Several national surveys provide data for estimation of smoking behavior among adolescents and young adults in the United States. These data sources include Monitoring the Future Study (MTF), National Health Interview Survey (NHIS), National Longitudinal Study of Adolescent Health (Add Health), National Survey on Drug Use and Health (NSDUH), National Youth Tobacco Survey (NYTS), and Youth Risk Behavior Surveillance System (YRBSS). This chapter summarizes the rates of adolescent and young adult tobacco use as reported in these sources as well as in the 2012 Surgeon General’s report Preventing Tobacco Use Among Youth and Young Adults (HHS, 2012). When discussing the rates of tobacco use, “tobacco use” is defined to include use of cigarettes, smokeless tobacco, cigars, and electronic nicotine delivery systems (ENDS), or “e-cigarettes.” Data on rates of tobacco use among different groups, including at-risk populations, are also presented. A comprehensive synthesis of these data is described in the 2012 Surgeon General’s report. This chapter then continues with evidence about the effect of age of initiation on patterns of nicotine dependence and cessation.
Cigarette smoking is the most common way that adolescents and young adults use tobacco, and data on prevalence of cigarette smoking are the most comprehensive and systematic and have the longest history of collection among all data on tobacco use. Additionally, combusted tobacco such as traditional cigarettes is responsible for the vast majority of tobacco-
related death and disease in the United States (HHS, 2014). Thus, much of this review will focus on adolescent and young adult cigarette use; however, data on other tobacco products will be provided where available.
Table 2-1 provides current cigarette smoking rates from the 2013 YRBSS by gender, race/ethnicity, and grade. Data from the 2013 YRBSS show that slightly fewer than one in five high school seniors (19 percent) were current cigarette smokers, defined as having smoked within the 30 days immediately before the survey (Kann et al., 2014). Monitoring the Future reports similar data, with 16 percent being current smokers (Johnston et al., 2014b). These prevalence data indicate that there has been a continued decline in smoking among high school students in recent years, although the decline has been occurring at a slower rate than in the early 2000s (HHS, 2012). Both YRBSS and MTF show a substantial increase in cigarette use with increasing grade level (although YRBSS shows a decline from the 11th to the 12th, which is likely due to the fact that a number of students drop out between the 11th and 12th grades). For comparable grades (10th and 12th), the estimates for YRBSS are slightly and consistently higher than for MTF, probably due to differences in how questions are asked. The different estimates from the surveys could result from a variety of factors, and each of the surveys has relative strengths and weaknesses (SAMHSA, 2012b). YRBSS and MTF are school-based samples, so these surveys exclude school dropouts and young adults who have graduated from high school. NSDUH, on the other hand,
TABLE 2-1 Percentage of High School Students Who Currently Smoke Cigarettes by Gender, Race/Ethnicity, and Grade—YRBSS, 2013
NOTE: Current smoking defined as having smoked on at least 1 day during the 30 days before the survey.
SOURCE: Kann et al., 2014.
includes dropouts and has all ages 12 and older. Current smoking prevalence is highest among white adolescents, followed by Hispanic and black adolescents. Trends are similar among young adults (HHS, 2012). While black and Hispanic males smoke more than females, prevalence rates of current smoking are the same for males and females among whites.
Table 2-2 shows NSDUH estimates of monthly cigarette use by age. Note that prevalence of use continues to increase post-high school, with a
TABLE 2-2 Percentages Used Cigarettes in Past Month by Age, NSDUH, 2012
SOURCE: Table 2.12B from SAMHSA, 2013a.
FIGURE 2-1 Trends in 30-day cigarette smoking prevalence by age group, 18–26, MTF, 2002 through 2012.
SOURCE: Johnston et al., 2013.
sharp increase at age 18, then leveling off around ages 21 to 22. The sharp increase from 16.1 percent at age 17 to 25.1 percent at age 18 is presumably due at least in part to the fact that the minimum legal age for purchase of tobacco products is 18.
Although MTF is a school-based sample, the study includes a longitudinal component, allowing for estimates for smoking rates for young adults who are high school graduates. Figure 2-1 shows trends from 2002 to 2012 in prevalence of 30-day cigarette smoking by age groups, from 18 to 26.
The trends show continuing declines in cigarette use among young adult high school graduates, with some convergence among age groups. NSDUH, which includes dropouts, also shows declines through 2012 among those ages 18 to 25 (SAMHSA, 2013a).
Finding 2-1: Almost one in five high school seniors is a current (in the past 30 days) cigarette smoker, compared with one in three young adults.
