Plasma neuropeptide Y levels relate cigarette smoking and smoking cessation to body weight regulation

Loss and disproportionate gain of body weight often seen respectively in smokers and quitters are believed to be due to disrupted energy homeostasis induced by nicotine, the major constituent of cigarette smoke. Energy homeostasis is suggested to be regulated by the coordinated actions of peripheral adipose tissue derived leptin and the brain hypothalamic orexigenic neuropeptide Y (NPY). While the studies probing the role of leptin and NPY in weight modulating effect of nicotine have so far been inconsistent and based largely on animal systems, there is a paucity of data involving human subjects. Here we measured the plasma levels of orexigenic neuropeptide Y (NPY) and leptin in 35 non-smokers and 31 cigarette smokers before and three months after smoking cessation. Compared to non-smokers, smokers were leaner and had reduced NPY and leptin levels. Smoking cessation resulted in a significant weight gain and increased waist circumference accompanied by increased leptin and NPY levels. NPY levels were significantly correlated with body weight (r=0.43, p<0.05), BMI (r=0.41, p<0.05), and waist circumference (r=0.37, p<0.05), while leptin correlated with BMI (r=0.42, p<0.05) and waist circumference (r=0.39, p<0.05). Association of leptin with smoking status, but not that of NPY, was lost after controlling for anthropometric parameters. Weight modulating effect of cigarette smoke may thus involve its direct action on NPY, independent of leptin. Altered leptin levels in smokers and quitters may merely reflect changes in body weight or precisely fat mass.