Burden of NAFLD in the U.S.
NAFLD is a manifestation of systemic metabolic abnormalities, including insulin resistance, dyslipidemia, central obesity, and hypertension. In this short review, we summarize data on the burden of NAFLD in the U.S. and its prognostic determinants and review what clinical and public health approaches may be needed to mitigating its impact.
Epidemiology of NAFLD
Worldwide, the prevalence of NAFLD is estimated at 6% to 35%, with biopsy-based studies reporting NASH in 3% to 5%.1 U.S. estimates for the prevalence of NAFLD range from 10% to 46%.2 In our own analysis of the National Health and Nutrition Examination Survey (NHANES) data, transient elastography-detected steatosis was found in 36%, which projected to a minimum of 73 million American adults.3
NAFLD represents a spectrum of disorders ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), the latter leading, in some cases, to progressive hepatic fibrosis and cirrhosis.4 Out of a large number of subjects with NAFLD, the proportions of NASH patients that develop severe liver problems such as end-stage liver disease (ESLD) or hepatocellular carcinoma (HCC) are progressively smaller. For example, we recently reported that less than 2,000 liver-related deaths are attributable to NAFLD in the U.S. per annum, which corresponds to a crude case fatality rate of < 0.005% per year.5
According to the Centers for Disease Control and Prevention (CDC), there have been substantial increases in liver-related deaths over the last 2 decades. Mortality from liver disease including hepatobiliary cancers more than doubled from 41,966 deaths (including 15,321 women and 26,645 men) in 2000 to 85,884 deaths (33,000 women and 52,884 men) in 2020. The proportion of deaths specifically attributed to NAFLD among liver-related deaths was miniscule in 2000, accounting for 1.1% in women and 0.7% in men. By 2020, the proportions increased several folds in both sexes (7.4% in women and 2.7% in men).6 Moreover, it is likely that a substantial portion of deaths from chronic liver disease from unknown causes (“cryptogenic”) are likely end-stage NAFLD, making these figures underestimates of the true impact of NAFLD in the U.S.
From a comparative epidemiologic perspective, there are significant racial and ethnic and socioeconomic disparities in NAFLD prevalence, wherein Hispanic persons and individuals experiencing food insecurity – independent of poverty status, education level, race and ethnicity – are disproportionately more affected by NAFLD.7,8 Furthermore, these disparities persist when examining long-term complications of NAFLD, such as developing HCC.
Prognosis in NAFLD: NASH versus fibrosis
Given the enormous prevalence and increasing public health burden of NAFLD, systematic interventions to mitigate its impact are urgently needed. Clearly, patients who already have developed advanced liver disease need to be directed to specialty care so the disease progression may be halted and complications of ESLD may be prevented or managed. On the other hand, in order to mitigate the future impact of ESLD, prompt identification of at-risk patients and proactive interventions to improve liver health are needed.