The increasing burden of nonalcoholic fatty liver disease among young adults in the United States: A growing epidemic
Authors: Rachel Abou Mrad, Nawal Merjaneh, Ghassan Mubarak, Rocio Lopez, Nizar N. Zein, Naim Alkhouri
Journal: Hepatology (2016)

Potential conflict of interest: Nothing to report. TO THE EDITOR: A silent epidemic of chronic liver disease (CLD) is affecting young adults in the United States because of the surge in intravenous drug use, alcohol use, and obesity. Nonalcoholic fatty liver disease (NAFLD) is a common cause of CLD and its prevalence continues to rise in parallel with the growing obesity epidemic.1 The aim of this study was to estimate changes in NAFLD prevalence among U.S. young adults and to assess factors associated with suspected NAFLD. Cross‐sectional data from 14,371 subjects between 18 and 35 years of age, who were enrolled in the National Health and Examination Survey (NHANES) in three periods (1988‐1994, 1999‐2004, and 2005‐2010) were used to estimate trends in suspected NAFLD. Exclusion criteria included known CLD, treatment with hepatotoxic medications, heavy drinking, missing alanine aminotransferase (ALT), or missing body mass index (BMI). NAFLD was defined as elevated ALT in subjects with BMI ≥25 kg/m2. Elevated ALT was defined either as >30 U/L for males and >19 U/L for females. Other cutoffs for elevated ALT were explored including >40 U/L for males and >30 U/L for females or >50 U/L for males and >45 U/L for females. Regression analysis was used to assess trends across the different time periods. In addition, logistic regression analysis was used to assess factors associated with suspected NAFLD. P values of <0.05 were used to assess statistical significance. There was a step‐wise increase in suspected NAFLD prevalence among young adults when using all three cutoffs of ALT (Fig. 1). Prevalence rose from 9.6% (0.81) in 1988‐1994 to 24.0% (0.83) in 2005‐2010 (P value <0.001) when NAFLD was defined as ALT >30 U/L for males or >19 U/L for females. In stratified analyses, increasing trends in suspected NAFLD prevalence were observed among all ethnic subgroups, among both males and females, and among those overweight or obese. Prevalence of NAFLD in the 2005‐2010 period was highest among Mexican Americans and those with BMI >40 kg/m2 (35.3% [1.6] and 57.4% [4.7], respectively; P < 0.05 for both). On multivariable analysis, older age, male sex, ethnicity (Mexican American), and study period were found to be associated with higher odds of having suspected NAFLD. Our study has several limitations, including the cross‐sectional nature of NHANES, which does not allow the investigation of a sample population over time. The true prevalence of NAFLD is probably higher than what we report, given the fact that NAFLD may affect lean individuals and those with completely normal ALT values. Finally, we were not able to assess the severity of NAFLD in terms of presence of steatohepatitis and stage of liver fibrosis.Figure 1: Prevalence of suspected NAFLD among young adults in the United States, NHANES 1988‐1994 and 1999‐2010.This study has shown that prevalence of suspected NAFLD has more than doubled over the past three decades and now affects one quarter of U.S. young adults. Measures should be taken to target young adults for screening for CLD in order to prevent the development of cirrhosis and its complications.