A new congressionally mandated report from the United States National Academies of Sciences, Engineering and Medicine on the evidence of human health effects of e-cigarettes[i] is reportedly one of the most comprehensive studies in this area[ii]. The report is 680 pages long, and is available to download for free.
Despite e-cigarettes having only been in use for a relatively short time, and the evidence base being limited, the committee identified and examined more than 800 scientific studies. The main finding of the report is that though e-cigarettes may be associated with some health risks, they are likely to be far less harmful than conventional cigarettes. E-cigarettes contain fewer and lower levels of toxic substances than conventional cigarettes. The committee found that among adults who smoke conventional cigarettes, use of e-cigarettes make help them to stop smoking, whereas among youth, use of e-cigarettes increases the risk of transitioning to conventional cigarette use.
David Eaton, chair of the committee that wrote the report, said, “E-cigarettes cannot be simply categorized as either beneficial or harmful. In some circumstances, such as their use by non-smoking adolescents and young adults, their adverse effects clearly warrant concern. In other cases, such as when adult smokers use them to quit smoking, they offer an opportunity to reduce smoking-related illness.” [iii]
The report offers conclusions in a number of areas, and the strength of the evidence for each conclusion is noted. Some key conclusions are:
Exposure to nicotine: Exposure to nicotine is highly variable and depends on factors such as the type of device and type of liquid (conclusive evidence). Nicotine intake from e-cigarettes among adult users can be comparable to that from conventional cigarettes (substantial evidence).
Exposure to toxic substances: Most e-cigarettes contain and emit many potentially toxic substances (conclusive evidence). Exposure to potentially toxic substances from e-cigarettes is significantly lower than that from conventional cigarettes (substantial evidence).
Dependence and abuse: E-cigarette use results in dependence (substantial evidence). Risk and severity of dependence is lower for e-cigarettes than for conventional cigarettes (moderate evidence). Risk and severity of e-cigarette dependence depends on the type of product.
Harm reduction: Complete substitution of e-cigarettes for conventional cigarettes reduces exposure to many toxicants and carcinogens (conclusive evidence). Completely switching form regular use of conventional cigarettes to e-cigarettes results in reduced short-term adverse health outcomes (substantial evidence).
Use by youth and young adults: E-cigarette use by youth and young adults increases their risk of ever using conventional cigarettes (substantial evidence).
Secondhand exposure: E-cigarette use increases concentrations of particles and nicotine in indoor environments (conclusive evidence), but second-hand exposure to substances from e-cigarettes is less than that from conventional cigarettes (moderate evidence).
Cancer: There is no evidence available to suggest whether or not use of e-cigarettes is associated with intermediate cancer endpoints in humans. Intermediate cancer endpoints are precursors to possible cancer development, for example, polyps in the intestine. Animal studies suggest that long-term e-cigarette use could increase the risk of cancer (limited evidence).
Respiratory effects: There is no available evidence to suggest whether or not e-cigarettes cause respiratory diseases in humans. In adolescents, there is increased cough and wheeze, or exacerbation of asthma symptoms, in those who use e-cigarettes (moderate evidence).
Injuries and poisonings: E-cigarettes can explode and cause burns and injuries, and the risk is increased when batteries are of poor quality, stored improperly or modified (conclusive evidence). Exposure to the liquids in e-cigarettes can result in adverse effects such as seizures, brain injury due to lack of oxygen, vomiting and buildup of lactic acid (conclusive evidence). Drinking or injecting e-liquids can cause death (conclusive evidence).
Reproductive and developmental effects: There is no available evidence whether or not e-cigarettes affect pregnancy outcomes, and insufficient evidence whether or not maternal e-cigarette use affects fetal development.
Modelling can address the question of whether, overall, e-cigarettes are beneficial or detrimental to public health. In the short-term, assuming the e-cigarettes reduce levels of smoking in adults, there is overall benefit to public health. In the long-term, if conventional smoking by current young adults increases, and the health effects of this manifest several decades later, the overall public health benefit is less, or the net impact may be harmful.
The report says that maximizing the potential health benefits of e-cigarettes will require determining how exactly e-cigarettes help people to stop smoking, and discouraging use of e-cigarettes among youth.
[i] National Academies of Sciences, Engineering, and Medicine. 2018. Public Health Consequences of E-Cigarettes. Washington, DC: The National Academies Press. https://doi.org/10.17226/24952 Available at https://www.nap.edu/catalog/24952/public-health-consequences-of-e-cigarettes (Accessed 29 January 2018)
[ii] New Report One of the Most Comprehensive Studies on Health Effects of E-Cigarettes; Finds that Using E-Cigarettes May Lead Youth to Start Smoking, Adults to Stop Smoking. The National Academies of Sciences, Engineering and Medicine. 23 January 2018. http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=24952&_ga=2.112969357.806311064.1517178215-280332697.1517178215 (Accessed 29 January 2018)