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What characterizes adolescent development?

What characterizes adolescent development?

In this section you read about how important it is for adolescents to have caring adults in their lives. In previous chapters, what did you learn about the role parents play in their children’s lives leading up to adolescence that might influence adolescents’ development?

Reflect Your Own Personal Journey of Life
· Was your adolescence better described as a stormy and stressful time or as one of trying out new identities as you sought to find an identity of your own? Explain.

Page 341

2 Physical Changes
LG2 Describe the changes involved in puberty, as well as changes in the brain and sexuality during adolescence.

Puberty

The Brain

Adolescent Sexuality

One father remarked that the problem with his teenage son was not that he grew, but that he did not know when to stop growing. As we will see, there is considerable variation in the timing of the adolescent growth spurt. In addition to pubertal changes, other physical changes we will explore involve sexuality and the brain.

PUBERTY
Puberty is not the same as adolescence. For most of us, puberty ends long before adolescence does, although puberty is the most important marker of the beginning of adolescence.

Puberty is a brain-neuroendocrine process occurring primarily in early adolescence that provides stimulation for the rapid physical changes that take place during this period of development (Berenbaum, Beltz, & Corley, 2015; Shalitin & Kiess, 2017; Susman & Dorn, 2013). Puberty is not a single, sudden event. We know whether a young boy or girl is going through puberty, but pinpointing puberty’s beginning and end is difficult. Among the most noticeable changes are signs of sexual maturation and increases in height and weight.

Sexual Maturation, Height, and Weight Think back to the onset of your puberty. Of the striking changes that were taking place in your body, what was the first to occur? Researchers have found that male pubertal characteristics typically develop in this order: increase in penis and testicle size, appearance of straight pubic hair, minor voice change, first ejaculation (which usually occurs through masturbation or a wet dream), appearance of kinky pubic hair, onset of maximum growth in height and weight, growth of hair in armpits, more detectable voice changes, and, finally, growth of facial hair.

What is the order of appearance of physical changes in females? First, either the breasts enlarge or pubic hair appears. Later, hair appears in the armpits. As these changes occur, the female grows in height and her hips become wider than her shoulders. Menarche —a girl’s first menstruation—comes rather late in the pubertal cycle. Initially, her menstrual cycles may be highly irregular. For the first several years, she may not ovulate every menstrual cycle; some girls do not ovulate at all until a year or two after menstruation begins. No voice changes comparable to those in pubertal males occur in pubertal females. By the end of puberty, the female’s breasts have become more fully rounded.

Marked weight gains coincide with the onset of puberty. During early adolescence, girls tend to outweigh boys, but by about age 14 boys begin to surpass girls. Similarly, at the beginning of the adolescent period, girls tend to be as tall as or taller than boys of their age, but by the end of the middle school years most boys have caught up or, in many cases, surpassed girls in height.

As indicated in Figure 1, the growth spurt occurs approximately two years earlier for girls than for boys. The mean age at the beginning of the growth spurt in girls is 9; for boys, it is 11. The peak rate of pubertal change occurs at 11½ years for girls and 13½ years for boys. During their growth spurt, girls increase in height about 3½ inches per year, boys about 4 inches. Boys and girls who are shorter or taller than their peers before adolescence are likely to remain so during adolescence; however, as much as 30 percent of an individual’s height in late adolescence is unexplained by his or her height in the elementary school years.

image5 FIGURE 1 PUBERTAL GROWTH SPURT. On average, the peak of the growth spurt during puberty occurs two years earlier for girls (11½) than for boys (13½). How are hormones related to the growth spurt and to the difference between the average height of adolescent boys and that of girls?

Is age of pubertal onset linked to how tall boys and girls will be toward the end of adolescence? One study found that for girls, earlier onset of menarche, breast development, and growth spurt were linked to shorter height at 18 years of age; however, for boys, earlier age of growth spurt and slower progression through puberty were associated with being taller at 18 years of age (Yousefi & others, 2013).

Hormonal Changes Behind the first whisker in boys and the widening of hips in girls is a flood of hormones , powerful chemical substances secreted by the endocrine glands and carried through the body by the bloodstream.

