Obesity and asthma at school entry: co-morbidities and temporal trends.

Aim: A decline in asthma prevalence from 2000 to 2005 was reported previously. The objective is to examine the temporal trends for the prevalence of obesity and other childhood disorders and consider the extent to which associations between asthma and other co-morbidities can be accounted for by body mass index.

Methods: Serial cross-sectional surveys of primary school entrants (n = 18,999) in the Australian Capital Territory between 2001 and 2005 were used. Asthma, recent respiratory symptoms and diabetes data were extracted from parental reports. Anthropometric measurements were obtained from health assessments by school nurses. Child obesity was defined using the age and sex-specific Cole criteria. Time trends for the prevalence of obesity and other disorders, and the association between 'current asthma' and co-morbidities were analysed using multiple logistic regression and other analyses.

Results: Obesity prevalence was 5.24% in 2001 decreasing to 3.60% in 2005 (test of linear trend P = 0.02). Overweight (adjusted odds ratio (AOR) 1.30 (95% confidence interval (CI) 1.16, 1.46), P < 0.001) and obese (AOR 1.36 (95% CI 1.13, 1.62), P = 0.001) children were more likely to report 'asthma ever'. Children with diabetes (AOR 9.35 (95% CI 3.11, 28.12, P < 0.001)) and attention deficit (AOR 3.39 (95% CI 2.04, 5.64), P < 0.001) were more likely to report 'current asthma'.

Conclusions: The pattern of association with co-morbidities was different for asthma and obesity. The temporal decline/plateau effect in 'current asthma' could not be explained by concurrent body mass index changes. The decline in obesity was largely driven by the 2005 findings. Longer term trends need to be evaluated further.