Effects of cold and hot temperature on dehydration: a mechanism of cardiovascular burden from extreme weather condition

摘要

Background: The association between extreme temperature, cold or heat, and cardiovascular mortality has been well documented. However, there have been few studies explaining the mechanism of cold or heat-related cardiovascular mortality or morbidity. Aims: The main goal of this study was to examine the effect of temperature on dehydration markers to explain pathophysiological disturbances caused by extreme temperature. Methods: We investigated the relationship between outdoor temperature and dehydration markers for 43,549 adults in Seoul, Korea during 1995-2008. We used piecewise linear regression to find the threshold of temperature and estimate the effects below or above the threshold. We also evaluated their association stratified by sex, age, body mass index, and hypertension. Results: Levels of dehydration markers decreased linearly with an increase in the temperature until some points between 22-25°C which are regarded as thresholds, then increased with temperature. The coefficients of temperature on BUN/Cr ratio were -0.036 and 0.083 when temperatures were below and above thresholds, respectively. The coefficients were -0.073 and 0.292 for urine specific gravity; -0.045 and 0.169 for plasma tonicity; and -0.009 and 0.038 for hematocrit. When we performed the analyses stratified by age, gender, BMI and hypertension, the associations between hydration markers and the mean temperature were largely similar among the subgroups. Conclusions: These findings suggest that dehydration increases in both cold and hot outdoor temperatures and the temperature-related change of dehydration underlie an increased cardiovascular mortality or morbidity during extreme weather conditions.