Long-term use of multivitamins and risk of colorectal adenoma in women

BACKGROUND: Use of multivitamins may reduce the risk of colorectal adenoma, but the duration of use needed is unclear. METHODS: We prospectively examined years of multivitamin use and risk of colorectal adenoma among 43,641 women who had a first endoscopy between 1991 and 2007 in the Nurses' Health Study II. Use of multivitamins was assessed through biennial questionnaires since 1989. RESULTS: We documented 2277 colorectal adenoma cases. Reporting multivitamin use at any time during the study period compared with never reporting its use was associated with a reduced risk of adenoma (multivariable relative risk (RR)=0.86, 95% confidence interval (CI): 0.76-0.97). There was no clear trend with duration of multivitamin use: years of use compared with never use, ≤ 4 years (RR=0.84, 95% CI: 0.74-0.96), 5-9 years (RR=0.89, 95% CI: 0.77, 1.02), 10-14 years (RR=0.86, 95% CI: 0.74, 1.01), 15-19 years (RR=0.85, 95% CI: 0.70, 1.02), and 20-26 years (RR=0.80, 95% CI: 0.64, 1.01); (P trend=0.87). The strongest associations (years of use vs never user) were for size of adenoma: large (≥ 1 cm) <4 years (RR=0.75, 95% CI: 0.58-0.96) and in alcohol users (≥ 1.4 g per day) 20-26 years (RR=0.67, 95% CI: 0.49-0.91). CONCLUSION: Our findings suggest that use of multivitamins is associated with lower risk of colorectal adenoma, even with relatively short duration of use.