The concentrations of certain hormones Page 342increase dramatically during adolescence (Berenbaum, Beltz, & Corley, 2015; Herting & Sowell, 2017; Nguyen, 2018; Piekarski & others, 2017). Testosterone is a hormone associated in boys with genital development, increased height, and deepening of the voice. Estradiol is a type of estrogen that in girls is associated with breast, uterine, and skeletal development. In one study, testosterone levels increased eighteenfold in boys but only twofold in girls during puberty; estradiol increased eightfold in girls but only twofold in boys (Nottelmann & others, 1987). Thus, both testosterone and estradiol are present in the hormonal makeup of both boys and girls, but testosterone dominates in male pubertal development, estradiol in female pubertal development (Benyi & Savendahl, 2017). A study of 9- to 17-year-old boys found that testosterone levels peaked at 17 years of age (Khairullah & others, 2014).

The same influx of hormones that grows hair on a male’s chest and increases the fatty tissue in a female’s breasts may also contribute to psychological development in adolescence (Berenbaum, Beltz, & Corley, 2015; Wang & others, 2017). In one study of boys and girls ranging in age from 9 to 14, a higher concentration of testosterone was present in boys who rated themselves as more socially competent (Nottelmann & others, 1987). However, a research review concluded that there is insufficient quality research to confirm that changing testosterone levels during puberty are linked to mood and behavior in adolescent males (Duke, Balzer, & Steinbeck, 2014). And hormonal effects by themselves do not account for adolescent development (Susman & Dorn, 2013). For example, in one study, social factors were much better predictors of young adolescent girls’ depression and anger than hormonal factors (Brooks-Gunn & Warren, 1989). Behavior and moods also can affect hormones (DeRose & Brooks-Gunn, 2008). Stress, eating patterns, exercise, sexual activity, tension, and depression can activate or suppress various aspects of the hormonal system (Marceau, Dorn, & Susman, 2012). In sum, the hormone-behavior link is complex (Susman & Dorn, 2013).

Timing and Variations in Puberty In the United States—where children mature up to a year earlier than children in European countries—the average age of menarche has declined significantly since the mid-nineteenth century (see Figure 2). Also, recent studies in Korea and Japan (Cole & Mori, 2018), China (Song & others, 2017), and Saudi Arabia (Al Alwan & others, 2017) found that pubertal onset has been occurring earlier in recent years. Fortunately, however, we are unlikely to see pubescent toddlers, since what has happened in the past century is likely the result of improved nutrition and health.

image6 FIGURE 2 AGE AT MENARCHE IN NORTHERN EUROPEAN COUNTRIES AND THE UNITED STATES IN THE NINETEENTH AND TWENTIETH CENTURIES. Notice the steep decline in the age at which girls experienced menarche in four northern European countries and the United States from 1845 to 1969. Recently the age at which girls experience menarche has been leveling off.

Why do the changes of puberty occur when they do, and how can variations in their timing be explained? The basic genetic program for puberty is wired into the species (Day & others, 2017; Kiess & others, 2016). Weight also is linked to pubertal onset. A cross-cultural study in 29 countries found that childhood obesity was linked to early puberty in girls (Currie & others, 2012). And a study of Chinese girls confirmed that childhood obesity contributed to an earlier onset of puberty (Zhai & others, 2015).

Experiences that are linked to earlier pubertal onset include nutrition, an urban environment, low socioeconomic status, adoption, father absence, family conflict, maternal harshness, child maltreatment, and early substance use (Bratke & others, 2017). For example, a recent study found that child sexual abuse was linked to earlier pubertal onset (Noll & others, 2017). In many cases, puberty comes months earlier in these situations, and this earlier onset of puberty is likely explained by high rates of conflict and stress in these social contexts.

image7 What are some of the differences in the ways girls and boys experience pubertal growth? ©Fuse/Getty Images

For most boys, the pubertal sequence may begin as early as age 10 or as late as 13½, and it may end as early as age 13 or as late as 17. Thus, the normal range is wide enough that, given two boys of the same chronological age, one might complete the pubertal sequence before the other one has begun it. For girls, menarche is considered within the normal range if it appears between the ages of 9 and 15. An increasing number of U.S. girls are beginning puberty at 8 and 9 years of age, with African American girls developing earlier than non-Latino White girls (Herman-Giddens, 2007; Selkie, 2018; Sorensen & others, 2012).

