Decreased Physical Working Capacity in Adolescents With Nonalcoholic Fatty Liver Disease Associates With Reduced Iron Availability.

ABSTRACT

BACKGROUND & AIMS: Non-alcoholic fatty liver disease (NAFLD) is common and related to obesity and insulin resistance. Iron metabolism is impaired in obese individuals and iron deficiency has been associated with physical inactivity. We investigated whether iron bioavailability is reduced in patients with NAFLD and contributes to reduced cardiorespiratory fitness. METHODS: We collected information on weight-adjusted, submaximal physical work capacity (PWC), ultrasound-determined hepatic steatosis, iron indices, and hematologic and metabolic parameters from 390 female and 458 male participants of the Raine Study-a longitudinal study of disease development in 2868 children in Western Australia. X2 and linear regression analyses were used to compare characteristics of study participants according to NAFLD status at age 17 years. RESULTS: Fourteen percent of the cohort had NAFLD. PWC was significantly reduced in adolescents with NAFLD compared to adolescents without NAFLD (reduction of 0.17 W/kg, P = .0003, adjusted for sex and body mass index [BMI]). Iron bioavailability (assessed by mean corpuscular volume [MCV], mean corpuscular haemoglobin [MCH], transferrin saturation, and serum levels of iron) was inversely correlated with BMI in adolescents with NAFLD (P ≤ .01 for all, adjusted for sex) but not in adolescents without NAFLD (P > .30). MCV and MCH correlated with PWC (MCV, P = .002 for female and P = .0003 male participants; MCH, P = .004 for female and P = .01 for male participants), irrespective of NAFLD status. Reduced PWC was associated with lower transferrin saturation in adolescents with NAFLD (reduction of 0.012 W/kg per unit decrease in transferrin saturation, P = .007) but not in adolescents without NAFLD (reduction of 0.001 W/kg, P = .40), adjusted for sex. This association was independent of MCV or MCH. CONCLUSIONS: In a well-defined cohort of adolescents, we found NAFLD to be associated with decreased cardiorespiratory fitness, independent of BMI. The relationship between transferrin saturation and PWC in adolescents with NAFLD indicates that functional iron deficiency might contribute to reductions in cardiorespiratory fitness.