Childhood body mass index trajectories and asthma and allergies: A systematic review

Background Previous systematic reviews have focused on associations between single time point measures of Body Mass Index (BMI) and asthma and allergic diseases. As BMI changes dynamically during childhood, examination of associations between longitudinal trajectories in BMI and allergic diseases is needed to fully understand the nature of these relationships. Objective To systematically synthesise the association between BMI trajectories in childhood (0–18 years) and allergic diseases (asthma, eczema, allergic rhinitis, or food allergies outcomes). Design We conducted a systematic review following the PRISMA guidelines, and two independent reviewers assessed the study quality using the ROBINS‐E and GRADE tools. A narrative synthesis was performed as the statistical heterogeneity did not allow a meta‐analysis. Data Sources A search was performed on PubMed and EMBASE databases on 4th January 2023. Eligibility Criteria Longitudinal cohort studies assessing the associations between childhood BMI trajectories and allergic diseases were included. Results Eleven studies met the inclusion criteria with a total of 37,690 participants between 0 and 53 years of age. Ten studies examined asthma outcomes, three assessed association with allergic rhinitis, two assessed eczema, and one assessed food allergy. High heterogeneity and high risk of bias were observed. Overall, the quality of evidence was very low. Nevertheless, two consistent findings were identified: (1) a persistently high BMI between 6 and 10 years of age may be associated with an increased risk of asthma at 18 years and (2) a rapid increase in BMI in the first 2 years of life may be associated with subsequent asthma. Conclusions Maintaining a normal BMI trajectory during childhood may reduce the risk of asthma. Future research that adequately addresses confounding and includes longer‐term follow‐up is needed. Moreover, additional studies examining potential associations with eczema, food allergies, and allergic rhinitis outcomes are needed. We observed that catch‐up growth in the first 2 years or a persistently high BMI trajectory between 6 and 10 years of age may be associated with subsequent asthma. The risk of bias (assessed using ROBINS E) was high among all studies. The overall quality of evidence (determined by GRADE) was very low. There was insufficient evidence to draw conclusions for eczema, allergic rhinitis, and food allergy outcomes. Well‐designed prospective studies examining the association