Cross-Sectional Study Finds No Significant Association Between Vaping and Heart Disease
A new study published in the American Journal of Medicine found no significant association between e-cigarette use and heard diseases. The findings come just one month after a similar study linked vaping to heart attacks coronary artery disease and even depression. So what’s the truth?
Well, as far as I am concerned neither of these recent studies are relevant when it comes to the risk of electronic cigarettes causing heart diseases. Even though researchers analyzed data from a large pool of participants, it’s important to note that both studies were cross-sectional, meaning it was virtually impossible for them to determine which came first, the chicken or the egg, or in this case, vaping or heart disease. As the authors of this most recent study conclude, longitudinal studies are required to determine whether the risk of cardiovascular disease risk is associated with e-cigarette use.
Simply put, cross-sectional studies are like snapshots of different people taken at a single point in time, whereas longitudinal ones follow the same group of people over a long period of time, sometimes several years, allowing researchers to detect developments or changes in the areas they are studying. While both types of studies are observational, the key difference between them is that longitudinal ones establish sequences of events, allowing scientists to determine causality, but cross-sectional ones cannot.
For example, the cross-sectional study recently published in the American Journal of Medicine analyzed data from the Behavioral Risk Factor Surveillance System, a large, national telephone survey, to determine whether there was an association to be made between vaping and heart diseases. Researchers looked at self-reported data from 449,092 participants, of which 15,863 (3.5%) were current e-cigarette users, 12,908 (2.9%) were dual users (e-cigarettes & tobacco cigarettes) and 44,852 (10.0%) claimed to be suffering from cardiovascular diseases.
The authors found “no significant association between e-cigarette use and cardiovascular disease among never combustible cigarette smokers”, but noted that dual users were associated with 36% higher odds of cardiovascular disease, which was higher than the odds of tobacco smokers developing heart disease. They concluded that longitudinal studies are required to properly establish a link between vaping and cardiovascular disease.
As I mentioned, this was a cross-sectional study, which by definition cannot establish causality, but renowned tobacco control researcher and vaping opponent, Stanton Glantz, was quick to conclude that dual use is causally associated with cardiovascular disease, while completely ignoring the fact that the authors of the study found no association between heart disease and vaping among never smokers.
“The fact that the authors did not find an effect of e-cigarettes alone may be because they stratified the sample on e-cig and cigarette use, which reduces the sample size for each comparison, and so the power to detect an effect,” Glantz wrote on the UCSF blog.
As Dr. Michael Siegel, a professor at the Boston University School of Public Health, points out, Glantz’s argument doesn’t really hold up, as the sample size of never smoking vapers was larger than that of dual-users. So if you consider the findings about dual-use valid, how can you dismiss the ones about never smoking vapers? Doesn’t really makes sense, does it?
But that’s not even the point. Cross-sectional studies can’t provide the answers we want. For example, who’s to say that the vaping caused the cardiovascular disease and not the other way around? We already know that the vast majority of vapers are former or current smokers and that smoking causes heart-disease, so what if these people were already suffering from cardiovascular conditions that “caused” the vaping? It’s not that wild of an idea. After all, being diagnosed with a high risk of heart attack or stroke is a pretty strong motivation to quit smoking or at least cut down on cigarettes with the help of electronic cigarettes.
A longitudinal study would have taken into consideration whether participants were or weren’t already suffering from heart disease at baseline, and also determine if some of them developed such conditions during the study, thus establishing causality. Cross-sectional studies cannot do that.
So until someone finally decides to do a proper longitudinal study in order to establish an association between vaping and heart diseases, take the findings of cross sectional studies, be they positive or negative, with a big grain of salt. They are not what they seem!
