Impact of cigarette smoking on onset of nonalcoholic fatty liver disease over a 10-year period

Background Metabolic syndrome, which includes obesity, hyperglycemia, dyslipidemia, and hypertension, is a major risk factor for the development of nonalcoholic fatty liver disease (NAFLD). Cigarette smoking is a well-known risk factor for metabolic syndrome, but the epidemiological impact of cigarette smoking on development of NAFLD is unclear. Methods In this retrospective study, 2,029 subjects underwent a complete medical health checkup in 1998 and again in 2008. Those who were positive for hepatitis B surface antigen or hepatitis C virus antibody, or had an alcohol intake of > 20 g/day as assessed by questionnaire, were excluded. Fatty liver was diagnosed by abdominal ultrasonography. Independent risk factors associated with the development of NAFLD were determined by multiple logistic regression analysis. Smoking status was expressed using the Brinkman index (BI), which was calculated as the number of cigarettes smoked per day multiplied by the number of years of smoking. Results Of 1,560 subjects without NAFLD in 1998, 266 (17.1%) were newly diagnosed with NAFLD in 2008. Multiple logistic analysis identified age [adjusted odds ratio (AOR) 0.95, 95% confidence interval (95% CI) 0.94-0.97], male sex (AOR 1.46, 95% CI 1.01-2.10), body mass index a parts per thousand yen25 (AOR 3.08, 95% CI 2.20-4.32), dyslipidemia (AOR 1.79, 95% CI 1.25-2.58) and cigarette smoking (AOR 1.91, 95% CI 1.34-2.72) as risk factors associated with the development of NAFLD. Smoking status at baseline was also associated with the development of NAFLD (BI 1-399: AOR 1.77, 95% CI 1.02-3.07, BI a parts per thousand yen400: AOR 2.04, 95% CI 1.37-3.03). Conclusion Cigarette smoking is an independent risk factor for onset of NAFLD.