Active smoking, passive smoking, and risk of nonalcoholic fatty liver disease (NAFLD): a population-based study in China.

BACKGROUND: The effect of active smoking on development of nonalcoholic fatty liver disease (NAFLD) is controversial, and there are limited clinical data on the relationship between passive smoking and NAFLD. We investigated whether active and passive smoking are associated with NAFLD.

METHODS: A total of 8580 subjects (2691 men) aged 40 years or older participated in a community-based survey in Shanghai, China. Information on active and passive smoking was collected using a validated questionnaire. NAFLD was diagnosed by abdominal B-mode ultrasound testing and serum liver enzymes.

RESULTS: NAFLD prevalence was 29.4% in never smokers, 34.2% in former smokers, 27.8% in light smokers (<20 cigarettes/day), 30.8% in moderate smokers (20-39 cigarettes/day), and 43.5% in heavy smokers (≥40 cigarettes/day). Fully adjusted logistic regression analyses revealed that, as compared with never smoking, former and heavy smoking were associated with increased risk of prevalent NAFLD, with odds ratios of 1.45 (95% CI 1.05-2.00) and 2.29 (95% CI 1.30-4.03), respectively. Active smoking and body mass index (BMI) had a synergistic effect on the risk of prevalent NAFLD; the combination of these risk factors was associated with the highest observed odds ratio for NAFLD: 8.58. In never-smoking women, passive smoking during both childhood and adulthood was associated with a 25% increase in the risk of prevalent NAFLD (OR = 1.25, 95% CI 1.05-1.50) as compared with no passive smoking.

CONCLUSIONS: Passive smoking and heavy active smoking are associated with prevalent NAFLD in middle-aged and elderly Chinese. Active smoking and BMI have a synergistic effect on prevalent NAFLD.