Patterns of Multivitamin Use after Colorectal Cancer Diagnosis in Association with Long-term Survival

Multivitamin use has been related to a modest reduced risk of colorectal cancer (CRC), but evidence on its use after diagnosis in relation to survival has been limited. Incident, invasive CRC cases were identified through cancer registries from 1997–2008 and enrolled in four population-based sites of the Colon Cancer Family Registry (Fred Hutchinson Cancer Research Center, Cancer Care Ontario, Mayo Clinic, and the Universities of Queensland and Melbourne). At enrollment, a standardized interview ascertained multivitamin use in the year prior to diagnosis. A follow-up questionnaire was administered approximately 5 years after baseline, with 2,586 participants providing information on their multivitamin use at both time points. Survival outcomes were identified through linkage to national death registries. Delayed-entry Cox regression was used to estimate the association between patterns of multivitamin use and overall or CRC-specific survival (Hazard Ratio (HR) and 95% Confidence Interval (CI)), with survival time beginning at the 5-year follow-up survey. Models were adjusted for age at diagnosis, sex, body mass index, smoking history, stage, study center, and number of days from diagnosis to baseline survey. Over a median 4.8 years after the follow-up survey, 397 participants died (103 from CRC). Multivitamin use was common: at the 5-year follow-up, 37% reported continued use since before diagnosis, 12% had initiated use, 17% had discontinued use, and only 34% participants reported never using multivitamins. Compared to never use of multivitamins, continued use was significantly associated with increased subsequent overall survival (HR = 0.71, 95% CI: 0.55–0.91). However, this association did not reach statistical significance for CRC-specific survival (HR = 0.76, 95% CI: 0.47–1.24). No significant association was observed for discontinuing (HR = 0.92, 95% CI: 0.68–1.25) or initiating (HR = 0.80, 95% CI: 0.55–1.13) multivitamin use from baseline to follow-up, compared to never users, though initiating use trended towards increased survival. These findings suggest that continuing multivitamin use after a CRC diagnosis may increase survival; replication and details on the specific micronutrients included are needed.