Prospective cohort studies of vitamin B-6 intake and colorectal cancer incidence: Modification by time?

Abstract

Background: The relation between vitamin B-6 intake and colorectal cancer risk remains uncertain. Objective: We prospectively evaluated whether a higher vitamin B-6 intake in the remote past is more strongly associated with a lower risk of colorectal cancer than is an intake in the recent past in the Nurses' Health Study and the Health Professionals Follow-Up Study. Design: We assessed vitamin B-6 intake every 4 y by using validated food-frequency questionnaires and followed 86,440 women and 44,410 men for ≤28 y. Cox proportional hazards regression was used to estimate multivariable RRs and 95% CIs. Results: The total vitamin B-6 intake was significantly associated with an ∼20-30% lower risk of colorectal cancer in age-adjusted results, but this association became attenuated and nonsignificant after additional adjustment for nondietary and dietary factors. When the highest to lowest quintiles of cumulative total vitamin B-6 intake were compared, RRs (95% CIs) for colorectal cancer were 0.99 (0.80, 1.24; P-trend = 0.55) for women and 0.95 (0.73, 1.23; P-trend = 0.75) for men. For the same comparison, RRs were 0.92 (0.73, 1.16) for total vitamin B-6 intake 0-4 y before diagnosis, 0.99 (0.78, 1.26) for intake 4-8 y before diagnosis, 0.92 (0.71, 1.21) for intake 8-12 y before diagnosis, and 0.93 (0.69, 1.26) for intake 12-16 y before diagnosis in women. Corresponding RRs for men were 0.86 (0.63, 1.17), 0.96 (0.70, 1.32), 0.90 (0.63, 1.29), and 1.16 (0.75, 1.79). Results did not differ by cancer subsite, source of vitamin B-6 (food or supplement), alcohol consumption, or folate intake. Conclusion: Our data do not support a strong role of adulthood vitamin B-6 intake in colorectal carcinogenesis in these US health professionals. © 2012 American Society for Nutrition.