The Impact of Temperature Variability on Years of Life Lost

Abstract

To the Editor: The relationship between temperature and mortality is generally found to be bathtub shaped (rising at both extremes).1,2 However, there are limited data on the potential health effects of temperature variability3–5 and on temperature itself.6 We used a quasi-Poisson linear regression combined with a distributed lag nonlinear model to examine the relationship between temperature variability and years of life lost in Brisbane, Australia, from 1996 to 2004 (additional details in the eAppendix, https://links.lww.com/EDE/A764). Temperature variability refers to the standard deviation (SD) of minimum temperature within a given week. We found that years of life lost increased with a rise in the variability of weekly minimum temperature (Figure). Women (eFigure 2, https://links.lww.com/EDE/A764) and persons younger than 65 years (eFigure 3, https://links.lww.com/EDE/A764) were more sensitive to this variability. Years of life lost due to cardiovascular illnesses increased strongly with increases in variability of weekly minimum temperature, while years of life lost due to respiratory-related illnesses were not as sensitive to variations in minimum temperature (eFigure 4, https://links.lww.com/EDE/A764).FIGURE: The association between temperature variability (standard deviation of minimum temperature within 1 week) and years of life lost. (No reference value was set.)eTable 2 (https://links.lww.com/EDE/A764) shows the impact of a 1°C increase in weekly minimum temperature SD on years of life lost. Years of life lost increased by 8% (95% confidence interval = 1%–15%), with a 1°C increment of weekly minimum temperature SD. For each 1°C increase in the variability of weekly minimum temperature, annual health care costs were projected to increase by more than AUD$255 million. Increased temperature variability may stress the ability of the thermoregulation system to adapt to sudden and extreme temperature changes, especially when those changes happen frequently in a relatively short time period. Such adaptive ability may be reduced in the presence of other illness. Recently, Zanobetti et al5 found that summer temperature variability was associated with reduced long-term survival among people over 65 years with preexisting diseases. Bull7 has suggested that sudden changes in weather conditions may affect humoral or cellular immunity. Some researchers have reported sudden temperature changes associated with increases in blood cholesterol levels, blood pressure, and heart rate.8 In total, temperature variability should be considered as a factor in addition to temperature change when assessing possible health effects of climate change. ACKNOWLEDGMENTS We thank Adrian G. Barnett for his valuable comments on the manuscript revision. Zhiwei Xu Wenbiao Hu School of Public Health and Social Work Queensland University of Technology Brisbane, Australia Xiaoming Wang CSIRO Climate Adaptation Flagship and CSIRO Ecosystem Sciences Commonwealth, Scientific and Industrial Research Organisation Melbourne, Australia Cunrui Huang Centre for Environment and Population Health School of Environment Griffith University Brisbane, Australia Shilu Tong School of Public Health and Social Work Queensland University of Technology Brisbane, Australia Institute of Health and Biomedical Innovation Queensland University of Technology Brisbane, Australia [email protected]