Air pollution and hip fracture risk in older people: a multi-center time-series DLNM study

To investigate the impact of air pollutants on the incidence of hip fractures among older hospitalized patients in Hebei Province.

This epidemiological study was conducted across multiple hospitals in Hebei Province over a five-year period, focusing on older people with hip fractures. A generalized linear model (GLM) and a generalized additive model (GAM) were applied to identify potential factors influencing hospitalization risk. To evaluate the association between exposure to air pollutants (PM2.5, PM10, NO2 SO2, CO, and O3) and the incidence of hip fractures, a distributed lag nonlinear model (DLNM) based on the GLM framework was employed to account for lag effects. Air quality data were obtained from fixed monitoring stations within the environmental monitoring networks of each city. The selection of monitoring sites strictly followed national standards, ensuring locations were distant from major roads, industrial emission sources, and clusters of high-rise buildings, while avoiding direct residential coal-burning emissions. This ensured that the air pollutant measurements accurately reflected regional pollution levels. Natural cubic spline functions and categorical variables were incorporated to adjust for long-term trends, seasonality, and day-of-week effects. Sensitivity analyses were performed by varying the degrees of freedom (6-8 df per year) for the time trend to assess the robustness of the results.

The study included 16,765 older hip fracture patients with an average age of 77.33 ± 7.60 years; the majority were female (7,216 cases, 68.50%). Using the P50 concentration of air pollutants as a reference, each 10 µg/m³ increase in PM2.5, PM10, and NO2 concentrations over 1 day (or a 0.1 mg/m³ increase in CO) was linked to a higher risk of hip fractures (PM2.5: RR = 1.02, 95% CI: 1.012, 1.027; PM10: RR = 1.017, 95% CI: 1.013, 1.023; NO2: RR = 1.068, 95% CI: 1.049, 1.088). Cumulative 12-day exposure to SO2 and CO increased hospitalization risk (SO2: RR = 1.19, 95% CI: 1.12, 1.28; CO: RR = 1.035, 95% CI: 1.027, 1.044). A 14-day cumulative lag showed that SO2 levels between 0 and 6 µg/m³ significantly increased the likelihood of hospitalization.

Short-term and cumulative exposure to air pollutants, including PM2.5, PM10, SO2, CO, and NO2 may be associated with an increased risk of hospitalization for hip fractures in older people. It should be noted that, as an observational study, the potential influence of unmeasured confounding factors cannot be excluded.