- Dual use is not one single behaviour as it covers a wide range of patterns
- Heavier vapers who also smoke showed lower toxicant exposure than people who only smoked
- Major national surveys often fail to measure how often and how long people vape
- Weak exposure data can distort findings on disease risk and quitting
For years, “dual use” – the term for people who both smoke cigarettes and use vapes – has been treated as one simple category in public health research.
Dual users are often described as a single group, either at higher risk or less likely to quit.
But a new methodological commentary by Gal Cohen, Steven Cook and Arielle Selya – published online as an accepted manuscript – suggests that the category itself may be misleading. The problem isn’t necessarily the people. It’s how the data is collected.
The authors write: “dual use is not a unitary behavior; it spans a range of multiproduct use patterns.” In other words, dual use is not one single, uniform behaviour. Some people vape every day. Others vape once a week. Some are cutting down on cigarettes. Others are not. But in many studies, they are all grouped together.
One label, very different behaviours
One of the studies examined levels of toxicants – harmful chemicals linked to smoking – in people who had used cigarettes and/or vapes in the past 30 days. The dual-use group was divided by how frequently they used each product.
That breakdown revealed that the dual-use population was split into two very different patterns – about 45 per cent used vapes roughly once a week, while the rest used them on most or all days of the month.
When the commentary authors reanalysed the data, they found that “a higher frequency of vape use (20+ days per month) in dual-users was associated with reduced exposure to nonnicotine toxicants vs. exclusive CC use.”
In other words, people who vaped more frequently while also smoking had lower exposure to certain toxicants than people who only smoked cigarettes.
That lower exposure “was characteristic of the majority (55 per cent) of the DU cohort.”
But when all dual users are lumped together, those differences can disappear in the averages. Someone who vapes daily while reducing cigarette use is treated the same as someone who mostly smokes and occasionally vapes.
The authors also point out that: “Actual environmental exposure was not directly measured, as there was no nontobacco-use control group.” Without measuring background exposure from the environment, it is harder to isolate how much of the toxicant level is truly due to tobacco use.
Measuring disease risk without measuring dose
A second study followed participants for nearly four years to look at links between product use and cardiometabolic conditions. It excluded former users and people with preexisting disease. This was a strength.
But there was a major weakness. The commentary notes: “Limitations included imprecise exposure quantification and a lack of dose‒response analyses.”
Participants were included if they had used a product at least once in the past 30 days. That means someone who smoked heavily for decades and vaped once last month could be grouped with someone who had dramatically cut down on cigarettes while vaping regularly.
Without carefully measuring how much people smoked, for how many years, and how frequently they used vapes, it becomes very difficult to draw firm conclusions about risk.
The same issue appeared in a study looking at smoking cessation. In the raw data, daily vape users had higher quit rates than non-users. After statistical adjustments, that flipped.
But the commentary points out that product use between survey waves was not fully tracked, and prior smoking intensity before starting vapes was not carefully measured. In other words, the details that matter most may not have been captured clearly enough.
A survey problem hiding in plain sight
The broader concern goes beyond any one study. The commentary warns that “a lack of precise and comprehensive EC use metrics in national survey databases imperils the accuracy of cross-sectional studies of their data.”
Several major national surveys do not consistently record how many days per month people use vapes. Some do not track how long someone has been a regular user. Only one major survey follows patterns of use over time in detail.
And yet, duration and frequency of use are “central metrics.”
Without them, researchers are trying to answer complex health questions with incomplete information.
The authors are not claiming that dual use is safe – or unsafe. Their point is that when researchers use a broad label without measuring how intensely or how long products are used, the category can become too blunt to be meaningful.
Dual use may not be one stable, uniform state. It may be a shifting spectrum of behaviours – some transitional, some long term, some involving reduced cigarette use and others not.
Therefore, when headlines talk about “dual users,” it’s worth asking: how often were they vaping? How much were they smoking? For how many years?
Without those answers, the label “dual use” risks oversimplifying a complex reality, and turning a diverse set of behaviours into what the authors suggest may be a statistical fiction.
