Dietary Supplement Use and Life Expectancy After Breast Cancer-The Danish Diet, Cancer and Health Cohort

Dietary supplement use is widespread among women with breast cancer, but evidence regarding the possible health benefits or harms remains limited.

To investigate the association between the use of dietary supplements and life expectancy after breast cancer.

In this prospective cohort study, data from the Danish Diet, Cancer and Health cohort were used. We followed 1951 incident cases of breast cancer from diagnosis until migration, death, end-of-follow-up, or 20 y. Both prediagnostic and postdiagnostic dietary supplement use were assessed with a food frequency questionnaire, with prediagnostic use as the main exposure. Dietary supplement use and differences in 20-y life expectancy and life years lost due to breast cancer and other causes, respectively, were estimated using pseudo-observations and regression models adjusted for potential confounders.

During follow-up (median: 12 y, IQR: 8-17 y), 725 individuals died, with 450 deaths attributed to breast cancer. No association was found for overall dietary supplement use. Multivitamin use indicated an association with longer life expectancy after breast cancer (1.01 y; 95% confidence interval: 0.03 y, 1.98 y), primarily due to fewer years lost to breast cancer (-1.06 y; 95% confidence interval: -1.85 y, -0.27 y). In exploratory analyses, high supplementary intakes of vitamins A, B12, iron, and magnesium showed tendencies toward poorer life expectancy, whereas both high and low vitamin D intake were associated with lower life expectancy. Exploratory analyses also suggested that antioxidant supplements may be associated with poorer life expectancy among chemotherapy recipients, but not those receiving radiation therapy.

Our results suggest that womens with breast cancer may benefit from multivitamin use alone, but should avoid excessive use of dietary supplements-especially antioxidant supplements during chemotherapy and high intakes of certain micronutrients-and should not exceed recommended levels.