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There's good news, even better news, and a bit of bad news in a novel analysis of teens' use of tobacco products.

As previous studies have indicated, overall use, as measured by "nicotine product days" (NPDs) -- the number of days an individual smoked cigarettes or used smokeless tobacco or nicotine-containing vapes in the past month, according to data -- declined substantially from 1999 to 2020 among high-school and middle-school students, reported Ruoyan Sun, PhD, of the University of Alabama at Birmingham, and colleagues.

That's not all. When the researchers factored in the probability that vaping is less harmful than conventional cigarette smoking, the adjusted exposure to risk from nicotine products stabilized or even fell from 2014 t0 2020, at least for high-school kids. This despite the massive increase in vaping seen during that interval.

But at the middle-school level, the trend was not so favorable, the group's indicated. Even at the lowest risk for vaping products Sun and colleagues used in their modeling, the adjusted risk for kids in grades 6-8 crept upward from 2014 onward and reached levels like those in the pre-vaping era, thanks to an enormous spike in vape use by that age group.

The study's chief importance, Sun and colleagues said, was their introduction of risk-adjusted NPDs for modeling health impacts from tobacco products in teenagers. "By considering the frequency of use of nicotine products and offering a platform for contemplating the health implications of different mixes of products," the team wrote, "we hope that NPDs represent a step forward in assessing adolescent exposure to nicotine products."

The authors noted, however, that this was just a first tentative step in that direction, with many specific factors affecting those risks still unquantified.

That point was emphasized in an by Emma Karey, PhD, of New York University in New York City.

"Although NPDs constitute a clever approach to quantifying nicotine product risk, their applicability may be restricted by certain underlying assumptions," she wrote, going on to compile a lengthy list of caveats to Sun and colleagues' study (which, to be fair, the study authors also acknowledged).

Among them:

• Vaping products vary widely in nicotine content and bioavailability

• Vaping behaviors also vary considerably, in both frequency and inhalation intensity

• Health effects from vaping remain incompletely characterized

• Many people use multiple types of nicotine products, which may synergize in unknown ways

Sun and colleagues also pointed out that NYTS data don't distinguish vaping of nicotine from other types of agents such as THC, thus potentially overestimating the nicotine exposure from vapes.

Still, Karey stressed that NPDs are an important step forward in assessing risk. "NPDs provide a substantial improvement compared with other models, which often use product frequency as a proxy for risk (with the underlying assumption being that all nicotine products are equally toxic)," she wrote.

Study Details

The basic data are already familiar to anyone who has followed . Smoking prevalence among school-age children has been in steady decline for many years, with the NYTS data indicating that it still had not bottomed out as of 2020. Use of smokeless tobacco, never very popular among teens, also fell. But the widespread availability of e-cigarettes beginning in about 2013 fueled a surge in use by high-schoolers and, to a lesser extent, middle-school students.

In the NYTS data cited by Sun and colleagues, mean overall raw NPD levels stood at about 5.5 for high-school kids and 1.5 at the middle-school level in 2000. Both fell as time went on, reaching a nadir in about 2017, at roughly 2.5 and 0.5 for high- and middle-schoolers, respectively. These then quickly soared, hitting nearly 5.0 again for high-school students and about 1.0 for middle-school students in 2019, before falling back in 2020 (probably in reaction to the that scared the entire nation the previous year).

Sun and co-authors then modeled the risk exposure by assigning ratios of 0.1 to 1.0 to vaping NPDs relative to combustible nicotine products.

At 0.1 -- i.e., that vaping has one-tenth the health impact of cigarette smoking -- the adjusted overall mean NPD level was less that 1.5 for high-school students in 2020, lower than at any time in the previous 20 years. The same was true for a vaping risk adjustment of 0.25. At 0.5, the mean adjusted NPD for high-school kids was the same as in 2013.

On the other hand, with risk adjustments of 0.75 or 1.0, total adjusted exposure was on the increase after 2013. A similar pattern was seen for middle-school use, except that the adjusted exposure increased after 2013 even for a 0.1 risk ratio.

Besides the limitations already cited, the analysis did not take into account the potential for vaping to serve as a "gateway" to conventional smoking, which several studies have indicated does occur.

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