Taking daily calcium and vitamin D supplements does not result in the significant health benefits for older women that many had hoped for. According to results from the Women's Health Initiative (WHI), healthy postmenopausal women older than age 50 who took the supplements achieved a small but significant improvement in hip bone density but not a significant reduction in their risk of hip fracture until they reached their 60s.
Previous research had suggested that calcium and/or vitamin D supplements might slow bone loss and reduce the risk of falls in older women, but the evidence of any reduction in fracture risk has been scanty.
The First Study
The current study involved more than 36,000 postmenopausal women, ages 50 to 79, all of whom received daily either 1,000 milligrams (mg) of elemental calcium as calcium carbonate plus 400 international units (IU) of vitamin D-3 or a placebo. Calcium is a major component of bone, and vitamin D helps the body properly absorb calcium through the intestines.
The women took the calcium supplement in addition to their average daily calcium intake of 110 mg from food or multivitamins, for a total calcium intake of 1,110 mg, which "is close to the national recommendation" for women older than 50, according to Andrea LaCroix, coprincipal investigator of the WHI Clinical Coordinating Center at Fred Hutchinson Cancer Research Center in Seattle.
After tracking the women's bone health for seven years, the researchers found that hip bone density rose an average of 1.06% in the group taking the supplements compared with the placebo group. And, although women who took the supplements had an average 12% reduction in their incidence of hip fracture, this finding was not considered statistically significant, according to the researchers.
In addition, the women taking calcium plus vitamin D had an increased risk of kidney stones.
The news did look slightly better for women older than 60, who had a 21% reduction in hip fractures. Calcium plus vitamin D "looked more effective in women over 60 who adhered to the study medication," LaCroix says.
Looking At The Results
The results were not surprising, say 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," says Dr. Joel Finkelstein, 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 says. "I recommend that women should take calcium and vitamin D, but shouldn't rely on it as adequate protection for osteoporosis."
The Second Study
A second study found that daily calcium plus vitamin D had no effect whatsoever on colorectal cancer risk in the same group of women. 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.
"For colorectal cancer, this means that we can't count on calcium for prevention," explains LaCroix. She stresses 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 notes.
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," according to John Hathcock, vice president for scientific and international affairs at the Council for Responsible Nutrition.