Recent prospective evidence suggests that vitamin B6, which is involved in DNA synthesis and methylation, may influence the risk of colorectal neoplasia. We examined the association between plasma vitamin B6 (pyridoxal 5′‐phosphate, PLP) and colorectal cancer risk in a female cohort, the Nurses' Health Study (NHS), and two male cohorts, the Health Professionals Follow‐up Study (HPFS), and the Physicians' Health Study (PHS). A total of 570 cases were identified up through 2000 (2004 for HPFS) and individually matched to two controls. Multivariable adjusted relative risks and 95% confidence intervals (CI) were calculated using conditional logistic regression. Men had higher plasma PLP levels compared to the women (geometric mean in controls (pmol/ml): HPFS: 98; PHS: 70; NHS: 53). In the HPFS, we observed a non‐linear reduction in risk; relative risks (RR) and 95% CIs for increasing levels of plasma PLP from quartile 1 to 4 were: 1.00 (ref), 0.81 (0.47–1.40), 0.57 (0.32–1.02), and 1.04 (0.60–1.79; median 203 pmol/ml). The association in women tended to be more linear; women in quartile 4 (median 131 pmol/ml) versus quartile 1 had a RR of 0.56 (0.31–1.01; previously published). The strongest inverse association was observed in the PHS with an apparent threshold effect starting at the median level; the RR for Q4 vs Q1 was 0.52 (0.29–0.93; previously published). We pooled the results from the three cohorts using meta‐analytic techniques and the relative risks were 0.84 (0.62–1.14), 0.60 (0.41–0.88), and 0.68 (0.44–1.06) across the quartiles. Our results strongly suggest that low vitamin B6 levels are associated with an increased risk of colorectal cancer. However, there may be a threshold level above which additional plasma levels of PLP has marginal, if any, benefit.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):B102.