Taking calcium supplements slightly increased the risk of cardiovascular events in older patients, according to a meta-analysis published in the July 30th online issue of the British Medical Journal.
Researchers at the University of Auckland, New Zealand wanted to determine the relationship between calcium supplementation and cardiovascular risk. Observational studies have shown blood calcium levels are positively associated with increased risk of heart attack. Researchers theorized that increased calcium levels may increase vascular calcification which leads to hardening of the arteries.
Instead of conducting new research, scientists pored over a large number previously published calcium studies, opting to include just 15 in their analysis. Inclusion criteria were double-blind, placebo controlled studies; >500 mg of calcium administered daily; at least 100 participants with the mean age of 40 years at baseline; and trial lasting at least a year. Studies that co-administered vitamin D in the treatment group were excluded from the analysis.
The 15 studies involved almost 12,000 patients, who were primarily white women, with a mean age of 75 years and average weight of 143 pounds (68 kilograms). Average dietary calcium intake was 805 mg per day; and average vitamin D status was 65 nmol/liter per day. The average trial duration was 3.6 years.
When the trial data for the 15 studies was combined, 166 people (2.7%) had heart attack who took calcium supplements vs. 111 (2.2%) who did not take the supplements. No increased risk of heart attack was observed in patients taking calcium intake below the median of 805 mg/day.
No statistically significant differences in risk for stroke or death was observed between the treatment and control groups.
The current findings are in direct contrast to both observational and interventional calcium studies. Observational studies indicate that high calcium intake protects against vascular disease. In particular, results from the Women’s Health Initiative indicated that calcium and vitamin D had no effect on the risk of coronary heart disease or stroke.
The meta-analysis drew criticism for several reasons. The original studies did not have cardiovascular events (heart attack, stroke or death) as end points so data collection was either absent or not completed in a standardized manner.
Importantly, studies that administered calcium in conjunction with vitamin D were excluded from the analysis. Vitamin D deficiency is associated with increased risk of cardiovascular disease. In the current analysis, average vitamin D levels were not available in 4 of the studies and in two, vitamin D status was below 54 ng/dl, lower than the optimal range of 60- 80 ng/dl.
In 2008, the same New Zealand researchers conducted a smaller study, examining calcium supplementation in postmenopausal women and risk of cardiovascular events. The study results which were published in BMJ also received criticism.
The link between calcium supplements and heart attack suggested by the New Zealand team "seems implausible," said Robert P. Heaney, MD, John A. Creighton University professor at Creighton University in Omaha, Neb., and a long-time researcher of calcium's effect on health.
Typically, Heaney said "Extra calcium doesn't build up in your arteries. The body regulates the blood concentration of calcium.'' Only in people who have lost the ability to regulate calcium levels could the blood concentration of calcium increase, he says, and this condition is rare.
The Council for Responsible Nutrition (CRN), Washington, D.C., responded to the current study saying a broad range of scientific research has demonstrated that an adequate intake of calcium plays an important role in building and maintaining optimum bone mass, and that this meta-analysis should not cause consumers to doubt the value of calcium supplements for maintaining bone health.
“The authors characterize these findings as though all of the selected studies suggest increased risk. In fact, the opposite is true: most of the studies do not suggest increased risk,” said Andrew Shao, PhD, senior vice president, Scientific & Regulatory Affairs, CRN.
The Bottom Line
Unfortunately, clinical studies often generate more questions than answers and this meta-analysis is no different.
It is not clear if the same results would have occurred in younger women or those taking vitamin D plus calcium. The body of evidence indicates that the combination of calcium plus vitamin D supplements is beneficial to bone health and does not pose any additional risk for cardiovascular events.
We believe that the current study does not warrant any change in the recommendation to get sufficient calcium, vitamin D, magnesium and other bone supporting nutrients through diet and supplements. A good quality supplement, like VitaMedica’s Bone Support covers gaps in the diet by providing reasonable amounts of a wide-variety of bone supporting nutrients.
Aside from diet, bone density can be strengthened by making lifestyle changes such as quitting smoking, limiting soft drink consumption and engaging in weight bearing exercises 2-3 times a week.