Ecigs likely to have negative population health effects if more than 20-30% as bad as cigs

Today Sara Kalkhoran and I published “Modeling the Health Effects of Expanding e-Cigarette Sales in the United States and United Kingdom” in JAMA Internal Medicine. 
 
There have been many commentaries and opinion pieces on the potential health effects of e-cigarettes that describe some of the various scenarios that could play out.  This paper applies numbers to these potential scenarios to compare them in a more quantitative manner.
 
Specifically, in the debate over the desirability or effects of e-cigarettes entering the market, particularly among e-cigarette optimists, people have tended to focus on very simple models of how things would change, often assuming that the only effect e-cigarettes have on population health would be established smokers switching partly or entirely from combustible cigarettes to e-cigarettes or using them to quit entirely.  The assumption was always that e-cigarettes were “harmless water vapor” or, at least, minimally risky.
 
The real situation is more complicated.
 
The entry of e-cigarettes is having several interacting effects:
 

• Some people are switching to ecigs
• Some people end up continuing to smoke cigs because of dual use with ecigs
• Some people (kids and young adults) initiate nicotine use with ecigs, some of whom go on to smoke cigs
• The actual long-term risks of ecigs are not known, but there are reasons to think that they could be substantial (albeit lower than cigarettes).

 
The model that we developed allowed us to determine the net effect of e-cigs under a wide range of possible futures and determine what the important variables are.
 
For the reasons described above we really did not know how things would turn out when we started.  Indeed, that was the whole reason for doing the study.
 
Having said that, we were surprised that the likelihood of a favorable net effect in UK is consistently lower than in the US.  This was a surprising result given the fact that many health authorities in UK have enthusiastically embraced e-cigs as a harm reduction strategy.  Ecigs are more likely to increase harm in UK than the US.
 
The key finding of the paper is that under all the likely scenarios, if ecigs turn out to be 20-30% as dangerous as conventional cigarettes there will be net harm.  No one know what the actual risks will be, but I would be surprised if the risks are not at least that high.
 
In addition, work published since we did our work is showing higher youth initiation and higher odds of progression to cigarette smoking among new users than we used in our simulation (which were based on data collected before the market was a fully developed as it is now), which will mean that the risk crossover point will move to lower e-cigarette risks.
 
Bottom line:  The effects of the entry of e-cigarettes into the market is a lot more complicated than just smokers switching to them.  E-cigarettes can also be an entry product for nicotine addiction and can lead to and discourage quitting cigarettes.  Unless e-cigarettes turn out to have very low risks, the net effect on the population will be negative. 
 
The regulatory environment of e-cigarettes can help shape which scenario ultimately plays out.  For example, measures that aim to decrease the uptake of e-cigarettes by never-smoking youth, such as prohibiting sale of e-cigarettes to youth and limiting advertising and mass-marketing of e-cigarettes can help improve the probability that one of the more positive scenarios develops.
 
In addition, policymakers should keep in mind that it is virtually impossible to separate youth use from adult use (since cigarettes are promoted as a way for kids to look grown up).  The longer that they wait to take action the harder it will be to prevent or reverse negative consequences.  Integrating e-cigs into clean indoor air laws and smokefree home policies is very important to discourage dual use and the use of ecigs as a bridge for nicotine use when people cannot smoke cigs.
 
The full paper is available here.  The commentary on it in JAMA Internal Medicine is here.