1. Introduction
Tobacco consumption is the direct cause of ~7 million deaths annually worldwide [
1]. More specifically, in Canada, cigarette smoking is the largest modifiable risk factor contributing to the burden of disease (including premature death and disability-adjusted life years) [
2]. Approximately 15% of Canadians are considered cigarette smokers, including 10.6% of Canadian youth (aged 15–19) [
3]. Smoking prevalence among Canadian youth is especially a concern as early adoption of smoking behaviour decreases the likelihood of quitting smoking in adulthood [
4]. Further, many Canadians have vaped, with adolescents and young adults reporting the highest rate of vaping of any age category, with 23% of students in grades 7–12 having tried vaping [
5]. Vaping in the youth population is also a risk factor for subsequent cigarette smoking [
6,
7]. Preventing smoking and vaping initiation during adolescence should be considered a public health priority.
Adolescence is a key transitional phase in development, with increased autonomy potentially impacting behaviour. Increased autonomy results in a wider variety of choices that can lead to experimentation. This may be true for both cigarette smoking and other health behaviours, including beverage consumption, many of which contain caffeine. Caffeine intake begins to increase at ~13 years of age and continues to increase steadily until ~56 years old [
8]. The majority (~73%) of US youth consume caffeine on a daily basis [
9], primarily in the form of sugar-sweetened beverages (SSBs), high-energy drinks, and coffee [
9]. Increased SSB consumption is associated with a range of adverse health outcomes, such as Type II diabetes, cardiovascular disease, and obesity [
10]. High-energy drinks have shown acute adverse effects in which consumers report difficulties sleeping, rapid heart rate, chest pain, nausea, and seizures [
11].
Conversely, adults’ primary source of caffeine is coffee [
12], and the association between coffee consumption and smoking behaviour has been established, with smokers being more likely to consume caffeine than non-smokers [
13]. There appears to be a dose–response relationship, with each additional cigarette smoked per day being associated with an additional 0.10 cups of coffee consumed [
14]. Both physiological and psychological mechanisms have been proposed to explain why caffeine consumption impacts nicotine use. In animal models, chronic exposure to caffeine potentiates nicotine self-administration [
15,
16,
17], suggesting a cumulative stimulation of dopamine through adenosine receptor antagonization (caffeine) and cholinergic stimulation (nicotine) [
15]. Nicotine may also shorten the half-life of caffeine [
18], prompting smokers to consume more caffeine. Conditioning may also play a role in this relationship, where coffee consumption triggers a conditioned response to smoke a cigarette [
19]. Alternatively, high-energy drink consumption and smoking behaviours have been identified as risky behaviours [
20,
21]. When one participates in one risky behaviour, their likelihood to participate in others is higher [
22]. Mental health symptoms (i.e., stress, anxiety, and depression) have been shown to play a role in both consumption of SSBs and smoking behaviours [
23,
24,
25,
26]. Finally, during adolescence, social influences (e.g., peer pressure) have been related to substance use [
27].
Our research team have established an association between beverage consumption and smoking and vaping behaviour in a cross-sectional analysis of a Canadian sample of high school students [
28]. We demonstrated that high-energy drinks have the strongest association with cigarette smoking and vaping out of all of the examined beverages (e.g., coffee/tea with and without sugar and SSBs) [
28]. This study identified that the association in this sample was larger, in general, for vaping when compared to smoking. However, this study’s cross-sectional nature did not allow us to determine the potential temporal nature of this relationship. As far as we are aware, one study in Finnish adolescents demonstrated that high-energy drink consumption predicted later smoking and vaping [
29]. This study did not examine the association between other types of SSBs or other caffeinated drinks but rather focused only on high-energy drinks. Additionally, smoking rates are higher in Finland compared to Canada (18.2% CI:14.4–21.8 vs. 13.7% CI: 11.5–16.2, respectively) [
30]; SSB consumption differs in Europe and North America as well [
31]. As such, we will examine the longitudinal association between beverage consumption (i.e., SSB, high-energy drink, and coffee/tea) and smoking/vaping behaviours, with particular attention paid to both high-energy drinks and vaping. We hypothesize that an increased frequency of caffeinated beverages/SSB consumption will be associated with smoking behaviours in youth after controlling for grade, sex, BMI, school clustering, and ethnic background. More specifically, high-energy drink consumption will be the strongest predictor of smoking/vaping behaviours (i.e., smoking initiation, vaping initiation, current/former smokers, current vape users).
