The present study is among the first longitudinal investigations of the relationship between smoking initiation and later cigarette consumption in adolescence to address important limitations observed in previous studies. Specifically, it does not use retrospective reports of age at smoking initiation and includes frequent, biannual assessments of smoking behavior. Adolescents’ smoking behavior was assessed every 6 months, from the beginning of 9th grade to the end of 10th (School A) or 11th (School B) grade. Contrary to our hypothesis and to commonly held beliefs, our findings indicated that earlier age of smoking initiation was not associated with greater cigarette consumption later in adolescence. Instead, a 6-month delay in smoking initiation was associated with significantly more cigarettes consumed by the end of 10th or 11th grade. This effect was significant even after accounting for number of friends who had smoked at least one whole cigarette, and was replicated in two separate schools. Overall, these findings suggest that the relationship between age at initiation and later cigarette consumption may not be negative and linear over time, as previously assumed, but may be marked by a period of heightened vulnerability in mid or later adolescence.
There are several possible explanations for why later smoking initiation may lead to greater cigarette consumption by age 16 or 17. Adolescence is characterized by neurodevelopmental changes that are likely to affect adolescents’ decisions to smoke cigarettes (Steinberg 2008
). Research suggests that, while reasoning abilities are fairly well-developed by adolescence, the neural circuitry associated with cognitive control may be less developed than that associated with reward systems. As a result, there may be a period of vulnerability in which adolescents may place more emphasis on and be more responsive to the rewards of smoking than younger children and adolescents. In addition, animal studies show that adolescent brains are particularly responsive to the effects of nicotine, which may place adolescents at higher risk for becoming addicted to cigarettes (O’Dell 2009
). This may be particularly dangerous in light of evidence showing that adolescents do not understand nicotine addiction and assume that it will be easy for them to quit smoking in the future (Arnett 2000
; Halpern-Felsher et al. 2004
; Slovic 1998
Changes in the social landscape may also make older initiators likely to smoke more. Our results showed that peer smoking only predicted cigarette consumption among adolescents who reported smoking more than 10 cigarettes at the end of 10th grade or 11th grade. Research shows that friends’ influence on adolescent behavior increases during adolescence, and that adolescents’ susceptibility to anti-social or deviant peer influence may peak in mid-adolescence (Sumter et al. 2009
). Increased susceptibility to peer influence, if coupled with an increase in the number of friends who smoke, may create a period of greater vulnerability for heavier cigarette consumption that peaks in mid- or late adolescence.
Later experimentation may also lead to greater consumption because older adolescents may have easier access to cigarettes. They may have friends who are old enough to purchase cigarettes for them, they may be allowed greater freedom in going to social events where cigarettes are readily available, and they may have a job that provides them with money to pay for cigarettes. Adolescents may also be more exposed to smoking in the media and tobacco industry marketing as they age, because freedom may increase as parental supervision decreases. Research indicates that smoking in the media, such as smoking in the movies, may have a powerful influence on adolescent smoking behavior (Dalton et al. 2009
). The tobacco industry also deliberately targets teens in their advertizing campaigns, and these efforts have been shown to be successful (Pierce et al. 1991
). It is unclear whether or not adolescents’ susceptibility to these marketing strategies changes over time. However, if older adolescents are more exposed and/or more susceptible to such marketing campaigns, then later initiators may be more likely to consume more cigarettes.
Finally, early initiators may try smoking for different reasons than later initiators, and these reasons may have different implications for continued smoking. For example, children and adolescents who start smoking at an early age may experiment primarily out of curiosity, whereas older adolescents may start smoking because of a desire to relieve negative mood or to fit in with peers. The latter reasons may be more strongly associated with continued smoking, because of chronic exposure to stressors that may induce negative mood, and because of the increasing importance of peers during adolescence (Sumter et al. 2009
Strengths and Limitations
Our study has a number of strengths, including a longitudinal design, prospective measurement of smoking initiation, and continuous measurement of age at smoking initiation. Nevertheless, our findings should be interpreted in light of several limitations. While we can draw limited conclusions about smoking initiation before the age of 14 because our sample included adolescents who started smoking prior to recruitment into the study at age 14, we cannot speak to how earlier initiation influences cigarette consumption after age 17. Furthermore, our results do not speak to how age at initiation may influence nicotine dependence, because we did not measure nicotine dependence.
