Abstract
Objective Cigarette smoke and non-alcoholic fatty liver disease are risk
factors for type 2 diabetes mellitus. However, the impact of smoking on diabetes
risk among patients with non-alcoholic fatty liver disease remains unclear.
Methods This study included 15,464 Japanese individuals. We defined
non-alcoholic fatty liver disease based on abdominal ultrasound findings where
excess alcohol intake and other liver diseases were excluded. We used Cox
proportional regression analysis to identify risk factors for type 2 diabetes
onset.
Results During 16,446 person-years of follow-up, 223 of 2,714
non-alcoholic fatty liver disease patients developed type 2 diabetes; the
cumulative incidence rate of type 2 diabetes was 13.6 per 1,000 person-years.
The proportions of never, former, and current smokers (self-report) were
35.3%, 31.1%, and 33.6%, and 88.5%,
5.1%, and 6.4% in men and women, respectively. In a Cox
regression model adjusted for sex, age, body mass index, waist circumference,
alcohol intake, exercise, and alanine aminotransferase, aspartate
aminotransferase, gamma-glutamyl transferase, lipid profiles, and blood pressure
values, relative to never smokers, current smokers with non-alcoholic fatty
liver disease had an increased risk of type 2 diabetes (hazard
ratio=2.05; 95% confidence interval: 1.43–2.94). In
addition, former smoking affected the risk of type 2 diabetes; however, this
effect was not statistically significant.
Conclusions This longitudinal study showed that current smoking may act as
a “second hit” and increase the risk of type 2 diabetes in
patients with non-alcoholic fatty liver disease.
Key words
Cigarette smoking - Type 2 diabetes mellitus - Non-alcoholic fatty liver disease