4. Discussion
Our study provides evidence for the longitudinal associations of increased caffeinated beverage consumption and smoking and vaping behaviours in a large prospective cohort study of Canadian youth. In line with our hypothesis, a one-day increase in high-energy drink consumption was associated with cigarette and vaping initiation, and with the status of cigarette smoking and vaping use, after controlling for grade, sex, BMI, school median income, and ethnicity. Similar results were seen for coffee and tea consumption with or without sugar. However, no significant association was identified with current smoking status or vaping use and coffee and tea without sugar consumption. Contrary to our hypothesis, little evidence was found for the longitudinal effects of SSB on smoking or vaping behaviours.
With the significant health burden that smoking cigarettes creates in Canada [
2], and the recent surge in vaping, where the adverse health risks are slowly being realized [
35], it is vital to uncover what may be preceding this behaviour in youth. We hypothesized that beverage consumption and, in particular, caffeinated beverage consumption might enhance smoking and vaping behaviour in youth as beverage consumption, especially beverages that contain caffeine, has been associated with smoking behaviours in adults [
13,
36]. Additionally, adult smokers consume more sugar than a non-smoker, which may be caused by an altered taste due to smoking, and the presence of sugar in tobacco products can facilitate smoking behaviour [
37,
38,
39]. Adolescence and young adulthood are associated with increasing autonomy over food and beverage consumption and with viewing more advertisements for beverages containing caffeine [
40]. This period is associated with increased caffeine and SSB consumption [
41,
42,
43]. With the many beverages available to youth, it is important to identify which beverages may impact smoking and vaping behaviour.
High-energy drinks have been associated with drug use and smoking in young adults [
44,
45] and have been longitudinally associated with smoking and vaping in a sample of Finnish adolescence [
29]. This longitudinal study (n = 5742) found that daily energy drink use was associated with ever vaping more than twice (multivariate model OR = 2.36 95% CI: 1.50–3.70 for boys; multivariate model OR = 3.94, 95% CI: 1.66–9.32 for girls) and smoking more than 50 cigarettes (multivariate model OR = 1.80, 95% CI: 1.06–3.05 for boys; multivariate model OR = 1.87, 95% CI: 0.75–4.63 for girls). Our study builds on these findings by showing that other beverages that contain caffeine are longitudinally associated with smoking and vaping behaviours, suggesting that caffeine, and not sugar, may be influential in these associations.
Interestingly, our study found little evidence for change in SSB being a risk factor for subsequent smoking and vaping behaviours. This is not consistent with the preceding cross-sectional study [
28], which saw an association between SSB and smoking and vaping behaviours. Other cross-sectional work has shown a link between SSB and smoking behaviours in adults. In a large American cohort (n = 12,214), nicotine consumption was associated with increased SSB consumption in a young adult population (mean age: ~24 years) [
46]. This was also seen in a general adult population as SSB consumption predicted smoking behaviour [
47]. Potential reasons for this may be the broad classification of SSBs in the COMPASS study, which includes flavoured milk, for example. Not all of the SSBs in this category contain caffeine, as the question prompts students with examples of soda pop, Gatorade, and Kool-Aid (2/3 do not contain caffeine). If it is caffeine and not sugar that is driving the association between beverage consumption and smoking and vaping behaviour, the large number of SSBs not containing caffeine examined in the COMPASS questionnaire may weaken potential associations in the current study. The observed association between high-energy drink consumption, a subtype of SSB and a large source of caffeine in youth [
45], and smoking and vaping behaviour supports this hypothesis.
