Temperature and risk factors for ischaemic heart disease in the Caerphilly prospective study.

Abstract

Objective-To examine the associations between air temperature and risk factors for ischaemic heart disease. Method-Data on risk factors are available from up to 2036 men in the Caerphilly Prospective Heart Disease Study. Daily temperatures were obtained from the Meteorological Office. Relations between these were examined by regression. Results-The coldest month of the year has a mean temperature that is 16°C lower than that in the warmest month. A fall in temperature of this magnitude is associated with higher blood pressures (by 3-5 mm Hg) and a lower concentration of high density lipoprotein cholesterol (by 0-08 mmolRl). The most important effects however, seem to be on the haemostatic system. Fibrinogen is 0*34 gil higher in the coldest month than in the warmest (p < 0.001) and a, macroglobulin, a protein that inhibits fibrinolysis, is also raised. Platelet count is increased by 30%!. of a standard deviation and the sensitivity of platelets in whole blood to adenosine diphosphate is increased by cold. Conclusions-These effects on haemostasis, together with the effect on blood pressure, could explain a large part of the increase in ischaemic heart disease in the winter but are unlikely to explain much of the difference in mortality within different areas of England and Wales. (Br Heart3J 1993;70:520-523) Deaths from ischaemic heart disease and admissions to hospital for both myocardial infarction and pulmonary embolus are considerably higher in winter than the summer.l1 The meteorological factor of greatest importance seems to be temperature.25 West and Lowe have further suggested that the between town variation in the mortality of ischaemic heart disease in England and Wales may be a consequence of differences in environmental temperatures.6 The extent to which the seasonal rise in ischaemic heart disease and related mortality is truly cardiovascular is uncertain. Some have suggested that the effect of temperature is on respiratory disease and the apparent excess in cardiovascular deaths in winter is simply due to miscoding of the cause of death.7 Bainton et al showed that the proportionate increase in deaths was similar in both young and old patients, leading them to conclude that the effect of temperature on the cardiovascular system is direct.8 On the other hand, Mackenbach et al, who examined the seasonal pattern of deaths in The Netherlands over nine years, suggest that there is both an instantaneous effect of winter on the cardiovascular system, and a delayed effect mediated by respiratory infections.9In this report we examine the associations between ambient air temperature and a range of risk factors for ischaemic heart disease, including blood pressure, lipids, platelets, and other factors related to thrombosis. Patients and methodsThe Caerphilly study is fully described elsewhere.'10 1 It is based on a large cohort of men in South Wales. Each man was first seen at an afternoon or evening clinic at which blood pressure was recorded on a random zero muddler sphygmomanometer. Men were ...

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“…In Raynaud's phenomenon, an unusual degree of digital vaso-contraction occurs in response to cold and causes severe pain, although cold-induced changes in blood viscosity and red cell deformability have also been implicated [3,6]. Seasonal changes in temperature may also influence blood rheology and have been associated with increased risk of cardiovascular mortality in winter [8,20]. The direct effect of temperature on blood viscosity may be excaberated by damage to vessel walls and haemoconcentration [31].…”

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