Relationship between adipose tissue dysfunction, vitamin D deficiency and the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease(NAFLD)is the most common chronic liver disease worldwide.Its pathogenesis is complex and not yet fully understood.Over the years many studies have proposed various pathophysiological hypotheses,among which the currently most widely accepted is the"multiple parallel hits"theory.According to this model,lipid accumulation in the hepatocytes and insulin resistance increase the vulnerability of the liver to many factors that act in a coordinated and cooperative manner to promote hepatic injury,inflammation and fibrosis.Among these factors,adipose tissue dysfunction and subsequent chronic low grade inflammation play a crucial role.Recent studies have shown that vitamin D exerts an immune-regulating action on adipose tissue,and the growing wealth of epidemiological data is demonstrating that hypovitaminosis D is associated with both obesity and NAFLD.Furthermore,given the strong association between these conditions,current findings suggest that vitamin D may be involved in the relationship between adipose tissue dysfunction and NAFLD.The purpose of this review is to provide an overview of recent advances in the pathogenesis of NAFLD in relation to adipose tissue dysfunction,and in the pathophysiology linking vitamin D deficiency with NAFLD and adiposity,together with an overview of the evidence available on the clinical utility of vitamin D supplementation in cases of NAFLD.

Overview of studies of the vitamin D/vitamin D receptor system in the development of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease(NAFLD)is the most common chronic liver disease in the world.NAFLD is known to be associated with obesity,type 2 diabetes,metabolic syndrome and increased cardiovascular events:for these reasons,it is becoming a global public health problem and represents an important challenge in terms of prevention and treatment.The mechanisms behind the pathogenesis of NAFLD are multiple and have not yet been completely unraveled;consequently,at moment there are not effective treatments.In the past few years a large body of evidence has been assembled that attributes an important role in hepatic aberrant fat accumulation,inflammation and fibrosis,to the vitamin D/vitamin D receptor(VD/VDR)axis,showing a strong association between hypovitaminosis D and the diagnosis of NAFLD.However,the data currently available,including clinical trials with VD supplementation,still provides a contrasting picture.The purpose of this editorial is to provide an overview of recent advances in the pathogenesis of NAFLD in relation to VD/VDR.Based on recent data from literature,we focused in particular on the hypothesis that VDR itself,independently from its traditional ligand VD,may have a crucial function in promoting hepatic fat accumulation.This might also offer new possibilities for future innovative therapeutic approaches in the management of NAFLD.