Calcium and Fracture Prevention

Posted by • October 18th, 2013

The latest article in our Clinical Practice series reviews recommendations regarding calcium intake and uncertainty about benefits as well as potential risks of calcium supplementation. In particular, some studies have suggested an increased cardiovascular risk, but findings have been inconsistent. Both clinicians and patients are likely to be confused by the inconsistent and sometimes conflicting advice about the amount of calcium intake required to reduce the risk of fracture and, in particular, whether calcium supplements are necessary. Long-term calcium deficiency can clearly confer a predisposition to osteoporosis, but many persons mistakenly believe that postmenopausal and age-related bone loss and the associated increase in susceptibility to fracture can largely be avoided with the use of calcium supplementation.

Clinical Pearls

What are the Institute of Medicine (IOM) recommendations about appropriate dietary intake of calcium?

Primarily on the basis of studies of calcium balance in persons younger than 50 years of age and the known acceleration of bone loss that occurs with menopause and advanced aging, the IOM has issued recommendations regarding the most appropriate dietary intake of calcium according to sex and age. The recommended dietary intake of calcium for women 19 to 50 years of age and men 19 to 70 years of age is 1000 mg per day; women older than age 50 and men older than age 70 require 1200 mg per day. Calcium intake above 2500 mg per day should be avoided.

Table 1. Recommended Dietary Intake of Elemental Calcium for Healthy Persons.

What are differences between common over-the-counter calcium supplements?

Determination of the dose of an over-the-counter supplement required to meet daily calcium requirements is based on the amount of elemental calcium. Commonly used preparations include purified calcium carbonate, calcium citrate, and, to a lesser extent, calcium lactate and calcium phosphate; preparations differ in the amount of elemental calcium provided. Calcium carbonate provides relatively high elemental calcium content (40%) and is inexpensive and widely available. As compared with other calcium supplements, calcium carbonate is more likely to cause constipation and bloating and should be taken with meals, since gastric acidity is required for sufficient absorption. As compared with calcium carbonate, calcium citrate provides less elemental calcium (21%), but it is a reasonable alternative in patients with bothersome gastrointestinal symptoms; it may be taken with or without meals, since absorption is not dependent on gastric acidity.

Table 3. Widely Available Calcium Supplements.

Morning Report Questions

Q: Is calcium supplementation associated with cardiovascular risk?                         

A: Several studies have raised concerns about a possible increase in cardiovascular risk associated with calcium supplementation. A meta-analysis of published results of 15 placebo-controlled trials of calcium supplements without vitamin D showed an increased risk of myocardial infarction among persons randomly assigned to calcium (odds ratio, 1.31; 95% CI, 1.02 to 1.67). Among the trials not included in this meta-analysis was the Women’s Health Initiative (WHI) trial, which involved more than 36,000 women and showed no significant increase in adjudicated cardiovascular events or overall mortality among women who received calcium plus vitamin D. Observational studies have also yielded conflicting results. For example, whereas two large prospective cohort studies showed that the use of calcium supplements was associated with an increased risk of cardiovascular events or death, a large Canadian prospective cohort study and the extended follow-up of the WHI trial showed no significant association between the use of calcium supplements and cardiovascular events. In summary, the evidence suggesting adverse cardiovascular effects of calcium supplementation is inconsistent, and an accepted biologic explanation is lacking; the clinical significance of transient supplement-related increases in serum calcium levels is unknown. Pending further data, an approach many have taken is to preferentially encourage dietary calcium intake and discourage the routine use of calcium supplements.

Q: What are the current U.S. Preventive Services Task Force recommendations on calcium supplementation?

A: In a 2013 update, the U.S. Preventive Services Task Force found insufficient evidence to assess the benefits and harms of daily supplementation with more than 1000 mg of calcium (plus more than 400 IU of vitamin D) for the primary prevention of fractures in noninstitutionalized postmenopausal women. The task force recommended against routine daily supplementation with less than 400 IU of vitamin D or less than 1000 mg of calcium. They found insufficient evidence to recommend for or against the use of calcium supplements in men and premenopausal women.

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