Long- and short-term effects of tobacco smoking on circulating concentrations of B vitamins.

BACKGROUND: Smoking is associated with decreased concentrations of several antioxidant vitamins. We sought to determine the relation between circulating concentrations of selected B vitamins and smoking status, with particular attention to longitudinal associations.
METHODS: We used baseline data from 2 B-vitamin intervention trials that included 6837 patients with ischemic heart disease. Smoking habits were ascertained by interview. Vitamins and metabolites, including the nicotine metabolite cotinine, were measured in plasma and serum by microbiological assays or gas/liquid chromatography-tandem mass spectrometry.
RESULTS: The highest circulating concentrations of folate and pyridoxal 5'phosphate (PLP) and lowest concentrations of total plasma homocysteine, a functional marker of folate status, were observed for self-reported never smokers, followed by self-reported ex-smokers and current smokers (P(trend) < 0.001). Cobalamin and its functional marker methylmalonic acid were not associated with smoking status. Based on their low cotinine concentrations, we were able to identify a group of smokers that had abstained from smoking for 3 days or more. Compared with smokers with high plasma cotinine, smokers with low cotinine had significantly higher circulating concentrations of folate, PLP, and riboflavin (all P < 0.005), and this trend continued for ex-smokers, with increasing time since smoking cessation.
CONCLUSIONS: Smoking lowered circulating concentrations of folate, PLP, and riboflavin, but concentrations increased significantly after a few days of smoking cessation. We propose that short-term effects may be related to acute smoking-induced oxidative stress, whereas the longer-lasting effects among ex-smokers may reflect changes in diet and/or restoration of vitamin concentrations in tissue during the first few months to years after smoking cessation.