[Study on the association between temperature and relative humidity with fall risk in Hubei Province]

Objective: To explore the associations of temperature, relative humidity, and their interaction effect with fall risk. Methods: Data on fall cases were collected using the national injury surveillance system from May to September, in 2006-2022 in Hubei Province. Combined with the meteorological and air pollution data, we conducted a time-stratified case-crossover design and used conditional logistic regression models and distributed lag nonlinear models to examine the exposure-response relationships between temperature, humidity, and fall risk. We further divided the low and the high temperature groups and the low and the high relative humidity groups and analyzed the excess risk (ER) of falls attributed to dry-hot or wet-hot events. Finally, we calculated the additive interactions of temperature and humidity on fall risk. Results: A total of 55 401 fall cases were included. With the increase in temperature and relative humidity decrease, the exposure-response curves of fall showed nonlinear upward trends among all populations. Gender and age differences were found in temperature-fall and relative humidity-fall risk relationships. Compared with wet-non-hot (normal temperature and high relative humidity) events, the ER of fall in dry-hot (high temperature and low relative humidity) events was 14.80% (95%CI: 9.69%- 20.15%), and the ER of wet-hot (high temperature and high relative humidity) events was 9.59% (95%CI: 2.52%-17.13%). However, there was no statistically significant difference between dry-hot and wet-hot events in the fall, and no statistically significant difference between different genders, ages, occupations, and fall occurred place (all P>0.05). No significant synergistic additive interaction was found between temperature and relative humidity on fall risk (relative excess risk due to interaction=-0.08, 95%CI: -0.19-0.02). Conclusions: Higher temperatures and lower relative humidity were associated with increased fall risk. Both dry-hot and wet-hot events had a higher risk of fall, while high temperature and low humidity have no synergistic effect on fall risk.