title: A systematic review of health effects of electronic cigarettes.
abstract: OBJECTIVE
  To provide a systematic review of the existing literature on health consequences of vaporing of electronic cigarettes (ECs).
  
  
  METHODS
  Search in: PubMed, EMBASE and CINAHL.
  
  
  METHODS
  Original publications describing a health-related topic, published before 14 August 2014. PRISMA recommendations were followed. We identified 1101 studies; 271 relevant after screening; 94 eligible.
  
  
  RESULTS
  We included 76 studies investigating content of fluid/vapor of ECs, reports on adverse events and human and animal experimental studies. Serious methodological problems were identified. In 34% of the articles the authors had a conflict of interest. Studies found fine/ultrafine particles, harmful metals, carcinogenic tobacco-specific nitrosamines, volatile organic compounds, carcinogenic carbonyls (some in high but most in low/trace concentrations), cytotoxicity and changed gene expression. Of special concern are compounds not found in conventional cigarettes, e.g. propylene glycol. Experimental studies found increased airway resistance after short-term exposure. Reports on short-term adverse events were often flawed by selection bias.
  
  
  CONCLUSIONS
  Due to many methodological problems, severe conflicts of interest, the relatively few and often small studies, the inconsistencies and contradictions in results, and the lack of long-term follow-up no firm conclusions can be drawn on the safety of ECs. However, they can hardly be considered harmless.
authors.affiliation: Research Centre for Prevention and Health, Glostrup Hospital, DK-2600 Glostrup, Denmark. Electronic address: charlotta.pisinger@regionh.dk.
authors.forename: Charlotta
authors.initials: C
authors.lastname: Pisinger
authors.affiliation: Medicinsk Afdeling, Frederikssund Hospital, DK-3600 Frederikssund, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Døssing
mesh_terms: D000818:Animals; D016265:Conflict of Interest; D003603:Cytotoxins / Q000494:pharmacology; D066300:Electronic Nicotine Delivery Systems / Q000009:adverse effects*; D006018:Glycols / Q000032:analysis; D006801:Humans; D019216:Metals, Heavy / Q000032:analysis; D051379:Mice; D052638:Particulate Matter / Q000009:adverse effects; D013227:Steam / Q000009:adverse effects* / Q000032:analysis*; D014835:Volatilization
chemical_list: D003603:Cytotoxins; D006018:Glycols; D019216:Metals, Heavy; D052638:Particulate Matter; D013227:Steam
keywords: E-cigarette; ENDS; Electronic cigarette; Electronic nicotine delivery device; Electronic nicotine delivery system