CHICAGO – New research gives women another good reason to get plenty of bone-strengthening calcium and vitamin D: The nutrients may reduce the risk of developing breast cancer.
A team of Harvard researchers reported Monday that premenopausal women who get more calcium and vitamin D – either from food or supplements – are less likely to get breast cancer.
Only about 20 percent of breast cancer cases occur in women younger than 50, but it is often more aggressive.
Though post-menopausal women can take medication to reduce their risk of developing breast cancer, nothing is available for premenopausal women.
Although the evidence is not strong enough to advise all women to take calcium and vitamin D, experts say it might help reduce the risk of breast cancer and it’s not likely to hurt.
“It’s probably reasonable to consider,” said Dr. Leslie Laufman, an editor of the National Cancer Institute’s screening and prevention Web site. “There’s no proof that making a change (in intake of calcium and vitamin D) matters – but it probably does.”
The bottom line for Jennifer Lin, one of the researchers in the Harvard study: “Adequate intake of calcium and vitamin D is necessary for women to keep up their health and, additionally, may help prevent the development of breast cancer, especially among premenopausal women.”
Other researchers called the findings “striking.”
“There is no known way to reduce (the incidence of) premenopausal breast cancer, and this is a major finding,” said Frank Garland, an epidemiologist.
“We think this is the most important development in the prevention of premenopausal breast cancer in history,” said Cedric Garland, an expert in preventive medicine.
The Garland brothers and Edward Gorham, collaborators in the field of cancer prevention at the University of California-San Diego, proposed in 1989 that vitamin D and calcium could prevent breast cancer.
Laufman cautioned that it’s not possible to prove the supplements prevent breast cancer without a more rigorous trial.
Researchers would have to randomly select a large number of women to receive either a supplement or a placebo, Laufman said, and then follow up to see whether one group developed more breast cancer. (The women in the Harvard study were not randomized, so it’s possible that whatever caused some of them to take dietary supplements also affected their chances of getting cancer.)
The Harvard study, published in this week’s issue of Archives of Internal Medicine, found that calcium and vitamin D reduced breast cancer risk significantly in premenopausal women. There was no protection for postmenopausal women, except for those taking the highest doses of both calcium and vitamin D.
Postmenopausal women already are advised to take calcium and vitamin D supplements to protect their bones, and many doctors recommend that women start taking the supplements well before menopause.
“To get an effect, you need bigger doses,” said Cedric Garland. He recommends that women get up to 2,000 international units a day of vitamin D(-3) (the only form found to be effective) orally plus an additional 1,500 units by exposing their skin to sunlight between five and 15 minutes a day.
The minimum daily intake of calcium recommended by the U.S. Office of Dietary Supplements is 1,000 mg for premenopausal women and 1,200 mg for postmenopausal ones. The recommended minimum daily intake of vitamin D is 200 units before menopause, 400 units for women 50-70, and 600 units for those over 70.
According to the Institute of Medicine, part of the National Academy of Science, adults can safely take up to 2,500 mg per day of calcium and up to 2,000 units of vitamin D. People who take more than 1,000 mg of calcium per day over long periods may increase their risk of kidney stones.
In the Harvard study, Lin’s subjects were divided into five equal groups, or quintiles, based on the amount of vitamin D they reported taking. The lowest quintile got less than 162 units of vitamin D a day from food and supplements; the highest quintile included everything over 547 units a day.
The Harvard researchers followed a group of more than 30,000 women for an average of 10 years. They found that the premenopausal women in the highest quintile of vitamin D intake had 35 percent less breast cancer than those in the lowest quintile. Likewise, the highest quintile of calcium intake (more than 1,360 mg a day) had 39 percent less breast cancer than those in the lowest quintile (less than 617 mg per day).