Women's Health Initiative ( WHI ) found that taking Calcium and Vitamin D slightly decreased the risk of hip fractures in older women, but not the risk for other types of fractures or for colorectal cancer.
Additionally, the supplements slightly increased the incidence of kidney stones.
A researcher at the Stanford University School of Medicine who helped oversee the WHI study said the results don't change current recommendations that women over age 50 should consume 1,200 milligrams of Calcium and 400-600 international units of Vitamin D each day to maintain their bone health. However, Marcia Stefanick, at the Stanford Prevention Research Center, pointed out that adequate levels of these nutrients don't have to come from supplements.
The findings are published in the New England Journal of Medicine.
They are the latest clinical results from the WHI, a 15-year, broad-based look at the causes and prevention of diseases affecting older women. Previous WHI studies have involved hormone therapy, low-fat diets and heart disease.
The Calcium/Vitamin D study involved more than 36,000 postmenopausal women between the ages of 50 and 79 who were tracked over the course of seven years. Researchers wanted to determine whether women who took the supplements could reduce their risk of bone fractures, especially hip fractures, and colorectal cancer.
Half of the trial participants were randomly assigned to take daily supplements of 1,000 mg. of elemental Calcium ( as Calcium carbonate ) and 400 IU of Vitamin D3-the recommended dosage to prevent osteoporosis that was in effect when the WHI trial was designed in the early 1990s.
The remaining women were given a placebo.
The study found that women assigned to take the Calcium and Vitamin D pills experienced a 12 percent reduction in hip fractures, a difference that was not statistically significant ( 14 fractures per 10,000 women on the supplements compared with 16 per 10,000 in the placebo group ) over the course of the seven-year study. But not all women adhered completely to the supplement regimen. What the study revealed, though, is that among those who took 80 percent or more of the recommended dosage, there was a 29 percent decrease in hip fractures.
The supplements didn't make a difference in reducing the rates of spine, wrist and other fractures, or in reducing the risk of colorectal cancer.
Although most women tolerated the supplements well, there was a 17 percent increase in the rate of kidney stones ( 34 cases per 10,000 women in the supplement group, compared with 29 cases per 10,000 women taking a placebo ).
Kidney stones are hardened mineral deposits that form in the kidney and often cause pain when discharged from the body.
Calcium and Vitamin D have long been staples in the effort to improve bone health among older women, who are four times more likely than men of the same age to suffer from osteoporosis - a disease in which bones become fragile and more likely to break.
The condition contributes to 1.5 million fractures each year in the United States, including more than 300,000 hip fractures.
Forty percent of women over age 50 experience a fracture of the hip, spine or wrist in their lifetime.
Additionally, some observational studies have suggested that a higher intake of Calcium and Vitamin D could lower the risk for colorectal cancer, but results from past clinical trials have been mixed.
Colorectal cancer is the second-leading cause of cancer deaths in the United States for men and women combined.
With the new evidence from the WHI trial, Stefanick said women should continue to make sure they get enough Calcium and Vitamin D for their bone health, but that they shouldn't expect this to make a difference in preventing colorectal cancer.
" Because we don't have good evidence of how to prevent colorectal cancer, the importance of early detection through regular screenings should be emphasized for both women and men from age 50 onward, " Stefanick said.
The Calcium/Vitamin D study is the last of three WHI randomized clinical trials to be published.
Source: Stanford University Medical Center, 2006