Wednesday 4 January 2023

Junk vaping study retracted

Last July I wrote about a study which claimed, very implausibly, that vapers not only had a higher risk of cancer than smokers but also got cancer at a younger age. The authors looked at data from the USA’s National Health and Nutrition Examination Survey (NHANES) between 2015 and 2018. They found 154,856 living participants, of whom 5% were e-cigarette users, 63.6% were nonsmokers and 31.4% were smokers. They then looked to see which of them had ever had cancer and concluded that...

Our regression analysis showed that e-cigarette users have 2.2 times higher risk of having cancer compared to non-smokers (odds ratio (OR): 2.2; 95% confidence interval (CI): 2.2 - 2.3; P < 0.0001). Similarly, traditional smokers have 1.96 higher odds of having cancer compared to non-smokers (OR: 1.96; 95% CI: 1.96 - 1.97; P < 0.0001).

This didn't pass the smell test and there was a fairly obvious reason why it was wrong. The average age of the smokers was 62 and the average age of the vapers was 25. So straight away we have an answer to the question of why vapers who got cancer developed it at a younger age than the smokers (and non-smokers, whose average age was 50). They are a much younger cohort.
What about the increased probability of having had cancer? Well, they didn't. As the authors admit in the abstract, 'The e-cigarette users have lower prevalence of cancer compared to traditional smoking (2.3% vs. 16.8%; P < 0.0001)'. They could have added that they had a lower rate than non-smokers too (9.5%). The claim that they had a 2.2 times higher risk of having had cancer comes from a regression analysis in which they had a (presumably cack-handed) go at adjusting for age (but not for former smoking, d'oh!). 
What was true was that, of those who had had cancer, vapers were more likely to have had certain types of cancer than smokers and non-smokers, but - tellingly - they were not smoking-related cancers. Vapers were much less likely to have had lung cancer, for example.
Instead, as I wrote...

The only cancers that were more common among the vapers - not in absolute terms, but as a proportion of cancers among the people who had ever had cancer - were cervical cancer, thyroid cancer, leukemia and one form of skin cancer. What these have in common is that they are either not ‘smoking-related’ (or not strongly associated with smoking) and have a tendency to affect younger people more than most cancers.

Of the people who had had cancer, it is hardly surprising that the younger cohort was less likely to have cancers which mainly afflict old people. It tells you nothing about vaping which, in practice, is an incidental third variable in this study. You might as well say that vapers are more likely to rent than to own a house outright. It would be true, but not useful.
Similarly, the headline claim - that vapers get cancer at an earlier age than smokers and non-smokers - is obviously due to the fact that the vapers in this study were much younger on average than the other groups. Unless you follow these people until the end of their lives, you can't conclude anything.
I ended my article by asking... 

Don’t these things get peer reviewed?

It seems that someone has finally reviewed it because it has now been retracted.

This retracts the article “Cancer Prevalence in E-Cigarette Us-ers: A Retrospective Cross-Sectional NHANES Study”, by Anusha Chidharla et al, published in Vol. 13, No. 1, 2022, p20-26, doi: [1]. After publication of this article, concerns have been raised regarding the article’s methodology, source data processing including statistical analysis, and reliability of conclusions, the authors failed to provide justified explanations and evidence for the inquires, subsequently this article has been retracted at the request of Editor-in-Chief.

Strangely, the article itself does not have a retraction notice on it. Hopefully it will soon.

Regular readers will know that this study is just one of dozens of pieces of scaremongering piffle about e-cigarettes that are published in journals every month. Fortunately, it didn't get much media attention, although crank-in-chief Stanton Glantz, who has also had an anti-vaping study retracted in the past, was all over it on his blog...
First epidemiological evidence linking e-cigs to cancer in people

E-cigarette advocates like to point out that because there is no combustion, e-cigarettes expose users to lower levels of many carcinogens (cancer-causing chemicals).  Even so, there are still some carcinogens in e-cigarette aerosol exposure to e-cigarette aerosol damages DNA and reduces repair in animal and human cells and causes cancer in animals.  Now there is also direct evidence that people who use e-cigarettes are at increased risk of some cancers.
Not any more there isn't, Stan. 
Faced with the uncomfortable fact that none of the (spurious) associations between vaping and cancer involved parts of the body which come into contact with vapour, the great professor appealed to the magical properties of e-cigarette fluid.

The interesting thing about this finding is that these are not the major smoking-induced cancers (lung and bladder).  This result reinforces the view than e-cigarettes are not simply cigarettes without some of the bad chemicals; they expose users to a different mix of toxic chemicals than cigarettes.

There are no prizes for guessing whether he's blogged about the retraction.

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