# Changes in body mass index during early childhood on school‐age asthma prevalence classified by phenotypes and sex

## TL;DR

This study finds that changes in BMI during early childhood are linked to asthma risk in school-age children, with different effects for boys and girls.

## Contribution

The study is the first to analyze the relationship between BMI changes in early childhood and asthma phenotypes by sex using a large longitudinal dataset.

## Key findings

- Children with increasing BMI (Q1Q4) had higher risks of bronchial asthma, allergic asthma, and nonallergic asthma.
- In boys, Q1Q4 was associated with increased risks of bronchial and nonallergic asthma but not allergic asthma.
- In girls, consistently high BMI (Q4Q4) was linked to higher allergic asthma risk but not nonallergic asthma.

## Abstract

Few studies have explored the relationship between changes in body mass index(BMI) during early childhood and asthma prevalence divided by phenotypes and sex, and the limited results are conflicting. This study assessed the impact of BMI changes during early childhood on school‐age asthma, classified by phenotypes and sex, using a nationwide longitudinal survey in Japan.

From children born in 2001 (n = 47,015), we divided participants into BMI quartiles (Q1, Q2, Q3, and Q4) and the following BMI categories: Q1Q1 (i.e., Q1 at birth and Q1 at age 7), Q1Q4, Q4Q1, Q4Q4, and others. Asthma history from ages 7 to 8 was analyzed, with bronchial asthma (BA) further categorized as allergic asthma (AA) or nonallergic asthma (NA) based on the presence of other allergic diseases. Using logistic regression, we estimated the asthma odds ratio (OR) and 95% confidence intervals (CIs) for each BMI category.

Q1Q4 showed significantly higher risks of BA, AA, and NA. In boys, BA and NA risks were significantly higher in Q1Q4 (adjusted OR: 1.47 [95% CI: 1.17–1.85], at 1.56 [95% CI: 1.16–2.1]), with no significant difference in AA risk. In girls, no increased asthma risk was observed in Q1Q4, but AA risk was significantly higher in Q4Q4 (adjusted OR: 1.78 [95% CI: 1.21–2.6]).

Our results demonstrated that BMI changes during early childhood impact asthma risks, particularly that the risk of NA in boys increases with BMI changes during early childhood, and the risk of AA in girls increases with consistently high BMI.