Associations between extreme temperature events and daily step counts by weight status and modifying effects of sociodemographic factors: a longitudinal study.

Background: Although the health risks of increasing extreme weather events such as heatwaves and cold spells are well recognized, there remains a research gap on how these events specifically affect physical activity, particularly among individuals with different weight status. In addition, limited attention has been given to how sociodemographic factors might interact with extreme weather to influence physical activity.

Objectives: This study aimed to examine the association between extreme weather events and daily step counts by body weight and to investigate whether these associations are modified by other sociodemographic factors.

Methods: To address this, we conducted a longitudinal panel study in Henan Province, China, and applied distributed lag nonlinear models to examine how daily step counts were influenced by extreme weather events-including heatwaves and cold spells-and their intensity and duration. We also explored whether sociodemographic factors modified these effects.

Results: Our findings showed that extreme weather events significantly reduced step counts. Specifically, heatwaves were associated with a substantial decline in individuals with overweight [-959.68 steps; 95% confidence interval (CI): -1198.13, -721.22], which was significantly larger than the reduction observed in participants with normal weight (-331.16 steps; 95% CI: -625.50, -36.83). Conversely, cold spells were associated with a disproportionately larger reduction in step counts among participants with normal weight (-1832.46 steps; 95% CI: -2136.15, -1528.76), compared with a milder reduction in the overweight group (-1067.66 steps; 95% CI: -1317.40, -817.91). Interaction analysis revealed that high income consistently attenuated these disparities (P-interaction < 0.05). Although age and sex also modified these associations, body weight emerged as a primary factor.

Conclusions: These findings suggest that individuals with low income or high body mass index (BMI) are associated with heightened vulnerability to heatwaves, whereas individuals with low income or normal BMI are linked to greater sensitivity during cold spells.