One reported that when taken with high doses of estrogen replacement therapy, soy protects against breast and uterine cell proliferation. However, when combined with low doses of estrogen replacement therapy, soy causes breast cell proliferation. Other studies have indicated that some phytoestrogens, such as black cohosh, also cause cell proliferation in the uterus under certain circumstances. Some experts advise that until more is known about phytoestrogens and breast cancer, women who are on hormone replacement therapy and at risk for breast cancer should also avoid consuming large amounts of plant products with high levels of phytoestrogens. Research continues to suggest that low levels of vitamin D may increase breast cancer risk, especially in older women.
Vitamin D is obtained from sunlight and fortified milk.
One study found that tocotrienol, a vitamin E compound found in unrefined palm oil, inhibits cancer cell proliferation and causes cancer cell death. Palm oil sold in the U.S. is refined and does not contain tocotrienol. Weight Restricting life-long weight gain after age 18 to four or five pounds may help prevent postmenopausal breast cancers. Breast Feeding Some studies have reported that breast feeding for more than four months is associated with a lower risk for cancer in pre menopausal women, and the longer the mother breast feeds, the better. Its effect on breast cancer after menopause is not yet determined.