of lactogluconate-carbonate.
As for vitamin D, of the nearly 40 studies that have been published involving both calcium and vitamin D combined, roughly half showed fracture reduction and half demonstrated no benefit.
Unless there is a clear benefit from something, we are unwilling to accept a risk. Although the risk of heart attack may seem small in absolute numbers, if tens of millions of women are swallowing large doses of calcium, the number of people who may be vulnerable is actually quite substantial.
We encourage visitors to actually read the BMJ article. It is free and very comprehensive. It is also understandable.
You may also want to listen to our radio show about the pros and cons of calcium supplements with Michael Castleman and Amy Lanou, PhD, authors of Building Bone Vitality and Water Willett, MD, DrPH, Chair of Nutrition at Harvard School of Public Health.
Getting Calcium Without Taking Calcium Supplements
Getting calcium from your diet is not risky. In fact, it is the BEST way to get calcium safely. When your mother said, drink your milk for strong bones, her common-sense approach was far better than today’s recommendation to swallow horse pills of calcium. If you don’t like or can’t tolerate milk, there are other options. Here are some non-dairy sources of calcium:
- Bok Choy
- Corn Tortillas
- Fortified Orange Juice
- Mustard Greens
- Salmon (canned, bone-in)
- Swiss Chard
- Turnip Greens
Our Guide to Osteoporosis discusses some of the other things you can do to reduce your risk of weakened bones.
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