Main characteristics of vitamin B6 biomarkers in terms of primary confounders, and linkage with metabolism and distribution of B6 vitamers and metabolites. The vertical lines to the left with a bullet at the end indicate confounders with positive (blue bullet) or negative (red bullet) effect modification. The size of the bullets indicates the effect size. Abbreviation used: 2OG, 2-oxoglutarate; 4-PA, 4-pyridoxic acid; AT, aminotransferase; Cys, cysteine; Cysta, cystathionine; Glu, glutamate; Gly, glycine; Hcy, homocysteine; HK, 3-hydroxykynurenine; Kyn, kynurenine; Met, methionine; PAr, PA/(PLP+PL) ratio; PL, pyridoxal; PLP, pyridoxal 5′-phosphate; PM, pyridoxamine; PMP, pyridoxamine 5′-phosphate; PN, pyridoxine; PNP, pyridoxine 5′-phosphate; Ser, serine; Trp, tryptophan; XA, xanthurenic acid.
*Urinary excretion of kynurenines may change during inflammation.