New research gives women another good reason to get plenty of bone strengthening calcium and vitamin D: The nutrients may reduce the risk of devel oping breast cancer.
A team of Harvard researchers reported on Monday that premenopausal women who get more calcium and vitamin D are less likely to get breast cancer.
Only about 20 per cent of breast cancer cases occur in women younger than 50, but is often more aggressive. Mammograms, X-rays intended to find breast cancer earlier, are less accurate for women in their 40s and generally are not recommended for those younger than 40.
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 Website.
According to 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."
"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 doing a more rigorous trial. "We know that sunlight, which is essentially vitamin D, is actually good for you. People exposed to sunlight have a lower risk of prostate, colon and breast 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 only in premenopausal women. There was no protection for postmenopausal women, except for those taking the highest doses of both calcium and vitamin D.
The researchers said a possible explanation for the difference might have to do with the interaction between calcium, vitamin D and certain growth factors.
Laboratory studies have found that calcium and vitamin D can stop breast cells from multiplying out of control when those cells contain high levels of insulin like growth factors. In humans, growth-factor levels decline with age, so the interaction is likely to be stronger in younger women.