Obesity at the age of 4-5 related to asthma diagnosis in later childhood: A longitudinal study using linked routinely collected data from Wales.

Introduction: Obesity and asthma are two of the most common childhood conditions and their prevalence have increased over the last decades. Several cross-sectional studies provide strong evidence for a positive association between these two conditions. However, few longitudinal studies have examined the temporal relationship between them.

Objective: To examine the relationship between body mass index (BMI) at school starting age and the risk of developing bronchial asthma later in childhood.

Methods: We used anthropometric measurements of children aged 4 to 5 years, obtained as part of a national surveillance programme in Wales, linked to multiple population-level longitudinal administrative and clinical datasets within a trusted research environment provided by the Secure Anonymised Information Linkage (SAIL) databank to examine whether obesity at age 4 to 5 years was associated with increased risk of having a recorded diagnosis of asthma during a nine year follow-up period.

Results: Out of 22,790 children included in the study, 7% had a recorded diagnosis of asthma during the nine years following anthropometric measurement. Children who were classified as obese (Body Mass Index [BMI] Z-score ≥98^th Centile) had a 41% increased risk of having a recorded diagnosis of asthma (adjusted odds ratio [aOR]: 1.41; 95% confidence interval [CI]: 1.17-1.7). Females were 26% less likely to have a recorded diagnosis of asthma after adjusting for weight status and deprivation index (aOR: 0.74; 95% CI: 0.67-0.82).

Conclusion: Obesity in children aged 4 to 5 years carries an increased risk of developing asthma. Anthropometric measurements obtained through standardised population-level surveillance programmes enable important research which would not be possible otherwise and expanding these programmes to older age groups is recommended. Lifestyle interventions aimed at weight loss may have a role in decreasing the risk of developing asthma.