Systemic Complications of Nonalcoholic Fatty Liver Disease: When the Liver Is Not an Innocent Bystander

Abstract

The top three leading causes of death in patients with nonalcoholic fatty liver disease (NAFLD) in descending order are cardiovascular disease, cancer, and liver disease. It is clear now that the increased risk of metabolic and macro- and microvascular complications in NAFLD stems from the associated features of metabolic syndrome. However, NAFLD itself may contribute to the spectrum of risk factors associated with insulin resistance. The primary focus of this review is to summarize the main systemic associations of NAFLD, as well as to discuss the mechanisms that link them to NAFLD. Hepatic lipid accumulation in NAFLD impairs hepatic glucose and lipid metabolism further increasing the risk of type 2 diabetes mellitus and of cardiovascular disease, independently of established risk factors. The incidence, prevalence, and severity of these complications are proportional to the histological severity of liver damage suggesting that NAFLD, but particularly nonalcoholic steatohepatitis, can also contribute to the low-grade inflammatory state through the systemic release of several markers of inflammation, oxidative stress, and of procoagulant factors. The clinical implication of these findings is that patients with NAFLD require a multidisciplinary evaluation, with a major focus on type 2 diabetes mellitus and cardiovascular disease complications and may benefit from more intensive surveillance and early treatment interventions to decrease the risk for cardiovascular and kidney complications.