Abstracts: ISEE 22nd Annual Conference, Seoul, Korea, 28 August–1 September 2010: Climate Change and Environmental Health
High and low ambient temperatures cause large numbers of deaths annually. Many studies show higher mortality rates during heat waves, with mortality increasing with heat wave duration. However, such effects have not been explicitly incorporated in models of temperature and mortality; while from a physiological basis, dehydration followed by cardiovascular stress is more likely to occur in such conditions.
We established time-series Poisson regression models based on cause-specific mortality and age stratified mortality in Stockholm County, 1990–2002, adjusting for time trends and potential confounders. We studied the effects estimates as functions of time within summers and winters.
Warmer temperatures increase all natural causes of death, while decreasing colder temperatures increases the risk of cardiovascular deaths. Moreover, persistent extreme heat exposure is associated substantially with additional deaths, and the risk of death increase significantly with longer heat exposure. Extreme exposure to heat is associated with higher death rates in people with lower age, compared to a rise in temperature. Furthermore, the impact of warm and cold temperatures decreases within the season, while the impact of persistent extreme heat exposure remains similar throughout the summer.
This study is the first to show that additional impacts of persistence of extreme heat exposure are important to account for in models of mortality related to ambient temperatures to avoid negatively biased estimates of the associated effects. Moreover, it appears that the impacts of temperature depend on the size of the pool of fragile individuals, while persistent extreme heat exposure increases the influx of new individuals to the pool and, thus, remain large throughout the season.