For some years cigarette smoking has been more concentrated among those with lower socioeconomic status but in recent years that concen-
tration has become more pronounced. In adolescents and young adults, socioeconomic status is typically assessed using measures of parental (often maternal) educational attainment or of the adolescent or young adult’s educational goals. Table 2-3 provides data from 10th graders in two MTF studies to illustrate the point. In 1997, when smoking rates among adolescents reached their recent peak, smoking rates were slightly higher among 10th graders whose parents had less education, but by 2013 the discrepancies had substantially widened due to a greater decline among students whose parents had more education compared with those whose parents had less education, with 13–14 percent of those whose parents had less education being smokers compared to 5–6 percent of those whose parents had more education.
The relationship between socioeconomic status and smoking also differs by racial/ethnic category (HHS, 2012). Bachman and colleagues (2011), for example, used data from MTF and found that for white students in 8th through 12th grades there was a clear negative linear relationship between parental education and smoking rates. For black students, a similar negative relationship existed between smoking and parental education, but the relationship was much smaller. For Hispanic students, the relationship was nonlinear, with smoking rates relatively high among Hispanic students with parents of higher education levels compared to white and black students, and relatively low among Hispanic students with the least educated parents compared to whites and blacks. It is possible, however, that these findings
TABLE 2-3 Percentage of 10th Graders Who Smoked Cigarettes in the Past 30 Days, by Parental Education, MTF, 1997 and 2013
NOTE: Parental education is an average of mother’s education and father’s education. Response categories are (1) completed grade school or less, (2) some high school, (3) completed high school, (4) some college, (5) completed college, and (6) graduate or professional school after college.
SOURCE: Johnston et al., 2014a.
TABLE 2-4 Percentage of 10th Graders Who Smoked Cigarettes in the Past 30 Days, by 4-Year College Plans, MTF, 1997 and 2013
|4-Year College Plans?||1997||2013|
NOTE: Respondents indicated how likely they were to graduate from a 4-year college program; those who said “definitely” or “probably will” were coded “yes.”
SOURCE: Johnston et al., 2014a.
are due to the high number of Hispanic parents with low socioeconomic status (as defined by parental education).
As a further illustration, Table 2-4 provides smoking rates for two grougps: those who expect to complete a 4-year college program versus those who do not. In 1997 those in the latter group were almost twice as likely to be current smokers as those in the former group (47.2 percent versus 26.8 percent), but by 2013 the ratio was more than 3 to 1 (23.3 percent versus 7.4 percent).
Among young adults, smoking rates similarly differ by education. Those who do not enroll in college are more likely to have started smoking at a younger age and to be current smokers, and they are less likely to attempt to quit smoking than their peers who enroll in college (Green et al., 2007). Also, among young adults not attending college, full-time employment is associated with higher rates of tobacco use (Welte et al., 2011).
Tables 2-5 and 2-6 provide the percentage of 12- to 17-year-olds who smoked cigarettes in the past month by region of the country and by state of residence, in combined years 2002–2003 and 2010–2011. (Combining two years of data is necessary because of the small numbers of cases available in many states.) Figure 2-2 provides a visual display of the considerable variation by state for 2010–2011. Utah had the lowest rate (5.1 percent), and West Virginia had the highest (11.8 percent) (SAMHSA, 2012c). The 10 highest states (red color in Figure 2-2, greater than 9.7 percent) were, in descending order: West Virginia, Montana, Kentucky, Missouri, Wyoming, Iowa, New Hampshire, Vermont, Oklahoma, and South Dakota. The nine lowest states, plus the District of Columbia (white color in Figure 2-2, 7.11 percent or less), were, in descending order: Texas, Virginia, Nevada,
TABLE 2-5 Percentage Using Cigarettes in the Past Month, Ages 12–17, by Region, NSDUH, 2002–2003 and 2010–2011
|Region||2002–2003||2010–2011||Percentage Point Change|
SOURCE: SAMHSA, 2012c.
Florida, New York, Hawaii, California, District of Columbia, Maryland, and Utah. Of the four regions of the country, the Midwest had the highest rates of smoking among 12- to 17-year-olds (8.8 percent), and the West had the lowest (7.1 percent). Between 2002–2003 and 2010–2011, all regions and all states showed declines.
FIGURE 2-2 Cigarette use in the past month among adolescents ages 12 to 17, by state. Average annual percentages, NSDUH, 2010 and 2011.
SOURCE: SAMHSA, 2012a.
TABLE 2-6 Percentage Using Cigarettes in the Past Month, Ages 12–17, by State, NSDUH, 2002–2003 and 2010–2011
|District of||7.1||5.99||−1.11||North Dakota||17.53||9.64||−7.89|
SOURCE: SAMHSA, 2012c.
