Markers of vitamin B6 status and metabolism as predictors of incident cancer: The Hordaland Health Study

Dietary intake and/or circulating concentrations of vitamin B6 have been associated with risk of cancer, but results are inconsistent and mechanisms uncertain. Pyridoxal 5'-phosphate (PLP) is the most commonly used marker of B6 status. We recently proposed the ratio 3-hydroxykynurenine/xanthurenic acid (HK/XA) as an indicator of functional vitamin B6 status, and the 4-pyridoxic acid (PA) /(pyridoxal (PL) +PLP) ratio (PAr) as a marker of vitamin B6 catabolism during inflammation. We compared plasma PLP, HK/XA and PAr as predictors of cancer incidence in a prospective community-based cohort in Norway. This study included 6,539 adults without known cancer at baseline (1998-99) from the Hordaland Health Study (HUSK). HR and 95% CI were calculated for the risk of overall and site-specific cancers using multivariate Cox proportional hazards regression with adjustment for potential confounders. After a median follow-up time of 11.9 years, 963 cancer cases (501 men and 462 women) were identified. Multivariate-adjusted Cox-regression showed no significant relation of plasma PLP or HK/XA with risk of incident cancer. In contrast, PAr was significantly associated with risk of cancer with HR (95% CI)=1.31 (1.12-1.52) per two standard deviation (SD) increment (p

What's new? Vitamin B6 status is reflected in the measure of its active form, pyridoxal 5'-phosphate (PLP). Studies disagree, however, as to whether or not PLP measures are meaningful in relation to cancer risk, which has necessitated a search for additional markers of vitamin B6 status. In this study, inflammation-related changes in vitamin B6 catabolism were captured effectively by a novel marker, the 4-pyridoxic acid (PA) /(pyridoxal (PL)+PLP) ratio (PAr). Analyses based on the detection of PAr suggest that increased vitamin B6 metabolism and disposal are linked to increased cancer risk, particularly for lung cancer.