Epidemiology and Natural History of Nonalcoholic Fatty Liver Disease and Nonalcoholic Steatohepatitis

As the prevalence of obesity and type 2 diabetes mellitus rises, so does the prevalence of NAFLD. In 2016, the global prevalence of NAFLD was estimated to be 24% and has grown to a current estimation of 30%. However, rates vary by country where Latin America, the Middle East and North Africa (MENA) reportedly have the highest NAFLD prevalence. The prevalence of NAFLD increases as age increases, but rates appear to peak at around 60–65 years old. Approximately 10% more men are diagnosed with NAFLD than women, but after menopause the prevalence rates become almost equal. NAFLD prevalence is higher in subpopulations, especially the obese and/or those with metabolic syndrome. The prevalence of lean NAFLD is 11.2% in the general population and 25.3% in the NAFLD population. The global prevalence of nonalcoholic steatohepatitis (NASH) is estimated to be 2–6% in the general population. Overall mortality related to NAFLD is 15–20 cases per 1000 person-years and increases substantially in those with NASH and in NASH patients who have components of metabolic syndrome. Sarcopenia also appears to be a significant factor in adverse outcomes among those with NAFLD. Advanced fibrosis is noted in up to 7% of the NAFLD population but ranges in prevalence among NASH from 21 to 50%. Both NAFLD and NASH can regress with significant weight loss of 5–10% of body weight. However, both can progress in the presence of inflammatory mediators, insulin resistance, type 2 diabetes, certain genes and exposure to environmental factors such as a diet high in fructose. As such, NAFLD and NASH are complex diseases that require a multidisciplinary treatment approach.