Abstract
Accumulation of fat in the liver and skeletal muscle is associated with obesity and poor health outcomes. Liver steatosis is a characteristic of non-alcoholic fatty liver disease (NAFLD) and myosteatosis, of poor muscle quality in sarcopenia. In this study of 403 men (33–96 years), we investigated associations between the fatty liver index (FLI) and muscle density, as markers of fat accumulation in these organs. We also investigated associations between the FLI and parameters of sarcopenia, including DXA-derived appendicular lean mass (ALM) and handgrip strength by dynamometry. Muscle density was measured using pQCT at the radius and tibia. FLI was calculated from BMI, waist circumference, and levels of triglycerides and gamma-glutamyltransferase. There was a pattern of decreasing muscle density across increasing quartiles of FLI. After adjusting for age and lifestyle, mean radial muscle density in Q4 was 2.1% lower than Q1 (p < 0.001) and mean tibial muscle density was 1.8% lower in Q3 and 3.0% lower in Q4, compared to Q1 (p = 0.022 and < 0.001, respectively). After adjusting for age and sedentary lifestyle, participants in the highest FLI quartile were sixfold more likely to have sarcopenia. In conclusion, our results suggest that fat accumulation in the liver co-exists with fat infiltration into skeletal muscle.
Highlights
Deposition of ectopic fat in the liver and infiltration of fat into skeletal muscle are both associated with impaired physiological function [1] and poor health outcomes [2]
Liver steatosis is a characteristic of non-alcoholic fatty liver disease (NAFLD) [2], and myosteatosis is a characteristic of poor muscle quality in sarcopenia [3]
Indices of adiposity, including mean body mass index (BMI), waist circumference, fat mass, %BF, android-togynoid ratio (AGR), and median triglyceride and GGT levels increased across increasing fatty liver index (FLI) quartiles; no interquartile differences were detected in median age
Summary
Deposition of ectopic fat in the liver (liver steatosis) and infiltration of fat into skeletal muscle (myosteatosis) are both associated with impaired physiological function [1] and poor health outcomes [2]. Sequelae of fat infiltration into skeletal muscle include muscle atrophy, reduced muscle mass and muscle dysfunction [3, 5, 7, 8], and higher mortality [9]. This is due, at least in part, to the adipose tissue in muscle producing and releasing adipokines and inflammatory factors that act locally and systemically [10]. The accumulation of intramuscular lipid disrupts cellular energy homeostasis and leads to reduced protein synthesis, calcium imbalance and loss of contractile function, strength and exercise capacity [10]
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