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Winter Temperatures and Mortality in England
Reference
McGregor, G.R.  2005.  Winter North Atlantic Oscillation, temperature and ischaemic heart disease mortality in three English counties.  International Journal of Biometeorology 49: 197-204.

Background
The author notes that "anomalous cold stress can increase blood viscosity and blood pressure due to the activation of the sympathetic nervous system which accelerates the heart rate and increases vascular resistance (Collins et al., 1985; Jehn et al., 2002; Healy, 2003; Keatinge et al., 1984; Mercer, 2003; Woodhouse et al., 1993)," and that "anomalously cold winters may also increase other risk factors for heart disease such as blood clotting or fibrinogen concentration, red blood cell count per volume and plasma cholesterol."

What was done
In light of the strong causative relationship between cold weather and ischaemic heart disease (IHD), i.e., the fact that cold kills, McGregor conducted an analysis to determine if there was any association between the level of IHD mortality in three English counties (Hampshire, West Midlands and West Yorkshire) and the winter-season North Atlantic Oscillation (NAO), which exerts a fundamental control on the nature of winter climate in Western Europe, focusing on the winters of 1974-1975 through 1998-1999.

What was learned
McGregor discovered that "generally below average monthly and all winter IHD mortality is associated with strong positive values of the monthly or winter climate index which indicates the predominance of anomalously warm moist westerly flows of air over England associated with a positive phase of the NAO."  Likewise, at the other extreme, he found that "winters with elevated mortality levels ... have been shown to be clearly associated with a negative NAO phase and anomalously low temperatures," adding that "the occurrence of influenza ... helps elevate winter mortality above that of summer."

What it means
As is typically the case almost everywhere, cold weather tends to result in more deaths than warm weather (see Health Effects (Temperature) in our Subject Index), which suggests that a modest warming of the globe would likely prove beneficial for human health and longevity.

References
Collins, K.J., Easton, J.C., Belfield-Smith, H., Exton-Smith, A.N. and Pluck, R.A.  1985.  Effects of age on body temperature and blood pressure in cold environments.  Clinical Science 69: 465-470.

Healy, J.D.  2003.  Excess winter mortality in Europe: a cross country analysis identifying risk factors.  Journal of Epidemiology and Public Health 57: 784-789.

Jehn, M., Appel, L.J., Sacks, F.M. and Miller III, E.R.  2002.  The effect of ambient temperature and barometric pressure on ambulatory blood pressure variability.  American Journal of Hypertension 15: 941-945.

Keatinge, W.R., Coleshaw, S.R.K., Cotter, F., Mattock, M., Murphy, M. and Chelliah, R.  1984.  Increases in platelet and red cell counts, blood viscosity, and arterial pressure during mild surface cooling: factors in mortality from coronary and cerebral thrombosis in winter.  British Medical Journal 289: 1404-1408.

Mercer, J.B.  2003.  Cold - an underrated risk factor for health.  Environmental Research 92: 8-13.

Woodhouse, P.R., Khaw, K. and Plummer, M.  1993.  Seasonal variation of blood pressure and its relationship to ambient temperature in an elderly population.  Journal of Hypertension 11: 1267-1274.

Reviewed 6 April 2005