Taking Calcium, Vitamin D Helps Prevent Fractures—Complicated Story
A Healthnotes Newswire Opinion:
A study published in the New England Journal of Medicine (2006;354:669–83) has questioned the widely held belief that calcium and vitamin D can prevent osteoporosis-related hip fractures. The study also concluded that taking calcium and vitamin D increases the risk of kidney stones. Closer analysis of the study reveals that these supplements probably do have benefit; however, the results should lead us to reconsider the optimal level of calcium intake, and whether supplementing with just calcium and vitamin D is sufficient to prevent osteoporosis.
In the new study, more than 36,000 postmenopausal women were randomly assigned to take calcium (500 mg twice a day) plus vitamin D (200 IU twice a day) or a placebo for an average of seven years. After seven years the supplement group had 12% fewer hip fractures than did the placebo group. That difference was not statistically significant, which led the researchers to conclude that the supplements “did not significantly reduce hip fractures.”
However, the failure to demonstrate statistical significance is not the same as demonstrating a treatment did not work. The correct conclusion from the data is that calcium and vitamin D reduced hip fracture risk by 12%, but we are less than 95% confident that the results were not due to chance. Furthermore, the reduction in fractures was even greater when women who were not adhering to the program were excluded from the analysis. In that subgroup, there were 29% fewer fractures in the supplement group than in the placebo group, a statistically significant difference.
Women who get enough calcium are less likely to benefit from a calcium supplement than women whose intake is low, so fracture risk may have been more reduced if participants had not been permitted to continue taking their own supplements. At the start of the study, the average daily calcium consumption in both groups was about 1,150 mg, which is close to the currently recommended intake for the age group being studied. As that intake didn’t drop, calcium intake remained relatively high, even in the placebo group. In the new study, calcium plus vitamin D reduced hip fracture risk by about 22% in women whose initial calcium intake was low or moderate, but increased fracture risk by 12% in women whose initial calcium intake was high (1,200 mg per day or more).
The relatively modest benefits may also be due to the fact that calcium and vitamin D are only two among many nutrients that play a role in promoting bone health. Other important nutrients include magnesium, vitamin K, silicon, manganese, strontium, zinc, copper, folic acid, vitamin B12, vitamin C, vitamin B6, boron, and phosphorus. It is likely that supplementing with all of these nutrients would provide greater protection against fractures than the 12 to 29% reduction observed in the new study with calcium and vitamin D alone.
An expert in nutritional therapies, Chief Medical Editor Alan R. Gaby is a former professor at Bastyr University of Natural Health Sciences, where he served as the Endowed Professor of Nutrition. He is past-president of the American Holistic Medical Association and gave expert testimony to the White House Commission on Complementary and Alternative Medicine on the cost-effectiveness of nutritional supplements. Dr. Gaby has conducted nutritional seminars for physicians and has collected over 30,000 scientific papers related to the field of nutritional and natural medicine. In addition to editing and contributing to The Natural Pharmacy (Three Rivers Press, 1999), and the A–Z Guide to Drug-Herb-Vitamin Interactions (Three Rivers Press, 1999), Dr. Gaby has authored Preventing and Reversing Osteoporosis (Prima Lifestyles, 1995) and B6: The Natural Healer (Keats, 1987) and coauthored The Patient's Book of Natural Healing (Prima, 1999).
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