Shiftwork Is Not Associated with Increased Risk of NAFLD: Findings from the National Health and Nutrition Examination Survey

There is increased focus on the metabolic impact of shiftwork, especially given the significant number of employees who work nighttime or rotating shifts. Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. We conducted a cross-sectional study to examine the association between shiftwork and the risk of NAFLD. We used aggregated data from the 2005-2006, 2007-2008, and 2009-2010 cycles of the National Health and Nutrition Examination Survey (NHANES). We defined NAFLD by elevated serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels (males: AST > 40 or ALT > 37; females: AST > 31 or ALT > 31) in the absence of excessive alcohol use and viral hepatitis. We defined shiftworkers as participants who self-reported currently working regular night shifts or rotating shifts. We calculated adjusted odds ratios (OR) and 95% confidence intervals (CI) using multivariable logistic regression. Overall, 8159 participants aged 20-79 years reported working at a job or business using the NHANES Occupation Questionnaire and were included in the analysis. Of these, 11.1% were classified as shiftworkers. Compared to non-shiftworkers, shiftworkers were younger, were less likely to be non-Hispanic White, and have health insurance or health care. The overall prevalence of NAFLD was 15.7%. NAFLD occurred more frequently in shiftworkers (17.0%) than non-shiftworkers (15.5%). However, in the overall multivariable analysis, shiftwork was not associated with the risk of NAFLD (OR 1.11, 95% CI 0.87-1.43). The findings from this NHANES-based cross-sectional study do not support an association between shiftwork and increased risk of NAFLD.