Menopause reduces women's levels of the hormone estrogen, and these lowered levels can contribute to calcium deficiencies, according to background information in the article. Calcium supplements can be used to correct this imbalance, but it is not known if these supplements can prevent fractures in bones weakened by the loss of calcium, a condition known as osteoporosis.
Richard L. Prince, M.D., University of Western Australia, Western Australian Institute of Medical Research and Sir Charles Gairdner Hospital, Devine, and colleagues studied the effect of calcium supplementation on 1,460 women older than age 70 years. Half of the patients were randomly assigned to take 600-milligram calcium carbonate tablets twice per day and the other half took identical placebo tablets. X-rays, bone ultrasounds and bone scans were performed at the beginning of the study and after five years, and adverse events that required a visit to a health care provider were recorded at four-month intervals. Participants returned their unused pills at the end of each year-long period and those who took fewer than 80 percent were classified as noncompliant.
After five years, 236 (16.2 percent) participants sustained one or more osteoporotic fractures. Overall, women who were assigned to the calcium group had the same risk of fracture as those in the placebo group, indicating that calcium supplementation did not reduce the risk of fracture in the entire study population. However, among the 830 women (56.8 percent of the entire study group)--310 in the calcium group and 320 in the placebo group--who took 80 percent or more of their pills and were classified as compliant, those in the calcium group were less likely to develop fractures than those in the placebo group (10.2 percent vs. 15.4 percent). Calcium treatment also improved results on several of the bone tests. Constipation was the only adverse effect that was more common in women taking calcium than in those taking placebo, but there was no difference in the percentage of women who stopped taking pills because of constipation.
Calcium supplements appeared to be ineffective at reducing fractures because so many patients were noncompliant, the authors write. In patients who were compliant, there was no difference in the amount of calcium they consumed through their regular diet, suggesting that 1.2 grams of calcium per day is enough to help protect women's bones. "In conclusion, the calcium supplementation regimen tested currently cannot be recommended as a public health approach to fracture prevention because of the lack of long-term compliance," the authors write. "However, these data supported the continued use of calcium supplements by women who are able to remain compliant with their use. In these individuals, especially if they are under the care of a clinician, calcium supplementation is a safe and effective therapy for reducing the risk of osteoporitic fracture."
(Arch Intern Med. 2006; 166: 869-875. Available pre-embargo to media at www.jamamedia.org.)
Editor's Note: This study was supported by a grant from the Healthway Health Promotion Foundation of Western Australia and by a project grant from the National Health and Medical Research Council of Australia.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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