Description of Evidence
No randomized prevention trials examining the effect of fruit and vegetable consumption on breast cancer incidence have been conducted; however, evidence for the lack of an association between fruit and vegetable consumption and prevention of breast cancer is supported by results of the Women's Healthy Eating and Living Randomized Trial. Although the trial was a secondary prevention study, the outcomes included new primary breast cancers. More than 3,000 women were enrolled and randomly assigned to an intense regimen of fruit and vegetable intake, high fiber and low fat, or a comparison group receiving printed materials on the "5-A-Day" dietary guidelines. Both groups were consuming more than seven servings of vegetables and fruits at baseline. Increased fruit and vegetable consumption was monitored through dietary assessment and measures of serum carotenoid concentrations. After a mean of 7.3 years follow-up, there was no reduction in new primary cancers (43 new primary breast cancers among the 1,537 randomly assigned to the intervention; compared with 35 new primary breast cancers in 1,551 randomly assigned to the comparison group). There was no difference in disease-free survival between the two groups and no difference in overall survival.
The potential role of specific micronutrients for breast cancer risk reduction has been examined in clinical trials, with cardiovascular disease and cancer as outcomes. The Women's Health Study, a randomized trial with 39,876 women found no difference in breast cancer incidence at 2 years between women assigned to take beta carotene versus placebo. In this same study, no overall effect on cancer was seen in women taking 600 IU of vitamin E every other day. The Women's Antioxidant Cardiovascular Study (WACS) examined total cancer and invasive breast cancer as secondary outcomes following supplementation with either vitamin C, vitamin E, or beta carotene, which were assigned randomly according to a 2 x 2 x 2 factorial design. Women were recruited from the parent Women's Health Study and were eligible for the trial if they had cardiovascular disease or at least three cardiac risk factors. A total of 8,171 women were enrolled. For the analysis of cancer outcome, women were excluded if they had a prior history of cancer (n = 544). Neither total cancer nor breast cancer incidence was statistically significantly different between supplementation groups and the placebo arm. Two years after enrollment for WACS, a subset of participating women who were willing not to use folic acid and vitamin B6 or B12 supplements (n = 5,442) were randomly assigned to supplementation with a combination of 1.5 mg of folic acid, 50 mg of vitamin B6, and 1 mg of B12, or placebo. After 7.3 years of treatment, there was no statistically significant difference in the incidence of total invasive cancer or invasive breast cancer between the supplemented group and the placebo arm.