A review of calcium and vitamin D supplementation trials revealed that current recommended doses, whether taken alone or in combination, are inadequate to prevent bone mineral density (BMD) loss in women undergoing breast cancer therapy.

Increased risk of osteoporosis due to accelerated bone loss is an unintended consequence of breast cancer treatment, noted Mridul Datta, PhD, and Gary G. Schwartz, PhD, both of Wake Forest School of Medicine in Winston-Salem, North Carolina, in their report for Critical Reviews in Oncology Hematology. Calcium and vitamin D supplements are widely recommended for osteoporosis prevention and management not only in healthy women but also in women with breast cancer who are receiving treatment.

Datta and Schwartz conducted a systematic review of trials in which calcium and/or vitamin D supplementation was used to maintain BMD in women with breast cancer. They learned that such supplementation in these patients had never been tested against an unsupplemented control group. However, results from 16 trials indicated that the commonly recommended calcium and/or vitamin D doses tested (500 mg to 1,500 mg for calcium; 200 IU to 1,000 IU for vitamin D) were inadequate to prevent BMD loss in women undergoing breast cancer treatment. Despite supplementation, these patients lost BMD in virtually every trial reviewed.

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“Despite evidence demonstrating reduction of BMD loss with 500 mg to       1,000 mg calcium supplementation in healthy postmenopausal women experiencing ‘natural’ menopause, similar supplementation studies in women with breast cancer that we reviewed failed to retard BMD loss,” the authors wrote.

This discrepancy might be at least partially explained by differences in circulating estrogen levels between healthy menopausal women and women undergoing treatment for breast cancer. Menopause-related estrogen deficiency is also known to lower intestinal calcium absorption.

Datta and Schwartz concluded that the ineffectiveness of 1,500-mg doses of calcium and 1,000-IU doses of vitamin D in retaining BMD among women receiving breast cancer treatment suggests that other lifestyle changes (such as exercise) and pharmacologic interventions may be required to prevent bone loss in these patients.

The researchers also pointed out that calcium supplements may increase the risk for cardiovascular disease, which is the main cause of mortality in women with breast cancer. “Clinical trials are urgently needed to evaluate the safety and efficacy of [calcium and/or vitamin D] supplementation in women with breast cancer,” they stated.