Relationship of vitamin D with insulin resistance and disease severity in non-alcoholic steatohepatitis

Abstract

The role of plasma vitamin D deficiency in the development of non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) remains poorly understood. Previous studies have suggested a role for vitamin D deficiency in the pathogenesis of NAFLD/NASH, but they have been rather small, and/or NAFLD was diagnosed using only aminotransferases or liver ultrasound. This study aimed to assess the role of vitamin D deficiency in relationship to liver fat accumulation and severity of NASH. A total of 239 patients were recruited and state-of-the-art techniques were used to measure insulin resistance (euglycemic insulin clamp with 3-(3)H-glucose), liver fat accumulation (magnetic resonance spectroscopy or (1)H-MRS), total body fat (dual energy X-ray absorptiometry), and severity of liver disease (liver biopsy). Patients were divided into 3 groups according to plasma 25-hydroxyvitamin D levels (normal: >30 ng/ml; insufficiency: 20-30 ng/ml; deficiency: <20 ng/ml). When well-matched for clinical parameters (BMI, total adiposity, or prevalence of prediabetes/type 2 diabetes), no significant differences were observed among groups in terms of skeletal muscle, hepatic, or adipose tissue insulin sensitivity, the amount of liver fat by (1)H-MRS, or the severity of histological inflammation, ballooning, or fibrosis. Patients were then divided according to liver histology into those with definite NASH and those without NASH. Although patients with NASH had higher insulin resistance, plasma vitamin D concentrations were similar between both groups. Our results suggest that plasma vitamin D levels are not associated with insulin resistance, the amount of liver fat accumulation, or the severity of NASH.