Calcium Supplementation and Cardiovascular Disease

Calcium supplementation has well established benefits for bone health in postmenopausal women. In addition, calcium supplementation is important to prevent the decline in bone mineral density associated with many breast cancer treatments, such as aromatase inhibitors. Research also suggests that high calcium intakes may protect against cardiovascular disease by their ability to increase the ratio of so-called “good” (HDL) cholesterol to “bad” (LDL) cholesterol. Because there is a high incidence of cardiovascular disease in postmenopausal women, calcium supplements may also offer important health benefits for women with vascular disease.

Studies investigating total calcium intake from either diet or supplements have shown mixed results in terms of its effect on cardiovascular disease. For instance, the Boston Nurses Study and the Iowa Women’s Health Study showed that women with the highest quarter compared with the lowest quarter of calcium intake had one-third reduction in deaths from cardiovascular disease [1]. In addition, the Boston nurses health study found that women in the highest fifth for calcium intake had an adjusted relative risk of ischaemic stroke of 0.69 (95% confidence interval 0.50 to 0.95) compared with those in the lowest fifth.

In contrast to these findings, a five-year study by Bolland[2] designed to determine the effect of calcium supplementation on heart attack (myocardial infarction), stroke, and sudden death in healthy postmenopausal women found that 1800 mg/day of supplemental calcium may increase rates of cardiovascular disease. The study included 1471 women who had already passed the menopause (average age 74) who were asked to take either a supplement containing calcium (732) or a supplement that contained no calcium (placebo) (739). Heart attack remained more common in the calcium group (21) vs placebo (10), (p= 0.047, relative risk 2.12, 95% confidence interval 1.01 to 4.47). Importantly, in their conclusion, the authors note that this potentially detrimental effect should be balanced against the likely benefits of calcium on bone. However, the very wide confidence intervals in this study (1.01-4.47) casts some doubt about the validity of the results. It is noteworthy that individuals with vitamin D deficiency (25(OH)D less than 25 nmol/L) were excluded from the study, exactly the patients who may benefit the most from extra calcium. This is because vitamin D is important for the absorption of calcium and development of bones. Vitamin D deficiency is common in postmenopausal women and may also contribute to bone and joint pain as well as bone loss in women taking aromotase inhibitors.

The daily calcium requirement for adults is 1,000 mg from food and supplemental sources. “The majority of individuals obtain at least some calcium in their diet, taking more than 1000 mg of supplemental calcium each day unlikely to add any additional benefit”, suggests Kellie Bilinski, Dietitian at Westmead Breast Cancer Institute. “Ideally, individuals should try to improve their calcium intake from foods, rather than having to rely on supplements. This can be achieved by eating three serves of low fat dairy foods or fortified dairy alternatives like soy or rice milk. Other foods such as nuts and seeds, dried fruit, canned salmon and sardines are sources of calcium.”

“It is also important to keep in mind that calcium has well established benefits in terms of osteoporosis prevention, and some research suggests it may also offer protection against some forms of cancer such as breast cancer although the evidence is mixed,” said Professor John Boyages, Director of the Westmead Breast Cancer Institute[3] .

[1] Bostick RM, et al. Am J Epidemiol 1999;149:151-61.

[2] Bolland MJ, et. al. BMJ 2008 Feb 2: 336(7638):262-6.

[3] http://www.cancer.gov/cancertopics/factsheet/prevention/calcium