OBJECTIVE: To investigate trends in BMI z-scores (BMIz) of Western Australian (WA) children at T1D diagnosis over the 1999-2012 period. We aimed to elucidate associations of BMIz with age, sex and socioeconomic status (SES) to determine if an increased BMIz at T1D onset was associated with earlier disease manifestation, and poorer glycaemic control at 3 years post-onset.
DESIGN AND METHODS: The relationships between BMIz at 2-5 months post-diagnosis with demographic variables (age, sex, SES) and mean glycated haemoglobin (HbA1c) calculated from 3 months to 3 years post-diagnosis were examined in children aged 2-14 years at T1D onset residing in WA from 1999-2012. Multivariable linear regression models were used to assess associations, examining for interaction effects and adjusting for potential clinical confounders.
RESULTS: Mean BMIz at T1D diagnosis decreased over 1999-2012 by an average of 0.015 BMIz scores each year [p<0.05, 95% CI(-0.028,-0.002)], with the greatest decrease observed for older children (10-14 yrs). Comparatively, younger children (2-4 years) became progressively heavier whilst incidence in this age group remaining steady. Mean BMIz between age groups (2-4, 5-9, 10-14yrs) were significant (p<0.01), and children from lower SES were likely to be 0.451 BMIz scores heavier than their socioeconomically advantaged counterparts (p<0.01). Finally, there was no evidence for a strong relationship between mean 3-year HbA1c and BMIz category (p=0.11) with little variation over the 13 year study period.
CONCLUSION: The mean BMIz of WA T1D children is decreasing over time comparative to the plateauing overweight/obesity rates in Australian children, but that this trend is observed only for those aged 4-14years at diagnosis, with the youngest age group becoming increasingly heavier at diagnosis. Age group, year-diagnosed and SES were all significant predictors of mean BMIz, with no evidence currently to suggest a greater BMIz at diagnosis is associated with poorer glycaemic control at 3-years.