E-cigarette use increases the risk of stroke and heart attack: conclusions that constitute epidemiological malpractice


 By Dr Farsalinos

A recently published study and a conference abstract released just today raised substantial concerns that use of e-cigarettes is associated with an increased risk for cardiovascular disease. The published study mentions in the abstract conclusion: “Daily e-cigarette use, adjusted for smoking conventional cigarettes as well as other risk factors, is associated with increased risk of myocardial infarction.”. Today’s media coverage of the conference abstract mention: “E-cigarettes linked to higher risk of stroke, heart attack, diseased arteries.

Both these conclusions are simply wrong and constitute epidemiological malpractice and misinformation. “Increasing the risk” means that someone is FIRST exposed to a condition (in this case, exposed to e-cigarette use) and THEN, BECAUSE OF THIS EXPOSURE, he/she develops disease. Both studies CANNOT provide any of this information to substantiate an increased risk. Both are cross-sectional surveys, meaning that they asked participants if they have heart disease and if they use e-cigarettes. The studies provide no information on whether e-cigarette use was initiated before (and how long before) or after the development of disease. What if participants used e-cigarettes after they developed the disease in order to quit smoking? Two scientists from the University of California Los Angeles published a letter about the recently published study saying that if only 10% of participants were misclassified as using e-cigarette users before (instead of after) having the heart attack, the association mentioned in the study would be invalid. So, does this constitute a risk of developing a disease that was already developed BEFORE being exposed to e-cigarettes? This sounds more like a nice joke. It is very similar to another comment I made several weeks ago about someone who was a smoker and was diagnosed with COPD and laryngeal cancer, and decided to quit smoking with the use of e-cigarettes. He initiated e-cigarette use after 46 years of smoking, 15 years AFTER the diagnosis of COPD and 3 years AFTER the diagnosis of laryngeal cancer. This is a person with COPD and laryngeal cancer who uses e-cigarettes, and he would be used to justify an “increased risk” in both the studies mentioned! Absurd…

There are even more funny stories coming from such analysis. We analyzed the data from the National Health Interview Survey of 2016 and 2017 using the same methodology as the recently published study. In this case, we examined the association between ever using medications to lower cholesterol and having a heart attack. We found that ever use of anti-cholesterol medications was associated with a 115% higher odds (more than double the odds) of having had a heart attack. And that was on top of having hypercholesterolemia and adjusted for all other risk factors for heart attack. Should we claim that “Ever taking prescribed medicine to lower cholesterol, adjusted for having hypercholesterolemia as well as other risk factors, is associated with increased risk of heart attack”? Of course not, that would be absurd.  

There are even more problems in these studies that preclude any claim that e-cigarettes increase the risk for any disease. In the published study, 94.7% of daily e-cigarette users were current or former smokers. In the conference abstract, 79% of e-cigarette users were smokers (they do not mention if this refers to current only or current and former smokers). So, there is an obvious problem in the analysis, that is not necessarily addressed by simply adding the smoking status in the analysis.

In conclusion, both studies provide no information about any risk associated with the use of e-cigarettes. They do not prove an increased risk and of course they do not prove that no such risk exists. They simply cannot address the question of whether e-cigarettes increase the risk for heart disease or not. I am confident that the authors of the published study and the American Heart Association, which released the press statement for the conference abstract, are very well aware of these basic epidemiological principles. This is simple, basic knowledge for a medical student, let alone for acknowledged scientists. And they know that the statements about “increased risk” are wrong. So, why do they use these statements? Perhaps we should ask them…



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