Ahead of the conference, the AHA issued a press release headlined “E-cigarettes take serious toll on heart health, not safer than traditional cigarettes.” One of the studies being presented involved 476 people aged between 21 and 45. From the 476, 285 participants were smokers, 94 were non-smokers, 45 were vapers and 52 were dual users of both e-cigarettes and traditional cigarettes.
The findings indicated that the 45 participants who vaped, had lower total cholesterol and higher LDL (bad) cholesterol, while those who both vaped and smoked had lower “good” cholesterol levels. “Total cholesterol was lower and the bad cholesterol, LDL, was higher in sole e-cigarette users compared to nonsmokers. Good cholesterol, HDL, was lower in dual smokers.”
Hence, concluded the study, “Although primary care providers and patients may think that the use of e-cigarettes by cigarette smokers makes heart health sense, our study shows e-cigarette use is also related to differences in cholesterol levels. The best option is to use FDA-approved methods to aid in smoking cessation, along with behavioral counseling.”
A correlation is not a causation
“In a cross-sectional study, you have to be very careful in extrapolating from correlation to causation because this type of study design is very susceptible to confounding.”
This is not the first time that a study is linking vaping and heart disease based solely on correlations. This particular study found a cross-sectional association between e-cigarette use and riskier lipoprotein (cholesterol) profiles, and based solely on that cross-sectional correlation, the investigators concluded that vaping increases “bad” cholesterol levels and has a detrimental effect on cardiovascular health.
“Thus, this paper provides no evidence of any effect of vaping on cholesterol levels. That relationship is completely confounded by diet and physical activity, and it has already been demonstrated in the literature that former smokers have worse cholesterol profiles than nonsmokers, even before e-cigarettes were ever invented!”
Discussing the findings on his blog page, Professor in the Department of Community Health Sciences at Boston University’s School of Public Health, Dr. Michael Siegel, pointed out something that all researchers know very well.
“In a cross-sectional study, you have to be very careful in extrapolating from correlation to causation because this type of study design is very susceptible to confounding — that is, a third variable that is associated with both smoking/vaping status and cholesterol levels and makes it look like they are related, but the relationship is actually driven by this third variable.”
Ignoring important variables
Stating what should have been obvious to the researchers, Siegel pointed out that the study did not take diet and physical activity into account. “In this example, there is a very strong potential confounder: diet. It is very likely that smokers and former smokers have significantly less healthy diets than nonsmokers and therefore, worse cholesterol profiles. There may be differences in physical activity as well, which would lead to a finding of worse cholesterol profiles in current and former smokers than in nonsmokers.”
The professor pointed out that therefore the paper provides no evidence that vaping increases cholesterol levels, and the fact that this should be so obvious to researchers indicated a bias against vaping products. “Thus, this paper provides no evidence of any effect of vaping on cholesterol levels. That relationship is completely confounded by diet and physical activity, and it has already been demonstrated in the literature that former smokers have worse cholesterol profiles than nonsmokers, even before e-cigarettes were ever invented!”
“This is why I think that the conclusion of this paper (that e-cigarette use leads to an unhealthy cholesterol profile and that vaping is therefore just as dangerous as smoking in terms of heart health) is unwarranted and indicates a bias against e-cigarettes,” he added.