Abstracted by Marcia J. Egles, MD, June 24, 2008 from “Effect of calcium supplementation on fracture risk: a double-blind randomized controlled trial” by Heike A Bischoff-Ferrari, Judy R Rees, Maria V Grau, Elizabeth Barry, Jiang Gui and John A Baron in The American Journal of Clinical Nutrition, Vol. 87, No. 6, 1945-1951, June 2008.
The medical literature contains conflicting findings and opinions about calcium supplements, with or without vitamin D, for bone health and osteoporosis prevention (1). A clinical trial begun in 1988 at six US locations, from Minnesota to southern California, found a clear benefit in reducing fracture risk among generally healthy Americans receiving 1,200 mg of supplemental calcium daily for four years. This was a follow-up to the Calcium Polyp Prevention Study (2).
The study
Calcium Polyp Prevention included 1,118 men and women aged 27–79 (mean age 61) who had recently had a benign polyp* detected and removed during colonoscopy. They were randomly assigned to placebo tablets or 3 grams of calcium preparation (1,200 mg elemental calcium) daily for four years, without vitamin D or other calcium-containing supplements. Mean dietary calcium intake was 865 mg/day in the placebo group and 889 mg/day in the calcium group. Average blood vitamin D levels were slightly low, though nearly normal, in both groups. More than 83% reported taking at least 80% of the tablets over four years.
The original study reported a
modest reduction in bowel polyps at repeat colonoscopy in the calcium group compared with placebo. Participants were told the results but not their group allocation. Only 2% used calcium supplements before the trial, whereas 26% reported taking them for at least half of the follow-up years.
The new study
examined fractures in both groups during the four-year calcium treatment and through the end of follow-up in 2003. It recruited 930 participants, 72% men, for extended follow-up. Fractures were reported by telephone interviews, classified and confirmed through medical-record review by two independent physicians. Fractures were classified as minimal-trauma or significant-trauma. Minimal trauma meant a fracture following a fall from standing height or while sitting, standing or walking. Significant trauma included sports injuries, accidents or falls down stairs.
During the four years of treatment
, there were no minimal-trauma fractures in the calcium group versus nine in the placebo group. After calcium treatment ended, minimal-trauma fracture rates were statistically similar in both groups. Significant-trauma fracture rates were similar between groups during treatment and follow-up.
This is an important clinical trial
showing a modest reduction in fractures among generally healthy adults receiving 1,200 mg supplemental calcium daily. Including their usual dietary intake, total calcium intake among treated Americans was about 2,100 mg/day. The source reports that the US National Institutes of Health and other experts generally recommend 1,200 mg calcium daily for adults and regard a total of 2,000–2,500 mg/day from food and supplements as safe.
REFERENCE
1 Bischoff-Ferrari HA, Dawson-Hughes B, Baron JA, et al. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials. Am J Clin Nutr 2007;86:1579–80
2 Baron JA, Beach M, Mandel JS, et al. Calcium supplements for the prevention of colorectal adenomas. Calcium Polyp Prevention Study Group. N Engl J Med 1999;340(2):101–7