Ambient Temperature and Stroke Risk: Evidence Supporting a Short-Term Effect at a Population Level From Acute Environmental Exposures.

Abstract

These are times of increasing concern about the impact on global health of climate change and political turmoil on how to tackle global warming.1,2 Global warming produces not only hotter summers and more frequent episodes of heat waves but also colder winters, especially in more temperate zones, with populations not accustomed to these unusual weather conditions.3 These changes affect human physiology and have the potential of acutely influencing the occurrence of cardiovascular diseases, such as stroke, but the evidence has been until recently conflicting, a great number of which initially came from observational studies on season rather than temperature.4–6 In this review, we examine the current evidence on the association of acute ambient temperature changes and the risk of stroke morbidity and mortality by pathological subtypes. Ambient temperature is defined as the temperature of the surrounding air, and as such, it is modified by humidity, so that in many studies, the exposure is a combination of temperature and humidity level or dew point temperature and may be expressed as thermo-hydrological index when humidity is controlled for.7 Ambient temperature is usually measured at or near airport monitoring stations and thus may introduce bias on real indoor exposures and in urban to rural comparison.8 The effect of ambient temperature on stroke has been studied in relation to daily or monthly mean, maximum, and minimum temperatures and temperature change or variation. It is suggested that mean ambient temperature is the best exposure measure because it can represent the exposure throughout the whole day and night and provide more easily interpretable results, although some authors state that all measurements of temperature have the same predictive ability on health outcomes.9 Two methodological issues have been given special attention: temperature lag effect (exposure response association) and …