Contrasting longitudinal and cross-sectional relationships between insulin resistance and percentage of body fat, fitness, and physical activity in children-the LOOK study.
BACKGROUND
Knowledge of individual changes in insulin resistance (IR) and longitudinal relationships of IR with lifestyle-associated factors are of important practical significance, but little longitudinal data exist in asymptomatic children. We aimed to determine (a) changes in the homeostatic model of insulin resistance (HOMA-IR) over a 2-yr period and (b) comparisons of longitudinal and cross-sectional relationships between HOMA-IR and lifestyle-related risk factors.


METHODS
Our subjects, 241 boys and 257 girls, were assessed at age 8.1 yr (SD 0.35) and again 2 yr later for fasting blood glucose and insulin, dual X-ray absorptiometry-assessed percentage of body fat (%BF), pedometer-assessed physical activity (PA), and cardio-respiratory fitness (CRF) by multistage running test.


RESULTS
HOMA-IR was initially 9% greater in girls than boys and 27% greater 2 yr later. There was no evidence of longitudinal relationships between HOMA-IR and %BF in boys or girls, despite significant cross-sectional relationships (p < 0.001). In boys, there was evidence of a longitudinal relationship between HOMA-IR and both PA (p < 0.001) and CRF (p = 0.05). In girls, we found a cross-sectional relationship between HOMA-IR and CRF (p < 0.001).


CONCLUSIONS
HOMA-IR increases between 8 and 10 yr of age and to a greater extent in girls. Longitudinal, unlike cross-sectional, relationships do not support the premise that body fat has any impact on HOMA-IR during this period or that PA or CRF changes affect HOMA-IR in girls. These data draw attention to difficulties in interpreting observational studies in young children.
Telford
Richard D
RD
Medical School, Australian National University and Commonwealth Institute, Canberra, ACT, Australia. rtelford@cominst.org.au
Cunningham
Ross B
RB
Shaw
Jonathan E
JE
Dunstan
David W
DW
Lafferty
Antony R A
AR
Reynolds
Graham J
GJ
Hickman
Peter E
PE
Southcott
Emma
E
Potter
Julia M
JM
Waring
Paul
P
Telford
Rohan M
RM
D000273:Adipose Tissue; D044362:Australasia / Q000453:epidemiology; D002648:Child; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005260:Female; D006706:Homeostasis; D006801:Humans; D007333:Insulin Resistance; D008019:Life Style; D008137:Longitudinal Studies; D008297:Male; D024821:Metabolic Syndrome / Q000453:epidemiology*; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology; D010809:Physical Fitness; D012307:Risk Factors