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Vaping: The new wave of nicotine addiction

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BAD THINGS IN E-LIQUID AEROSOL

Studies of vape liquids consistently confirm the presence of toxic substances in the resulting vape aerosol.37–40 Depending on the combination of flavorings and solvents in a given e-liquid, a variety of chemicals can be detected in the aerosol from various vaping devices. Chemicals that may be detected include known irritants of respiratory mucosa, as well as various carcinogens. The list includes:

  • Organic volatile compounds such as propylene glycol, glycerin, and toluene
  • Aldehydes such as formaldehyde (released when propylene glycol is heated to high temperatures), acetaldehyde, and benzaldehyde
  • Acetone and acrolein
  • Carcinogenic nitrosamines
  • Polycyclic aromatic hydrocarbons
  • Particulate matter
  • Metals including chromium, cadmium, nickel, and lead; and particles of copper, nickel, and silver have been found in electronic nicotine delivery system aerosol in higher levels than in conventional cigarette smoke.41

The specific chemicals detected can vary greatly between brands, even when the flavoring and nicotine content are equivalent, which frequently results in inconsistent and conflicting study findings. The chemicals detected also vary with the voltage or power used to generate the aerosol. Different flavors may carry varying levels of risk; for example, mint- and menthol-flavored e-cigarettes were shown to expose users to dangerous levels of pulegone, a carcinogenic compound banned as a food additive in 2018.42 The concentrations of some of these chemicals are sufficiently high to be of toxicologic concern; for example, one study reported the presence of benzaldehyde in e-cigarette aerosol at twice the workplace exposure limit.43

Biologic effects

In an in vitro study,44 57% of e-liquids studied were found to be cytotoxic to human pulmonary fibroblasts, lung epithelial cells, and human embryonic stem cells. Fruit-flavored e-liquids in particular caused a significant increase in DNA fragmentation. Cell cultures treated with e-cigarette liquids showed increased oxidative stress, reduced cell proliferation, and increased DNA damage,44 which may have implications for carcinogenic risk.

In another study,45 exposure to e-cigarette aerosol as well as conventional cigarette smoke resulted in suppression of genes related to immune and inflammatory response in respiratory epithelial cells. All genes with decreased expression after exposure to conventional cigarette smoke also showed decreased expression with exposure to e-cigarette smoke, which the study authors suggested could lead to immune suppression at the level of the nasal mucosa. Diacetyl and acetoin, chemicals found in certain flavorings, have been linked to bronchiolitis obliterans, or “popcorn lung.”46

Nicotine is not benign

The nicotine itself in many vaping liquids should also not be underestimated. Nicotine has harmful neurocognitive effects and addictive properties, particularly in the developing brains of adolescents and young adults.47 Nicotine exposure during adolescence negatively affects memory, attention, and emotional regulation,48 as well as executive functioning, reward processing, and learning.49

The brain undergoes major structural remodeling in adolescence, and nicotine acetylcholine receptors regulate neural maturation. Early exposure to nicotine disrupts this process, leading to poor executive functioning, difficulty learning, decreased memory, and issues with reward processing.

Fetal exposure, if nicotine products are used during pregnancy, has also been linked to adverse consequences such as deficits in attention and cognition, behavioral effects, and sudden infant death syndrome.5

Much to learn about toxicity

Partly because vaping devices have been available to US consumers only since 2007, limited evidence is available regarding the long-term effects of exposure to the aerosol from these devices in humans.1 Many of the studies mentioned above were in vitro studies or conducted in mouse models. Differences in device design and the composition of the e-liquid among device brands pose a challenge for developing well-designed studies of the long-term health effects of e-cigarette and vape use. Additionally, devices may have different health impacts when used to vape cannabis or other drugs besides nicotine, which requires further investigation.

E-CIGARETTES AND SMOKING CESSATION

Conventional cigarette smoking is a major public health threat, as tobacco use is responsible for 480,000 deaths annually in the United States.50

And smoking is extremely difficult to quit: as many as 80% of smokers who attempt to quit resume smoking within the first month.51 The chance of successfully quitting improves by over 50% if the individual undergoes nicotine replacement therapy, and it improves even more with counseling.50

There are currently 5 types of FDA-approved nicotine replacement therapy products (gum, patch, lozenge, inhaler, nasal spray) to help with smoking cessation. In addition, 2 non-nicotine prescription drugs (varenicline and bupropion) have been approved for treating tobacco dependence.

Can vaping devices be added to the list of nicotine replacement therapy products? Although some manufacturers try to brand their devices as smoking cessation aids, in one study,52 one-third of e-cigarette users said they had either never used conventional cigarettes or had formerly smoked them.

Bullen et al53 randomized smokers interested in quitting to receive either e-cigarettes, nicotine patches, or placebo (nicotine-free) e-cigarettes and followed them for 6 months. Rates of tobacco cessation were less than predicted for the entire study population, resulting in insufficient power to determine the superiority of any single method, but the study authors concluded that nicotine e-cigarettes were “modestly effective” at helping smokers quit, and that abstinence rates may be similar to those with nicotine patches.53

Hajek et al54 randomized 886 smokers to e-cigarette or nicotine replacement products of their choice. After 1 year, 18% of e-cigarette users had stopped smoking, compared with 9.9% of nicotine replacement product users. However, 80% of the e-cigarette users were still using e-cigarettes after 1 year, while only 9% of nicotine replacement product users were still using nicotine replacement therapy products after 1 year.

While quitting conventional cigarette smoking altogether has widely established health benefits, little is known about the health benefits of transitioning from conventional cigarette smoking to reduced conventional cigarette smoking with concomitant use of e-cigarettes.

Campagna et al55 found no beneficial health effects in smokers who partially substituted conventional cigarettes for e-cigarettes.

Many studies found that smokers use e-cigarettes to maintain their habit instead of quitting entirely.56 It has been suggested that any slight increase in effectiveness in smoking cessation by using e-cigarettes compared with other nicotine replacement products could be linked to satisfying of the habitual smoking actions, such as inhaling and bringing the hand to the mouth,24 which are absent when using other nicotine replacement methods such as a nicotine patch.

As with safety information, long-term outcomes regarding the use of vape devices for smoking cessation have not been yet established, as this option is still relatively new.

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