Generalizability may be limited by the fact that our sample was comprised of adolescents from Northern California and therefore may not be representative of the rest of the nation. Compared to statewide adolescent prevalence rates, smoking rates in the current sample were higher among 14–15 year olds and approximately equivalent among 16–17 year olds (Al-Delaimy et al. 2008
). Given that statewide prevalence rates are calculated as the mean rates across the state, our sample may be more representative of those schools whose smoking rates are above the mean for 14–15 year olds. In addition, adolescent smoking rates in the present study were lower than the national average; however, this difference is to be expected given that California is second only to Utah in having the lowest state-specific prevalence rates (CDC 2010a
). Generalizability may also be limited by the fact that the relationship between friend smoking and teen smoking was weaker in the present study than observed in previous research. It is likely that peer influence to promote smoking is weaker in our sample because there is considerable social stigma associated with smoking in California.
It should also be noted that the highest rate of consumption measured in our study was “ten or more cigarettes,” which does not correspond with a very high rate of consumption. However, studies have shown that adolescents report loss of autonomy over tobacco use, such that quitting is difficult or produces discomfort, after smoking as few as one or two cigarettes (e.g., Savageau et al. 2009
; Scragg et al. 2008
; Ursprung and DiFranza 2009
). Additionally, we did not biochemically verify smoking status. Self-reported smoking may underestimate true smoking in adults, but studies of adolescents suggest that self-reported smoking status may be reasonably accurate, especially when self-report is compared to cotinine levels (Dolcini et al. 2003
; Gorber et al. 2009
; Kentala et al. 2004
; Park and Kim 2009
; Parker et al. 2002
; Post et al. 2005
). Nevertheless, future studies may be improved by using biochemical measures to confirm self-reported smoking status.
A few potential limitations with respect to study measurement must also be considered. We were unable to measure variables in addition to friends’ smoking that may also account for the relationship between age at smoking initiation and later consumption, such as personality factors, exposure and sensitivity to tobacco marketing, drug or alcohol use, and family smoking. These factors and others may serve to mediate or moderate the effect of age at initiation on cigarette use in later years, and thus the current results must be interpreted with caution. Furthermore, we did not measure how much participants’ friends smoked. It may be useful in future studies to measure the level of friends’ cigarette consumption, as friends who are heavier smokers may have a greater impact on participants’ decisions to smoke. We also did not evaluate different trajectories in adolescent smoking behavior. Previous work has shown that adolescent smoking behavior may follow one of several different trajectories over time (Chassin et al. 2000
; Riggs et al. 2007
), and clarification of these trajectories may be useful in improving tailored interventions for adolescent smoking prevention and cessation.
Finally, the fact that we repeatedly measured smoking behavior over time may have affected our results by introducing participant reactivity. This is an inherent risk in longitudinal research designs that was outweighed by the goal of the present study to elucidate a temporal sequence of events, which cannot be accomplished with a cross-sectional design. This design also allowed us to address other gaps in the existing literature, such as retrospective bias and lack of temporal sensitivity, by using more frequent assessments of behavior than found in previous longitudinal adolescent smoking studies. It is difficult to determine the extent to which repeated measurements may have influenced our study outcome, but spacing survey time points 6 months apart is likely to have minimized potential reactivity.
The present longitudinal study showed that, among adolescents between the ages of 14 and 17, those who start smoking cigarettes later are more likely to smoke a greater number of whole cigarettes by age 16 or 17. This finding appears to contradict the common assertion that earlier age at smoking initiation predicts heavier consumption later, but may instead highlight a period of vulnerability in adolescence where experimentation is more likely to lead to heavier smoking. Results suggest that specifically targeting prevention efforts to this age group may further reduce smoking initiation among youth, thus limiting subsequent smoking-related morbidity and mortality in adulthood.