The cross-sectional study looked at data from the National Health Interview Surveys of 2014 and 2016 involving 69,725 participants, and controlled for conventional cigarette use, demographic characteristics such as age, gender and body mass index, and health characteristics such as hypertension, diabetes, and high cholesterol.
The respondents reported their current vaping and smoking statuses and whether they had ever had a heart attack, and the researchers found a significant association (odds ratio = 1.8) between daily vaping and ever having a heart attack. Based on this observation, the researchers concluded that daily use of e-cigarettes doubles one’s chances of suffering a heart attack. But is this really the case?
A correlation does not equate to causation
Dr. Siegel pointed out that this study indicates a correlation, not causation, and this correlation could be bidirectional. “Before accepting the conclusion that vaping causes heart attacks in unsuspecting smokers, remember the old adage: correlation does not equal causation. This study is a perfect demonstration of that phenomenon,” said the public health professor.
“Because this is a cross-sectional study, and because respondents were asked whether they had ever had a heart attack, one cannot determine whether the heart attacks followed e-cigarette use or preceded it. In other words, we do not know that vaping preceded the heart attack for any of the subjects. It is entirely possible that in most of these cases, the smokers suffered a heart attack and then started vaping in an attempt to quit smoking,” added Siegel.
It is likely that smokers switched to vaping after experiencing a heart attack
Siegel explained that it is not even “biologically plausible” that vaping would elevate the the risks of cardiovascular disease beyond that of smoking, because the cardiovascular effects of smoking get saturated at very low levels, and beyond that there is very little additional risk. On the other hand, he added, it is very plausible that smokers may try quitting smoking by switching to e-cigarettes, after having experienced a heart attack.
Hence, concluded Siegel, before reaching such conclusions about causation, longitudinal studies are required to confirm the findings. “This single cross-sectional study is not enough because there is no way to tell the direction of the observed association between current use of e-cigarettes and having experienced a heart attack in the past.” concluded Siegel.