OBJECTIVE: To determine whether age at asthma diagnosis has an impact on the previously described relationship between asthma and obesity.METHODS: Data were provided from Cycle 1.1 (2000/2001) of the Canadian Community Health Survey, a nationally representative health survey that included 6871 participants (2464 males and 4407 females) with asthma. Body mass index was used to categorize participants as normal weight (18.5 kg/m2 to 24.9 kg/m2), overweight (25 kg/m2 to 29.9 kg/m2) or obese (30 kg/m2 or greater). Multivariate logistic regression analyses were used to estimate the odds of overweight and obesity by self-reported age at asthma diagnosis, after accounting for current age and other covariables.RESULTS: In fully adjusted models, males diagnosed with asthma during adolescence (12 to 20 years of age) were at elevated odds of obesity (OR 1.58; 95% CI 1.03 to 2.43) compared with asthmatic patients diagnosed during childhood (0 to 11 years of age). Women diagnosed with asthma in mid life (21 to 44 years of age) and later life (45 to 64 years of age) were 43% (OR 1.43; 95% CI 1.08 to 1.90) and 56% (OR 1.56; 95% CI 1.00 to 2.44) more likely to be obese than those diagnosed in childhood, respectively.CONCLUSIONS: The impact of age at asthma diagnosis on the asthma-obesity relationship differed between males and females. However, the identification of high-risk groups of asthmatic patients may strengthen primary prevention strategies for obesity and related comorbidities at multiple levels of influence.