May 29, 2007 — There is growing evidence linking vitamin D and calcium in the diet to a reduced risk of breast cancer, but the benefits may be limited to younger women. 
In a new study from Brigham and Women’s Hospital and Harvard Medical School in Boston, a high intake of calcium and vitamin D through food sources and nutritional supplements was linked to modestly lower risk of breast cancer in premenopausal women.
The link appeared strongest for the most aggressive tumors, and it was not seen after menopause.
Researcher Jennifer Lin, PhD, says older women are more likely to be deficient in calcium and vitamin D, so they may need higher levels of the nutrients than were measured in the study.
“Calcium and vitamin D are important for overall health and, additionally, they may help prevent breast cancer,” she tells WebMD.
Roughly 31,000 women enrolled in the larger Women’s Health Study were included in the analysis by Lin and colleagues. The findings were published May 28 in the Archives of Internal Medicine.
All of the women were aged 45 or older, and two-thirds were postmenopausal. The women completed questionnaires at study entry and periodically after that were designed to determine their medical history and lifestyle, including the foods they ate and supplements they took.
Over an average of 10 years of follow-up, 276 premenopausal and 743 postmenopausal study participants developed breast cancer.
Premenopausal women with the highest intakes of calcium and vitamin D had modestly reduced risk of breast cancer compared with women who got the lowest amount of the nutrients through food and supplemental sources.
The findings are similar to those reported in 2002 by another group of Harvard researchers. In that study, calcium and vitamin D through dairy sources were associated with a decreased risk of breast cancer before, but not after, menopause.
Dietary calcium and vitamin D were found to lower breast cancer risk in a cancer prevention study reported by researchers from the American Cancer Society (ACS).
ACS nutritional epidemiologist Marji McCullough, ScD, RD, who reported the findings, tells WebMD that more study is needed to understand how vitamin D and calcium influence breast cancer risk.
“The evidence of a modest protective benefit [for dietary vitamin D and calcium] is fairly consistent, but we still don’t know if premenopausal and postmenopausal women benefit equally,” she says.
Current dietary recommendations call for people aged 50 and under to consume just 200 international units (IU) of vitamin D a day, with 400 IU recommended for those between the ages of 51 and 70, and 600 IU recommended after age 70.
Many experts now agree that these levels are too low. Longtime vitamin D researcher Cedric Garland, DrPH, says most people should get between 1,000 IU to 1,500 IU a day.
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