The associations between modifiable risk factors and nonalcoholic fatty liver disease: A comprehensive Mendelian randomization study

BACKGROUND AND AIMS: Early identification of modifiable risk factors is essential for the prevention of nonalcoholic fatty liver disease (NAFLD). We aimed to systematically explore the relationships between genetically predicted modifiable risk factors and NAFLD. APPROACH AND RESULTS: We applied univariable and multivariable Mendelian randomization analyses to explore the relationships between 35 modifiable risk factors and NAFLD. We also evaluated the combined results in three independent large genome-wide association studies. Genetically predicted alcohol frequency, elevated serum levels of liver enzymes, triglycerides, C-reactive protein, and obesity traits, including body mass index, waist circumference, and body fat mass, were associated with increased risks of NAFLD (all with p < 0.05). Poor physical condition had a suggestive increased risk for NAFLD (odds ratio [OR] = 2.63, p = 0.042). Genetically instrumented type 2 diabetes (T2DM), hypothyroidism, and hypertension all increased the risk for NAFLD, and the ORs (95% confidence interval) were 1.508 (1.20-1.90), 13.08 (1.53-111.65), and 3.11 (1.33-7.31) for a 1-U increase in log-transformed odds, respectively. The positive associations of T2DM and hypertension with NAFLD remained significant in multivariable analyses. The combined results from the discovery and two replication datasets further confirmed that alcohol frequency, elevated serum liver enzymes, poor physical condition, obesity traits, T2DM, and hypertension significantly increase the risk of NAFLD, whereas higher education and high-density lipoprotein cholesterol (HDL-cholesterol) could lower NAFLD risk. CONCLUSIONS: Genetically predicted alcohol frequency, elevated serum liver enzymes, poor physical condition, obesity traits, T2DM, and hypertension were associated with an increased risk of NAFLD, whereas higher education and HDL-cholesterol were associated with a decreased risk of NAFLD.