Neighborhood-level socioeconomic factors moderate the mitigating role of physical activity in the relative age effect: A cross-sectional survey study of early adolescents in widespread areas of Japan

Abstract Background: Relative age effect is defined as a phenomenon where children born early generally perform better than children born later in the same cohort. Physical activity is an important factor that mitigates the relative age effect. Socioeconomic factors (e.g., parent’s income, education level) are also associated with the adolescent’s physical activity. However, no existing study has examined whether socioeconomic factors moderate the relative age effect on the adolescent’s physical activity. This study aims to clarify how birth month and socioeconomic factors moderate sports and physical activity among adolescents in Japan.Methods: We conducted a questionnaire survey targeting 21491 adolescents who live in a widespread neighborhood. We included 7138 adolescents (3701 males and 3437 females: mean age 13.06±1.44) in the analysis. Based on the participants’ birth month, we divided them into four groups (April-June, July-September, October-December, January-March). We asked participants to report their organized sports participation. Using the International Physical Activity Questionnaire for Japanese Early Adolescents, we identified their levels of sports activity and moderate to vigorous physical activity (MVPA). Neighborhood-level socioeconomic factors (areal deprivation, average annual income, education level) were analyzed based on national surveys, such as the population census. We performed multilevel logistic and linear regression analysis for organized sports participation and MVPA, respectively. Moreover, a simple slope analysis was implemented if the interaction between birth month and socioeconomic factor was significant in the multilevel linear regression analysis.Results: Among relatively younger adolescents (adolescents who were born later in the same grade), females were less likely to participate in organized sports activities (OR=0.91, 95% CI 0.85-0.98, p<0.01), while both males and females engaged in less MVPA (b=-4.08, b=-2.50, p<0.01, respectively). We observed an interaction between birth month and socioeconomic factors. Only low-income participants, females from more deprived neighborhoods, and relatively younger adolescents engaged in less MVPA. Conclusions: Socioeconomic factors moderate the relative age effect on adolescents’ physical activity. The relative age effect on adolescents’ physical activity might be more likely to appear among adolescents from socioeconomically disadvantaged neighborhoods.