What was done
Based on daily mortality data from 1997 to 2002, which they obtained from the Hong Kong Census and Statistics Department, the authors examined the association between diurnal temperature range (DTR = daily maximum temperature minus daily minimum temperature), focusing on cardiovascular disease among the elderly (people aged 65 and older).

What was learned
Tam et al. discovered "a 1.7% increase in mortality for an increase of 1°C in DTR at lag days 0-3," which results they describe as being "similar to those reported in Shanghai."

What it means
In discussing their findings, the four Hong Kong researchers state that "a large fluctuation in the daily temperature - even in a tropical city like Hong Kong - has a significant impact on cardiovascular mortality among the elderly population." In addition, we note that it has long been known that the DTR has declined significantly over many parts of the world as mean global temperature has risen over the past several decades (Easterling et al., 1997), which is perhaps another reason why colder temperatures are a much greater risk to human life than are warmer temperatures. For more on this latter subject, see Temperature (Health Effects - Warm vs. Cold Weather) in our Subject Index.

Reference
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.