Elsevier

The Lancet

Volume 368, Issue 9536, 19–25 August 2006, Pages 647-658
The Lancet

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Tobacco use and risk of myocardial infarction in 52 countries in the INTERHEART study: a case-control study

https://doi.org/10.1016/S0140-6736(06)69249-0Get rights and content

Summary

Background

Tobacco use is one of the major avoidable causes of cardiovascular diseases. We aimed to assess the risks associated with tobacco use (both smoking and non-smoking) and second hand tobacco smoke (SHS) worldwide.

Methods

We did a standardised case-control study of acute myocardial infarction (AMI) with 27 089 participants in 52 countries (12 461 cases, 14 637 controls). We assessed relation between risk of AMI and current or former smoking, type of tobacco, amount smoked, effect of smokeless tobacco, and exposure to SHS. We controlled for confounders such as differences in lifestyles between smokers and non-smokers.

Findings

Current smoking was associated with a greater risk of non-fatal AMI (odds ratio [OR] 2·95, 95% CI 2·77–3·14, p<0·0001) compared with never smoking; risk increased by 5·6% for every additional cigarette smoked. The OR associated with former smoking fell to 1·87 (95% CI 1·55–2·24) within 3 years of quitting. A residual excess risk remained 20 or more years after quitting (1·22, 1·09–1·37). Exclusion of individuals exposed to SHS in the never smoker reference group raised the risk in former smokers by about 10%. Smoking beedies alone (indigenous to South Asia) was associated with increased risk (2·89, 2·11–3·96) similar to that associated with cigarette smoking. Chewing tobacco alone was associated with OR 2·23 (1·41–3·52), and smokers who also chewed tobacco had the highest increase in risk (4·09, 2·98–5·61). SHS was associated with a graded increase in risk related to exposure; OR was 1·24 (1·17–1·32) in individuals who were least exposed (1–7 h per week) and 1·62 (1·45–1·81) in people who were most exposed (>21 h per week). Young male current smokers had the highest population attributable risk (58·3%; 95% CI 55·0–61·6) and older women the lowest (6·2%, 4·1–9·2). Population attributable risk for exposure to SHS for more than 1 h per week in never smokers was 15·4% (12·1–19·3).

Conclusion

Tobacco use is one of the most important causes of AMI globally, especially in men. All forms of tobacco use, including different types of smoking and chewing tobacco and inhalation of SHS, should be discouraged to prevent cardiovascular diseases.

Introduction

Tobacco use is one of the most important avoidable causes of cardiovascular diseases worldwide.1 The number of smokers worldwide is currently estimated to be 1·3 billion, of which 82% are in developing countries.2 During the 20th century, 100 million individuals died worldwide as a result of tobacco-related diseases.3 This number is expected to increase to 1 billion during the 21st century.4 About half of these deaths will occur among middle-aged adults (35–69 years old), who will lose on average 22 years of life.5 Most tobacco-related deaths occur among men, but female mortality from tobacco is expected to increase substantially as a result of large increases in smoking among women in many developed countries, and high rates of use of non-smoking tobacco, especially in women, in several developing countries.2

The risk of coronary heart disease associated with smoking has been documented in studies in developed countries,6, 7, 8 few large studies have been done to examine the effects of tobacco in other geographical regions. The available studies are difficult to compare, and extrapolations from studies in developed countries to other regions of the world might not be appropriate because of varying methods and markedly different patterns of tobacco use (eg, the type of smoking varies in different countries: cigarettes or beedies, smoking or chewing, different ages at starting the habit, numbers smoked).9, 10, 11, 12, 13, 14, 15, 16 Moreover, the few studies that have been done in developing countries include relatively small numbers of cases, so that there is uncertainty about the magnitude of the risk associated with smoking in these countries.

Emerging data suggest that second hand smoke (SHS) is associated with adverse health effects, including coronary heart disease,17, 18 but the available studies recorded relatively few events, and might not have fully adjusted for other lifestyle factors such as diet. However, some of the research that suggested a failure to adjust for such confounders has itself been challenged on both methodological grounds and undisclosed links to the tobacco industry.19 Therefore, considerable uncertainty exists about the size of the effect of SHS. We undertook a study to document the risks associated with various forms of active tobacco use (both smoking and non-smoking) and SHS in all regions of the world, controlling for potential confounders.

Section snippets

Participants

INTERHEART was a standardised case-control study of 15 152 cases of first acute myocardial infarction (AMI) and 14 820 age-matched and sex-matched controls who were recruited from 262 centers in 52 countries in Asia, Europe, Middle East Crescent, Africa, Australia, North and South America. Details have been published previously.20, 21 Consecutive cases of first AMI presenting within 24 h of symptom onset were eligible. We included all consenting cases without cardiogenic shock or history of

Results

A previous report showed that abnormal lipid profiles, smoking, hypertension, diabetes, abdominal obesity, psychosocial factors, consumption of fruits, vegetables, and alcohol, and physical activity accounted for most of the risk of AMI worldwide.21 The demographic, health history and characteristics for the 27 098 participants (12 461 cases and 14 637 controls) have been reported.21 The distribution of various risk factors between cases and controls are summarised in table 1. Here, we focus on

Discussion

Our study resulted in several key findings about tobacco use. First, use of tobacco is associated with increased risk of AMI, consistently across all regions. Tobacco use is one of the largest contributors to AMI worldwide. The risk is greater in the young than in the old, for men and women. Although the PAR of AMI was low in women because of the low prevalence of smoking, the excess risk associated with smoking in women was similar to that in men. Second, smoking patterns differed

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