Extreme temperatures affect cardiac mortality

Sep 19 2012

By Piriya Mahendra, medwireNews Reporter

Extreme temperatures experienced during cold spells and heat waves may increase a person's risk for premature death from cardiovascular disease (CVD), say researchers.

Cunrui Huang (Queensland University of Technology, Brisbane, Australia) and team examined the association between daily mean temperature and years of life lost due to CVD after adjusting for trend, season, day of week, and humidity. They found that on average, 72 years of life were lost each day due to CVD for every one million people.

During days with a mean temperature of 10.0°C, which was below the average temperature of 11.7°C on the coldest 1% of days, 31 years of life per one million people were lost per day. During days with a mean temperature of 32.0°C, which was above the average temperature of 29.2°C on the hottest 1% of days, 45 years of life per one million people were lost per day.

The findings from the study are important because of how the body responds to temperate extremes, the growing obesity trend, and the earth's climate changes, said Huang in a press statement.

"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," she explained.

The study in Brisbane, Australia revealed that the exposure-response curve between daily mean temperature and years of life lost due to CVD was U-shaped, with the lowest years of life per one million people lost at 24°C.

The researchers found that the greatest effect of heat occurred on the first day of exposure, then declined rapidly, and returned to baseline within 5 days.

The effect of a cold spell peaked 2 days after exposure, then declined slightly with a delayed effect even after 10 days.

Using a heat wave definition of 2 consecutive days with a temperature above the 99th percentile, 85 years of life per one million people were lost each day to CVD, demonstrating that the risk for CVD rose when extreme heat was sustained for 2 or more days.

"This might be because people become exhausted due to the sustained strain on their CV systems without relief, or health systems become overstretched and ambulances take longer to reach emergency cases," remarked co-author Adrian Barnett, also from Queensland University of Technology, in a press statement.

"We suspect that people take better protective actions during prolonged cold weather, which might be why we did not find as great a risk of CVD during cold spells."

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