Body Image One psychological aspect of physical Page 343change in puberty is universal: Adolescents are preoccupied with their bodies and develop images of what their bodies are like (Senin-Calderon & others, 2017; Solomon-Krakus & others, 2017). Preoccupation with body image is strong throughout adolescence but is especially acute during early adolescence, a time when adolescents are more dissatisfied with their bodies than in late adolescence.

The recent dramatic increase in Internet and social media use has raised concerns about their influence on adolescents’ body images. For example, a recent study of U.S. 12- to 14-year-olds found that heavier social media use was associated with body dissatisfaction (Burnette, Kwitowski, & Mazzeo, 2017). Also, in a recent study of U.S. college women, spending more time on Facebook was related to more frequent body and weight concern comparisons with other women, more attention to the physical appearance of others, and more negative feelings about their own bodies (Eckler, Kalyango, & Paasch, 2017), In sum, various aspects of exposure to the Internet and social media are increasing the body dissatisfaction of adolescents and emerging adults, especially females.

Gender differences characterize adolescents’ perceptions of their bodies (Hoffman & Warschburger, 2017; Mitchison & others, 2017). In general, girls are less happy with their bodies and have more negative body images than boys throughout puberty (Griffiths & others, 2017). In a recent U.S. study of young adolescents, boys had a more positive body image than girls (Morin & others, 2017). Girls’ more negative body images may be due to media portrayals of the attractiveness of being thin and the increase in body fat in girls during puberty (Benowitz-Fredericks & others, 2012). One study found that both boys’ and girls’ body images became more positive as they moved from the beginning to the end of adolescence (Holsen, Carlson Jones, & Skogbrott Birkeland, 2012).

Early and Late Maturation You may have entered puberty earlier or later than average, or perhaps you were right on schedule. Adolescents who mature earlier or later than their peers perceive themselves differently (Lee & others, 2017; Wang & others, 2018). In the Berkeley Longitudinal Study some years ago, early-maturing boys perceived themselves more positively and had more successful peer relations than did their late-maturing counterparts (Jones, 1965). When the late-maturing boys were in their thirties, however, they had developed a stronger sense of identity than the early-maturing boys had (Peskin, 1967). This identity development may have occurred because the late-maturing boys had more time to explore life’s options, or because the early-maturing boys continued to focus on their advantageous physical status instead of on career development and achievement. More recent research confirms, though, that at least during adolescence it is advantageous to be an early-maturing rather than a late-maturing boy (Graber, Brooks-Gunn, & Warren, 2006).

Early and late maturation have been linked with body image. In one study, in the sixth grade, early-maturing girls showed greater satisfaction with their figures than did late-maturing girls, but by the tenth grade late-maturing girls were more satisfied (Simmons & Blyth, 1987) (see Figure 3). A possible reason for this is that in late adolescence early-maturing girls are shorter and stockier, whereas late-maturing girls are taller and thinner. Thus, late-maturing girls in late adolescence have bodies that more closely approximate the current American ideal of feminine beauty—tall and thin. Also, one study found that in the early high school years, late-maturing boys had a more negative body image than early-maturing boys (de Guzman & Nishina, 2014).

image8 FIGURE 3 EARLY- AND LATE-MATURING ADOLESCENT GIRLS’ PERCEPTIONS OF BODY IMAGE IN EARLY AND LATE ADOLESCENCE. The sixth-grade girls in this study had positive body image scores if they were early maturers but negative body image scores if they were late maturers (Simmons & Blyth, 1987). Positive body image scores indicated satisfaction with their figures. By the tenth grade, however, it was the late maturers who had positive body image scores.

