Novel metric allows for comparison of relative risk of e-cigs vs other nicotine/tobacco products

Nicotine product days (NPD), a novel metric for evaluating adolescent exposure to nicotine products, may be superior to measuring any 30-day tobacco product use when it comes to measuring the health consequences of different combinations of nicotine products over time, researchers argued.

Cigarette smoking has steadily dropped among U.S. adolescents over the past 20 years, with 12.8% of middle school students and 34.8% of high school students reporting cigarette use in the preceding 30 days in 1999 versus 1.6% and 4.6%, respectively, in 2020. However, e-cigarette popularity has skyrocketed among this population in recent years—from 2017 to 2018, current e-cigarette use jumped from 11.7% to 20.8% among high school students, and from 3.3% to 4.9% among middle school students, then jumped even higher in 2019 to 27.5% and 10.5%, respectively.

With these fluctuations in use of conventional and electronic nicotine products, “it is unclear whether total exposure to nicotine products has changed among adolescents,” Ruoyan Sun, PhD, of the University of Alabama at Birmingham, and colleagues wrote in JAMA Network Open. And, they added, most measures do not account for frequency of product use, changes in exposure to various products, and the differential health risks associated with different smoking products, particularly cigarettes.

“Our main motivation for this paper is to find a better measure to assess adolescents’ exposure to nicotine products and its associated long-term health risks,” Sun told BreakingMED in an email correspondence. “The current measure from the CDC, any tobacco product (ATP) use, is a simple binary (0 versus 1) measure that fails to capture the frequency of use or differential product risk implications. “

In this study, Sun and colleagues developed NPD—a measure that “adjusts any past 30-day use to reflect the frequency (number of days) of individuals’ use of products during that period”—and assessed how nicotine exposures among middle and high school students have changed in the past 22 years according to this new metric.

“The results of this cross-sectional study show substantial decreases in adolescent nicotine and tobacco product use prior to the popularity of e-cigarettes (1999-2013); this decrease slowed and then reversed sharply in subsequent years,” they wrote. “However, risk-adjusted NPDs may have continued to decline from 2014 to 2020, depending on the risk weight associated with e-cigarettes. By considering the frequency of use of nicotine products and offering a platform for contemplating th ehealth implications of different mixes of products, we hope that NPDs represent a step forward in assessing adolescent exposure to nicotine products.”

In an editorial accompanying the study, Emma Karey, PhD, of New York University Langone School of Medicine in New York City, acknowledged that NPDs allows for side-by-side comparisons of nicotine products, thus offering a substantial leg up over other models that use product frequency as a proxy for risk. However, she added that the applicability of NPDs may be hindered by a number of underlying assumptions.

For example, NPDs assign nicotine products into three categories—combustibles, smokeless tobacco, and e-cigarettes. “At first glance, these designations seem reasonable,” she wrote. “However, grouping products based solely on a superficial shared feature (e.g., if the product is vaped) implies that all e-cigarettes pose equal risk. However, a growing body of literature now implicates multiple culprits—including constituent toxic effects, exposure frequency, and product-specific behaviors—that cumulatively contribute to the risk profile of a given nicotine product.” To illustrate this point, she pointed to variations in nicotine exposure in various e-liquids depending on whether they use protonated or freebase nicotine, which results in variations in toxicity level.

And, she added, while defining the risk of individual nicotine products is important, “so too is understanding how consumption patterns are associated with risk.” Specifically, she pointed to polynicotine use, or use of multiple types of products, which is inversely associated with quit attempts and may be associated with more severe health consequences—”In fact, several studies have suggested a potential interaction between nicotine products,” she wrote.

Sun told BreakingMED that the study group did not consider compounding risk from use of multiple nicotine products as part of their analysis, but he acknowledged that it is an important subject “and a potential next step when we have more scientific evidence on the potential health risks of poly-tobacco product use.”

She concluded that, while NPDs provide a useful template for “mapping a product’s potential range of risk along a continuum,” metrics such as this can continue to be refined, and input data could be made more detailed and relevant, “which will ultimately serve to improve our understanding of the relative risks associated with new and emerging nicotine products.”

