Calcium: Strong Bones, Weak Heart?

Oct 3, 2017

Calcium is an essential mineral supporting multiple physiological processes. Well known for its role in bone health—99% of the body’s calcium is stored in bone tissue—calcium is also critical for cellular function because it acts as a facilitator of cell signaling.1 Calcium is stored as hydroxyapatite crystals, which is what provides rigidity to bone tissue and helps to minimize fracture risk. Thus, calcium is indispensable for healthy bones.

Some recent investigations, however, relate calcium intake with a higher risk of heart disease. Because calcium also supports heart muscle contraction, the process of blood clotting, and hormonal modulation, some researchers believe that excessive calcium intake may contribute to increased cardiovascular risk.2 This has also caused some to question the necessity or wisdom of calcium supplementation at all, with some researchers even questioning whether calcium is truly indispensable for bone health.

Given calcium’s essential physiological role, however, it’s hard to imagine this mineral not being critically important to health. Calcium insufficiency is known to lead to bone-tissue defects as well as adverse impacts on several other bodily functions. The challenge is to sort through the recent studies in an attempt to understand whether calcium intake truly leads to elevated cardiovascular risk, what a sufficient intake level of calcium might be, and what other factors may play a role in supporting calcium supplementation in a healthy way. Striking a happy medium with respect to a balanced and beneficial intake of calcium is critical for supporting health while avoiding any unwanted or undesired effects.


Increased Cardiovascular Risk with Calcium Supplements?

A recent study led by John Anderson of the Gillings School of Public Health at the University of North Carolina (Chapel Hill, NC) looked at the risk of cardiovascular events associated with dietary and supplemental intake of calcium.3 Participants were free of cardiovascular disease at inclusion and were followed for 10 years. 

The study included 5,448 adults aged 45 to 84. At baseline, researchers measured subjects’ total calcium intake from dietary sources and from calcium supplements. Participants were then divided into five groups based on their average daily calcium intake. Coronary artery calcification was also assessed at baseline. 

In the 1,567 participants who had no coronary artery calcification at baseline, higher total calcium intake over the 10-year period was found to lower the risk of atherosclerosis. The highest intake of total calcium (average of 2157 mg/day) was associated with a relative risk of developing coronary artery calcification of 0.73. 

However, the authors found that calcium supplement use was associated with an increased relative risk of coronary artery calcification of 1.22. Based on this data, the researchers concluded that high total dietary calcium intake had a protective effect on atherosclerosis, while the use of calcium supplements may increase the risk of coronary artery calcification. 

Offering a hypothesis for this apparent paradox, the authors postulate that calcium intake from supplements presents a bolus dose to the body. This large, one-time dose leads to transiently elevated serum calcium concentrations, which can then potentially lead to vascular calcification and other adverse effects.3 Calcium from food, on the other hand, does not lead to such bolus doses and can, therefore, be more effectively utilized by the body. Furthermore, the authors cite previously published evidence suggesting that healthy adults require a total dietary calcium intake of between 550 and 1200 mg/day to account for the calcium needs of the body and to maintain zero net balance. Additional studies have shown that calcium intakes greater than 1400 mg/day can result in positive calcium balance, an amount of calcium in excess of what the body needs. 

Mark Bolland’s group from the University of Auckland (Auckland, New Zealand) has also conducted several analyses of data from randomized controlled trials indicating an elevated risk of cardiovascular events related to calcium supplementation. A secondary analysis of a 2008 study which included 1,471 postmenopausal women randomized to receive 1,000 mg of elemental calcium daily as calcium citrate over a five-year period found that the rate of occurrence for myocardial infarctions was significantly higher in the calcium group than the placebo.4 However, the study population was older (average age of 74, with a significant percentage aged 80 or over) and overwhelmingly white, rendering the results less applicable to other populations. Furthermore, nearly 43% of participants discontinued treatment (or placebo) prior to the five-year end point.

Additionally, Bolland’s group conducted a meta-analysis published in 2010 in which they included 15 randomized, placebo-controlled studies of calcium supplementation (>500 mg per day).5 Their analysis and conclusion showed an increased risk of myocardial infarction. The average age of participants from included trials was 75. Studies that included the co-administration of vitamin D along with calcium were excluded from the analysis.


…Or a Reduced Cardiovascular Risk with Calcium Supplements?

In contrast to the studies above, the Women’s Health Initiative (WHI) study showed no increased coronary or cerebrovascular risk with calcium supplementation.6 The WHI was a large multicenter study in which 36,282 postmenopausal women aged 50 to 79 were randomized to supplement with 500 mg of elemental calcium (as calcium carbonate) with 200 IU vitamin D3 twice daily, or placebo. After seven years of follow-up, the researchers failed to see an increased risk of myocardial infarction or stroke. The patient population in the WHI tended to be younger (average age of 62) than the individuals analyzed in the studies associating calcium supplementation with increased cardiovascular risk (average age of 75). The WHI subjects were also assigned to supplement with vitamin D, which may have conferred additional protective effects. 

An earlier prospective cohort study led by Roberd Bostick at the University of South Carolina (Columbia, SC) assessed the relationship between dietary and supplemental calcium intake and the risk of ischemic heart disease in 34,486 postmenopausal women aged 55 to 69.7 The results of the analysis indicated a substantially reduced risk of heart disease (estimated at a statistically significant 33% risk reduction) with higher calcium intake, whether the calcium was consumed in the form of dietary calcium, supplements, or both.

Furthering the notion of cardiovascular protection associated with calcium supplementation, Josh Lewis and colleagues from the University of Western Australia (Crawley, Australia) evaluated data from a five-year randomized controlled trial of calcium carbonate supplementation along with 4.5 years of follow-up and concluded that calcium supplementation did not increase the rate of death or first-time hospitalization from atherosclerotic vascular disease.8 The study included 1,460 women with an average age of 75 who were randomized to 1,200 mg of calcium or a placebo daily for five years. The analysis also showed that for those with pre-existing atherosclerosis, calcium supplementation actually reduced the risk of hospitalization and mortality.

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  3. Anderson JJ et al., “Calcium intake from diet and supplements and the risk of coronary artery calcification and its progression among older adults: 10-Year follow-up of the Multi-Ethnic Study of Atherosclerosis (MESA),” Journal of the American Heart Association. Published online October 11, 2016.
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  11. Office of Dietary Supplements – Calcium. Available at: Accessed July 30, 2017.
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