An increasing number of researchers have found that early maturation increases girls’ vulnerability to a number of problems (Selkie, 2018). Early-maturing girls are more likely to smoke, drink, be depressed, have an eating disorder, engage in delinquency, struggle for earlier independence from their parents, and have older friends; and their bodies are likely to elicit responses from males that lead to earlier dating and earlier sexual experiences (Ibitoye & others, 2017; Pomerantz & others, 2017; Wang & others, 2018). In a recent study, onset of menarche before 11 years of age was linked to a higher incidence of distress disorders, fear disorders, and externalizing disorders in females (Platt & others, 2017). Another study found that early maturation predicted a stable higher level of depression for adolescent girls (Rudolph & others, 2014). Further, researchers recently found that early-maturing girls had higher rates of depression and antisocial behavior as middle-aged adults, mainly because their difficulties began in adolescence and did not lessen over time (Mendle & others, 2018). Further, early-maturing girls tend to have sexual intercourse earlier and to have more unstable sexual relationships, and they are more at risk for physical and verbal abuse in dating (Chen, Rothman, & Jaffee, 2017; Moore, Harden, & Mendle, 2014). And early-maturing girls are less likely to graduate from high Page 344school and tend to cohabit and marry earlier (Cavanagh, 2009). Apparently as a result of their social and cognitive immaturity, combined with early physical development, early-maturing girls are easily lured into problem behaviors, not recognizing the possible long-term negative effects on their development.

In sum, early maturation often has more favorable outcomes in adolescence for boys, especially in early adolescence. However, late maturation may be more favorable for boys, especially in terms of identity and career development. Research increasingly has found that early-maturing girls are vulnerable to a number of problems.

THE BRAIN
Along with the rest of the body, the brain changes during adolescence, but the study of adolescent brain development is still in its infancy. As advances in technology take place, significant strides are also likely to be made in charting developmental changes in the adolescent brain (Cohen & Casey, 2017; Crone, Peters, & Steinbeis, 2018; Sherman, Steinberg, & Chein, 2018; Steinberg & others, 2018; Vijayakumar & others, 2018). What do we know now?

The dogma of the unchanging brain has been discarded, and researchers are mainly focused on context-induced plasticity of the brain over time (Romeo, 2017; Steinberg, 2017; Zelazo, 2013). The development of the brain mainly changes in a bottom-up, top-down sequence with sensory, appetitive (eating, drinking), sexual, sensation-seeking, and risk-taking brain linkages maturing first and higher-level brain linkages such as self-control, planning, and reasoning maturing later (Zelazo, 2013).

Using fMRI brain scans, scientists have recently discovered that adolescents’ brains undergo significant structural changes (Aoki, Romeo, & Smith, 2017; Crone, Peters, & Steinbeis, 2018; Goddings & Mills, 2017; Rudolph & others, 2017). The corpus callosum , where fibers connect the brain’s left and right hemispheres, thickens in adolescence, and this improves adolescents’ ability to process information (Chavarria & others, 2014). We have described advances in the development of the prefrontal cortex—the highest level of the frontal lobes involved in reasoning, decision making, and self-control. However, the prefrontal cortex doesn’t finish maturing until the emerging adult years, approximately 18 to 25 years of age, or later (Cohen & Casey, 2017; Juraska & Willing, 2017; Sousa & others, 2018).

developmental connection
Brain Development
Although the prefrontal cortex shows considerable development in childhood, it is still not fully mature even in adolescence. Connect to “Physical and Cognitive Development in Middle and Late Childhood.”

At a lower, subcortical level, the limbic system , which is the seat of emotions and where rewards are experienced, matures much earlier than the prefrontal cortex and is almost completely developed in early adolescence (Mueller & others, 2017). The limbic system structure that is especially involved in emotion is the amygdala . Figure 4 shows the locations of the corpus callosum, prefrontal cortex, and the limbic system.

image9 FIGURE 4 THE CHANGING ADOLESCENT BRAIN: PREFRONTAL CORTEX, LIMBIC SYSTEM, AND CORPUS CALLOSUM

With the onset of puberty, the levels of neurotransmitters change (Cohen & Casey, 2017). For example, an increase in the neurotransmitter dopamine occurs in both the prefrontal cortex and the limbic system during adolescence (Cohen & Casey, 2017). Increases in dopamine have been linked to increased risk taking and the use of addictive drugs (Webber & others, 2017). Researchers also have found that dopamine plays an important role in reward seeking during adolescence (Dubol & others, 2018).

