Formal uniforms as an environmental constraint on NEAT and adolescent obesity: a cross-sectional study in boarding...

The rising prevalence of obesity in adolescents is commonly attributed to a decrease in moderate to vigorous physical activity (MVPA), but the role of environmental constraints on thermogenesis from non-exercise activities (NEAT) remains under-explored. School uniforms are a daily necessity and may be associated with physical or perceived barriers to spontaneous low-intensity movement. This study investigated the relationship between type of school uniform (formal versus athletic) and body mass index (BMI) and examined whether NEAT-related behaviors showed a statistical mediation pattern in a gender-specific manner.

A cross-sectional study was conducted in four 100 percent boarding secondary schools in China. A total of 1,068 adolescents were stratified by mandatory uniform type. NEAT-related behaviors were assessed using an adapted self-reported questionnaire and compared with accelerometry-derived metrics in a sedentary validation sub-sample (n = 108). Mediation analyses and moderated mediation analyses were conducted to examine the uniform type, NEAT-related behaviors, and BMI associations.

Formal uniforms were significantly associated with higher BMI in women (Δ = 0.7 kg/m², p < 0.01) but not in men (p > 0.05). Mediation analyses suggested that this association was statistically mediated by lower NEAT-related behaviors [β_indirect = 0.123, 95% CI (0.054, 0.208)], accounting for 60.3% of the total effect. Exploratory subgroup analyses showed a larger uniform-BMI difference among students in the lowest NEAT-related activity decile: in the lowest decile of sedentary behavior, the difference in body mass index between homogeneous groups widened from a negligible amount in highly active girls to a larger observed difference of 1.3 kg/m² (p < 0.01).

Formal school uniforms were associated with lower NEAT-related movement and higher body mass index in adolescent females in this study population. This relationship was more pronounced among students with lower baseline activity levels, suggesting that restrictive clothing may act as an environmental constraint on spontaneous low-intensity movement. These findings suggest that movement-friendly school uniform designs may warrant further investigation in residential school settings.