E-cigarettes are not associated with increased heart attack incidence among people without a history of smoking combustible cigarettes, according to a new study. It found previous research claiming such a link to be methodologically flawed. The paper, published in the American Journal of Preventive Medicine, refuted three earlier studies which had broadly associated e-cigs with higher risk of heart attack, even among people who’d never smoked.
“Among never-smokers, the use of electronic cigarettes is not associated with an increased risk of having a heart attack,” Dr. Michael Siegel, a community health sciences professor at Boston University and one of the authors of the new study, told Filter.
A 2018 study, also published in the American Journal of Preventive Medicine, claimed that daily vapers increased their odds of heart attack. Yet it only included participants who used both e-cigarettes and combustible cigarettes—none who used e-cigarettes alone. Suspicious of that methodology, a different group of researchers published a reply, arguing the importance of examining the purported link among people who had never smoked combustible cigarettes. Authors of the original study then published a reply to that reply, arguing that such a distinction wasn’t necessary.
The second of those two papers—one of whose coauthors, prominent tobacco harm reduction opponent Dr. Stanton Glantz, had once been Siegel’s mentor—was retracted in 2020 for basing its claim that vaping caused heart attacks on evidence that included heart attacks from before the participants had even started vaping.
What’s clear is that the previous conclusion—that e-cigarette use in itself causes heart attack—was wrong.
The new study, authored by Siegel and University of California, Berkeley, business professor Dr. Clayton Critcher, analyzed data from 175,546 respondents to the annual National Health Interview Survey from 2014 to 2019. They found that daily e-cigarette use was only associated with higher heart attack incidence among people who were also currently smoking combustible cigarettes—and that there was no evidence at all for increased risk among vapers who had never smoked combustible cigarettes. Meaning, the initial study had drawn its conclusions about a perceived cause (vaping) and effect (heart attack) without factoring in a key variable (smoking).
Seemingly inexplicably, the original 2018 paper omitted data from the year 2015, as did the subsequent papers based on it. “It does seem odd that they would just omit data from that year when the data are readily available,” Siegel said.
Reanalysis of the dataset used in the original study, with the addition of the most recently available data as well as the missing 2015 data, revealed that the association between e-cigarette use and heart attack depends on one’s history of smoking.
Correlation is not causation, and it’s concerning when researchers fall into such pitfalls.
Critcher and Siegel acknowledge that a more thorough analysis of previous research would have noted that e-cigarettes are relatively new, limiting our ability to assess long-term health effects and make comparisons with combustible tobacco smoking. But what’s clear is that the conclusion of the previous research—that e-cigarette use in itself causes heart attack—was wrong.
Bad research has already led to bad policy in the tobacco harm reduction field, making it unnecessarily harder for smokers to switch to a much safer option. Correlation is not causation, and it’s concerning when highly qualified researchers fall into such pitfalls—at the expense of accurate public health messaging. A correlation between e-cigarette use and heart attack incidence cannot be used as evidence that e-cigarette use will increase heart attack incidence.
“By analogy, if one models height as a function of weight, one cannot then use that output to play out counterfactual scenarios to learn how much shorter a person will become upon losing weight,” Critcher and Siegel wrote.
Photograph via National Institutes of Health