Age-related stroke risk is increased by hot weather: Study

Emergency visits for stroke are increased during a heatwave, according to study presented at ESC Asia, a scientific conference organised by the European Society of Cardiology (ESC), the Asian Pacific Society of Cardiology (APSC), and the Asean Federation of Cardiology (AFC).

“Climate change and global warming are worldwide problems and stroke is a leading cause of death,” said study author Dr Ryohei Fujimoto of Tsuyama Central Hospital and Department of Epidemiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Japan.
“Our study indicates that older adults may be more susceptible to stroke after exposure to hot weather. Preventative measures such as insulated housing and air conditioning should be considered a public health priority to protect people from this debilitating and life-threatening disease.”

The impact of high temperatures on the risk of stroke is not well understood. This study looked at the connection between elderly people’s emergency room visits for stroke and heat exposure. 3,367 citizens of Okayama, a city in Western Japan, participated in the survey. Between 2012 and 2019, participants who were 65 years of age or older were sent to emergency hospitals for strokes that began during and many months following the rainy season.

The Okayama weather station, which is operated by the Japan Meteorological Agency and the Okayama Prefectural Government, provided hourly data on outdoor temperature, relative humidity, barometric pressure, and the average atmospheric concentration of particulate matter smaller than 2.5 mm in diameter (PM2.5).

Analysis of the relationship between temperature and stroke was done during the rainy season as well as one, two, and three months later. For each participant, the researchers utilised a time-stratified case-crossover study design to compare the temperature on the day of the week a stroke occurred (for example, Monday) with the temperature on the same day of the week without strokes (for example, all other Mondays in the same month).

By doing this, the possible impacts of individual traits, long-term temporal trends, seasonality, and day of the week were avoided. One month following the rainy season, the researchers discovered, the link between temperature and stroke was at its highest. After controlling for relative humidity, barometric pressure, and PM2.5 concentration, there was a 35% increase in the likelihood of emergency visits for stroke for every 1°C rise in temperature. Each 1°C rise in temperature was linked to a 24% higher chance of hemorrhagic stroke, a 36% higher chance of ischemic stroke, and a 56% higher chance of transient ischaemic attack when each kind of stroke was examined independently.

The researchers examined if there may be “impact modification” based on the wet season in a subsequent analysis. Effect modification refers to the possibility that the relationship between an outcome (emergency visit for stroke) and an exposure (hot air temperature) may vary based on a third variable (during and after the rainy season). The wet season served as the reference period for this investigation.

Once more, the bond was at its greatest one month following the wet season. For every 1°C increase in temperature throughout the reference period, the risk of stroke increased by 31%.

Dr. Fujimoto explained: “The results of the second analysis suggest that environmental conditions immediately after the rainy season intensify the relationship between hot weather and stroke. In addition to high temperatures, this period is characterised by an increase in sunshine duration and less rain, which may explain the findings.”

He concluded: “Our study suggests that older adults should try to keep cool during hot spells, for example by staying indoors during peak temperatures. Public health systems can help by providing cool spaces for members of the public to escape the heat during the hottest months of the year.”