Two large studies show calcium and vitamin D supplements provide modest help in preserving bone mass in women and preventing hip fractures in those over 60.
But, contrary to previous reports, the supplements didn't prevent other types of fractures or colon cancer.
The studies in today's New England Journal of Medicine followed 36,282 women nationwide ages 50 to 79, including 963 from Western New York, as part of the $415 million Women's Health Initiative.
The findings are considered the most definitive to date on calcium and vitamin D supplements, although experts said shortcomings in the studies mean the role of these nutrients is far from settled.
Calcium and vitamin D are widely used in women to treat osteoporosis, a progressive disease that causes bones to become thin and brittle, making them more likely to break.
Previous studies have suggested that the supplements may prevent colorectal cancer, so the latest findings cloud the picture. "Unfortunately, this long-term clinical trial, in which some of the women were followed for more than nine years, does not support this assumption," said Jean Wactawski-Wende, a University at Buffalo researcher who was lead author on the cancer study and a co-author on the hip fracture study.
She said the results should not be applied to men.
An estimated 10 million people in the United States suffer from osteoporosis, and 34 million more have low bone mass, placing them at greater risk for fractures, according to the National Osteoporosis Foundation. Osteoporosis contributes to an estimated 300,000 hip fractures in the United States each year.
The study did not find as much of a benefit from supplements as expected. Still, the researchers advised healthy women to get adequate amounts of calcium and vitamin D, preferably from foods, and to use supplements only if their diet is deficient.
"Food provides you with so many more nutrients than supplements," said Joan McGowan of the National Institute of Arthritis and Musculoskeletal and Skin Diseases and a co-author on the paper.
Recommended daily dosages for older women are 1,200 mg of calcium and 400 to 600 IU of vitamin D.
The studies were designed mainly to study the effect of the supplements on preventing hip fracture, with the effect on other fractures and colon cancer secondary objectives.
Among the key findings:
*Women taking calcium combined with vitamin D had a small but significant 1 percent higher hip bone density.
*374 women suffered hip fractures, with a fracture rate of 14 per 10,000 cases per year, in the supplemented group compared with 16 per 10,000 per year in the placebo group. The 12 percent difference was not statistically significant and was much less than the 18 percent reduction that was expected.
*However, women who consistently took the supplements experienced a significant 29 percent decrease in hip fractures, and women older than 60 had a significant 21 percent reduction in hip fractures.
*The supplements had no effect on spine or total fractures.
*The only adverse effect from supplements was a 17 percent increase in kidney stones.
"A hip fracture is the most debilitating fracture. An intervention that can reduce the incidence can have a significant impact on quality of life," said Dr. Rebecca D. Jackson, an endocrinologist and the study's lead investigator at Ohio State University.