Tobacco use is associated with increased plasma BDNF levels in depressed patients.

Since serum Brain Derived Neurotrophic Factor (BDNF) levels are higher in tobacco smokers than in non-smokers and since Major Depressive Disorder (MDD) is associated with a 2-fold increased risk of smoking, we assessed the association of smoking and plasma BDNF levels in 359 depressed MDD patients. Plasma BDNF levels were positively correlated with the magnitude of tobacco consumption (current number of cigarettes/day and number of packs/year). Accordingly, current tobacco users had significantly higher plasma BDNF levels than non-users. In further studies of MDD, peripheral measures of BDNF should take into account tobacco use.