There is a paucity of information on the prevalence of dietary supplement use in breast cancer survivors. Only a few studies have examined the impact of dietary supplements, particularly antioxidants, on breast cancer prognosis and the results are inconclusive.We examined pre- and postdiagnosis use of supplements in postmenopausal breast cancer survivors in Germany and investigated associations between postdiagnosis use of antioxidants and other supplements, and prognosis (total and breast cancer mortality, and recurrence-free survival) both overall and in women who received chemotherapy and radiation therapy.Data from 2223 postmenopausal women diagnosed with nonmetastatic breast cancer from the population-based Mamma Carcinoma Risk Factor Investigation (MARIE) study were used. Women were interviewed at recruitment in 2002-2005 and again in 2009 and followed-up until 30 June 2015. Multivariate Cox regression analysis was used to estimate HRs and corresponding 95% CIs.Pre- and postdiagnosis supplement use was reported by 36% and 45% of the women, respectively. There were 240 deaths (134 from breast cancer) and 200 breast cancer recurrences after a median follow-up time of 6.0 y after the 2009 re-interview. After adjusting for relevant confounders, concurrent antioxidant use with chemotherapy or radiation therapy among 1940 women was associated with increased risk of total mortality (HR: 1.64; 95% CI: 1.01, 2.66) and worsened recurrence-free survival (HR: 1.84; 95% CI: 1.26, 2.68). Overall postdiagnosis supplement use was not associated with breast cancer prognosis.Antioxidant use during chemotherapy or radiation therapy was associated with worsened breast cancer prognosis in postmenopausal women. There was no overall association between postdiagnosis supplement use and breast cancer prognosis. Results from our study align with the current recommendation to possibly avoid the use of antioxidants during chemotherapy or radiation therapy.