The physiological [
13,
14,
15,
16,
17,
18,
19] and psychological [
20,
21,
23,
24,
25,
26,
27] mechanisms documented in the literature also support this hypothesis. As mentioned above, chronic exposure to caffeine potentiates nicotine self-administration [
15,
16,
17], suggesting a cumulative stimulation of the dopamine through adenosine receptor antagonization (caffeine) and cholinergic stimulation (nicotine) [
15]. High-energy drink consumption and smoking/vaping behaviours have been identified as risky behaviours [
20,
21], and youth who participate in one risky behaviour are more likely to participate in other risky behaviours. Stress, anxiety, and depression have been linked to both SSBs and smoking behaviours [
23,
24,
25,
26] and peer pressure has also been related to substance use in adolescence [
27].
The findings have implications for practice and policy and the need to consider the inter-relationships between smoking behaviour, particularly vaping use, and caffeinated beverage consumption. There has been much progress in preventing cigarette use in Canada, such as sales restriction to anyone under the age of 18, graphic warning labels taking up 75% of the packaging space, plain packaging, and the prohibition of most forms of advertising [
48]. Vaping products are subject to many of the same restrictions, with one notable exception: graphic warning labels are not used on vaping packaging and simple, text-only warnings are required [
48]. The lack of graphic warning labels may contribute to many students being more willing to try the product. However, it is the aggressive marketing of vaping that is suspected to have driven the recent increase in their use. The vaping market was liberalized in Canada in 2018. Between 2017 and 2019, the percentage of youth who reported noticing vaping promotions often or very often doubled from 13.6% to 26.0%. Youth who reported noticing marketing often or very often were more likely to report vaping in the past 30 days, past week, and on >20 days in the last month [
49]. In Canada, provinces that have lower restrictions on the marketing of vaping products saw higher percentages of vaping [
49]. This suggests an association between the exposure to vaping marketing and its use among youth. Greater regulation of marketing is required to reduce vaping use in adolescents.
Marketing may also play a role in the consumption of high-energy drinks. For example, the primary target of energy drink marketing is teenagers and young adults aged 18–34 years old [
50]. This age group generally lead busy lifestyles and are receptive to the types of advertisements that these products usually employ. Energy drinks are exceptionally popular among young adults as 34% of 18- to 24-year-olds are considered regular users [
51]. The marketing for these brands reflects their demographic, using cross-promotional techniques by integrating their products with things that appeal to young adults, such as extreme sports and popular culture icons [
51]. Youth are not immune to these marketing efforts. In a study evaluating the exposure of Canadian youth and young adults (age: 12–24) to high-energy drink marketing, over 80% of respondents reported ever seeing energy drink marketing; conversely, only 32% of survey respondents reported ever seeing education massages about the potential harms of energy drinks [
52]. Increased exposure to energy drink marketing is associated with increased consumption in adults [
53]. Enforcing responsible marketing and increasing education surrounding the risks of consuming energy drinks and vaping use will be necessary tools as part of a comprehensive strategy to reduce the use of both these substances.
Limitations
This is the first study to examine the longitudinal effects of a one-day increase in beverage consumption on smoking and vaping behaviours in a large national sample of Canadian youth. However, some limitations should be acknowledged. A ceiling effect, where students with high frequency of beverage consumption at Time 1 are less likely to demonstrate a large increase in beverage consumption, may explain why no associations were identified for SSBs. To account for this, we reported the ORs for a one-day increase in beverage consumption. The COMPASS study uses self-report measures, which can be subject to error. Additionally, social desirability bias may have impacted how the students self-reported beverage and vaping consumption. Academic achievement was not used as a covariate due to the lack of variability in the self-reported response. The beverage consumption measures were not validated, and the sugar-sweetened beverages question did not differentiate between caffeinated and non-caffeinated drinks.