California Institute for Energy and Environment (CIEE)

Several studies found that extremes temperatures are associated with increased mortality worldwide. The extent to which this represents confounding by air pollutants, or is modified by those pollutants, remains unclear. We examined the association between mean apparent temperature and total mortality in nine cities across the US during from May to September 1999 to 2002. We applied both case-crossover and time-series analyses, adjusting for day of the week and season in time series analysis. City-specific estimates were combined using a meta-analysis. A total of 213,438 deaths for all causes occurred in these cities during the study period. We found a significant effect of apparent temperature on mortality with a 1.8% increase (95%CI: 1.09-2.5) per 5.5 °C (10°F) increase in apparent temperature in the case-crossover analysis, and a 2.7% increase (95% CI: 2.01, 3.5) in the time-series analysis. Ozone and fine particulate were not found to be significant confounders or effect modifiers. This study provides evidence of increased mortality due to mean temperature exposure, even when adjusting by air pollution. Global warming is a serious public health issue; more studies to help identifying where public health programs should be directed in order to prevent heat-related morbidity and mortality are warranted.