Seasonal variations in ischemic and hemorrhagic stroke and their relationship with air pollutants: A retrospective analysis

Introduction: To evaluate the relationship between the clinical parameters of ischemic and hemorrhagic stroke and atmospheric air quality, to determine seasonal variation in stroke incidence, and to identify which air pollutants independently predict stroke severity.Methods: A total of 729 stroke patients (671 ischemic, 58 hemorrhagic) admitted to the hospital between January 1, 2022, and December 31, 2023, were retrospectively reviewed. Demographic, clinical, laboratory, and NIHSS data were recorded. Daily SO2, NO2, PM2.5, PM10, O3, and CO levels were obtained from air quality data. Associations were assessed with Spearman correlation and chi-square tests. Statistical significance was set at p < 0.05. Ethics committee approval was obtained, and the data were anonymized.Results: A total of 729 patients were included, 391 men and 338 women. The mean age was 70.0±13.44 years. The seasonal distribution of stroke subtypes is shown in Table 1. The incidence of ischemic stroke was significantly higher in winter and spring than in autumn (p < 0.05). In contrast, no seasonal variation was found in hemorrhagic stroke. In September, the proportion of male hemorrhagic stroke cases (19.35%) was significantly higher than that of male ischemic stroke cases (7.20%) (p = 0.018). In hemorrhagic stroke cases, a significant negative correlation was found between PM₁₀ and hemoglobin level (ρ=−0.259, p=0.049). In ischemic stroke cases, SO₂ was positively correlated with NIHSS scores (ρ=0.086, p=0.025), O₃ was negatively correlated with systolic blood pressure (ρ=−0.085, p=0.027), and SO₂ was negatively correlated with triglyceride levels (ρ=−0.120, p=0.024). In multivariable analysis, age, diabetes mellitus, and low hemoglobin level were identified as independent risk factors for ischemic stroke, whereas high systolic and diastolic blood pressure were independent predictors of hemorrhagic stroke (p<0.001) (Figure 1 and 2 and Table 1).Discussion/Conclusion: The incidence of ischemic stroke increases in the colder months. Certain air pollutants, such as PM₁₀, SO₂, and O₃, were associated with stroke severity and laboratory findings. Incorporating air quality monitoring into public health strategies may help reduce the burden of stroke and support the development of targeted preventive policies. Environmental improvements may play a potential role in reducing the incidence of stroke.Keywords: