Fruit flavored vapes and a nighttime dry cough – what’s the connection?

In a recent study published in PLoS ONE, a group of researchers examined the longitudinal association between exposure to electronic cigarette (ECIG) flavors and nocturnal dry cough among ECIG users.

Background 

The use of ECIGs among youth and young adults is a serious public health concern. ECIGs heat and aerosolize a liquid containing propylene glycol (PG) and/or vegetable glycerin (VG), with added flavorings and often nicotine. These constituents are associated with negative health effects.

Flavorings contribute to the toxicity of ECIG aerosols, including aldehydes and reactive species. In vitro and animal studies have shown that flavors like menthol, strawberry, vanillin, and cinnamon can cause respiratory inflammation (Swelling and irritation in the airways) and oxidative stress (Cellular damage caused by free radicals).

Despite assumptions of lower harm than combustible cigarettes, ECIGs pose health risks, including respiratory disease and symptoms. Further research is needed to understand better both the short-term and long-term health effects of ECIG constituents, including their impact on respiratory health.

About the study 

The present study analyzed data from the Population Assessment of Tobacco and Health (PATH) Study (2014-2019), a nationally representative longitudinal cohort of non-institutionalized adults and youth in the United States (US).

The study sample included adults from Wave 2 due to the absence of the outcome variable in Wave 1, resulting in 18,925 participants and a total of 38,638 observations across three one-year intervals. Data were collected through annual audio computer-assisted surveys, except for Wave 5, which was conducted two years after Wave 4.

The outcome variable was self-reported nocturnal dry cough in the past 12 months. Participants reported whether their regular or last brand of e-cigarette was flavored, with six categories: menthol/mint, tobacco, fruit, multiple flavors, candy/sweet, and others. Potential confounders included sex, age, race/ethnicity, education, household income, body mass index (BMI) (a measure of body fat based on weight and height), disease status, overall tobacco use, marijuana use, and secondhand smoke exposure.

Weighted descriptive statistics reported baseline characteristics and the incidence proportion of nocturnal dry cough. Weighted Rao-Scott chi-squared tests examined associations among covariates by e-cigarette flavor exposure. Generalized estimating equations (GEE) models quantified unadjusted and adjusted associations between e-cigarette flavor use and dry cough, accounting for time-varying variables. Analyses used SAS v9.4, with two-sided p-values of

Study results 

Weighted estimates of the baseline sociodemographic and health characteristics of participants at Wave 2 indicated that 35.3% were young adults, 34.6% were middle-aged adults, and 52.2% were females. Educational attainment was low, with 37.7% having achieved a high school level or less. The majority (67.1%) were non-Hispanic White, and 43.6% reported having a health condition.

Regarding overall tobacco use, 24.1% were never tobacco users, 20.7% were current established tobacco users, and 25.6% were former established tobacco users. Among participants, 2.9% were classified as current established ECIG users, 4% as former established ECIG users, and 92.8% as non-ECIG users.

The incidence of nocturnal dry cough was analyzed, revealing associations with most potential confounders except for age and health insurance coverage. Among never-tobacco users, the weighted incidence proportion (WIP) was 10.2% (95%CI 9.1, 11.3). Current and former established tobacco users showed WIPs of 15.1% (95%CI 13.3, 16.9) and 11.9% (95%CI 10.0, 13.8), respectively. Among established ECIG users, current users had a higher WIP (14.8%; 95%CI 13.1, 16.6) compared to former users (8.9%; 95%CI 8.2, 9.7).

The WIP of nocturnal dry cough by ECIG flavor category showed that compared to non-ECIG users (WIP: 11.1%; 95%CI 10.6, 11.6), current and former fruit-flavored ECIG users had significantly higher WIPs (16.6%; 95%CI 10.5, 21.2 and 16.6%; 95%CI 11.3, 21.9, respectively). Across all flavor categories, former ECIG users showed a higher WIP of cough than their non-ECIG counterparts.

Longitudinal associations by ECIG flavor use revealed that, after controlling for all sociodemographic variables, marijuana use, health status, and overall tobacco use, current ECIG users of fruit flavors had a 40% higher risk of reporting nocturnal dry cough compared to non-ECIG users (aRR: 1.40, 95%CI 1.01, 1.94).

Current menthol and mint ECIG users had an adjusted relative risk of 1.26 (95%CI 0.77, 2.07) compared to non-ECIG users. Former ECIG users of multiple flavors and other flavors had a 233% and 66% higher risk of developing a cough, respectively (aRR: 3.33, 95%CI 1.51, 7.34 and aRR: 1.66, 95%CI 1.09, 2.51), relative to non-ECIG users.

Conclusions 

To summarize, the study highlights that fruit flavors in ECIGs significantly contribute to nocturnal dry cough among current established ECIG users, even after adjusting for various confounders. This aligns with previous findings linking fruit-flavored ECIG use to higher reports of dry cough. Flavors in ECIGs, particularly cinnamaldehyde and menthol, can cause oxidative stress and inflammation in the respiratory system. Coughing, a common symptom among ECIG users, signals potential respiratory toxicity.