ArticlesCold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe
Introduction
Comparisons of cold-related mortality in different climates are complicated by disparities in baseline mortality rates, age structure, and influenza epidemics. Simple percentage differences in mortality between summer and winter vary substantially within Europe.1 Mortality from ischaemic heart disease (IHD) and cerebrovascular disease (CVD), which together account for about half of all excess cold-related mortality, increases more steeply with falling temperature in London than in New York.2 These deaths seem to result from thrombosis due to haemoconcentration in the cold,3, 4 and from other consequences of cardiovascular reflexes that are briefly induced by low temperatures.5, 6, 7, 8 Increase in respiratory disease (RD), which accounts for nearly half of the remaining excess cold-related mortality, is generally attributed to cross-infection from indoor crowding, to the adverse effects of cold on the immune system's resistance to respiratory infection, and to the fact that low temperatures assist survival of bacteria in droplets.9 The rise in respiratory infections during cold weather further increases numbers of deaths from arterial thrombosis,10, 11, 12 probably owing to increased plasma fibrinogen13 and endotoxin inhibition of fibrinolysis.14
It remains unclear whether protective measures against cold substantially reduce mortality. Certain information would clarify this issue: whether the rises in mortality that accompany falling temperatures differ greatly in extent from one European region to another; whether variations in these increases relate to differences in protection against cold; and how both these factors are associated with the usual winter climate of the region. We are not aware of any previous attempts to relate mortality to extent of personal protection against indoor and outdoor cold, probably owing to a lack of pre-existing data on methods of personal protection in different regions and groups.
The aims of this study were, first, to assess the increases in mortality from all-causes, from IHD, CVD, and RD; to assess the increases per 1°C fall in outdoor temperature with allowance for sex, age, influenza, and baseline mortality; and to relate these increases to the usual winter climate. Second, to measure by active surveys the extent of personal protection against indoor and outdoor cold stress at a standard outdoor temperature. Third, we aimed to relate the summary variables for cold-related mortality to the variables for protection against cold. Separate male and female groups, whose members were of working age (50–59 years) and retired age (65–74 years), were studied in eight European regions with widely varying climates.
Section snippets
Mortality population and temperature data
We recorded the deaths per day of men and women separately, in two age groups (50–59 and 65–74 years), and for eight regions. The regions, which were not chosen randomly but because there was an appropriate research team in each, were north Finland (Kuopio, Vaasa, and Oulu provinces), south Finland (rest of Finland), Baden-Württemberg (Germany), Netherlands, Greater London (UK), north Italy (Imola, Bologna, Modena, and Faenza districts), Athens (Greece), and Palermo (Sicily). Data were
Mortality related to coldness of winter
Mortality rates in each region from IHD, CVD, RD, and all causes, were at or near their minimum value when mean daily temperature was 18°C, and rose in a broadly linear way as the temperature fell. Figure 1 gives examples, with data combined for men and women and both age groups, in Athens and in south Finland. The increases in deaths per 1°C fall from 18°C were greater in the warm region than in the cold region, both absolutely and as a percentage of mortality at 18°C.
Table 1 shows data on
Discussion
The results show that the percentage increases in all-cause and RD mortality with fall in temperature were greater, and that protective measures against a given degree of cold were fewer, in regions with mild winters. The same was generally true of IHD and CVD mortality. The results also show direct associations between mortality indices and protective measures against cold. Evidence of independent associations between mortality rates and specific protective measures was limited by a clear
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