Only 1 hour of extreme heat exposure can increase risk of stroke, scientists discover

Being in hot temperatures for as little as one hour can increase the risk of a stroke, a new study has found.

Exposure to temperatures of 33C and above can immediately double the risk of having a specific kind of stroke, called acute ischemic stroke (AIS), as compared to temperatures of 12C or below.

This kind of stroke occurs when the blood supply to part of the brain is blocked. AIS accounts for 70 per cent of all strokes reported around the world and it can result in disability or death.

This direct association between hourly high temperatures and the onset of AIS was found by researchers at China’s Fudan University. The study was published on Thursday in scientific journal JAMA Network.

While previous research has shown links between daily high temperatures and stroke-related hospitalisations and mortality, this study specifically focused on the hourly impact of ambient heat on AIS onset.

Researchers looked at data from more than 200 stroke centres across China, covering 82,000 adults who had AIS and were hospitalised during the warm seasons from 2019 to 2021.

The study checked the hourly temperatures up to 24 hours before a person had a stroke. The results showed that as temperatures went up, the risk of having a stroke also increased.

The risk was highest immediately at exposure to heat, lasting for 10 hours after it got really hot. The chances of having a stroke were almost twice as high if it was extremely hot, around 33.3 C, compared to when it was cooler, around 12.1C.

The study also found that people with a history of certain health problems might have a slightly higher risk, although this wasn’t a major difference.

Researchers say their findings “underscore the ongoing need for public health agencies to advocate for interventions that mitigate heat exposure and bolster cooling measures, particularly among populations at high risk for acute ischemic stroke.”

The climate crisis, fuelled by dangerous pollution from fossil fuel burning, has increased the number of heatwaves around the world with more people exposed to higher temperatures for longer duration.

Several studies in recent years have shown how this exposure is leading to a rise in hospitalisations and illnesses.

Earlier studies have found that exposure to extreme temperatures combined with suffocating air pollution can double the risk of dying from a heart attack.