Cao, J., Cheng, Y., Zhao, N., Song, W., Jiang, C., Chen, R. and Kan, H. 2009. Diurnal temperature range is a risk factor for coronary heart disease death. Journal of Epidemiology 19: 328-332.
What was done
Working within the nine urban districts of Shanghai, China, the authors used time-series and case-crossover approaches to assess the relationship between diurnal temperature range (DTR = the difference between a day's maximum and minimum air temperature) and coronary heart disease (CHD) deaths that occurred between 1 January 2001 and 31 December 2004, based on mortality data for elderly (66 years of age or older) people that they obtained from the Shanghai Municipal Center of Disease Control and Prevention, and temperature data they obtained from a fixed-site station in the Xuhui District of Shanghai, which they adjusted to account for the mortality impacts of long-term and seasonal trends in CHD mortality, day of week, temperature, relative humidity and concomitant atmospheric concentrations of PM10, SO2, NO2 and O3, which they obtained from the Shanghai Environmental Monitoring Center.
What was learned
Cao et al. determined that "a 1°C increase in DTR (lag = 2) corresponded to a 2.46% increase in CHD mortality on time-series analysis, a 3.21% increase on unidirectional case-crossover analysis, and a 2.13% increase on bidirectional case-crossover analysis," and that "the estimated effects of DTR on CHD mortality were similar in the warm and cool seasons."
What it means
The seven scientists conclude that their "data suggest that even a small increase in DTR is associated with a substantial increase in deaths due to CHD [italics added]." And since it has long been known that the DTR has declined significantly over many parts of the world as mean global air temperature has risen over the past several decades (Easterling et al., 1997), it can be appreciated that the global warming with which this DTR decrease is associated (which is driven by the fact that global warming is predominantly caused by an increase in daily minimum temperature) has likely helped to significantly reduce the CHD mortality of the world's elderly people.
Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.