COPD mortality linked to 24-hour temperature variation
By MedWire Reporters
09 October 2008
Respirology 2008; Advance online publication

MedWire News: Temperature is a known risk factor for chronic obstructive pulmonary disease (COPD) mortality, but a Chinese study has also shown that how much the temperature changes over 24 hours also poses a risk to COPD patients.

Over the 4-year study, there was an observed association between temperature variation within 1 day, known as diurnal temperature range (DTR), and COPD mortality, and the association remained statistically significant after adjustment for temperature levels and other covariates, report Haidong Kan (Rudan University, Shanghai, China) and colleagues in the journal Respirology.

There is already a known U-shaped relationship between temperature and COPD mortality, with mortality risk decreasing from the lowest temperatures to an inflection point and then increasing with higher temperatures.

The researchers hypothesized that DTR, defined as the difference between daytime maximum and night-time minimum temperatures, is also a risk factor for COPD death, independent of absolute temperature levels.

They analyzed mortality data from 2001 to 2004 from nine urban districts of Shanghai and assessed the daily number of deaths due to COPD. Temperature data were collected from the Shanghai Meteorological Bureau. Over the 4-year period, there were 17,874 COPD deaths, or roughly 12 deaths daily. The mean DTR during this time was 6.7°C, with a low of 1.1°C and a high of 16.6°C.

After adjusting for long-term and seasonal trends in daily mortality and other covariates, the effect of DTR on COPD mortality was statistically significant. In a statistical model considering temperature change across multiple days, a 1°C increase in the 4-day moving average for DTR corresponded to a 1.25% increase in COPD mortality.

Previous studies have shown sudden temperature changes increase cardiovascular workload and induce the onset of cardiovascular events, while others have suggested environmental stresses can adversely affect the respiratory system, write Kan and colleagues.

DTR is a meteorological indicator associated with climate change and urbanization, so efforts to combat these factors could reduce COPD-related mortality, comment the researchers. These findings, however, need to be replicated, particularly in areas with different weather patterns.

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