Dietary antioxidants and breast cancer survival

Clinical and epidemiological studies, which have examined the relationship between antioxidants and risk of breast cancer recurrence or mortality are limited in number, despite the protective associations observed with breast cancer incidence. A meta-analysis of six previous studies revealed that highest intake of vitamin C was modestly and significantly associated with a reduced risk of breast cancer related mortality (Random effects relative risk estimate = 0.66, 95% CI, 0.48–0.90). Proportional hazards modeling was used to estimate rate ratios of breast cancer recurrence and mortality among 407 postmenopausal women diagnosed with breast cancer between 1986 and 1988, enrolled into a case-control study on diet and cancer. These women were re-contacted with a questionnaire to ascertain their use of nutritional supplements during 12 to 14 years of post-diagnosis follow-up time. Five-year logistic regression was used to examined post-diagnosis vitamin intakes. One or more dietary supplements were used by 80.5% of women, and use of supplements increased significantly after diagnosis. Antioxidant supplement use (vitamin C, E, beta-carotene, selenium or an antioxidant combination) increased from 34% pre-diagnosis to 56% after diagnosis, and was used by 64% of this cohort at some time overall. Vitamin E supplements showed the strongest protective effect on recurrence and mortality when used for more than 3 years (OR = 0.33, 95% CI: 0.10–1.07). Exclusion of proxy questionnaires for women who had died during follow-up (N = 47) resulted in a lessening of effect (R.R = 0.52, 95% CI: 0.15–1.83). Highest pre-morbid intakes of vitamin E and C from diet alone were not related to risk. Limited modification of risk estimates for vitamin E and recurrence were observed among women who received radiation therapy, in which strongest protective effects were found among vitamin E users without radiation therapy. Risks of recurrence and disease related mortality were reduced among women using vitamin E supplements for more than 3 years. Recall bias among proxy respondents may not have strongly influenced these findings since results were similar when compared with living cases. This study provided limited support for the hypothesis that lifetime and post-diagnosis use of vitamin C and E supplements may reduce the risk of breast cancer recurrence or cancer related mortality.