Use of smokeless tobacco and risk of myocardial infarction and stroke: systematic review with meta-analysis

OBJECTIVE To assess whether people who use smokeless tobacco products are at increased risk of myocardial infarction and stroke. DESIGN Meta-analysis of observational studies from Sweden and the United States. DATA SOURCES Electronic databases and reference lists. DATA EXTRACTION Quantitative estimates of the association between use of smokeless tobacco products and risk of myocardial infarction and stroke among never smokers. REVIEW METHODS Both authors independently abstracted risk estimates and study characteristics. Summary relative risks were estimated on the basis of random effects models. RESULTS 11 studies, mainly in men, were included. Eight risk estimates were available for fatal myocardial infarction: the relative risk for ever use of smokeless tobacco products was 1.13 (95% confidence 1.06 to 1.21) and the excess risk was restricted to current users. The relative risk of fatal stroke, on the basis of five risk estimates, was 1.40 (1.28 to 1.54). The studies from both the United States and Sweden showed an increased risk of death from myocardial infarction and stroke. The inclusion of non-fatal myocardial infarction and non-fatal stroke lowered the summary risk estimates. Data on dose-response were limited but did not suggest a strong relation between risk of dying from either disease and frequency or duration of use of smokeless tobacco products. CONCLUSION An association was detected between use of smokeless tobacco products and risk of fatal myocardial infarction and stroke, which does not seem to be explained by chance.