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Alfésio L. F. Braga,^{1, 2} Antonella Zanobetti,¹ and Joel Schwartz¹

¹Environmental Epidemiology Program, Harvard School of Public Health, Boston, Massachusetts, USA; ²Environmental Pediatrics Program, University of Santo Amaro School of Medicine, and Laboratory of Experimental Air Pollution, Department of Pathology, University of São Paulo School of Medicine, São Paulo, Brazil

Abstract

We carried out time-series analyses in 12 U.S. cities to estimate both the acute effects and the lagged influence of weather on respiratory and cardiovascular disease (CVD) deaths. We fit generalized additive Poisson regressions for each city using nonparametric smooth functions to control for long time trend, season, and barometric pressure. We also controlled for day of the week. We estimated the effect and the lag structure of both temperature and humidity based on a distributed lag model. In cold cities, both high and low temperatures were associated with increased CVD deaths. In general, the effect of cold temperatures persisted for days, whereas the effect of high temperatures was restricted to the day of the death or the day before. For myocardial infarctions (MI) , the effect of hot days was twice as large as the cold-day effect, whereas for all CVD deaths the hot-day effect was five times smaller than the cold-day effect. The effect of hot days included some harvesting, because we observed a deficit of deaths a few days later, which we did not observe for the cold-day effect. In hot cities, neither hot nor cold temperatures had much effect on CVD or pneumonia deaths. However, for MI and chronic obstructive pulmonary disease deaths, we observed lagged effects of hot temperatures (lags 4-6 and lags 3 and 4, respectively) . We saw no clear pattern for the effect of humidity. In hierarchical models, greater variance of summer and winter temperature was associated with larger effects for hot and cold days, respectively, on respiratory deaths. Key words: cardiovascular deaths, nonparametric smoothing, respiratory deaths, temperature, time series, weather. Environ Health Perspect 110:859-863 (2002) . [Online 18 July 2002]

http://ehpnet1.niehs.nih.gov/docs/2002/110p859-863braga/ abstract.html

Address correspondence to J. Schwartz, Environmental Epidemiology Program, Department of Environmental Health, Harvard School of Public Health, 665 Huntington Ave., Bldg. I, Room 1414, Boston, MA 02115 USA. Telephone: (617) 384-8752. Fax: (617) 384-8745. E-mail: jschwrtz@hsph.harvard.edu

This work was supported in part by NIEHS grant ES 00002 and U.S. EPA Research Center Award R827353. A.L.F.B. received personal grants from São Paulo State Research Support Foundation (98/130214) and University of Santo Amaro (UNISA) .

Received 17 August 2001 ; accepted 7 February 2002.

Weather is known to modulate health. Seasonal changes of temperature promote changes in the daily number of respiratory and cardiovascular diseases (CVD) as well as in total and cause-specific mortality. These effects are more prominent among elderly people and children (1) .