Study Questions Benefits of Calcium and Vitamin D Supplements
Published April 2006
Calcium and vitamin D supplements can provide a modest benefit in preventing bone loss and hip fractures, a new study finds, but they don’t deliver on an earlier hope that they can also reduce the risk of colorectal cancer.
These are the latest results from the 15-year, national Women’s Health Initiative (WHI) investigation of postmenopausal women’s health, which evaluated the effects of calcium and vitamin D supplements, hormone therapy and dietary modification as a means of preventing some of the chronic conditions associated with aging.
“Previous studies suggested that calcium and vitamin D may help prevent colorectal cancer,” says Margery Gass, MD, professor of obstetrics and gynecology at UC and the principal investigator for the WHI site at UC.
“This study doesn’t show that to be true. However, there was a 1 percent increase in hip bone density in the group assigned to take the supplements.”
More than 36,000 women aged 50 to 79, including 903 from the Cincinnati area, were involved in the calcium and vitamin D arm of the study.
For seven years, half were randomly assigned to take daily supplements of 1,000 mg of elemental calcium and 400 IU of vitamin D, the recommended dosage to prevent osteoporosis that was in effect when the WHI trial was designed in 1991. The remaining women were given a placebo.
Women in both groups were permitted to take calcium and vitamin D supplements on their own, since it was thought to be unethical to tell women in the placebo group that they could not take any. As a result, very few of the women in the placebo group were calcium deficient.
Overall, women taking the supplement had a 12 percent reduction in hip fractures, a difference that was not statistically significant. Those who took 80 percent or more of the recommended calcium/ vitamin D supplements (not all participants consistently followed the dosage) had a significant 29 percent decrease in hip fractures, and women over age 60 taking the supplements benefited from a 21 percent decrease in hip fractures.
Although most women tolerated the supplements well, there was a 17 percent increase in the rate of kidney stones. So, what do these findings mean?
“Calcium and vitamin D are still considered to be beneficial for bone health, but not the prevention of colorectal cancer,” Dr. Gass says. “We don’t have good evidence of how to prevent colorectal cancer, so early detection is important. Both women and men should get regular screenings from age 50 on.”
How much calcium and vitaminD is needed?
“Women over 50 should follow the current recommendations of1,000 to 1,200 mg of calcium and 400 to 600 IU of vitamin D each day, either through dietary intake or supplements to maintain their bone health. Women with a history of kidney stones should consult their physician first,” says Dr. Gass.
The WHI study will continue to follow the women for five more years, which may provide more long-term information on the effects of calcium and vitamin D supplements, Dr. Gass says.