The Associations of Multivitamin and Antioxidant Use With Mortality Among Women and Men Diagnosed With Colorectal Cancer.

BACKGROUND: Colorectal cancer survivors often use multivitamins and other over-the-counter dietary supplements, but evidence is limited regarding their potential associations with mortality. METHODS: This prospective analysis included women and men from the Cancer Prevention Study-II Nutrition Cohort who were cancer-free at baseline (1992 or 1993) and diagnosed with colorectal cancer through June 2015. Detailed information on multivitamin use, vitamin C supplements, and vitamin E supplements was self-reported on questionnaires at baseline, in 1997, and every 2 years thereafter. Pre- and postdiagnosis data were available for 3176 and 2006 colorectal cancer survivors, respectively, among whom 2116 (648 from colorectal cancer) and 1256 (242 from colorectal cancer) died. Multivariable-adjusted Cox proportional hazards regression models examined associations. All statistical tests were 2-sided. RESULTS: Among colorectal cancer survivors, 49.7% and 58.5% reported multivitamin use before and after diagnosis, respectively (vitamin C use before and after diagnosis: 27.8% and 28.1%; vitamin E use before and after diagnosis: 27.5% and 29.4%, respectively). There were no statistically significant associations of pre- or postdiagnosis multivitamin use with all-cause, colorectal cancer-specific, or noncolorectal cancer mortality. Vitamin C was also not associated with any mortality outcomes. However, prediagnosis vitamin E use was associated with a non-statistically significant increased risk of all-cause mortality (multivariable adjusted hazard ratio = 1.08, 95% confidence intervals = 0.96 to 1.23) and all other noncolorectal cancer mortality (multivariable adjusted hazard ratio = 1.13, 95% confidence intervals = 0.97 to 1.31). CONCLUSIONS: These results suggest that multivitamin use before or after diagnosis is not associated with mortality in colorectal cancer survivors. However, vitamin E use may be associated with increased risk of mortality and merits further investigation.