Effects of Extreme Temperatures on Years of Life Lost for Cardiovascular Deaths: A Time Series Study in Brisbane, Australia

Abstract

Extreme temperatures are associated with cardiovascular disease (CVD) deaths. Previous studies have investigated the relative CVD mortality risk of temperature, but this risk is heavily influenced by deaths in frail elderly people. To better estimate the burden of extreme temperatures, we estimated their effects on years of life lost due to CVD. The data were daily observations on weather and CVD mortality for Brisbane, Australia, between 1996 and 2004. We estimated the association between daily mean temperature and years of life lost due to CVD, after adjusting for trend, season, day of the week, and humidity. To examine the nonlinear and delayed effects of temperature, a distributed lag nonlinear model was used. The model's residuals were examined to investigate whether there were any added effects due to cold spells and heat waves. The exposure-response curve between temperature and years of life lost was U-shaped, with the lowest years of life lost at 24°C. The curve had a sharper rise at extremes of heat than of cold. The effect of cold peaked 2 days after exposure, whereas the greatest effect of heat occurred on the day of exposure. There were significantly added effects of heat waves on years of life lost. Increased years of life lost due to CVD are associated with both cold and hot temperatures. Research on specific interventions is needed to reduce temperature-related years of life lost from CVD deaths.