Table 2-7 provides prevalence of 30-day smoking by age group and by metropolitan status for adolescents and young adults. In each age group, the nonmetropolitan segment has the highest rate of smoking and the large metropolitan has the lowest, with the small metropolitan segment being intermediate.
Use of other tobacco products similarly varies by metropolitan status, with greater use in more rural communities and less use in more urban areas. Adolescents and young adults residing in rural communities are more likely to use tobacco and, particularly, smokeless tobacco or chew because of the cultural norms set within their communities (Melnick et al., 2001; Peek et al., in preparation). Rural life is often associated with the rodeo or being a cowboy (Peek et al., in preparation), with males playing sports such as baseball (whose athletes use smokeless tobacco at high rates), and with men being more macho and tough (Melnick et al., 2001; Peek et al., in preparation). These attitudes often translate into a situation in which it is socially normative to use tobacco in order to mirror these images. Furthermore, in these often insular, small communities where everyone is connected and knowledgeable of each other’s action, younger adolescents are able to obtain chew and other tobacco products from members of their community more easily (Peek et al., in preparation).
TABLE 2-7 Percentage Smoking in the Past 30 Days by Age and Metropolitan Status, NSDUH, 2012
SOURCE: Committee analysis from SAMHSA, 2013a.
Tobacco use is also more common among those with mental illness, in part because these individuals use nicotine as a means of “self-medication,” mood regulation, and stress mitigation (Ziedonis et al., 2008). On the other hand, Goodman and Capitman (2000) assessed 8,704 adolescents and found that depressive symptoms did not predict smoking. Instead, smoking predicted subsequent depressive symptoms. Similarly, greater levels of smoking during adolescence and early adulthood have been associated with a higher risk for agoraphobia, general anxiety disorder, and panic disorder (Johnson et al., 2000), suggesting that while there is a strong relationship between mental illness and smoking, the nature of this relationship is still unclear.
Lesbian, gay, bisexual, transgender, questioning, or queer (LGBTQ) adolescents and young adults appear to use smoking as a means of coping with the stigma associated with their sexual identity (Rosario et al., 1997). Higher smoking rates among LGBTQ youth persist even after accounting for psychosocial factors such as depression, self-esteem, and familial smoking habits (Austin et al., 2004). However, it is also the case that supportive social environments (operationalized by assessing the proportion of same sex couples living in the counties studied, the proportion of schools with gay–straight alliances, the proportion of schools with policies protecting gay students, and the proportion of schools with antidiscrimination policies) have been associated with lower rate of tobacco use (Hatzenbuehler et al., 2011).
Finding 2-2: Significant disparities in tobacco use remain among adolescents and young adults nationwide. The lowest rates are found in the western United States, in large metropolitan areas, among African Americans, adolescents who plan to go to college, and adolescents whose parents’ education includes graduate school or a professional degree.
The Surgeon General’s 2012 report stated that one of the most important and widely cited findings from the 1964 Surgeon General’s report on smoking and health was that cigarette smoking almost always begins
before adulthood (HHS, 2012). The 2012 report corroborated that the finding still held. Table 2-8 in this report updates that information and shows that the finding is still true. Among adults ages 30 to 34 who ever smoked daily, 89.8 percent had first tried a cigarette before age 19, and 99.2 percent before age 26. The 2012 Surgeon General’s report emphasized that a relatively high proportion of adult smokers initiate at a relatively early age. For example, more than one-third (36.7 percent) of adults who had ever tried a cigarette reported trying their first cigarette by age 14. The figure in Table 2-8 (36.2 percent) is virtually identical to this number (36.2 percent).
The preceding data on initiation has used the typical definition of initiation as being the point in time at which one first tries a cigarette, which is the way that initiation is measured by most surveys of adolescents and young adults. However, the NHIS survey used a different definition of age of initiation, which is often used in surveys of adults, and does not treat a person as having initiated smoking until that person has smoked at least 100 cigarettes. In the models reported in Chapter 8, NHIS data are used as the basis for estimating the effects that changing the minimum legal age has on initiation. This raises the question of how different these definitions are in practice. NSDUH asks about both the age of first use and whether the respondent has ever used 100-plus cigarettes in his or her life, so these data can be used to compare the distributions of ages of initiation for all NSDUH respondents versus just those who progressed to smoking 100-plus cigarettes. To summarize the results of this comparison, while the distributions are not identical, they are quite close, suggesting that this adjustment is not a major concern.
