Calcium, Bones, and the Heart

Abstract & Commentary

By Barbara A. Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips reports no financial relationship to this field of study.

Synopsis: A study to determine the effect of calcium supplementation on myocardial infarction, stroke, and sudden death in healthy postmenopausal women.

Source: Bolland MJ, et al. Vascular events in healthy older women receiving calcium supplementation: randomized controlled trial. BMJ. 2008; Jan 15 ePub ahead of print.

This report is a secondary analysis of a study that was designed to evaluate the effects of calcium supplements on bone health in post-menopausal women in New Zealand. It included 1471 women, mean age 74 years, who were randomized to either calcium or placebo. Outcomes were death, myocardial infarction (MI), angina or chest pain, stroke, and transient ischemic attack. Exclusions included being under 55 years of age, having a life expectancy of less than 5 years, already being on calcium supplements, active treatment for osteoporosis, vitamin D deficiency, ongoing liver, kidney, thyroid, or bone disease, and malignancy. The calcium supplement and placebo groups were well matched for age, weight, body mass index (BMI), blood pressure, and a variety of other measures, although there were slightly higher, statistically insignificant rates of current and former smoking, previous hypertension, previous dyslipidemia, and previous cardiovascular disease in the calcium supplementation group. Active treatment was a gram of elemental calcium citrate in a split dose. Follow-up occurred every 6 months for 5 years. At 5 years, 90% of the cohort was still being followed-up, although about 300 women in each group stopped taking the study drug. Including the drop-outs, compliance with either the active calcium or the placebo was 55% and 58%, respectively. For self-reported cardiovascular events, the group assigned to calcium had statistically more myocardial infarctions (45 vs 19) and "composite events" (MI, stroke or sudden death) than did those who were taking placebo (101 vs 54). However, when the reported events were adjudicated (review of hospital records and death certificates) only myocardial infarction was statistically increased in those who took calcium (24 events vs 10, p = 0.047). In the final analysis, after inclusion of events not reported by participants, a statistically significant increase in the number of women with any of the end points in the calcium group was no longer found. Controlling for compliance with treatment did not affect these findings. The authors conclude, "Calcium supplementation in healthy postmenopausal women is associated with upward trends in cardiovascular event rates. This potentially detrimental effect should be balanced against the likely benefits of calcium on bone."

Commentary

I must confess that I skimmed the title and abstract of this paper with personal alarm. Many, many women take calcium supplements, and may be questioning the wisdom of doing so in the wake of this report published in a prestigious medical journal. Indeed, use of a variety of vitamins and supplements has been shown to either have no benefit or to cause actual harm in recent years. Calcium supplementation, on the other hand, has stood the test of time as being beneficial for bone health for women, particularly postmenopausal women. A recent large metanalysis1 confirmed and synthesized what is known about calcium supplementation, and concluded, "Evidence supports the use of calcium, or calcium in combination with vitamin D supplementation, in the preventive treatment of osteoporosis in people aged 50 years or older. For best therapeutic effect, we recommend minimum doses of 1200 mg of calcium, and 800 IU of vitamin D." This paper noted that the beneficial effect of calcium on reduction of fractures depends on compliance. (what doesn't?) Indeed, the parent study for the current paper2 found that calcium supplementation was associated with a reduction in bone loss over a 5-year period, but noted that compliance limits it effectiveness.

Beyond its effects on bone health, there is evidence that calcium supplementation has a salutary effect on several intermediate endpoints, including reduction in cholesterol,3 blood pressure,4,5 and weight.5

These authors have definitely taken a "cup half empty" approach to their findings. Despite lack of solid statistical evidence that calcium supplementation causes cardiovascular disease in this (or any of the other studies they reviewed), they cite the trends noted in this paper, and note, "The present data do not permit definitive conclusions to be reached in this regard but do flag cardiac health as an area of concern in relation to calcium use ... this potentially detrimental effect should be balanced against the likely benefits of calcium on bone, particularly in elderly women."

Savvy women patients may be asking you about this report and about the wisdom of continued use of calcium supplements. The data are much stronger that calcium (taken compliantly, at 1200 mg/day with vitamin D) reduces bone loss than that calcium contributes to cardiovascular disease. I'm still taking mine.

References

1. Tang BMP, et al. Lancet. 2007;370:657-666.

2. Reid IR, et al. Randomized controlled trial of calcium in healthy older women. Am J Med. 2006;119:777-785.

3. Reid IR, et al. Effects of calcium supplementation on serum lipid concentrations in normal older women: a randomized controlled trial. Am J Med. 2002;112:343-347.

4. Griffith LE, et al. The influence of dietary and nondietary calcium supplementation on blood pressure—an updated metaanalysis of randomized controlled trials. Am J Hypertens. 1999;12:84-92.

5. Reid IR, et al. Effects of calcium supplementation on body weight and blood pressure in normal older women: a randomized controlled trial. J Clin Endocrinol Metab. 2005;90:3824-3829.