Earlier we described the increased focal activation that is linked to synaptic pruning in a specific region, such as the prefrontal cortex. In middle and late childhood, while there is increased focal activation within a specific brain region such as the prefrontal cortex, there are limited connections across distant brain regions. As adolescents develop, they have more connections across brain areas (Lebel & Deoni, 2018; Quinlin & others, 2017; Sousa & others, 2018; Tashjian, Goldenberg, & Galvan, 2017). The increased connectedness (referred to as brain networks) is especially prevalent across more distant brain regions. Thus, as children develop, greater efficiency and focal activation occurs in close Page 345-by areas of the brain, and simultaneously there is an increase in brain networks connecting more distant brain regions. In a recent study, reduced connectivity between the brain’s frontal lobes and amygdala during adolescence was linked to increased depression (Scheuer & others, 2017).

Many of the changes in the adolescent brain that have been described here involve the rapidly emerging fields of developmental cognitive neuroscience and developmental social neuroscience, in which connections between development, the brain, and cognitive or socioemotional processes are studied (Lauharatanahirun & others, 2018; Mueller & others, 2017; Romer, Reyna, & Sattherthwaite, 2017; Sherman, Steinberg, & Chein, 2018; Steinberg & others, 2018). For example, consider leading researcher Charles Nelson’s (2003) view that, although adolescents are capable of very strong emotions, their prefrontal cortex hasn’t adequately developed to the point at which they can control these passions. It is as if their brain doesn’t have the brakes to slow down their emotions. Or consider this interpretation of the development of emotion and cognition in adolescents: “early activation of strong ‘turbo-charged’ feelings with a relatively unskilled set of ‘driving skills’ or cognitive abilities to modulate strong emotions and motivations” (Dahl, 2004, p. 18).

Of course, a major question is which comes first, biological changes in the brain or experiences that stimulate these changes (Lerner, Boyd, & Du, 2008; Steinberg, 2017). In a longitudinal study, 11- to 18-year-olds who lived in poverty conditions had diminished brain functioning at 25 years of age (Brody & others, 2017). However, the adolescents from poverty backgrounds whose families participated in a supportive parenting intervention did not show this diminished brain functioning in adulthood. Another study found that the prefrontal cortex thickened and more brain connections formed when adolescents resisted peer pressure (Paus & others, 2007). Scientists have yet to determine whether the brain changes come first or whether they result from experiences with peers, parents, and others (Lauharatanahirun & others, 2018; Webber & others, 2017). Once again, we encounter the nature-nurture issue that is so prominent in an examination of development through the life span. Nonetheless, there is adequate evidence that environmental experiences make important contributions to the brain’s development (Cohen & Casey, 2017; Crone, 2017; Sherman, Steinberg, & Chein, 2018).

In closing this section on the development of the brain in adolescence, a further caution is in order. Much of the research on neuroscience and the development of the brain in adolescence is correlational in nature, and thus causal statements need to be scrutinized (Steinberg & others, 2018). This caution, of course, applies to any period in the human life span.

ADOLESCENT SEXUALITY
Not only is adolescence characterized by substantial changes in physical growth and the development of the brain, but adolescence also is a bridge between the asexual child and the sexual adult (Diamond & Alley, 2018; Savin-Williams, 2017, 2018). Adolescence is a time of sexual exploration and experimentation, of sexual fantasies and realities, of incorporating sexuality into one’s identity. Adolescents have an almost insatiable curiosity about sexuality. They are concerned about whether they are sexually attractive, how to do sex, and what the future holds for their sexual lives. Although most adolescents experience times of vulnerability and confusion, the majority will eventually develop a mature sexual identity.

In the United States, the sexual culture is widely available to adolescents. In addition to any advice adolescents get from parents, they learn a great deal about sex from television, videos, magazines, the lyrics of popular music, and the Internet (Bleakley & others, 2017; Kinsler & others, 2018; van Oosten & Vandenbosch, 2017). In some schools, sexting is common, as indicated in a recent study of 656 high school students at one school in which 15.8 percent of males and 13.6 percent of females reported sending and 40.5 percent of males and 30.6 percent of females reported receiving explicit sexual pictures on cell phones (Strassberg, Cann, & Velarde, 2017). And in another recent study of 13- to 21-year-old Latinos, engaging in sexting was linked to engaging in penetrative sex (oral, vaginal, and anal sex) (Romo & others, 2017).

