[PHNUTR-L] WCO: Meta-Analysis Defends Bone Benefit for Vitamin D with Calcium

[Kathrynne Holden, MS, RD]

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WCO: Meta-Analysis Defends Bone Benefit for Vitamin D with Calcium
http://www.medpagetoday.com/Endocrinology/Osteoporosis/dh/3471		
   	
By Michael Smith, MedPage Today Staff Writer
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of 
Pennsylvania School of Medicine.
June 06, 2006
MedPage Today Action Points

     * Advise patients who ask that two recent studies seemed to show 
that combined supplements of calcium and Vitamin D had little effect on 
the risk of osteoporotic fractures.

     * Note that this study—a meta-analysis of randomized 
placebo-controlled studies—comes to the opposite conclusion.

     * This study was published as an abstract and presented orally at a 
conference. These data and conclusions should be considered to be 
preliminary as they have not yet been reviewed and published in a 
peer-reviewed publication

Review
Steven Boonen, M.D., Ph.D., Leuven University
TORONTO, June 6 — The concept of calcium and vitamin D supplementation 
for prevention of osteoporosis, relegated recently to the realm of 
unfounded notion, got a spirited defense here.

The combination is "very effective, but you have to give it to the right 
people and in the right dose," Steven Boonen, M.D., Ph.D., of Leuven 
University in Belgium said at the World Congress on Osteoporosis here.

Dr. Boonen presented results of a meta-analysis of major randomized 
placebo-controlled trials that analyzed the effects of vitamin D alone 
or in combination with calcium. The meta-analysis found that in patients 
getting 800 units of vitamin D and more than 1,000 mg of calcium a day, 
there was a 21% reduction in risk of fracture compared to placebo.

The meta-analysis included the RECORD study, published last year in The 
Lancet, and data from the Women's Health Initiative, published earlier 
this year in the New England Journal of Medicine. Both the latter 
studies found no benefit to adding calcium to vitamin D to prevent 
fractures in menopausal women.

But Dr. Boonen said their methods were flawed, leading to an incorrect 
conclusion.

For one thing, he said, neither study had enough statistical power to 
find an effect. For instance, he said, the RECORD trial, looking at hip 
fractures, had 2,649 participants and only 93 events. By contrast, Dr. 
Boonen said, he and his colleagues had a patient pool of 16,978 
individuals and 812 fractures.

Also, he said, both studies were community-based, meaning that many of 
their participants were actually getting enough calcium and vitamin D 
without taking supplements. By including such healthy women, he said, 
"you dilute the treatment effect."

"It doesn't make sense to give calcium and vitamin D if there's no 
insufficiency," he said.

And finally, he noted, in both trials, compliance was on the order of 
40% and 50%. When the researchers analyzed those who actually took their 
supplements, he said, "they did see an effect."

Dr. Boonen and colleagues actually presented two analyses. In one, they 
looked at randomized clinical trials comparing vitamin D alone to 
placebo and found no effect. The odds ratio was actually slightly in 
favor of placebo at 1.10, but the 95% confidence interval ranged from 
0.89 to 1.36.

On the other hand, they found that when combined with calcium vitamin D 
had a significant benefit in reducing fracture. The odds ratio was 0.79, 
with a 95% confidence interval from 0.64 to 0.97. The number needed to 
treat to prevent one fracture was 132.

A subsidiary analysis showed that low doses of vitamin D—below 800 units 
a day—had no effect, he said.

For clinicians, "the point of (the study) is that you should always give 
both," said endocrinologist B. Lawrence Riggs, M.D., of the Mayo Clinic 
in Rochester, Minn., who chaired the session in which Dr. Boonen's 
research was presented.

"Some people believe that vitamin D is enough but vitamin D exerts its 
effect on bone predominantly by increasing absorption of calcium," Dr. 
Riggs said in an interview. "If you don't have enough calcium, it's not 
effective."

Dr. Boonen told reporters after his presentation that clinicians need to 
pay attention to four factors. They must prescribe a combination of 
calcium and vitamin D, the doses must be high enough, the patients must 
be in need of the supplements, and finally they must actually take their 
medication.

Primary source: Osteoporosis International
Source reference:
Boonen S et al. "Fracture Risk Reduction With Vitamin D Supplementation 
Requires Additional Calcium: Evidence From A Comparative Meta-Analysis." 
Osteoporos Int 2006; 17 (Suppl 2): 13.
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
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