The age of first use was cross-tabulated with having smoked at least 100 cigarettes across the lifetime for 26- to 34-year-old respondents and separately for all respondents 26 and older in the NSDUH surveys of 2002 through 2012, combined. The results for all respondents 26 and older have the advantage of being based on a larger number of respondents, but the restriction to 26- to 34-year-olds limits the analysis to younger respondents, whose cigarette initiation patterns may differ from those of older respondents from earlier generations.
Figure 2-3 shows the distributions of ages of initiation for 26- to 34-year-olds. The comparison of interest is between the thick black line (for all respondents) and the thick red line (just for those who progressed to 100-plus cigarettes). The black line in some sense corresponds to MTF and other data that ask about age of first use for all who have ever smoked any cigarettes; the red line corresponds to the NHIS data, the input for the models.
TABLE 2-8 Cumulative Percentage of Recalled Ages at Which Respondents First Used a Cigarette and Began Smoking Daily, by Smoking Status Among 30- to 34-Year-Olds, NSDUH, 2012
Persons Who Had Ever Tried a Cigarette
Persons Who Ever Smoked Daily
|Age||First Tried a Cigarette||Began Smoking Daily||First Tried a Cigarette||First Tried a Cigarette||Began Smoking Daily|
Persons Who Had Ever Tried a Cigarette
Persons Who Ever Smoked Daily
|Age||First Tried a Cigarette||Began Smoking Daily||First Tried a Cigarette||First Tried a Cigarette||Began Smoking Daily|
SOURCE: Committee analysis of data from HHS et al., 2014.
FIGURE 2-3 Age distribution of cigarette initiation reported by 26- to 34-year-olds, broken down by those who did versus those who did not progress to using 100-plus cigarettes in their lifetimes (62 percent progressed; 38 percent did not), NSDUH, 2002 through 2012.
SOURCE: Committee analysis of data from HHS et al., 2014.
Those who ended up smoking more heavily have a distribution of ages of initiation that skews slightly younger, with more initiating at ages 12–16 and fewer initiating after 17. The largest difference is at age 13; 9.7 percent of all smokers initiated at age 13, but 11.6 percent of those who progressed did so.
Figure 2-4, which shows data for all respondents age 26 and above, shows even smaller differences between those who did and those who did not progress to smoking 100-plus cigarettes.
FIGURE 2-4 Age distribution of cigarette initiation reported by those 26 years old and older, broken down by those who did versus those who did not progress to using 100-plus cigarettes in their lifetimes, NSDUH, 2002 through 2012.
SOURCE: Committee analysis from HHS et al., 2014.
Finding 2-3: Among adults who become daily smokers, nearly all report first use of cigarettes before 19 years of age (90 percent), with 99 percent reporting first use before 26 years of age.
The most commonly used metric of smoking intensity is the number of cigarettes smoked per smoking day. Table 2-9 provides the average number of cigarettes smoked per smoking day for those who smoked cigarettes in the past 30 days, by age, based on 2012 NSDUH data. The right-most two columns compare the data for those who smoked less than about half a pack per day with those who smoked half a pack or more per smoking day. There are substantial increases between ages 12 through 15 and age 16, and between ages 17 and 18, but then relatively little increase in the average number of cigarettes smoked per smoking day in the age range from 18 to 20. Intensity increases substantially after that. An alternative metric for gauging the overall exposure to cigarettes is the number of days that an individual has smoked in the past month. This metric captures the frequency or regularity of use.
TABLE 2-9 Average Number of Cigarettes per Smoking Day in Past 30 Days, NSDUH, 2012
|Number of cigarettes||<1||1||2–5||6–15
|½ Pack or
NOTE: Entries are percentages. The survey question was, “On the days you smoked cigarettes during the past 30 days, how many cigarettes did you smoke per day, on average?”
SOURCE: Committee analysis of data from HHS et al., 2014.
In general, the rates of cigarette smoking have been declining, although there have been recent signs of a deceleration in that decline (SAMHSA, 2013b). In addition to this general decline, there has also been clear evidence of an increasing trend toward lighter use. One indication of this is that among those who smoked cigarettes in the past 30 days, the proportion of those who smoke every day has been decreasing, and, conversely, the proportion of nondaily smokers has been increasing. Table 2-10 provides the percentages, from 1991 to 2013, of past-30-day smokers who smoked less often than daily for four age groups, based on the Monitoring the Future study. Among young adults ages 19 to 28, the percentage of current smokers who were nondaily smokers rose steadily from 23 percent in 1991 to 40 percent in 2013. The rise in this population of lighter smokers has important implications for the understanding of nicotine addiction and dependence (Shiffman, 2009).