Sexual arousal emerges as a new phenomenon in adolescence and it is important to view sexuality as a normal aspect of adolescent development.
—Shirley Feldman

Contemporary Psychologist, Stanford University

Developing a Sexual Identity Mastering emerging sexual feelings and forming a sense of sexual identity are multifaceted and lengthy processes (Diamond & Alley, 2018; Savin-Williams, 2017, 2018). They involve learning to manage sexual feelings (such as sexual arousal and attraction), developing new forms of intimacy, and learning how to regulate sexual behavior to avoid undesirable consequences.

An adolescent’s sexual identity involves activities Page 346, interests, styles of behavior, and an indication of sexual orientation (whether an individual has same-sex or other-sex attractions, or both) (Goldberg & Halpern, 2017). For example, some adolescents have a high anxiety level about sex, others a low level. Some adolescents are strongly aroused sexually, others less so. Some adolescents are very active sexually, others not at all (Hyde & DeLamater, 2017). Some adolescents are sexually inactive in response to their strong religious upbringing; others go to church regularly and yet their religious training does not inhibit their sexual activity.

It is commonly thought that most gays and lesbians quietly struggle with same-sex attractions in childhood, do not engage in heterosexual dating, and gradually recognize that they are a gay or lesbian in mid- to late adolescence. Many youth do follow this developmental pathway, but others do not (Diamond & Alley, 2018; Savin-Williams, 2017, 2018). For example, many youth have no recollection of early same-sex attractions and experience a more abrupt sense of their same-sex attraction in late adolescence. The majority of adolescents with same-sex attractions also experience some degree of other-sex attractions (Carroll, 2018). Even though some adolescents who are attracted to individuals of their same sex fall in love with these individuals, others claim that their same-sex attractions are purely physical (Diamond & Alley, 2018; Savin-Williams, 2017, 2018).

Further, the majority of sexual minority (gay, lesbian, and bisexual) adolescents have competent and successful paths of development through adolescence and become healthy and productive adults. However, in a recent large-scale study, sexual minority adolescents did engage in a higher prevalence of health-risk behaviors (greater drug use and sexual risk taking, for example) compared with heterosexual adolescents (Kann & others, 2016b).

The Timing of Adolescent Sexual Behaviors What is the current profile of sexual activity of adolescents? In a U.S. national survey conducted in 2015, 58 percent of twelfth-graders reported having experienced sexual intercourse, compared with 24 percent of ninth-graders (Kann & others, 2016a). By age 20, 77 percent of U.S. youth report having engaged in sexual intercourse (Dworkin & Santelli, 2007). Nationally, 46 percent of twelfth-graders, 33.5 percent of eleventh-graders, 25.5 percent of tenth-graders, and 16 percent of ninth-graders recently reported that they were currently sexually active (Kann & others, 2016a).

developmental connection
Sexuality
What characterizes the sexual activity of emerging adults (18 to 25 years of age)? Connect to “Physical and Cognitive Development in Early Adulthood.”

What trends in adolescent sexual activity have occurred in recent decades? From 1991 to 2015, fewer adolescents reported any of the following: ever having had sexual intercourse, currently being sexually active, having had sexual intercourse before the age of 13, and having had sexual intercourse with four or more persons during their lifetime (Kann & others, 2016a) (see Figure 5).

image10 FIGURE 5 SEXUAL ACTIVITY OF U.S. ADOLESCENTS FROM 1991 TO 2015

Sexual initiation varies by ethnic group in the United States (Kann & others, 2016a). African Americans are likely to engage in sexual behaviors earlier than other ethnic groups, whereas Asian Americans are likely to engage in them later (Feldman, Turner, & Araujo, 1999). In a more recent national U.S. survey of ninth- to twelfth-graders, 48.5 percent of African Americans, 42.5 percent of Latinos, and 39.9 percent of non-Latino Whites said they had experienced sexual intercourse (Kann & others, 2016a). In this study, 8 percent of African Americans (compared with 5 percent of Latinos and 2.5 percent of non-Latino Whites) said they had their first sexual experience before 13 years of age.

