Background: The respiratory tract of children in low-income families is more likely to be exposed to toxins, which may lead to poor lung function. The purpose of this study was to elucidate the impact of low household income on lung function among children and adolescents in Japan.

Methods: We analyzed a population-based sample of 1,224 children aged 5 to 17 years old from the Japanese Study on Stratification, Health, Income, and Neighborhood (J-SHINE). Forced expiratory volume in 1 s (FEV1) and in 6 s (FEV6) was measured. Annual household income and other potential covariates were assessed through a questionnaire. Low household income was defined as less than 3 million yen (approximately 27,000 United States dollars [USD]) per year. Multivariate regression analysis was used to adjust for potential covariates.

Results: We observed statistically significantly lower FEV1:FEV6 ratio with children in lowest-income families compared with those in highest-income families, after adjusting for child’s age and sex (coefficient = −0.082; 95% confidence interval [CI], −0.131 to −0.034). After adjusting for other covariates, including parental smoking status and parental diagnosis of asthma, a similar trend remained (coefficient = −0.054; 95% CI, −0.109 to 0.001).

Conclusions: Children in low-income families showed significantly lower lung function than those in high-income families. Prevention and early intervention are necessary to help the development of lung function among children living in low-income families.