Introducción

The patterns of tobacco use have been changing as the diversity of tobacco products has expanded in recent years. Dual use of cigarettes and e-cigarettes may increase the risk of nicotine dependence.¹ Moreover, the aerosol of e-cigarettes contains flavorings and other chemicals that could be potentially harmful to the respiratory system.^2,3,4 However, dual-use may be a temporary stage as smokers transition to quit smoking.⁵ Most dual use studies have been conducted in High-Income Countries (HIC), primarily those where e-cigarettes are legal, while few studies have evaluated dual use in low and middle-income countries (LMIC), specifically in Latin American. Most LMIC ban e-cigarettes, Mexico among them, yet have surprisingly non-negligible rates of e-cigarette use among current smokers, adolescents, and young adults.^6,7 This study evaluates the similarities and differences between exclusive cigarette users and dual users and the correlates of vaping frequency among dual users.

Materials and methods

This study’s data came from three waves (approximately 1 500 per wave) of an online survey of Mexican adult smokers and vapers (Wave 1=November-December 2018, Wave 2=March-April 2019, Wave 3=July-August 2019). The sample was recruited from a consumer panel for marketing research. Quotas for vapers were established so they would comprise at least 1/3 of the sample at each wave, resulting in a large enough sample size to study this group in detail. Adults 18 years old or older who lived in Mexico and smoked or used e-cigarettes in the last month were eligible to participate. The protocol was approved by the Institutional Review Board (IRB) and Ethics Committee at the National Institute of Public Health of Mexico (Instituto Nacional de Salud Pública, INSP) (Ethical Approval Code: CI 1572). Additional details of the study methodology have been published elsewhere.¹⁸

The sample of the first three waves of the Mexican online survey consists of 4 502 participants; we included 3 335 participants who responded for the first time this survey. We eliminated 82 participants who were exclusive e-cigarette users and, therefore, too small a subsample to analyze precisely. We also excluded 229 observations with missing data on study variables (7.5% of the sample). The final analytic sample of 3 024 included exclusive current smokers (n=2 070) and dual users (n=954) (figure 1).

Figure 1 Study flow chart. Online survey among adult smokers in Mexico, 2018-2019 

Results

About 31.5% of the participants were dual users. Dual use was higher for groups aged 18-29 (41.1%) and 30-39 years (36.8%) than for groups aged 40-49 (15.6%), and 50 years and over (6.5%). Dual use was also higher among participants with a college degree or more (52.9%) versus participants with high school or less (27.8). Compared to exclusive cigarette users, dual users had greater smoking dependence, and higher prevalence of binge drinking and marijuana use. Among dual users, most used cigalikes (35.9%) or vape-pens (38.8%), and only 5.1% used pod-style devices. About a third (31.3%) preferred tobacco flavors, 29.9% preferred fruit flavors, and 19.7% preferred exclusive or mixed menthol/mint flavors. Finally, 58.1% reported using e-cigarettes with nicotine (table I).

Discussion

Our cross-sectional study of this Mexican population indicated that, compared to exclusive cigarette users, dual users had a higher risk profile given that they had higher smoking dependence, preferred cigarettes with flavored capsules and used marijuana more often. We also found that some correlates of dual-use were similar to those found in other countries. Dual users in our sample were younger than exclusive cigarette users, consistent with studies in HICs.^6,8 Also, dual users were more likely than exclusive cigarette users to have recently tried to quit, consistent with previous US studies.^13,25 One possible explanation of this finding is that dual users are using e-cigarettes to quit cigarettes. However, dual-users in our sample were more dependent on cigarettes than exclusive cigarette users, suggesting that quitting smoking may be harder for them. This finding is inconsistent with a US study that found no differences in smoking dependence (using WISDM) between dual users and exclusive current smokers.⁸ Longitudinal studies, particularly in LMIC, are necessary to evaluate whether dual users are more or less likely to transition towards long-term smoking cessation.

