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.