While there are several sources of reliable information on cigarettes, there is less extensive information on other tobacco products, particularly for trends in their use. The situation regarding tobacco products other than traditional cigarettes is currently highly volatile, with new products being introduced and existing products being modified. NYTS asks questions about a range of non-cigarette tobacco products, including cigars, smokeless tobacco, tobacco smoked with a hookah, pipes, electronic cigarettes, snus, kreteks, bidis, and dissolvable tobacco. Table 2-11 provides results from the 2011 and 2012 surveys.
The various products are ordered in Table 2-11 according to their total prevalence in 2012, from highest to lowest. Overall, just about one in four high school students reported using at least one tobacco product during the previous 30 days (23.3 percent in 2012). Cigarettes were the most commonly used, at 14.0 percent, but cigars were not far behind at 12.6 percent. “Cigars” includes cigars, cigarillos, and little cigars. This class of products has seen major changes in the types and number of products available and in the marketing of the products. Little cigars may be very similar to cigarettes in size and shape, and may be flavored with fruit or candy. They are typically taxed at lower rates than cigarettes and may therefore be more affordable. While the rates of current cigarette use have seen a significant decrease, the rates of smokeless tobacco use, including the use of chew, dip, or moist snuff, have remained stable or even increased. For example, among Americans age 12 or older, 3.1 percent were current (past-month) users of smokeless tobacco in 1998, and that figure was at 3.5 percent in 2012 (SAMHSA, 2013a).
TABLE 2-10 Percentage of Past 30-Day Smokers Who Smoked Less Than Daily, MTF, 2013
SOURCE: Johnston et al., 2014c.
According to the 2011 YRBSS, 12.8 percent of adolescent males and 2.2 percent of adolescent females in the United States reported current use of smokeless tobacco (Eaton et al., 2012). Overall, current use of smokeless tobacco was higher among whites (9.3 percent) than among Hispanics (5.9 percent) or blacks (3.1 percent). In the NYTS survey, smokeless tobacco, which includes chewing tobacco, snuff, and dip, was used by 6.4 percent
TABLE 2-11 Percentage of High School Students Using Tobacco Products in Past 30 Days, by Gender, NYTS, 2011–2012
|2011||2012||2011||2012||2011||2012||Ratio in 2012|
SOURCE: Arrazola et al., 2013.
of those surveyed. Another form of smokeless tobacco is snus, which is a relatively new product in the United States and was used by 2.5 percent.
Approximately 5 percent of the respondents reported using the hookah (waterpipe), and an equal number reported smoking pipes. Electronic cigarettes are an increasingly visible part of the tobacco product scene, but as of 2012 less than 3 percent of high school students reported using them. Nevertheless, ENDS use is increasing rapidly among adolescents. In 2014, for the first time in a U.S. national study, Monitoring the Future reported that more high school students used e-cigarettes than traditional cigarettes or any other tobacco product. The difference in the use of e-cigarettes versus traditional cigarettes was greater among younger students: 9 percent of 8th grade students reported using an e-cigarette in the past 30 days, as compared with 4 percent for traditional cigarettes; 16 percent of 10th grade students reported using an e-cigarette, as compared with 7 percent for traditional cigarettes; and 17 percent of 12th grade students reported using an e-cigarette, as compared with 15 percent for traditional cigarettes (Wadley and Bronson, 2014). Kreteks, bidis, and dissolvable tobacco (another recent
addition to the group of smokeless tobacco products) all were used by 1 percent or less of respondents.
Males were more likely than females to use at least one tobacco product (28.3 percent versus 18.1 percent in 2012), and, for any given product, males were more likely than females to report using that product. The male/ female ratios were particularly high for smokeless tobacco and the newer smokeless snus. The Surgeon General’s 2012 report noted that as of 2010, about 1 in 10 high school senior males was a current smokeless tobacco user and about 1 in 5 high school senior males was a current cigar smoker (HHS, 2012). The 2013 YRBSS found that about one in six high school senior males was a current smokeless tobacco user, and about one in four high school senior males was a current cigar smoker (Kann et al., 2014). The use of these two classes of tobacco products clearly has not declined in recent years (HHS, 2012; Kann et al., 2014).
Table 2-12 provides some limited information on the use of tobacco products among adolescents and adults, as reported by NSDUH. As with NYTS, cigars are found to make up a relatively high proportion of tobacco product use, particularly among young adults.
