AAOS Bulletin - October, 2006

The debate over calcium plus vitamin D

What do our patients need for their bones?

By Mary I. O’Connor, MD

Since the recent article in the New England Journal of Medicine (NEJM) (“Calcium plus Vitamin D Supplementation and the Risk of Fractures,” NEJM 354:7, February 2006), there have been debate and confusion regarding the need for supplemental calcium and vitamin D to mitigate age-related bone loss.

The article claimed an equivocal connection between the use of calcium plus vitamin D supplementation and the prevention of hip and other fragility fractures in healthy postmenopausal women. More than 36,000 women who were enrolled in the Women’s Health Initiative (WHI) study were recruited for the study and randomly assigned to one of two groups: those taking 1,000 mg of calcium with 400 IU vitamin D or those taking placebo. Women who were not assigned to the calcium plus vitamin D supplementation cohort were permitted to continue with any personal supplementation of up to 1,000 mg of calcium and 600 IU of vitamin D per day.

Bone density and incidence of fracture were measured over a period of seven years. The authors concluded that “among healthy postmenopausal women, calcium and vitamin D supplementation resulted in a small but significant improvement in hip bone density, but did not significantly decrease hip fracture, and increased the risk of kidney stones.” Newspaper articles emphasized the conclusion that calcium and vitamin D did not decrease the risk of hip fracture, raising the question among many patients as to whether they should take such supplements.

A closer review of the published data, however, shows that this article does support the use of calcium and vitamin D to decrease the risk of hip fracture. The study data show a significant benefit—a 29 percent decrease in hip fractures—in women who adhered to the calcium and vitamin D regimen. But the study’s conclusions were based on an analysis of all patients prescribed the supplements, regardless of compliance. No significant decrease was identified in clinical vertebral fractures, fractures of the lower arm or wrist, or total fractures.

The Women’s Health Initiative
Begun in 1991, the WHI study was a major 15-year research program investigating the highest burdens of disease and disability—including osteoporosis—in postmenopausal women. The study enrolled women aged 50 to 79 who had no prior medical conditions with a predicted survival of less than three years. It excluded women who had hypercalcemia, kidney stones, corticosteroid use and calcitriol use. Additionally, participants in the osteoporosis study could be simultaneously enrolled in the WHI Hormone Therapy trials. Two studies comprised these trials: an estrogen-plus-progestin study of women with a uterus and the estrogen-alone study of women without a uterus.

The fact that more than half of the women in the WHI study were taking some form of estrogen further increases the potential confusion regarding the role of calcium and vitamin D supplementation. Numerous studies have shown that hormone replacement therapy (HRT) may significantly reduce the incidence of osteoporosis. Women who were taking calcium and vitamin D as well as HRT showed a lower (but not significant) incidence of hip fracture compared to women taking calcium and vitamin D supplements with placebo HRT.

The WHI selection of participants (mostly white, healthy women with a higher-than-average body mass index and no treated bone deficiencies) also likely skewed the results of the study. The impact of the daily supplements probably would be more significant for women with osteoporosis. The study design also included a daily supplementation of 400 IU of vitamin D and 1,000 mg of calcium, less than the amount recommended for postmenopausal women by the Surgeon General’s Report on Osteoporosis and Bone Quality (see Table 1). According to that report, postmenopausal women should take 1,200 mg of calcium and between 400 and 800 IU of vitamin D daily.

The NEJM study showed the greatest effectiveness of calcium plus vitamin D in age groups older than age 60. Calcium plus vitamin D does diminish bone loss at the hip. However, even women who have a sufficient intake of calcium and vitamin D are not completely protected from fragility fractures. Low bone mineral density and other factors may require the use of additional medication.

According to the National Institutes of Health, one-sixth of all women will have a hip fracture during their lifetime, with a 3-to-4 times higher frequency of fractures in women older than age 50. This risk of hip fracture is actually greater than the combined risk of breast, cervical and uterine cancers.

Concern regarding bone health should not be restricted to female patients. Men will and do develop osteoporosis. Good bone health is important for all our patients. Adequate intake of calcium and vitamin D, either by diet or supplementation, is an appropriate recommendation for us to make to our patients.

Mary I. O’Connor, MD, is chair of the AAOS Women’s Health Issues Advisory Board. She can be reached at oconnor.mary@mayo.edu

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