Mortality from ischaemic heart disease--association with weather.

There is evidence to suggest that mortality from ischaemic heart disease is associated with social class, water hardness, rainfall, and temperature. In a comparison of 61 county boroughs, Gardner, Crawford, and Morris (1969) investigated the relationship between cardiovascular mortality and 80 environmental indices which they reduced to five principal components-social factor score, domestic air pollution, latitude, water calcium, and rainfall. For both sexes mortality in age groups 45-74 was shown to be most significantly correlated with rainfall and with latitude, though for males it was also highly associated with water calcium. In a recent study, Roberts and Lloyd (1972) have compared for county boroughs the dependence of age-standardized mortality from ischaemic heart disease (IHD) on water hardness with the dependence on rainfall. They found that the correlation coefficient between male mortality and average rainfall, eliminating water hardness, was higher (r = 0 37) than that between mortality and water hardness, eliminating rainfall (r = -0 21). This finding leads to the question: what are the mechanisms by which water hardness or rainfall could affect ischaemic heart disease mortality? Gardner et al. have suggested that long-term average rainfall gives a better index of local mineral differences and that the primary association was with hardness. Other studies have illustrated the dependence of ischaemic heart disease on climatic factors. In the USA, Dudley, Beldin, and Johnson (1969) used a composite of temperature and humidity ('comfort index') to explain most of the inter-city variances in mortality. In that country the ranges of temperature are extreme compared with the range in the UK where discomfort is normally only in the sense of coldness. Rose (1966) has shown a very significant seasonal variation in IHD mortality in England and Wales. The death rate in winter months was approximately 50% higher than in the warmer summer months with a very strong correlation (r = -0-95 for males and -0-88 for females) between winter excess of deaths and coldness for the years 1950 to 1962. The present paper reports a further comparison of death rates from ischaemic heart disease in 114 boroughs in England and Wales and an analysis of their dependence on rainfall and temperature.