What was done
The authors conducted an observational population study in six different regions of France between 1991 and 1995 to assess the relationship between temperature and mortality in areas that experience widely-varying climatic conditions and lifestyles, including urban (Paris), oceanic (Finistere), semi-continental (Cote-d'Or), or mountain (the Hautes-Alpes) climates and two types of Mediterranean climate, one relatively mild and sheltered (the Alpes-Maritimes) and the other more extreme and windy (the Herault). Daily death and cause-of-death data were provided by the Epidemiological Centre on the Medical Causes of Death, which is part of the country's National Institute for Health and Medical Research.

What was learned
Laaidi et al. report that "mean daily counts of deaths showed an asymmetrical V-like or U-like pattern with higher mortality rates at the time of the lowest temperatures experienced in the area than at the time of the highest temperatures," noting that "between these two peaks, there is a critical temperature threshold, referred to as the thermal optimum, where mortality rates are minimal." This relationship varied somewhat between the two sexes and among different age groups and causes of death. In all cases, however, they found that "more evidence was collected showing that cold weather was more deadly than hot weather."

What it means
The researchers' findings are said by them to be "broadly consistent with those found in earlier studies conducted elsewhere in Europe (Kunst et al., 1993; Ballester et al., 1997; The Eurowinter Group, 1997; Keatinge et al., 2000a,b; Beniston, 2002; Muggeo and Vigotti, 2002), the United States (Curriero et al., 2002) and South America (Gouveia et al., 2003)." They also say their findings "give grounds for confidence in the near future," stating that even a 2°C warming over the next half century "would not increase annual mortality rates." In fact, it would in all likelihood reduce them, in light of the common finding of researchers all around the world that cold weather is more deadly than hot weather. See also, in this regard, the many items we have archived under the heading of Health Effects (Temperature - Hot vs. Cold Weather) in our Subject Index.

References
Ballester, F., Corella, D., Perez-Hoyos, S. and Saez, M. 1997. Mortality as a function of temperature. A study in Valencia, Spain, 1991-1993. International Journal of Epidemiology 26: 551-561.

Beniston, M. 2002. Climatic change: possible impact on human health. Swiss Medical Weekly 132: 332-337.

Curriero, F.C., Heiner, K.S., Samet, J.M., Zeger, S.L., Strug, L. and Patz, J.A. 2002. Temperature and mortality in 11 cities of the Eastern United States. American Journal of Epidemiology 155: 80-878.

Gouveia, N., Hajat, S. and Armstrong, B. 2003. Socioeconomic differentials in the temperature-mortality relationship in Sao Paulo, Brazil. International Journal of Epidemiology 32: 390-397.

Keatinge, W.R., Donaldson, G.C., Bucher, K., Jendritzky, G., Cordioli, E., Martinelli, M., Katsouyanni, K., Kunst, A.E., McDonald, C., Nayha, S. and Vuori, I. 2000a. Winter mortality in relation to climate. International Journal of Circumpolar Health 59: 154-159.

Keatinge, W.R., Donaldson, G.C., Cordioli, E., Martinelli, M., Kunst, A.E., Mackenbach, J.P., Nayha, S. and Vuori, I. 2000b. Heat related mortality in warm and cold regions of Europe: Observational study. British Medical Journal 321: 670-673.

Kunst, A.E., Looman, W.N.C. and Mackenbach, J.P. 1993. Outdoor temperature and mortality in the Netherlands: a time-series analysis. American Journal of Epidemiology 137: 331-341.

Muggeo, V.M.R. and Vigotti, M.A. 2002. Modelling trend in break-point estimation: an assessment of the heat tolerance and temperature effects in four Italian cities. In: Stasinopoulos, M. and Touloumi, G. (Eds.). Proceedings of the 17th International Workshop on Statistical Modelling, University of North London, Chania, Greece, pp. 493-500.

The Eurowinter Group. 1997. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. Lancet 349: 1341-1346.