Some limited trend data on smoking tobacco with a hookah are available from the Monitoring the Future study. Table 2-13 shows that smoking tobacco with a hookah is particularly popular among college students, with 26 percent reporting in 2013 having done so at least once in the previous 12 months. Even among 12th graders, the behavior is relatively common, with 21 percent reporting having done so in 2013. However, much of this behavior is light or experimental, with only 9 percent of 12th graders reporting having smoked with a hookah more than five times in the previous 12 months (Wadley and Barnes, 2013).
TABLE 2-12 Percentage Who Used Tobacco Products in Past 30 Days by Age, NSDUH, 2012
|Age||Smokeless Tobacco||Cigars||Pipe||Cigarettes||Any Tobacco Products|
SOURCE: SAMHSA, 2013a.
TABLE 2-13 Prevalence of Hookah Use in Past 12 Months, MTF, 2010 Through 2013
|Young adults (19–28)||20.1||19.1||20.4|
SOURCES: Johnston et al., 2014b; Wadley and Barnes, 2013.
The Surgeon General’s report of 2012 data concluded that concurrent use of multiple tobacco products (poly-tobacco use; usually using cigarettes and another tobacco product) was prevalent among adolescents. Among those who use tobacco, nearly one-third of high school females and more than one-half of high school males report having used more than one tobacco product in the past 30 days. By 2012, more than one-third of high school female users were poly-tobacco users. In the 2012 NYTS, of the 15.4 percent of high school females who reported tobacco use, 38 percent of them—or 5.9 percent of all high school females—reported using more than one tobacco product; the corresponding figures for high school males were 55 percent of 25.3 percent, or 13.8 percent of all high school males (Arrazola et al., 2014).
Finding 2-4: Concurrent use of multiple tobacco products is prevalent among adolescents.
Finding 2-5: It is difficult to assess trends in non-cigarette products because the products themselves are changing. While cigarette use has been declining, the use of some other products has not.
Tobacco use in adolescents and in young adults is not a unitary phenomenon; instead it is best characterized by a series of events that involve multiple behaviors and feelings (Mayhew et al., 2000) and transitions in a sequence from initial trials with tobacco to more occasional use, to the development of dependence and regular use, through to cessation. Tobacco use in adolescence is highly variable in terms of both frequency of use and intensity of use (Mermelstein et al., 2002).
Age-based prevalence data for tobacco use provide cross-sectional views of tobacco use from which one can assume patterns of progression. However, while such cross-sectional prevalence data can provide infor-
mation about the total number of smokers at a given age and even offer insights into how many individuals have started or stopped smoking in a given year, they are less directly informative about individual differences in progression of tobacco use behavior. With the use of newer data analytic techniques (e.g., latent variable growth mixture modeling), researchers have identified various trajectories of smoking behavior among adolescents and young adults (e.g., Bernat et al., 2008; Brook et al., 2008; Chassin et al., 2008; Colder et al., 2001, 2008; Costello et al., 2008; Jackson et al., 2008; Lessov-Schlaggar et al., 2008; Riggs et al., 2007; Stanton et al., 2004; Tucker et al., 2006). These approaches may help to better describe the heterogeneity of longitudinal patterns of use and to identify factors that discriminate among the different trajectories. Among the trajectories that have been identified are groups of adolescents who experiment but have non-escalating trajectories and other groups that escalate rapidly. Unfortunately, these studies have not to date provided the fine-grained age detail during the young adult period necessary to reliably identify the differences between those individuals who initiate and escalate starting in young adulthood and those who initiate during the earlier adolescent years. In addition, most of these studies have provided data on the broad population of adolescents, most of whom fall into the nonsmoking trajectories. As such, they provide less in-depth information on the patterns of progression of those adolescents who try tobacco use. Furthermore, all of these studies have focused exclusively on cigarette use, and none have considered how the use of other tobacco products (e.g., cigars, smokeless tobacco, hookah, etc.) may affect these trajectories. In addition, to date there has been no systematic data collected concerning how patterns of tobacco product use may vary by product or by combinations of products, including product switching. The changing landscape of available tobacco products may well affect overall patterns of use.
