A number of substances that have been studied and shown to reduce the risk for breast cancer. A retrospective study, appearing in Breast Cancer Research and Treatment (Epublished ahead of print, March 8, 2011) looked at breast cancer patients and vitamin D status. Vitamin D defThe subjects, 224 women with breast cancer (stage 0 -stage III), were divided into three groups. One group received no vitamin D, one group received 1,000 IU per day of vitamin D and a third group received a high dose, 50,000 IU per day dose of vitamin D. Only the high dose group experienced an increase of 25(OH)D levels. Another vitamin D study, a nested, case-controlled study, appeared in Cancer Epidemiology, Biomarkers & Prevention (2010 Sept; 19(9): 2341-50) and compared vitamin D levels in 636 breast cancer and 1,272 healthy controls.  Higher vitamin D levels were inversely associated with the incidence of breast cancer, especially in women under the age of 53. In postmenopausal women the risk reduction is less pronounced.

A study appearing in Cancer Research (2009; 69(24): 9323-9) compared 602 breast cancer patients to 626 controls. It found that the amount of carotenoids  circulating in the blood was inversely related to the risk for breast cancer. Women with high mammographic density enjoyed as much as a 50% reduction in breast cancer risk when they had high levels of carotenoids. The relationship did not exist in women with low mammographic density. Carotenoids are oil-soluble plant pigments that the body can convert to vitamin A. They are responsible for the bright colors of produce. The best known carotenoid is beta-carotene. Beta carotene also has the most vitamin A activity of all of the carotenoids.  Other carotenoids include alpha carotene, lycopene, lutein, astaxanthin, beta crpytoxanthin, and zeaxanthin.

Flavonoids are plant pigments that act as antioxidants, protecting the plant from the oxidative stress of photosynthesis. They act as antioxidants for humans who eat the plants as well. They protect cells from free radicals. A study appearing in the American Journal of Epidemiology (2007 165(5):514-523) looked at 1,434 subjects with breast cancer and 1,440 healthy controls. The researchers found that a higher intake of dietary flavonoids was associated with a lower risk of breast cancer.

Lignans are phytoestrogens with antioxidant activity. Lignans are from the cell walls of plants and are found in a variety of foods, including flax seeds, soybeans, whole grain cereals, rye, broccoli, pumpkin seed and some berries. A recent prospective study, appearing in the Journal of the National Cancer Institute (2007; 99(6): 475-86), analyzed the lignan intake of 58,049 postmenopausal French women. There was a link between lignan intake and lower breast cancer risk. Intake was assessed in the women, who were not taking any sort of soy isoflavone supplement, with a self-administered dietary history questionnaire. The women in the top quartile of lignan intake had a 17% lower risk of developing breast cancer than the women in the quartile with the lowest lignan intake.

Research appearing in Cancer Causes and Control (2006; 17(10): 1253-61) looked at diet and breast cancer risk. The population-based, case-controlled study looked at 3,024 patients between the ages of 25 and 74 years and compared them to 3,420 matched controls. Participants were given a food frequency questionnaire. It was found that the incidence of breast cancer and diet during adolescence. Eating lignans and isoflavones (phytoestrogens) during the teen years reduces the chance of developing breast cancer later in life.

In an animal study appearing in Carcinogenesis (2009;July:30(7)), scientists found that vitamin C may protect against estrogen induced breast tumors. The study was performed on rats bred to easily develop breast tumors. In animals given estradiol, 82% developed breast tumors. Rat who were given a combination of vitamin C and estradiol had 29% fewer tumors over the 240 day course of the study.