Nicotine absorption from e-cigarettes over 12 months

Background: Research indicates that, over time, exclusive e-cigarette users (vapers) gradually reduce the nicotine concentration in their e-liquid and transition to more sophisticated devices. Alongside this, consumption of e-liquid increases and constant cotinine levels are maintained. Aims: We aimed to confirm these observations in 27 experienced vapers tested at baseline and 12 months later, by measuring nicotine absorption (via salivary levels of the nicotine metabolite cotinine; ng/ml), nicotine concentrations in e-liquid (mg/mL), volume of e-liquid consumed (mL per day), device types and flavours used, both at baseline and 12 months. Results: Vapers reduced both their nicotine concentrations in e-liquid over 12 months (from 13.83 mg/mL at baseline to 9.91 at follow up) but significantly increased their e-liquid consumption (from 4.44 to 6.84 mL). No significant changes in salivary cotinine concentrations (370.88 ng/mL at baseline and 415.78 ng/mL at follow up) were observed. There was an increase in sub-ohming (using an atomiser coil with resistance of < 1 ohm with increased power) at 12 months, and in the use of fruit flavoured e-liquids. Conclusions: Our sample of experienced vapers reduced the concentration of nicotine in their e-liquid over time, but maintained their nicotine intake possibly through self-titration via more intensive puffing. Findings suggest there may be little benefit in reducing nicotine e-liquid concentration since this appears to result in higher e-liquid consumption which may incur both a financial and health cost. Gaining an understanding of underlying reasons for lowering e-liquid concentration would be a useful line of empirical enquiry.