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The Killing "Cold" of Sao Paulo, Brazil
Sharovsky, R., Cesar, L.A.M. and Ramires, J.A.F.  2004.  Temperature, air pollution, and mortality from myocardial infarction in Sao Paulo, Brazil.  Brazilian Journal of Medical and Biological Research 37: 1651-1657.

What was done
The authors investigated "associations between weather (temperature, humidity and barometric pressure), air pollution (sulfur dioxide, carbon monoxide, and inhalable particulates), and the daily death counts attributed to myocardial infarction in the city of Sao Paulo in Brazil, where 12,007 fatal events were observed from 1996 to 1998."

What was learned
The authors report finding "a significant association of daily temperature with deaths due to myocardial infarction (P<0.001), with the lowest mortality being observed at temperatures between 21.6 and 22.6C."  For all practical purposes, however, their data show little variation in death rates from 18C to just over 25C, the latter of which values represents the typical upper limit of observed temperature in Sao Paulo, which is located on the Tropic of Capricorn at an altitude of 800 m.  As mean daily temperature drops below 18C, however, death rates rise in essentially linear fashion to attain a value at 12C (the typical lower limit of observed temperature in Sao Paulo) that is more than 35% greater than the minimum baseline value registered between 21.6 and 22.6C.

What it means
Sharovsky et al. say they "demonstrated a strong association between daily temperature and myocardial infarction in Sao Paulo, Brazil," which suggests that "an acclimatization of the population to the local climate occurs and that myocardial infarction deaths peak in winter not only because of absolute low temperature but possibly secondary to a decrease relative to the average annual temperature," which indeed must be true, for deaths due to heart attacks are consistently greater in winter than in summer, as they note, "across many regions of the world (Marshall et al., 1998; Douglas et al., 1991; Seto et al., 1998; Sheth et al., 1999)."  Hence, it can be appreciated that the global warming of the past century, which increased minimum temperatures considerably more than maximum temperatures almost everywhere, likely prevented - or significantly forestalled - the deaths of many people around the world who otherwise would have succumbed to this deadly scourge of the human race, i.e., (relatively) cold temperature.

Douglas, A.S., Al-Sayer, H., Rawles, M.M. and Allan, T.M.  1991.  Seasonality of disease in Kuwait.  Lancet 337: 1393-1397.

Marshall, R.J., Scragg, R. and Bourke, P.  1988.  An analysis of the seasonal variation of coronary heart disease and respiratory disease mortality in New Zealand.  International Journal of Epidemiology 17: 325-331.

Seto, T.B., Mittleman, M.A., Davis, R.B., Taira, D.A. and Kawachi, I.  1998.  Seasonal variations in coronary artery disease mortality in Hawaii: observational study.  British Medical Journal 316: 1946-1947.

Sheth, T., Nair, C., Muller, J. and Yusuf, S.  1999.  Increased winter mortality from acute myocardial infarction and stroke: the effect of age.  Journal of the American College of Cardiology 33: 1916-1919.

Reviewed 23 February 2005