Cold weather raises risk of stroke

A study by The George Institute for Global Health has shown that cold weather leads to a heightened risk of the most lethal form of stroke – intracerebral haemorrhage (ICH).

The researchers studied 1997 ICH patients across the world (including 1191 from China) between 2008 and 2012 and found almost 80 per cent of strokes occurred below 20°C. They also discovered ICH was more likely to occur in the first two to three hours of exposure to cold temperatures.

The findings published in PLOS One are the result of a world first study that links hourly temperatures and ICH.

Previous studies had hypothesised that cold temperature may trigger ICH through the narrowing of blood vessels and elevations in blood pressure.  The George Institute research provides evidence that heightened blood pressure is the underlying mechanism for cold induced ICH.

Patient data was gathered from a previous George Institute trial called INTERACT2 which revealed a new way to treat ICH.  The landmark results showed that intensive blood pressure lowering (<140 mm Hg) in patients with intracerebral haemorrhage reduced the risk of major disability and improved chances of recovery by as much as 20 per cent. 

Principal Investigator of the INTERACT2 study, Professor Craig Anderson, said: ““Intracerebral haemorrhage is a serious disease, particularly in countries in the Northern Hemisphere where the population experiences cold and severe winters. Cold temperature increases the risk of stroke in populations with high blood pressure levels that are poorly controlled by treatment and lifestyle factors.”

Other key findings:

  • When compared to rates of ICH at 20°C, (considered the optimal temperature) the odds of experiencing ICH rose to 137 per cent when temperatures dropped to 10°C. 
  • At zero the odds rose to 192 per cent, at minus 10°C the odds climbed 313 per cent, and at minus 20°C the odds of having an ICH when compared to the reference temperature (20°C) were 576 per cent higher.

Patient records were studied at 144 hospitals in 21 countries including the UK, Australia, South America, India, Pakistan, the US and China. In China, patients from 16 cities (including Hong Kong SAR) were included in the study analyses.  

Chief author of the study, Danni Zheng from The George Institute, said: “ICH is a devastating disease with high mortality and morbidity rates. In 2010 alone there were there were 5.3 million new cases of ICH and over 3 million deaths from ICH worldwide.

According to the The Global Burden of Disease Study 2010, China has the highest age-standardised (taking into account population ageing) incidence of haemorrhagic stroke in the world.”

Among the 16 cities that were included  in the current study, many were from the Northern cities of China such Changchun, Beijing, Tangshang and Shijiazhuang with frequent sub-zero temperatures during the winter time.

“Cities in the middle part of China such as Nanjing and Changsha may also experience cold winters. For example, in this winter, the super-strong cold waves hit many parts of China and caused temperatures to plunge across the whole country.” said Zheng.

“Hopefully our research will contribute to ICH prevention by showing the potential need and opportunities for public health interventions such as the instalment of central heating in cold regions, public awareness promotions as well as targeted advice and warning for at risk individuals.”

Stroke facts and figures

  • Around 17 million people suffer stroke each year around the world. (WHO)
  • The annual stroke mortality rate in China is approximately 1.6 million, exceeding heart disease as the leading cause of adult death and disability.
  • The most lethal of all stroke subtypes is intracerebral haemorrhage.
  • China has 2.5 million new stroke cases each year and 7.5 million stroke survivors
  • Northeast China has the highest incidence (486 per 100,000 person-years), whereas in southern China, the incidence is significantly lower (136 per 100,000 person-years), with a male to female ratio of 1.3 to 1.5∶1

Read the journal article 'Low Ambient Temperature and Intracerebral Hemorrhage: The INTERACT2 Study' in PLOS One.