Original Article
Lower ambient temperature was associated with an increased risk of hospitalization for stroke and acute myocardial infarction in young women

https://doi.org/10.1016/j.jclinepi.2003.10.016Get rights and content

Abstract

Objective

Results of investigations into the impact of seasonal variation on the incidence of cardiovascular diseases (CVD) have been inconsistent. Using the WHO Collaborative Study of CVD and Steroid Hormone Contraception database, we attempted to examine the relationship between variation in three climatic variables and risk of hospitalization for venous thromboembolism (VTE), arterial stroke, and acute myocardial infarction (AMI).

Study design and setting

We compared the monthly mean temperature, rainfall, and humidity with rates of hospitalized VTE, stroke, and AMI among young women aged 15–49 from 17 different countries in Africa, Asia, Europe, Latin America, and the Caribbean by using a negative binomial regression model.

Results

The study included 1146, 2,269, and 369 cases of VTE, stroke, and AMI, respectively. Significant associations between temperature and hospital admission rates of stroke and AMI, but not VTE, were apparent. Lagging the effects of temperature suggested that these effects were relatively acute, within a period of a month.

Conclusion

These data may help in understanding the mechanisms whereby stroke and AMI events are triggered.

Introduction

Seasonal variation in morbidity and mortality due to cardiovascular disease (CVD) has been investigated in several countries with differing climatic conditions, and overall, findings have been inconsistent [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. When seasonal variation in cardiovascular events has been observed, it has frequently been found to be related to variation in temperature [3], [5], [6], [14], [15], [16]. Possible mechanisms postulated for this association include thermoregulatory responses in arterial pressure [15] and risk of thrombosis through increased blood platelets, red cells counts, blood viscosity [17], and fibrinogen [18], [19], which in turn, was linked with infections in one study of the elderly [19].

Data collected in the World Health Organization (WHO) Collaborative Study of CVD and Steroid Hormone Contraception [20] allowed an evaluation of the variation in monthly hospital admission rates of first time incident cases of venous thromboembolism (VTE), arterial stroke, and acute myocardial infarction (AMI) among young women from 17 countries associated with variation in temperature, humidity, and rainfall.

Section snippets

Subjects and methods

The WHO Collaborative Study was a large international multicenter hospital-based case–control study, a detailed description of which has been reported previously [20]. The main study was undertaken in 24 centers from 17 countries in Africa, Asia, Europe, and Latin America including the Caribbean [20]. Cases were incident cases of AMI, arterial stroke, and VTE among women aged 20–44 (15–49 in the African region and Jamaica), who were admitted to 1 of the 160 collaborating hospitals between

Results

Table 1 shows the number of VTE, stroke, and AMI cases recruited from each of the 24 centers analyzed and the range in average monthly temperature, humidity, and rainfall in each center. The lowest average monthly temperature was −4.6°C in Beijing, and the highest was 30.1°C in Thailand. Both Indonesia and the centers within Colombia showed very little variation in temperature. Zambia and Zimbabwe showed the largest variation in average monthly humidity, and the highest monthly rainfalls were

Discussion

These data show that among young women from 17 countries, the rate of hospitalized AMI, and to a lesser extent stroke, was higher with lower mean environmental air temperature. No such association was seen with VTE events nor were humidity and rainfall linked with either AMI, stroke, or VTE hospitalization rates. Although the negative association between AMI and stroke with mean air temperature was not seen in all countries, on average, a 5°C reduction in mean air temperature was associated

Acknowledgements

We are grateful to Dr. Tim Farley of WHO for his comments on the manuscript. The main study was funded by the UNDP/UNFPA/WHO/World Bank special program of Research, Development and Research Training in Human Reproduction and the National Institutes of Health Contraceptive Health and Reproductive Evaluation Branch. M.J.S. is supported by the British Heart Foundation, and M.G.M. is supported by an MRC Research Professorship.

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