# The correlation between temperature and the incidence of acute ischaemic stroke in Yanji, China: a time series study

## TL;DR

This study found that high temperatures increase the risk of acute ischaemic stroke in Yanji, China, with effects lasting up to 7 days.

## Contribution

The study identifies a lagged effect of heat exposure on stroke risk and provides insights into subgroups more vulnerable to temperature changes.

## Key findings

- Extreme and moderate heat increased the risk of acute ischaemic stroke with a lag effect lasting up to 7 days.
- Males and individuals under 65 showed higher stroke risk during early heat exposure.
- No harmful effects were observed for extreme or moderate cold temperatures.

## Abstract

Acute ischaemic stroke (AIS) is a common cerebrovascular disease; however, the relationship between temperature and its onset remains unclear. Therefore, we aimed to explore the association between temperature and the incidence of AIS in Yanji, a city in Northeast China.

We collected data on patients with AIS from the Affiliated Hospital of Yanbian University from Jan 1, 2019, to Dec 31, 2023, along with meteorological data during the same period. A distributed lag nonlinear model (DLNM) was constructed to estimate the correlation between temperature and the risk of developing AIS, and further subgroup analyses stratified by sex, age and period (non-pandemic, pandemic) were performed.

A total of 15,997 patients were diagnosed with AIS during the study period. Using the minimum morbidity temperature (MMT) of −8.3°C as a reference, extreme heat (26.5°C, 99th percentile of temperature) and moderate heat (21.9°C, 90th percentile of temperature) were found to increase the risk of developing AIS on the day of exposure, with this effect persisting even after a lag of 7 days. The relative risks (RRs) with 95% confidence intervals were 1.268 (95% CI: 1.143–1.407) and 1.239 (95% CI: 1.145–1.341), respectively. In contrast, no harmful effects were observed within a lag of 0–7 days for extreme cold (−17.4°C, 1st percentile of temperature) and moderate cold (−10.6°C, 10th percentile of temperature) conditions. Subgroup analysis revealed that in the early stages of exposure to extreme heat and moderate heat, the risk of developing AIS increased in males and individuals under 65 years of age, and there were differences in the risk of developing AIS between the pandemic and non-pandemic periods.

Our research suggests that exposure to high-temperature environments increases the risk of developing AIS and that the harmful effects of high temperatures have a lag effect. Reducing exposure to high temperatures may help alleviate the medical burden associated with AIS.