Dual-use was higher among smokers who preferred cigarettes with flavor capsules in the filter. In Mexico, capsule cigarettes are available in many flavors and have rapidly grown in popularity, as has been the case worldwide.^20,21,22,23 A nationally representative study found that 43% of the Mexican current smokers used flavor capsule cigarettes.²² Flavors in both cigarettes and e-cigarettes may not only attract young adults to nicotine consumption, but also impede the transition to exclusive e-cigarette use or cessation of all products. This research area is of critical importance given evidence that widespread and growing flavor capsule use may account for the relatively weak impact of policies recommended by the World Health Organization’s Framework Convention on Tobacco Control in Mexico.²⁶ Therefore, results from this study suggest that a ban on flavored tobacco products can help to reduce cigarette and e-cigarette appeal among youth and young adults.²⁷

In our second analysis, among dual users, we found that being a daily smoker and using marijuana more than once in the last month were associated with more frequent e-cigarette use. This means that dual users who are using e-cigarettes more frequently had a more prominent risk profile. On the one hand, the concurrent use of cigarettes and e-cigarettes with high intensity and frequency may increase the risk of nicotine dependence. On the other hand, the recent outbreak of cases of lung injury (EVALI) was associated with the use of e-cigarettes containing marijuana, particularly with the active chemical tetrahydrocannabinol.^2,3 However, our variable of marijuana use does not capture the difference between vaping marijuana and all other types of marijuana. Given the importance of the EVALI outbreak, futures studies should consider incorporating a specific variable of vaping marijuana. Nevertheless, our findings warn of possible negative health outcomes among Mexican dual users.

Dual users who preferred e-cigarettes with exclusive or mixed mint/menthol or fruit flavors (compared to tobacco flavors) were more likely to use e-cigarettes with greater frequency, although using e-cigarettes with nicotine was unassociated with the frequency of use. These results are consistent with a previous study among Mexican adolescents,²⁸ but inconsistent with a study of US adults, in which the frequency of e-cigarette use was unassociated with e-cigarette flavor preferences but positively associated with using e-cigarettes with nicotine containing liquids.¹⁴ The different regulatory and socio-cultural contexts for e-cigarettes in Mexico and the US could explain these inconsistencies. For instance, given that e-cigarette sales are banned in Mexico, it may be difficult for e-cigarette users to correctly identify nicotine content of liquids because product labeling is unregulated.²⁹

Most of the top reasons for vaping in our sample indicate that dual users perceive a variety of comparative advantages of e-cigarettes over smoking, but longitudinal research is needed to evaluate switching behavior and cessation. A prior study in the US, UK, Canada, and Australia that assessed the same range of motivations for e-cigarette use among dual users found that smoking fewer cigarettes was the primary motivation,³⁰ whereas our study found that only 10% of dual users endorsed this reason. Further studies on e-cigarette frequency of use using nationally representative samples are necessary to understand the different smoking pattern in the Mexican population, in which nondaily smokers are more than half of the current smokers.²²

This cross-sectional study has several limitations, including the inability to evaluate the temporal ordering of key variables and that the brief WISDM nicotine dependence scale has not yet been validated in the Mexican population. However, the 10 items were selected based on pilot research indicating they could discriminate between relatively low levels of smoking frequency (>6 cigarettes per day; <5 CPD; nondaily) among smokers of Mexican ancestry,³¹ as half of the Mexican smokers are nondaily smokers, and have relatively low levels of physical and psychological addiction.³² Also, our sample came from an online marketing research panel and over-represented young adults and groups with higher socioeconomic status, which is at least partly due to our effort to oversample e-cigarette users, who are more likely to be from these groups. While inferences from our study should not be extrapolated to the entire Mexican population, the patterns of smoking behavior in our sample are similar to national samples, suggesting that our results may not be too biased. Furthermore, our sampling strategy was necessary to efficiently recruit and study e-cigarette users in a country like Mexico, where e-cigarette use is relatively low (i.e., 5% of smokers).⁶ Future follow-up and comparison with representative Mexican samples are needed to more fully evaluate the public health impact of e-cigarette use. Therefore, a relevant recommendation from this study is to incorporate questions to evaluate e-cigarette frequency of use and e-cigarette product characteristics (flavors, type of device, type of e-liquids, e-cigarette price, and brand) into Mexican national surveys on tobacco.

To the best of our knowledge, this study is the first in the Latin-American region that characterizes dual users compared to exclusive smokers in a large sample. The detailed information we collected about e-cigarette use sheds additional light beyond what has been included in national surveys, including the main surveys of the Global Tobacco Surveillance System (GATS, GYTS).