Childhood BMI and Allergies: A Comprehensive Review
Allergic conditions such as asthma, eczema, allergic rhinitis, and food allergies are prevalent chronic ailments that affect both children and adults. They pose a range of challenges including psychological stress, disrupted sleep, reduced work productivity, and increased healthcare expenses. Researchers have over time pinpointed several factors contributing to these allergic diseases. These encompass a familial history of allergies, exposure to air pollutants, early-life exposure to microorganisms, and obesity.
The role of obesity in potentially exacerbating these conditions stems from its pro-inflammatory effects. While prior reviews have delved into the correlation between allergic diseases and Body Mass Index (BMI) at specific time points, the outcomes have shown inconsistency. This variance might be attributed to the narrow focus on a single BMI measurement, neglecting the influence of growth in height and weight during childhood on allergic diseases. Although certain studies have explored the link between growth patterns and allergic diseases, a comprehensive synthesis of these discoveries is yet to be established.
Consequently, the primary objective of this review is to meticulously assess the connection between childhood BMI trends and allergic diseases, including asthma, eczema, allergic rhinitis, and food allergies. This assessment will draw upon longitudinal studies to provide a systematic analysis. Worth noting is that this review centers exclusively on childhood BMI as an indicator of adiposity, given its widespread application in clinical practice.
Study Methods
The systematic review’s methodology was meticulously structured and aligned with rigorous standards. The International Prospective Register of Systematic Reviews (ID CRD42020178199) pre-registered the review’s protocol. To ensure transparency and consistency in reporting, the team adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.
The search for relevant articles was systematically conducted on the 4th of January 2023, using Ovid EMBASE and PubMed databases. The search terms were devised by employing advanced search techniques for key phrases such as ‘body mass index trajectories’ and the specific allergic diseases including ‘asthma,’ ‘eczema,’ ‘allergic rhinitis,’ ‘food allergy,’ and ‘longitudinal studies.’ It’s essential to note that future investigations with longer follow-up periods are warranted, and additional studies that explore associations with eczema, food allergies, and allergic rhinitis outcomes are deemed necessary.
The research identified that catch-up growth within the initial two years of life or a consistently high Body Mass Index (BMI) trajectory between the ages of 6 and 10 might correlate with subsequent asthma development. The evaluation of bias, using the ROBINS-E tool, indicated a high level of bias across all studies. Additionally, the overall quality of evidence, as determined by the GRADE methodology, was classified as very low. Notably, there was insufficient evidence to draw conclusive outcomes for eczema, allergic rhinitis, and food allergy conditions. The review underscores the need for well-designed prospective studies to comprehensively explore the link between childhood BMI trajectories and allergic diseases.
In terms of inclusion criteria, papers were considered if they met specific criteria, including being longitudinal studies (both prospective and retrospective cohorts), development of BMI trajectories from data collected at three or more time points (with the first measurement before the age of 18), and associations between identified childhood BMI trajectories and outcomes of asthma, eczema, allergic rhinitis, and food allergies. Publications in languages other than English and data not published in peer-reviewed journals were excluded.
The process involved two independent reviewers (CC and JP) conducting initial screenings based on titles and abstracts, with full articles reviewed when necessary. Duplicate and redundant studies were excluded. Any differences in opinion were resolved through consultation with a third reviewer (GA).
For data extraction, two reviewers (CC and JP) independently gathered study details and outcomes. This included information about authors, population, sample size, BMI collection time points, statistical methods employed for identifying BMI trajectories, number and shapes of identified trajectories, age range, outcome definitions, allergy outcome collection time, association measures, and adjusted variables. Any disagreements were addressed by consulting a third reviewer (AL).
The risk of bias was assessed using the Risk of Bias in Nonrandomized Studies-of Exposures (ROBINS-E) tool. This involved evaluating various domains of bias, scored as low, moderate, high, or critical, culminating in an overall quality assessment based on the most severe bias rating. The quality of evidence for each outcome was evaluated using the GRADE methodology guidelines. Discrepancies in assessments were resolved through discussions with a third reviewer (AL)
Regarding data synthesis, the plan was to conduct a meta-analysis if there were sufficient similar studies with comparable BMI trajectories, outcomes, and summary statistics. Statistical heterogeneity was assessed using the I2 statistic, determining whether studies could be pooled based on the extent of heterogeneity. Funnel plots were also employed to detect potential publication bias in instances where ten or more studies were available for analysis.
Results
A total of 3451 citations were found in the initial search. After removing duplicates, 3389 citations were excluded based on the titles and abstracts. The remaining 62 studies were reviewed in full, and 51 were excluded. The final 11 studies met the inclusion criteria and were included in the review.
The 11 studies were conducted in different countries: 3 in Europe, 3 in North America, 2 in Asia, and 3 in Australia. The sample sizes ranged from 258 to 12,050 participants. The age range of the participants was from 0 to 43 years.
The studies used a variety of methods to measure childhood BMI, including investigator-measured and self-reported measures. Most of the outcome measurements were based on parent-reported questionnaires. The 11 studies investigated different allergic diseases, including asthma, allergic rhinitis, eczema, and food sensitization. The asthma outcomes studies varied in scope, with some studies examining current asthma, incidence of asthma, persistence of asthma, or asthma relapse. The follow-up period ranged from 5 to 48 years.
Seven studies had a delayed follow-up period between the final BMI measurement and the evaluation of outcomes, while the remaining four studies did not involve such a delay.
Conclusion
A systematic review of 11 studies was conducted to evaluate the association between childhood BMI trajectories and the development of asthma and allergic diseases. The review found that children who followed a persistently high BMI trajectory or a rapid growth BMI trajectory were more likely to develop asthma at 18 years of age. The review also found that children who experienced a rapid increase in BMI in the first 6 months of life were more likely to develop asthma, even if they did not have a high BMI by 2 years of age.
The review authors concluded that there is a clear association between childhood BMI trajectories and asthma, but more research is needed to understand the underlying mechanisms. One possible explanation is that excess adiposity can alter the mechanics of the chest wall, leading to lung volume reduction. Another possibility is that excess adiposity can lead to the release of pro-inflammatory cytokines, which can contribute to the development of asthma.
The review had some limitations, including the use of different methods to identify BMI trajectories and the relatively short follow-up period of some studies. However, the findings of the review provide strong evidence that BMI trajectories are a risk factor for asthma in children.
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