Bone metabolism in non-alcoholic fatty liver disease: vitamin D status and bone mineral density

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease and abnormal liver enzyme worldwide. NAFLD is reported to be associated with other extra-hepatic diseases including cardiovascular disease, diabetes mellites and thyroid gland abnormalities. Liver is also the source of many proteins involved in bone metabolism and is the regulator of several bone metabolism pathways. Although underlying pathogenesis is not clear, the association between NAFLD and low bone mineral density (BMD) in the forms of osteoporosis and osteopenia has been recently reported. This study aimed to review current evidences supporting the association between bone metabolism including low BMD and serum vitamin D level in patients with NAFLD. Epidemiolocal studies indicating lower BMD and vitamin D in patients with NAFLD have been reviewed. The main pathophysiological mechanisms including association of insulin resistance, serum adiponectin, ghrelin, osteopontin, osteoprotegerin, and osteocalcin with NAFLD and low BMD have been briefly reviewed and summarized. Results of current clinical trials investigating the role of vitamin D supplementation for treatment of hepatic steatosis and non-alcoholic steatohepoatitis (NASH) have been also summarized. As a conclusion, increasing evidences are now available suggesting low BMD in patients with NAFLD. Some of these studies showed association of NAFLD severity with low vitamin D and BMD. Screening and surveillance of skeletal system regarding osteoporosis/osteomalacia in patients with NAFLD may be considered in future strategies and guidelines for NAFLD management.