Vitamin B-6 nutrition status and cigarette smoking.

: We investigated the vitamin B-6 status in smokers, nonsmokers, and exsmokers by measuring both B-6 aldehyde vitamers, pyridoxal-5'-phosphate (PLP) and pyridoxal (PL), in the plasma as well as in the erythrocyte compartment. Two hundred eighty-six healthy, sedentary male workers from a middle-income group were investigated. There were 159 smokers, 59 exsmokers, and 68 nonsmokers. Plasma PLP and PL concentrations were significantly lower in smokers than in the nonsmokers and exsmokers whereas erythrocyte PLP and PL did not differ significantly between groups. Because PLP mainly functions as an intracellular coenzyme, the clinical significance of a depressed plasma PLP concentration alone is uncertain. It is concluded that circulating plasma PLP is labile and not necessarily indicative of intracellular PLP concentrations. The measurement of erythrocyte PLP and/or PL may be more informative about vitamin B-6 status than is plasma PLP alone.