The often irregular pattern of tobacco use behavior presents a challenge for clearly identifying exactly when nicotine dependence develops in the progression of tobacco use. The level of dependence symptoms that individuals experience is believed to be the most important factor contributing to smoking persistence and failed cessation efforts. Nicotine dependence is characterized by physiological adaptations (e.g., tolerance, withdrawal) and other accommodating behaviors (e.g., time spent in activities necessary to obtain and use nicotine and to recover from its effects and the forfeiting or reduction of important social, occupational, or recreational activities) resulting from chronic smoking. Nicotine dependence predicts smoking regularity and quantity across adolescence into young adulthood (Dierker and Mermelstein, 2010; O’Loughlin et al., 2003; Selya et al., 2013). Ongoing longitudinal studies of adolescent smoking that have examined the development of nicotine dependence symptoms suggest that nicotine dependence
follows different developmental trajectories in different individuals (Hu et al., 2008) and that for some adolescents, nicotine dependence symptoms emerge very soon after the onset of smoking and at low levels of nicotine exposure, well before the establishment of daily smoking patterns (Dierker and Mermelstein, 2010; DiFranza et al., 2002). The McGill Study on the Natural History of Nicotine Dependence in Teens confirmed individual differences in the emergence of dependence and identified adolescents meeting the criteria for ICD-10 nicotine dependence even among sporadic and monthly smokers (O’Loughlin et al., 2003). Demographic (gender, ethnicity) differences may also affect the development of nicotine dependence at low levels of smoking exposure. For example, women have been shown to have higher rates of dependence than men who engage in the same amount of smoking (Kandel and Chen, 2000). In addition, compared to other racial groups, whites have been found to have lower rates of lifetime nicotine dependence (Hu et al., 2006; Kandel and Chen, 2000) and higher quit rates (Fagan et al., 2007). It may well be that some of the differences in the patterns of development of nicotine dependence, especially with regard to age sensitivity, may be explained by individual differences in patterns of brain development, genetics, or initial sensitivity to nicotine (Swan and Lessov-Schlaggar, 2007).
There is considerable evidence that age of initiation is associated with levels of nicotine dependence. As presented in the 2012 Surgeon General’s report (HHS, 2012), data from the NSDUH 2007–2010 surveys show that a younger age of initiation is strongly associated with greater nicotine dependence in both young adulthood (18 to 25 years old) and older adulthood (26 years and older). Consistent dose–response gradients were present, indicating that the younger the age of initiation, the greater the degree of nicotine dependence. Furthermore, these associations held true regardless whether age of initiation was measured as the age of the first puff or the age an individual first smoked daily and were also independent of the length of the transition from the first cigarette to daily smoking (HHS, 2012). Longitudinal studies following participants from adolescence to young adulthood also showed a statistically significant gradient, with younger ages of initiation associated with greater nicotine dependence (Buchmann et al., 2013; Hu et al., 2006). The association between earlier age of initiation and greater nicotine dependence in early life also persists into adulthood. Cross-sectional data in 21- to 30-year-olds (Breslau and Peterson, 1996) and in later adulthood (Lando et al., 1999; Park et al., 2004) also show clear gradients indicating that the earlier the age of starting cigarette smoking, the greater the nicotine dependence; in both studies the strong association between a younger age of initiation and greater nicotine dependence was clearly evident across ages of initiation ranging from adolescence to 25 years of age and older. These findings suggest that there is no apparent threshold beyond which this association does not apply.
Finding 2-6: Symptoms of nicotine dependence can develop even at low levels of exposure to smoking, well before the establishment of daily smoking.
Smoking intensity, defined as the number of cigarettes smoked per day, is strongly related to nicotine dependence and to all health outcomes. Strong associations between younger ages of smoking initiation and heavier smoking are evident even in studies that have examined this question among adolescents who started smoking before high school and assessed smoking intensity in high school (Escobedo et al., 1993; Everett et al., 1999; Reidpath et al., 2014). Strong and statistically significant associations were also observed in longitudinal studies that followed individuals from adolescence to young adulthood (Buchmann et al., 2013; Hu et al., 2006).
U.S. national cross-sectional data indicate that an earlier age of first puffing a cigarette or of smoking cigarettes daily were both strongly associated with a greater likelihood of being a heavier smoker both in 18- to 25-year-olds and in those 26 years and older and that this association remained consistent regardless of the transition time from first trying a cigarette to becoming a daily smoker (HHS, 2014). Additional cross-sectional studies document a strong dose-dependent association between a younger age of initiation and a greater number of cigarettes smoked per day in young adulthood (Breslau, 1993) and in older adulthood (Chen and Millar, 1998; D’Avanzo et al., 1994; Fernandez et al., 1999; Hu et al., 2006; Lando et al., 1999; Taioli and Wynder, 1991).
