Physical activity attenuates the mid-adolescent peak in insulin resistance but by late adolescence the effect is lost: a longitudinal study with annual measures from 9-16 years (EarlyBird 66).
OBJECTIVE
The aim of this work was to test whether the mid-adolescent peak in insulin resistance (IR) and trends in other metabolic markers are influenced by long-term exposure to physical activity.


METHODS
Physical activity (7 day ActiGraph accelerometry), HOMA-IR and other metabolic markers (glucose, fasting insulin, HbA1c, lipids and BP) were measured annually from age 9 years to 16 years in 300 children (151 boys) from the EarlyBird study in Plymouth, UK. The activity level of each child was characterised, with 95% reliability, by averaging their eight annual physical activity measures. Age-related trends in IR and metabolic health were analysed by multi-level modelling, with physical activity as the exposure measure (categorical and continuous) and body fat percentage (assessed by dual-energy X-ray absorptiometry) and pubertal status (according to age at peak height velocity and Tanner stage) as covariates.


RESULTS
The peak in IR at age 12-13 years was 17% lower (p < 0.001) in the more active adolescents independently of body fat percentage and pubertal status. However, this difference diminished progressively over the next 3 years and had disappeared completely by the age of 16 years (e.g. difference was -14% at 14 years, -8% at 15 years and +1% at 16 years; 'physical activity × age(2), interaction, p < 0.01). Triacylglycerol levels in girls (-9.7%, p = 0.05) and diastolic blood pressure in boys (-1.20 mmHg, p = 0.03) tended to be lower throughout adolescence in the more active group.


CONCLUSIONS
Our finding that physical activity attenuates IR during mid-adolescence may be clinically important. It remains to be established whether the temporary attenuation in IR during this period has implications for the development of diabetes in adolescence and for future metabolic health generally.
Institute of Health Research, University of Exeter Medical School, Exeter, UK. b.metcalf@exeter.ac.uk.|Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, St Luke's Campus, Heavitree Road, Exeter, EX1 2LU, UK. b.metcalf@exeter.ac.uk.
Brad S
BS
Metcalf
Department of Endocrinology and Metabolism, Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, UK.
Joanne
J
Hosking
Institute of Health Research, University of Exeter Medical School, Exeter, UK.
William E
WE
Henley
Department of Endocrinology and Metabolism, Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, UK.
Alison N
AN
Jeffery
Institute of Health Research, University of Exeter Medical School, Exeter, UK.
Mohammod
M
Mostazir
Department of Endocrinology and Metabolism, Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, UK.
Linda D
LD
Voss
Institute of Health Research, University of Exeter Medical School, Exeter, UK.
Terence J
TJ
Wilkin
D015502:Absorptiometry, Photon; D000293:Adolescent; D000375:Aging / Q000378:metabolism; D001786:Blood Glucose / Q000378:metabolism; D001794:Blood Pressure / Q000502:physiology; D001823:Body Composition / Q000502:physiology; D002648:Child; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D008055:Lipids / Q000097:blood; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D011627:Puberty / Q000502:physiology; D012727:Sex Characteristics; D014280:Triglycerides / Q000097:blood; D006113:United Kingdom / Q000453:epidemiology
D001786:Blood Glucose; D006442:Glycated Hemoglobin; D008055:Lipids; D014280:Triglycerides
Adolescence; Children; Exercise; Insulin resistance; Metabolic health; Physical activity; Teenagers