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Don’t Discard Your Calcium Supplements, Just Yet

Consistent use of calcium and vitamin D supplements helps prevent hip fracture in postmenopausal women

Last month, results from a large women’s study were published in The New England Journal of Medicine (NEJM). The study examined the effect of supplementing with calcium and vitamin D on bone density and the risk of developing hip or other fractures in postmenopausal women. The message that the mainstream media reported from this study was that these supplements provide limited protection against bone fractures. Not surprisingly, many women who regularly take these bone building supplements were puzzled by the findings. Unfortunately, what was not widely reported is that women who consistently took these supplements had fewer hip fractures than those in the comparison group. In addition, women over 60 benefited by a lower hip fracture rate.

The Women’s Health Initiative (WHI)
The results from the calcium and vitamin D research were based on a study conducted as part of the Women’s Health Initiative (WHI). The WHI, a long-term clinical study funded by the National Heart, Lung and Blood Institute (NHLBI) of the National Institutes of Health (NIH), is designed to investigate strategies for the prevention and control of cancer, cardiovascular disease and osteoporosis in postmenopausal women. The WHI was initiated in 1992 and has followed over 160,000 women ranging in age from 50 to 79, in over 40 U.S. clinical centers.  The study participants were assigned to either a clinical trial group or an observational study group. In the clinical trial group, subjects were randomized to one of three interventions: 1) a low-fat eating pattern, 2) hormone replacement therapy or 3) calcium and vitamin D supplementation.

Study Design
Rebecca D. Jackson, M.D. and researchers at Ohio State University in Columbus examined the effect of calcium and vitamin D intake in preserving bone mass and preventing hip fracture. The study was initiated because osteoporosis affects some 10 million Americans and contributes to more than 300,000 hip fractures annually. The study’s secondary objectives examined the effect of calcium and vitamin D supplementation on other types of fractures and on colorectal cancer.

Of the over 36,000 postmenopausal women who participated in the study, half were assigned to take 1,000 mg of calcium carbonate plus 400 international units (IUs) of vitamin D on a daily basis. Although the comparison group was not given any calcium or vitamin D supplements, if a participant was already taking these supplements, she could continue using them. Indeed, the average calcium intake in both groups prior to the study was about 1,150 mg per day. More than half of the women in the study were also taking hormone therapy and had a mean body-mass index (BMI) of 29*. The average age in both groups was 62 years and the average follow-up time was 7 years.

Study Findings
Women who received the calcium and vitamin D supplements had greater preservation of total-hip bone mineral density or BMD (as measured by bone density scans during annual visits at 3, 6 and 9 years). However, bone mineral density for the spine and whole body were the same for both groups.

Despite the higher BMD scores, the difference in the rate of total fractures and fractures of the vertebrae and lower arm or wrist were insignificant for the intervention and control group. For hip fractures, although the rate was 12% lower in the supplement group, the result was not considered statistically significant.

Upon closer inspection of study participants, when subjects who had good compliance with the supplements were analyzed separately, the hip fracture rate was reduced by 29% - a statistically significant result. And, the benefit of using supplements also appeared to favor women over 60 years of age, as their hip fracture rate was 21% lower.

The only adverse effect noted in the study was that women taking the supplements had a 17% higher risk of kidney stones.

What Next?
The WHI is the most comprehensive study to date of the causes and preventive strategies for the major diseases affecting postmenopausal women. And, given the study’s size and design, the findings are important. However, a number of questions remain unanswered.

Given that the rate of hip fracture was lower than expected (about half), this may have diluted the study findings since any benefit is harder to find against fewer fractures in total. Part of the reason for an overall lower fracture rate may have been because of the higher BMI of study participants. Heavier individuals typically have denser bones. As previously noted, many of the women were already taking calcium supplementation in both groups when the study began and were allowed to continue doing so. In addition, women in the study group were allowed to continue taking hormone therapy. Both of these measures most likely suppressed fracture rates. Finally, the study recruited fewer women over age 70 than originally projected (17.5% of participants), an age where fracture rates start climbing.

Critics argue that the study results would have been clearer if higher doses of vitamin D were used (e.g., 1,000 units per day). The majority of studies showing a benefit of calcium and vitamin D supplementation have used doses of 600 IUs, or higher of this vitamin.

Despite the study’s shortcomings, it still makes sense for women to obtain the recommended daily allowance (RDA) of 1,000 mg of calcium and 400 IUs of vitamin D daily. These amounts can easily be obtained through a combination of a healthy diet plus nutritional supplements.

Sources:
“Calcium plus Vitamin D Supplementation and the Risk of Fractures.” Published in the Feb. 16, 2006 The New England Journal of Medicine (Vol 354, No. X: 354-669). First author: Rebecca D. Jackson, M.D., Ohio State University.

Women’s Health Initiative, www.nih.gov/news/pr/feb2006/nhlbi-15.htm
* Body Mass Index or BMI is a tool for indicating weight status in adults. BMI is a measure of weight for height. For adults over 20 years old, BMI falls into one of these categories: BMI below 18.5 = Underweight; BMI 18.5 – 24.9 = Normal; BMI 25.0 – 29.9 = Overweight; BMI 30.0 and above = Obese.