The U-shaped association between urbanization and post-stroke disability: A nationwide longitudinal study in China

Background

In the 21st century, China experienced a rapid increase in urbanization, which has enhanced medical service availability, but has also increased exposure to adverse environmental and socioeconomic factors. Urbanization-related factors can affect the prognosis of stroke patients, particularly the progression of neurological disabilities. However, the overall association between urbanization and post-stroke disability remains unknown.

Method

A total of 21,678 stroke patients were selected from the China National Stroke Screening Survey (2013–2018); all included patients had at least one follow-up record. The modified Rankin Scale (mRS), a clinician-reported functional outcome measure for recovery from stroke, was utilized to assess post-disability at each visit. A larger mRS score means severer disability. The urbanization level before each visit was evaluated based on 5-year average satellite measurements of night-time light (NTL) or urban land cover (i.e., proportion of impervious surface). We used a fixed-effects model to estimate the association between urbanization level and risk of disability (i.e., mRS score). The non-linear relationship was modelled by penalized spline functions.

Results

According to linear models with multivariate adjustment, every 10 digital number (DN) increment in NTL was associated with a 0.050 (95% confidence interval [CI]: 0.026, 0.074) increase in mRS score, and every 10% increment in impervious surface was associated with a 0.052 (95% CI: 0.034, 0.070) increase in mRS score. The association was stronger in patients diagnosed with atrial fibrillation, dyslipidemia, hypertension, or diabetes compared with the corresponding reference group. Non-linear analysis showed a U-shaped relationship between urbanization and the mRS score, which indicates that high and low urbanization levels were both associated with an increased risk of post-stroke disability.

Conclusions

Our study revealed a complex association between urbanization and post-stroke disability. The optimal level of urbanization to prevent neurological disabilities in stroke patients could be inferred from the U-shaped curve. The reasons for the complex association between urbanization and post-stroke disability should be further explored to establish causality.