Changing weather heightens risk of stroke

New data from the Global Burden of Disease (GBD) study shows, for the first time, that low ambient temperature is an increasingly significant risk factor for stroke around the world.

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Global warming not only produces hotter summers and extreme weather events but also colder winters, especially in more temperate zones. These changes affect human physiology and have the potential to acutely influence the occurrence of cardiovascular diseases such as stroke.

While previous studies have made ecological observations of the effects of ambient temperature on the risk of stroke, the current study is the first to show the sizeable global effect of non-optimal, primarily low ambient temperature on the burden of stroke.

The paper, published in The Lancet Neurology, is a systematic analysis of updated data from the GBD study on stroke, including incidence, prevalence, mortality, disability, risk factors, and epidemiological trends on a global, regional, and national level.

Lead author of the paper, Valery Feigin – Professor of Neurology and Epidemiology, and Director of the National Institute for Stroke and Applied Neurosciences (NISAN) at Auckland University of Technology (AUT) – says there is increasing concern about the impact of climate change on global health.

The results show that low temperature now ranks sixth or seventh among the highest risk factors for all strokes in Central Asia, Eastern Europe, Western Europe, and North America – where it sits just behind smoking, hyperglycaemia, poor diet, and high cholesterol, respectively.

Low temperature falls below the Theoretical Minimum Risk Level (TMREL) with the lowest mortality. TMRELs vary by location, temperature zone, and year. In New Zealand, the temperature zones are 6C to 17C and the population weighted mean is 13.4C. There are 12 different TMREL values in this country for any given year.

“In New Zealand, 10 percent of the burden of stroke is attributable to low temperature, which suggests that healthier housing – that is well insulated, ventilated and fitted with good reliable heating – could prevent more than 370 new stroke cases each year,” says Feigin.

“The estimated cost saving to the country would be $27 million.”

The ‘burden of stroke’ measures the impact of living with illness and injury, and loss of life from premature death.

“Over the past 30 years, we have seen a 26 percent increase in the number of new stroke cases, and a 40 percent increase in the number of New Zealanders living with the after-effects of stroke,” says Feigin.

“There is an increased stroke burden overall, particularly in people younger than 70 years old. If no urgent measures are taken to improve primary stroke prevention, the burden of stroke in New Zealand and globally will double by 2050.”

The Global Burden of Disease (GBD) study is the most comprehensive worldwide, observational epidemiological study to date, analysing 369 diseases and 286 causes of death in more than 200 countries.

Led by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, with funding from the Bill and Melinda Gates Foundation, the GBD study brings together data and analysis from international researchers to help understand the health challenges facing people across the world.

Although he is based in Auckland, Feigin is an Affiliate Professor of the University of Washington, and principal contributor to the GBD study on stroke and related neurological disorders.

For three consecutive years, he has ranked among the top one percent of researchers for most cited publications, making him one of ‘the world’s most influential scientific minds’. He is by far the most cited scientist in Australia and New Zealand.

“A concerning trend we are seeing is that most countries have not achieved sufficient declines in stroke incident rates to offset the demographic force of population growth and ageing, resulting in overall increases in the number of fatal and disabling strokes over time,” says Feigin.

“We now need to look at developing both country-specific and stroke type-specific strategies to reduce the burden of stroke.”

Elevated blood pressure (48 percent), being overweight (30 percent), and poor diet (28 percent) are still the three highest stroke risk factors in New Zealand.

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