For this analysis, Sun and colleagues pulled 16 years of cross-sectional data from the 1999-2020 National Youth Tobacco Survey, an in-school survey of a nationally representative sample of students in grades 6 through 12. The investigators noted that each annual survey recruited between 15,000 and 36,000 participants.

To assess nicotine product exposure, they looked at past 30-day use of cigarettes, cigars, chewing tobacco, dip, snuff, e-cigarettes, bidis, hookah, and kreteks, measuring consumption frequency as the number of days each product was used. For cigarettes and cigars, the survey asked students how many of the product they smoked each day that they smoked.

The study authors measured NPDs as the number of days that an individual consumed a nicotine product in the past 30 days, and NPDs were also recorded by product type. To account for differential long-term health risks between products, they treated combustible tobacco products as having a risk weight of 1.0 and smokeless products as having a risk weight of 0.1, “consistent with evidence regarding the relative risk of most modern smokeless products… Because there is no agreed-upon risk weight for use of e-cigarettes, we varied the risk weight from 0.1 to 1.0 to demonstrate the full range of possibilities.”

“Nationally representative cross-sectional data for high school students showed that NPDs decreased steadily from 5.6 days per month in 1999 (95% CI, 5.0-6.2 days per month) to 2.2 days per month in 2017 (95% CI, 1.9-2.6 days per month), increased to 4.6 days per month in 2019 (95% CI, 4.1-5.1 days per month), and then decreased to 3.6 days per month in 2020 (95% CI, 3.0-4.1 days per month),” Sun and colleagues reported. “For a risk weight of 0.1 for e-cigarettes, compared with combustible products, risk-adjusted NPDs decreased from 2.5 days per month in 2013 (95% CI, 2.2-2.9 days per month) (prior to the popularity of e-cigarettes) to 2.0 days per month in 2019 (95% CI, 1.6-2.5 days per month) and 1.4 days per month in 2020 (95% CI, 1.0-1.8 days per month). However, with a risk weight of 1.0 for e-cigarettes (identical to that of combustible products), risk-adjusted NPDs increased to 5.3 days per month in 2019 (95% CI, 4.4-6.2 days per month) and 3.9 days per month in 2020 (95% CI, 3.1-4.7 days per month). Similar trends were found for middle school students.”

While the study authors pointed to the surge in e-cigarette use in 2018 and 2019 as a concerning development, they added that it is “impossible… to know the implications of current e-cigarette use for the future health of today’s adolescents. Although vaping is likely to be substantially less dangerous than smoking cigarettes, there is no definitive assessment of how much risk—or even what kinds of risk—are associated with the use of e-cigarettes. Furthermore, this undefined risk will depend to no small degree on how much and how long today’s young people use e-cigarettes, the level of nicotine concentration in e-cigarettes, the chemicals emitted by future versions of the products, and how many youthful e-cigarette users will transition to cigarette smoking (and how many of these individuals will then transition back to vaping).”

For this reason, “it’s important for pediatricians to keep monitoring youth vaping behaviors,” Sun told BreakingMED.

They added that most students who use e-cigarettes seem to use them infrequently, and frequent use is far more common among ever smokers than among students who have never smoked and those who have never used any tobacco products.

“For ever-smokers who are substituting vaping for smoking, either partly or completely, vaping may be contributing little if any meaningful increase in exposure to nicotine products,” they wrote. “Furthermore, a recent study reported that although the prevalence of nicotine product use has increased, no similar increases were found in the burden of nicotine dependence among U.S. high school students.”

Study limitations included NPDs inability to assess nicotine exposure directly due to variations within product types; the National Youth Tobacco Survey has changed questions for a few products over time; survey data did not distinguish between individuals who vaped nicotine and those who vaped THC; and Covid-19 may have impacted 2020 survey results.

  1. Nicotine product days (NPD), a novel metric for evaluating adolescent exposure to nicotine products, may be superior to measuring any 30-day tobacco product use when it comes to measuring the health consequences of different combinations of nicotine products over time.

  2. Metrics for measuring youth nicotine exposure should continue to be refined, and input data should be made more detailed and relevant, in order to improve understanding of the relative risks associated with new and emerging nicotine products.

John McKenna, Associate Editor, BreakingMED™

The study authors and editorialist had no relevant relationships to disclose.

Cat ID: 489

Topic ID: 89,489,730,138,139,143,192,489,925