Sunday, March 17, 2019

Purported Links Between Vaping and Heart Attacks are Based on Crappy Science

Another crappy study has come along, this one again using cross-sectional data from the National Health Interview Survey to claim that e-cigarette use is associated with a higher risk of having a heart attack, developing coronary artery disease, and having depression.

This study, being presented tomorrow (Monday) morning at the annual meeting of the American College of Cardiology in New Orleans, reports that "adults who report puffing e-cigarettes, or vaping, are significantly more likely to have a heart attack, coronary artery disease and depression compared with those who don’t use them or any tobacco products."

These conclusions were based on a cross-sectional analysis of data from the 2014, 2016, and 2017 National Health Interview Surveys. Respondents were asked to report whether they had ever been diagnosed with having had a heart attack, coronary artery disease, or depression. The analysis found that people who reported vaping were more likely to have ever had a heart attack, to have ever been told they have coronary artery disease, or to have ever been diagnosed with depression. The analysis did control for smoking by including smoking status as a variable in the regression model.

The Rest of the Story

This is yet another example of the junk science that is rapidly being spewed out by anti-tobacco researchers who are apparently more interested in demonizing vaping than in using rigorous scientific reasoning.

The problem with the study's conclusion is that this is a cross-sectional analysis and the researchers have no idea which came first: the vaping or the heart attack, heart disease, or depression.

Let's consider heart attacks. It is entirely possible (and actually quite likely) that most - if not all - of the respondents who reported that they are vapers had started vaping after, not before their heart attacks. In fact, a likely explanation for the findings is that smokers who experience a heart attack are much more likely to try to quit smoking, and since switching to vaping is a common method of attempting to quit smoking, they are more likely to respond that they are vapers.

The investigators claim that they have controlled for smoking. But here's the problem: smoking is not only a confounder in the analysis; it is also an effect modifier. This means that the association between vaping and having had a heart attack is different for nonsmokers and smokers. For nonsmokers, there is no association. The association only holds for former smokers and current smokers. In the presence of effect modification, treating smoking purely as a confounder will yield inaccurate results. In order to model the relationship correctly, you need to stratify the analysis on smoking status: that is, you need to report the relationship separately for nonsmokers, former smokers, and current smokers.

None of the papers that have claimed vaping causes heart attacks, heart disease, stroke, or COPD have done that. They treat smoking as a confounder, but do not test for effect modification.

It is unfortunate that this crappy science is being reported at scientific conferences and in scientific journals. But what makes this a real tragedy is that this junk science is being used to justify policies to regulate vaping more harshly than smoking, by: (1) heavily taxing these products; (2) banning e-cigarette flavors; and/or (3) completely banning the sale of e-cigarettes in convenience stores.

The rest of the story is that rather than demonstrating that vaping causes heart attacks, heart disease, COPD, and depression, what these studies show is that when smokers get very sick, they are highly motivated to quit in order to save their lives, and many of them do so by switching to vaping.

This is about 11 million lives, not 11 million lies.

1 comment:

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