Study suggests switching from smoking to vaping indoors may reduce children’s secondhand exposure to nicotine

By Vijay Kumar MalesuReviewed by Danielle Ellis, B.Sc.Jul 16 2024

In a recent study published in the JAMA Network Open, a group of researchers compared nicotine absorption among children exposed to secondhand tobacco smoke, secondhand vapor, and those with no exposure. 

Background 

Children's exposure to secondhand tobacco smoke has significantly declined in many countries, including the United States (US) and England, due to decreased parental smoking and smoke-free home rules. However, the rise of nicotine electronic (e)-cigarettes, also known as vaping, since the 2010s has introduced another source of secondhand exposure.

Vaping indoors is more common than smoking, even in homes with children. Cigarettes produce mainstream and sidestream smoke, while vaping generates aerosol only during puffs, with vapers retaining over 99% of inhaled nicotine.

Consequently, children's exposure to nicotine and other harmful substances from secondhand vapor is significantly lower than from secondhand smoke. Further research is needed to understand the long-term health effects of children's exposure to secondhand e-cigarette vapor compared to secondhand tobacco smoke.

About the study 

The present study utilized National Health and Nutrition Examination Survey (NHANES) data from 2017 to March 2020. Participants completed home interviews and provided blood samples at a mobile examination center. Proxy respondents (usually parents or guardians) answered questionnaires for children aged 11 years or younger. The response rates were 59% for 6- to 11-year-olds and 63% for 1- to 5-year-olds, with most visiting the examination center. Survey weights adjusted for nonresponse.

The study focused on children aged 3 to 11 years, excluding those with cotinine levels above 15 μg/L to ensure secondhand exposure. Secondhand smoke and vapor exposure were assessed through questions about household tobacco use and recent exposure in various locations. Children were categorized by exposure to secondhand smoke only, secondhand vapor only, or neither, excluding those exposed to both.

Covariates included age, family income, sex, race, weight, ethnicity, body and height. Nicotine absorption was measured through serum cotinine concentration assayed using validated methods. Log-normal tobit regression models estimated geometric mean cotinine levels, adjusting for covariates and accounting for undetectable levels and the survey design. The analysis used a significance threshold of α = .05. Data and analysis code are available on the Open Science Framework, with the final analysis conducted on January 9, 2024.

Study results 

Two of the 1827 surveyed children (0.1%) were excluded due to serum cotinine concentrations suggesting recent nicotine use (>15 μg/L). Among the remaining 1825 children, 271 (14.8%) were exposed to secondhand tobacco smoke only, 1476 (80.1%) to neither, and 45 (2.5%) to secondhand e-cigarette vapor only. After further excluding 33 children (1.8%) exposed to both secondhand smoke and vapor and 12 children (0.7%) with missing body weight or height data, the final analytic sample comprised 1777 children.

The mean age was 7.4 years (SD 2.6), with 882 (49.6%) females and 531 (29.9%) reporting family incomes below the poverty line. The sample included 477 Hispanic children (26.8%), 463 non-Hispanic Black children (26.1%), 519 non-Hispanic White children (29.2%), and 318 children (17.9%) who were multiracial or of other races and ethnicities.

Nicotine absorption, indexed by geometric mean serum cotinine concentration, was highest among children exposed to secondhand smoke only (0.494 μg/L; 95% CI, 0.386-0.633 μg/L), followed by those exposed to secondhand vapor only (0.081 μg/L; 95% CI, 0.048-0.137 μg/L). This indicates an 83.6% (95% CI, 71.5%-90.5%; P < .001) lower nicotine absorption for children exposed to secondhand vapor compared to those exposed to secondhand smoke.

Children with no secondhand exposure had the lowest geometric mean cotinine levels (0.016 μg/L; 95% CI, 0.013-0.021 μg/L), showing 96.7% (95% CI, 95.6%-97.6%; P < .001) lower nicotine absorption as compared to those with secondhand smoke exposure and 80.1% (95% CI, 64.9%-88.7%; P < .001) lower than those exposed to secondhand vapor. Consequently, children exposed to secondhand vapor had 402% (95% CI, 185%-786%; P < .001) higher cotinine levels than those with no reported exposure.

These findings persisted after adjusting for covariates. Notably, children exposed to secondhand vapor only had slightly lower cotinine levels when excluding those living with tobacco smokers from the analysis. 

Conclusions 

To summarize, this cross-sectional study found that about 1 in 5 children was exposed to secondhand tobacco smoke or e-cigarette vapor indoors primarily secondhand smoke.

Children exposed only to secondhand e-cigarette vapor had 84% lower nicotine absorption than those exposed to secondhand tobacco smoke, while those with no secondhand exposure had 97% lower absorption. These differences remained significant after adjusting for demographic and socioeconomic factors.

Similar to previous studies using silicone wristbands, this study shows that secondhand nicotine exposure is significantly lower from vaping than smoking, although vaping around children should still be avoided.