Introduction: Physical activity (PA) is inversely associated with nonalcoholic fatty liver disease (NAFLD) prevalence. However, there have been few studies to date that have evaluated the effect of PA on incident NAFLD with respect to visceral adipose tissue (VAT) and insulin resistance. We investigated whether PA at baseline and change in PA habits during follow-up have any effect on incident NAFLD.
Methods: We enrolled subjects who underwent health screenings between 2007 and 2008 and then participated in a voluntary follow-up health screening between 2011 and 2013. Incident NAFLD was defined as NAFLD absence at baseline and presence at follow-up based on hepatic ultrasonographic findings. PA was measured using a metabolic equivalent-based on detailed PA questionnaire at baseline and follow-up, and the difference in total PA during the follow-up period was calculated. Clinical and laboratory metabolic parameters and computed tomography-measured VAT were also evaluated.
Results: A total of 1,373 subjects were enrolled in the analysis, and 288 subjects (21.0%) developed NAFLD during the follow-up. Both total PA and leisure-time PA at baseline were inversely associated with incident NAFLD after adjustment for known risk factors (p for trend = 0.007 and 0.002, respectively). Decreased PA at follow-up compared with baseline was associated with an increased risk for incident NAFLD after adjusting for age, gender, body mass index, smoking, hypertension, diabetes, and diet [hazard ratio (HR) 1.45, 95% confidence interval (CI) 1.04-2.02, 4th quartile (most decreased PA) vs. 1st quartile (increased PA), p = 0.028]. This relationship was attenuated but remained statistically significant even after adjustment for VAT (HR 1.44, 95% CI 1.03-2.01, 4th quartile vs. 1st quartile) and insulin resistance (HR 1.50, 95% CI 1.06-2.14, 4th quartile vs. 1st quartile).
Conclusion: This study shows that PA at baseline had an independent protective effect on incident NAFLD after a 4-year follow-up period. In addition, sustained or increased PA had a preventive effect on incident NAFLD independent of visceral obesity and insulin resistance. These findings suggest beneficial effects of PA on incident NAFLD.