Smoking or Vaping? Nicotine Exposure About the Same

Teens who only smoked, only vaped e-cigarettes, or both smoked and vaped all experienced similar levels of nicotine exposure, David Hammond, PhD, of the School of Public Health Sciences, University of Waterloo, Ontario, Canada, and co-authors reported in JAMA Network Open, based on their cross-sectional study of 16- to 19-year-olds in England, Canada, and the U.S.

However, higher nicotine exposures seen among participants whose vaping products used nicotine salts versus non-salt products.

The researchers pointed out that although nicotine exposure levels were generally consistent across the United States, Canada, and England, teens in England who only smoked had moderately higher levels of biomarkers for nicotine exposure than did their counterparts in Canada.

"The reasons for this difference are unclear and may be due to differences in the sample of smokers recruited across countries. However, the findings are generally consistent with population-based data indicating higher levels of dependence among youths who smoke in England compared with Canada and the U.S. and with slower decreases in smoking prevalence among younger people in England in recent years," Hammond and colleagues noted.

"Given the central role of nicotine in tobacco addiction, the findings suggest that the current generation of vaping products may have comparable abuse liability as traditional cigarettes. The results also indicate potentially essential differences in exposure based on product design, including the use of nicotine salt e-liquids. While salt-based e-liquids may be more appealing to adults who vape to quit smoking, they may also increase exposure among youths, potentially prolonging long-term patterns of nicotine use," the study authors wrote in their conclusion.

For most individuals, vaping results in less nicotine exposure, compared with smoking. However, research published over the past five years indicates that nicotine exposure differs depending on the design of e-cigarettes and the characteristics of the e-liquids they convey. In one example, recent research has found that e-liquids containing nicotine salts instead of freebase nicotine "have been associated with higher levels of nicotine delivery comparable to nicotine levels from smoking," the authors noted.

Little research has been done on teens who vape, including those with little or no history of smoking. However, two U.S. studies of youths who vaped found, based on urinary metabolites of nicotine, that nicotine exposure was associated with higher dependence scores. A third U.S. study reported higher levels of nicotine metabolites among youths who exclusively vaped, versus youths who did not vape, but lower levels than among youths who both vaped and smoked.

In the context of a study indicating that nicotine biomarkers might be higher in youths who vaped pod devices (which most likely used nicotine salt e-liquids), compared with non-pod devices, Hammond and colleagues wrote, "Understanding the potential differences in exposure from freebase and salt-based nicotine e-liquids is essential given the popularity of salt-based products among youths."

The cross-sectional study was an extension of the International Tobacco Control Policy Evaluation Project’s Youth Tobacco and Vaping Surveys, online surveys involving national samples of adolescents ages 16 to 19 in Canada, England, and the United States.

"Respondents were eligible if their survey responses indicated they were in 1 of 4 groups of interest: past-week vaping only, past-week cigarette smoking only, past-week vaping and smoking (dual use), or no use (no smoking, vaping, or cannabis use in the past 30 days)," the study authors wrote.

Participants were compensated with a $40 Amazon.com gift card in the United States or a similar alternative in Canada or England.

Eligible study participants were mailed 934 urine collection kits, of which 371 (40.0%) were returned with a usable sample. The 364 participants included in the analysis comprised 129 from Canada, 131 from England, and 104 from the United States. Their mean age was 17.6 years, and 55.8% were females.

The outcome measures were urine concentrations of cotinine, trans-3′-hydroxycotinine (3OH-cotinine), and total nicotine equivalents (TNE-2, the molar sum of cotinine and 3OH-cotinine), normalized for creatinine concentration.

The geometric mean concentration of TNE-2 was 3.10 nmol/mg creatinine among those who exclusively vaped, 3.78 nmol/mg creatinine among those who exclusively smoked, 6.07 nmol/mg creatinine among those who both vaped and smoked (dual use), and 0.19 nmol/mg creatinine among those who neither vaped nor smoked (no use).

Hammond and colleagues added, "There were no significant differences in levels of cotinine, 3OH-cotinine, or TNE-2 among those who exclusively vaped compared with those who exclusively smoked or with dual use. Compared with no use, exclusive vaping was associated with higher concentrations of cotinine (β = 3.08; 95% CI, 2.47-3.69; P < .001), 3OH-cotinine (β = 2.40; 95% CI, 1.89-2.91; P < .001), and TNE-2 (β = 2.59; 95% CI, 2.07-3.11; P < .001), as were exclusive smoking (cotinine: β = 3.25 [95% CI, 2.64-3.86; P < .001]; 3OH-cotinine: β = 2.50 [95% CI, 1.98-3.01; P < .001]; TNE-2: β = 2.66 [95% CI, 2.13-3.19; P < .001]) and dual use (cotinine: β = 3.52 [95% CI, 2.89-4.16; P < .001]; 3OH-cotinine: β = 2.81 [95%CI, 2.29-3.34; P < .001]; TNE-2: β = 2.97 [95%CI, 2.43-3.51; P < .001]). No significant differences were observed in biomarkers of exposure between those reporting exclusive smoking and those reporting dual use."

In an analysis comparing nicotine biomarkers by country, the only significant differences observed within smoking and/or vaping status groups were lower concentrations of 3OH-cotinine and TNE-2 among those in Canada who exclusively smoked, compared to their counterparts in England.

Among the 73 adolescents who had exclusively vaped in the previous week, 45.2% reported that the last vaping product they used contained more than 20mg/mL nicotine, while 38.4% reported 20 mg/mL nicotine or less, 9.6% reported no nicotine, and 6.8% did not know.

After adjustment for creatinine concentration, country, age, sex, and past-week cannabis use, a self-reported nicotine concentration of 20mg/mL nicotine or less was associated with higher levels of all nicotine metabolites, compared with no nicotine (TNE-2: P = 0.002]) or not knowing (TNE-2: P = 0.01]). However, no significant differences were seen compared with self-reported nicotine concentration higher than 20mg/mL.

Regarding self-reported nicotine salt in e-liquid, among the 73 adolescents who exclusively vaped (excluding seven who reported no nicotine in their last vaping product used), 34.8% reported that the last vaping product they had used contained nicotine salt e-liquid, 43.9% reported the e-liquid was not nicotine salt, and 21.2% reported that they did not know.

In adjusted models, self-reported use of nicotine salt e-liquid was associated with higher levels of all nicotine metabolites, compared with use of nonsalt products (TNE-2: P = 0.03) or not knowing (TNE-2: P = 0.009), however, the comparison of cotinine for reporting salt versus nonsalt was not statistically significant.

Beyond the inherent limitations of using biomarkers and self-reported data, the authors noted difficulties in identifying and quantifying the amounts and types of nicotine in various products.

Hammond reported receiving grants from Health Canada and the U.S. National Institutes of Health during the conduct of the study, in addition to personal fees as an expert witness for public health authorities outside the submitted work.

The study was funded by grants from the Health Canada Substance Use and Addictions Program and the U.S. National Institutes of Health.

Hammond D, et al "Nicotine exposure from smoking tobacco and vaping among adolescents" JAMA Netw Open. 2025; DOI:10.1001/jamanetworkopen.2024.62544.