Vitamin, vitamer, and metabolite measurements and status markers
peripheral venous blood samples
EDTA plasma was obtained by centrifugation of peripheral venous blood samples at 1,600As functional markers of vitamin B6 status, we calculated the plasma 3′-hydroxykynurenine ratio (HK ratio [HK:KA+AA+XA+HAA], a higher ratio reflecting effects of vitamin B6 insufficiency on tryptophan catabolism), along with the cystathionine/cysteine ratio (a higher ratio reflecting effects of vitamin B6 insufficiency on transsulfuration pathway regulation) [