title: Is smokeless tobacco a risk factor for coronary heart disease? A systematic review of epidemiological studies.
abstract: BACKGROUND
  There is on-going debate about the wisdom of substituting smokeless tobacco products for cigarette smoking as a 'harm reduction' strategy. It is generally believed that health risks associated with smokeless tobacco use (ST) are lower than those with cigarette smoking. However, the population attributable risk of smoking is higher for cardiovascular diseases than for any cancers, and few studies or reviews have considered the cardiovascular outcomes of ST use. A systematic review was therefore carried out to highlight the gaps in the evidence base.
  
  
  METHODS
  Electronic databases were searched, supplemented by screening reference lists, smoking-related websites, and contacting experts. Analytical observational studies of ST use (cohorts, case-control, cross-sectional studies) were included if they reported on cardiovascular disease (CVD) outcomes, or risk factors. Data extraction covered control of confounding, selection of cases and controls, sample size, clear definitions and measurements of the health outcome and ST use. One or two independent reviewers carried out selection, extraction and quality assessments.
  
  
  RESULTS
  A narrative review was carried out. Very few studies were identified; only three from Sweden consider CVD outcomes and these are discrepant. There may be a modest association between use of Swedish snuff (snus) and cardiovascular disease (e.g., relative risk=1.4, 95% confidence interval 1.2-1.6) in one prospective cohort study. Several other studies have considered associations between ST use and intermediate outcomes (CVD risk factors).
  
  
  CONCLUSIONS
  There may be an association between ST use and cardiovascular disease. However, further rigorous studies with adequate sample sizes are required.
authors.affiliation: International Health Research Group, Liverpool School of Tropical Medicine, Liverpool, UK. juliac@liverpool.ac.uk
authors.forename: Julia A
authors.initials: JA
authors.lastname: Critchley
authors.forename: Belgin
authors.initials: B
authors.lastname: Unal
mesh_terms: D002318:Cardiovascular Diseases / Q000209:etiology*; D016021:Epidemiologic Studies; D006801:Humans; D012307:Risk Factors; D040242:Risk Reduction Behavior; D012907:Smoking / Q000009:adverse effects; D014030:Tobacco, Smokeless / Q000009:adverse effects*