WEDNESDAY, Feb. 15, 2006 (HealthDay News) -- Taking daily calcium and vitamin D supplements does not result in the significant health benefits for older women that many had hoped it would.
According to new results from the Women's Health Initiative (WHI) study, healthy postmenopausal women over age 50 who took the supplements achieved a small but significant improvement in hip bone density but no significant reduction in their risk of hip fracture until they reached their 60s.
And daily calcium plus vitamin D had no effect whatsoever on colorectal cancer risk in the same group of women, a second study found.
"For colorectal cancer, this means that we can't count on calcium for prevention," said Andrea LaCroix, co-principal investigator of the Women's Health Initiative Clinical Coordinating Center at Fred Hutchinson Cancer Research Center, in Seattle. She stressed that, despite the disappointing results, calcium is "just one avenue that looked promising" for the prevention of colon cancer. "It [still] leaves women with other avenues, such as early detection," she noted.
Hope remains that supplements might protect bones, too. "On the fracture side, there was a 21 percent reduction in hip fracture in women over 60, and that's encouraging for women who prefer not to take medicine," LaCroix noted.
Both studies appear in the Feb. 16 issue of the New England Journal of Medicine.
Representatives of the supplements industry downplayed the results.
The studies "showed disappointing outcomes inconsistent with the large body of scientific evidence and the prevailing wisdom about the beneficial effects of these two nutrients," John Hathcock, vice president for scientific and international affairs at the Council for Responsible Nutrition, said in a prepared statement. "Without discounting the value or importance of the studies, we think it is important for consumers not to over-interpret the results, as the authors themselves have noted limitations of the studies that may account for the unexpected results."
Calcium is a major component of bone, and vitamin D helps the body properly absorb calcium through the intestines. Previous research had suggested that calcium or vitamin D supplements might slow bone loss and reduce the risk of falls for older women, but the evidence on any reduction in fracture risk has been scanty.
There was a similar paucity of evidence when it came to the supplements' ability to cut risks for colorectal cancer.
This study involved more than 36,000 postmenopausal women aged 50 to 79, all of who received either 1000 milligrams of elemental calcium as calcium carbonate plus 400 IU of vitamin D3, or a placebo daily.
The calcium supplement was in addition to the women's average daily calcium intake of 110 milligrams from food or multivitamins, which "is close to the national recommendation," according to LaCroix. "This trial was basically asking, 'Is more better?'"
The researchers tracked the women's bone health for seven years. They found that hip bone density rose an average of 1.06 percent in the group taking the supplements vs. the placebo group. Women who took the supplements did have an average 12 percent reduction in their incidence of hip fracture, but this finding was not considered statistically significant, the researchers said.
At the same time, women taking calcium plus vitamin D experienced an increased risk for kidney stones, they added.
The results were not surprising, said some experts.
"The study looked at a large number of postmenopausal women who weren't specifically selected to be at risk for fractures, so the deck was largely stacked against the study," said Dr. Joel Finkelstein, author of an accompanying editorial and an endocrinologist at Massachusetts General Hospital in Boston. "In that setting, there was no overall effect on fracture risk, which wasn't terribly surprising because calcium and vitamin D are relatively weak therapies for osteoporosis."
"The message is it's a fairly mild to moderate effect," Finkelstein said. "I recommend that women should take calcium and vitamin D, but shouldn't rely on it as adequate protection for osteoporosis."
The news did look slightly better for women over 60, who had a 21 percent reduction in hip fractures. "It looked more effective in women over 60 who adhered to the study medication," LaCroix said.
The results were more clearly negative in the colorectal cancer portion of the trial. The incidence of invasive colorectal cancer did not differ appreciably between women taking the supplements and those taking the placebo.
The incidence of colon polyps -- a precursor to cancer -- was also similar in both groups.
Again, some questions remain, including whether or not the doses were high enough and whether or not the women were followed for long enough. "It's fairly arrogant to think you can stop a disease that takes 10 to 20 years to develop in seven years," LaCroix said. "We showed a strong relationship between serum vitamin D and colorectal cancer, and that may someday lead to more effective interventions."
More information
To learn more about vitamin D, visit the National Institutes of Health.