The evidence reviewed above that a younger age of initiation is associated with greater nicotine dependence and greater smoking intensity supports the suggestion that an earlier age of initiation would be associated with an increased likelihood of remaining a smoker throughout the life span, and the empirical data on this association supports that assumption. An earlier age of starting to smoke cigarettes has been associated with an increased likelihood of remaining a smoker (or reduced likelihood of quitting) in several studies that span periods of life starting at various points from pre-high school to high school (Everett et al., 1999) and progressing to young adults (Breslau and Peterson, 1996) and older adulthood (Chen and Millar, 1998; D’Avanzo et al., 1994; Eisner et al., 2000; Khuder et al., 1999). The influence of the age of initiation on smoking cessation does not appear to simply be an artifact of an early initiation of smoking being asso-
ciated with a longer duration of smoking, all else being held equal (Breslau and Peterson, 1996).
Finding 2-7: An earlier age of initiation is associated with greater levels of nicotine dependence.
Finding 2-8: An earlier age of initiation is associated with greater intensity and persistence of smoking beyond adolescence and through adulthood.
As noted above, a sizable portion of adolescent smokers, even those who are infrequent and light smokers, show signs of nicotine addiction and are likely to continue smoking into adulthood. The fact that adolescents do not seem to spontaneously “mature out” of smoking (Mermelstein, 2003) does not necessarily reflect a lack of motivation to quit. Rather, a majority of adolescent smokers want to quit, and many of them make serious attempts to do so (Bancej et al., 2007; Marshall et al., 2006). However, tobacco cessation among adolescents is challenging. Despite a lower frequency and intensity of use in adolescents compared with adults, the rates of cessation among adolescents are low, and most adolescents experience difficulty in quitting (Mermelstein, 2003; O’Loughlin et al., 2009). Most adolescents who want to quit attempt to do so without any formal assistance, and of the few who have formal assistance, even fewer use evidence-based approaches (Curry et al., 2009). Although there are a number of good behaviorally based interventions for adolescents, and these interventions increase the chances of adolescent smokers achieving cessation, their reach is limited and their overall success rates are lower than one finds with adult evidence-based programs (Curry et al., 2009). A recent Cochrane meta-analysis of tobacco cessation interventions for regular smokers younger than 20 reported mixed findings for interventions, with the more complex counseling approaches showing some promise, but few trials showing pharmacotherapy to be effective in helping adolescent smokers quit (Stanton and Grimshaw, 2013). The review concluded that there is not yet sufficient evidence to recommend one specific approach for widespread implementation for adolescent smokers.
The developmental challenges of adolescence may also interfere with an adolescent smoker’s ability to quit. These challenges include the adolescent’s stage of cognitive development and ability to problem-solve and maintain coping skills under periods of emotional arousal, particularly arousal brought on during nicotine withdrawal, as well as other age-based
challenges that come with an adolescent’s lack of control over his or her environment and lack of ability to modify cues that may promote smoking (Curry et al., 2009). Thus, not all adolescents who smoke may have the cognitive, environmental, and emotional resources to make cessation attempts successful. Cessation attempts are also less successful among adolescents who smoke more or who smoke daily (Bancej et al., 2007). In one of the few studies to examine the discontinuation of smoking among adolescents who are light and mostly intermittent smokers, O’Loughlin et al. (2014) found that males and older adolescents were more likely to discontinue smoking, and suggested that older adolescents may be more successful for a variety of reasons, including moving into adult roles, developing increased skills to manage a quit attempt, and having more exposure to cessation aids.
Young adults also find cessation challenging, and the evidence is mixed as to whether young adults are more successful than older adults, with relatively few studies having compared cessation rates across age groups. Messer et al. (2008) found that young adults ages 18 to 24 were more likely to quit successfully than older adults. However, Villanti et al. (2010) found that there is limited evidence for the efficacy of cessation interventions specifically geared to young adults. In a meta-analysis addressing the question of whether cessation interventions that are successful for older adults work equally well for young adults, Suls et al. (2012) found that interventions that are efficacious for the general adult population are equally effective for young adults. The larger problem, however, is attracting young adults to evidence-based cessation programs (Suls et al., 2012).
In sum, adolescents, even those who are light and intermittent adolescent smokers, have difficulty stopping their tobacco use, especially once dependence symptoms have emerged, even if the symptoms have not yet reached the level of fully developed nicotine dependence. In addition, evidence-based cessation interventions for adolescents are not as easily or widely available as they are for adults, and pharmacological approaches are limited in both reach and effectiveness (Curry et al., 2009). More cessation options are available for young adults, and success in quitting may be easier to achieve during the young adult years.
Finding 2-9: Tobacco cessation among adolescents is difficult to achieve, with few, if any, well-supported interventions that are available for widespread dissemination. More effective treatment options are available for young and older adults.
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