Post‐diagnostic multivitamin supplement use and colorectal cancer survival: A prospective cohort study.

Background: Use of multivitamin supplements has been associated with lower incidence of colorectal cancer (CRC). However, its influence on CRC survival remains unknown. Methods: Among 2424 patients with stage I–III CRC who provided detailed information about multivitamin supplements in the Nurses' Health Study and Health Professionals Follow‐up Study, the authors calculated multivariable hazard ratios (HRs) of multivitamin supplements for all‐cause and CRC‐specific mortality according to post‐diagnostic use and dose of multivitamin supplements. Results: During a median follow‐up of 11 years, the authors documented 1512 deaths, among which 343 were of CRC. Compared to non‐users, post‐diagnostic users of multivitamin supplements at a dose of 3–5 tablets/week had lower CRC‐specific mortality (HR, 0.55; 95% confidence interval [CI], 0.36–0.83, p =.005), and post‐diagnostic users at doses of 3–5 and 6–9 tablets/week had lower all‐cause mortality (HR, 0.81; 95% CI, 0.67–0.99, p =.04; HR, 0.79; 95% CI, 0.70–0.88), p <.001). The dose–response analysis showed a curvilinear relationship for both CRC‐specific (pnonlinearity <.001) and all‐cause mortality (pnonlinearity =.004), with the maximum risk reduction observed at 3–5 tablets/week and no further reduction at higher doses. Compared to non‐users in both pre‐ and post‐diagnosis periods, new post‐diagnostic users at dose of <10 tablets/week had a lower all‐cause mortality (HR, 0.81; 95% CI, 0.71–0.94, p =.005), whereas new users at a dose of ≥10 tablets/week (HR, 1.58; 95% CI, 1.07–2.33) and discontinued users (HR, 1.35; 95% CI, 1.14–1.59) had a higher risk of mortality. Conclusions: Use of multivitamin supplements at a moderate dose after a diagnosis of nonmetastatic CRC is associated with lower CRC‐specific and overall mortality, whereas a high dose (≥10 tablets/week) use is associated with higher CRC‐specific mortality. In this prospective study of 2424 patients with stage I–III colorectal cancer (CRC), the authors observed a curvilinear relationship in the use of multivitamin supplements: compared to non‐users, users at a dose of 3–9 tablets/week had a lower risk of CRC‐specific and all‐cause mortality, whereas users at a dose higher than 10 tablets/week had a higher CRC‐specific mortality. [ABSTRACT FROM AUTHOR]