Findings from Harvard University apply to younger middle-aged women, and to more aggressive breast tumors
by Craig Weatherby
Every year, one million women worldwide are diagnosed with breast cancer, with the highest rates occurring in the US and Holland, and the lowest in China.
Our newsletter archives include several reports on anti-cancer powers of vitamin D, including tumors of the ovaries, kidneys, colon, pancreas, and breast. To view the list, click here and search for vitamin D.
As with most investigation of links between foods, nutrients, and cancer, all of these were “epidemiological” studies, in which researchers compare people’s self-reported food and nutrient intakes or sun exposure to rates of cancer.
Given the limitations of epidemiological studies, none of these is considered conclusive, but the steady stream of positive results provides strong evidence in favor of the so-called “sunshine-and-seafood” vitamin, because these are the best sources.
A little over a year ago, we reported on two studies indicating that vitamin D reduces breast risks (see “Vitamin D May Diminish Breast Cancer Risk Drastically”).
New results reinforce promise of vitamin D-calcium combo
The latest findings hail from Harvard Medical School and its teaching center at Brigham and Women's Hospital in Boston.
Researchers there report that pre-menopausal women who consume higher amounts of calcium and vitamin D may lower their risk of developing breast cancer by almost 40 percent.
Animal studies suggest that the combination of calcium and vitamin D exert breast-cancer-preventive effects.
And an earlier study by a team that included renowned Harvard researcher Walter Willett, M.D. came to this conclusion: “…high intake of low-fat dairy foods, especially skim/low-fat milk, was associated with reduced risk of breast cancer. Similar inverse associations were seen with components (calcium and vitamin D) of dairy foods…” (Shin MH et al 2002).
However, the epidemiologic studies that compared women’s calcium and vitamin D intake levels to breast cancer have been inconclusive overall, so the Boston-based group set out to take another look… with positive results.
As lead author Jennifer Lin wrote, “Findings from the present study suggest that higher intakes of calcium and vitamin D from dietary plus supplemental sources may be associated with a lower risk of breast cancer among pre-menopausal women. The inverse association in pre-menopausal women may be more pronounced in more aggressive breast tumors” (Lin J et al 2007).
The Harvard-Brigham’s study and its findings
Dr. Lin and her team recruited 10,578 pre-menopausal and 20,909 post-menopausal women (average age 55) used questionnaires to gather information about their medical history, lifestyle, and consumption of 131 different foods, beverages and supplements during the year prior to the beginning of the study.
Ten years later, the researchers documented 276 cases of breast cancer in pre-menopausal women and 743 cases in post-menopausal women.
Among the pre-menopausal women, calcium and vitamin D intake were associated with 39 and 35 percent lower risks of breast cancer, respectively, after comparing the women with the highest intakes of both nutrients to women with the lowest intakes.
No risk reductions were found among post-menopausal participants.
The researchers hypothesized that the cancer-risk differences observed between pre- and post-menopausal women stem from a relationship among calcium, vitamin D and two hormonal chemicals called IGF-1 and IGF binding protein 3.
Test tube studies indicate that calcium and vitamin D exert anti-cancer effects on breast cancer cells that “express” high levels of the two hormonal factors.
It appears that calcium, vitamin D and one of the hormonal factors—IGF binding protein 3—interact in ways that inhibit the growth of breast cancer cells.
Women’s blood levels of both hormonal factors decline with age, so it makes sense that the calcium-vitamin D combo would have less protective power in post-menopausal women than in younger, pre-menopausal women.
We should note that the study had two limitations:
- The women were only asked about food and supplement intake at the start of the 10-year study.
- They were not asked about their average exposure to vitamin D-generating sunlight.
Nevertheless, the results provide more anti-cancer evidence in favor of the calcium-vitamin D combo.
- Lin J, Manson JE, Lee IM, Cook NR, Buring JE, Zhang SM. Intakes of calcium and vitamin d and breast cancer risk in women. Arch Intern Med. 2007 May 28;167(10):1050-9.
- Shin MH, Holmes MD, Hankinson SE, Wu K, Colditz GA, Willett WC. Intake of dairy products, calcium, and vitamin d and risk of breast cancer. J Natl Cancer Inst. 2002 Sep 4;94(17):1301-11.
- McCullough ML, Rodriguez C, Diver WR, Feigelson HS, Stevens VL, Thun MJ, Calle EE. Dairy, calcium, and vitamin D intake and postmenopausal breast cancer risk in the Cancer Prevention Study II Nutrition Cohort. Cancer Epidemiol Biomarkers Prev. 2005 Dec;14(12):2898-904.
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