The extreme temperatures that occur during cold spells and heat waves may raise the risk of heart-related deaths, according to an Australian study which for the first time looks at the link between daily average temperature and “years of life lost” due to cardiovascular diseases.
The study, which took place in Brisbane, was led by Cunrui Huang of the School of Public Health and Institute of Health and Biomedical Innovation at Queensland University of Technology (QUT).
Huang and colleagues write about their findings in the current issue of Circulation: Cardiovascular Quality and Outcomes, an American Heart Association journal.
Various studies have shown that exposure to extreme temperatures stresses the cardiovascular system in different ways: it changes blood thickness, blood pressure, heart rate, and cholesterol levels, for example.
The researchers note in their background information that while such studies reveal what is now a well-known link between cardiovascular disease and extreme temperature, the risk of dying of a cardiovascular disease as a result of such spells is “heavily influenced by deaths in frail elderly people”.
But, in view of the effect that exposure to extreme temperatures has on the body, and bearing in mind the growing obesity trend and the effects of climate change, it might be useful to look at the problem from a different perspective, so that is how they came up with the idea of measuring the effect of extreme temperatures “on years of life lost” due to cardiovascular disease.
“With increasing rates of obesity and related conditions, including diabetes, more people will be vulnerable to extreme temperatures and that could increase the future disease burden of extreme temperatures,” says Huang in a press statement.
By measuring years of life lost, the researchers estimate the extent of premature death relative to life expectancy.
For their study, they compared daily temperature readings for Brisbane between 1996 and 2004, with records of cardiovascular-related deaths for the same period. In Brisbane, summers are hot and humid, and winters tend to be mild and dry.
The results show that the average daily temperature was 20.5 deg C (68.9 deg F). During cold spells (defined as the coldest 1% of days) the average temperature was 11.7 deg C (53 deg F), and during heat waves (defined as the hottest 1% of days), it was 29.2 deg C (84.5 deg F).
The records for deaths reveal that 72 years of life were lost per 1 million people per day due to cardiovascular disease.
When they compared the two groups of data, the researchers found risk of premature death due to cardiovascular disease went up more when extreme heat lasted for two or more days.
Speculating on the reasons behind this result, co-author and associate professor of biostatistics at QUT, Adrian G. Barnett, says:
“This might be because people become exhausted due to the sustained strain on their cardiovascular systems without relief, or health systems become overstretched and ambulances take longer to reach emergency cases.”
The results did not show as great a rise in risk of premature death to cardiovascular disease during cold spells.
“We suspect that people take better protective actions during prolonged cold weather,” suggests Barnett, who recommends spending a few hours a day in a temperate environment as a way to help reduce illnesses due to extreme heat and cold.
The researchers point out their findings may not be true of people in other parts of the world, and that they only looked at deaths due to cardiovascular disease.
Written by Catharine Paddock PhD