Research indicates that oral sex is now a common occurrence among U.S. adolescents (Fava & Bay-Cheng, 2012; Song & Halpern-Felsher, 2010). In a national survey, 51 percent of U.S. 15- to 19-year-old boys and 47 percent of girls in the same age range said they had engaged in oral sex (Child Trends, 2015). Researchers have also found that among female adolescents who reported having vaginal sex first, 31 percent reported having a teen pregnancy, whereas among those who initiated oral-genital sex first, only 8 percent reported having a teen pregnancy (Reese & others, 2013). Thus, how adolescents initiate their sex lives may have positive or negative consequences for their sexual health.

Risk Factors in Adolescent Sexual Behavior Many adolescents are not emotionally prepared to handle sexual experiences, especially in early adolescence (Cai & others, 2018; Donenberg & others, 2018; Ihongbe, Cha, & Masho, 2017). Early sexual activity is linked with risky behaviors Page 347such as drug use, delinquency, and school-related problems (Boisvert, Boislard, & Poulin, 2017; Rivera & others, 2018). A recent study of more than 3,000 Swedish adolescents revealed that sexual intercourse before age 14 was linked to risky behaviors such as an increased number of sexual partners, experience of oral and anal sex, negative health behaviors (smoking, drug and alcohol use), and antisocial behavior (being violent, stealing, running away from home) at 18 years of age (Kastbom & others, 2016). Further, a recent study found that early sexual debut (first sexual intercourse before age 13) was associated with sexual risk taking, substance use, violent victimization, and suicidal thoughts/attempts in both sexual minority (in this study, gay, lesbian, and bisexual adolescents) and heterosexual youth (Lowry, Robin, & Kann, 2017). And in a recent study of Korean adolescent girls, early menarche was linked with earlier initiation of sexual intercourse (Kim & others, 2018).

In addition to having sex in early adolescence, other risk factors for sexual problems in adolescence include contextual factors such as socioeconomic status (SES) and poverty, immigration/ethnic minority status, family/parenting and peer factors, and school-related influences (Simons & others, 2016; Warner, 2018). The percentage of sexually active young adolescents is higher in low-income areas of inner cities (Morrison-Beedy & others, 2013). One study revealed that neighborhood poverty concentrations predicted 15- to 17-year-old girls’ and boys’ sexual initiation (Cubbin & others, 2010). Also, a national survey of 15- to 20-year-olds found that Spanish-speaking immigrant youth were more likely to have a sexual partner age difference of 6 or more years and less likely to use contraception at first sexual intercourse than their native Latino, non-Latino White, and English-speaking Latino immigrant counterparts (Haderxhanaj & others, 2014).

image11 What are some risks associated with early initiation of sexual intercourse? ©Stockbyte/PunchStock

A number of family factors are associated with sexual risk-taking (Ashcraft & Murray, 2017; Ruiz-Casares & others, 2017). For example, a recent study revealed that adolescents who in the eighth grade reported greater parental knowledge and more family rules about dating were less likely to initiate sex from the eighth to tenth grade (Ethier & others, 2016). Also, a recent study revealed that of a number of parenting practices the factor that best predicted a lower level of risky sexual behavior by adolescents was supportive parenting (Simons & others, 2016). Further, one study found that difficulties and disagreements between Latino adolescents and their parents were linked to the adolescents’ early sex initiation (Cordova & others, 2014). Also, having older sexually active siblings or pregnant/parenting teenage sisters placed adolescent girls at higher risk for pregnancy (Miller, Benson, & Galbraith, 2001).

Peer, school, sport, and religious contexts provide further information about sexual risk taking in adolescents (Choukas-Bradley & Prinstein, 2016). One study found that adolescents who associated with more deviant peers in early adolescence were likely to have more sexual partners at age 16 (Lansford & others, 2010). Also, a research review found that school connectedness was linked to positive sexuality outcomes (Markham & others, 2010). A study of middle school students revealed that better academic achievement was a protective factor in preventing boys and girls from engaging in early sexual intercourse (Laflin, Wang, & Barry, 2008). Also, a recent study found that adolescent males who play sports engage in a higher level of sexual risk taking, while adolescent females who play sports engage in a lower level of sexual risk taking (Lipowski & others, 2016). And a recent study of African American adolescent girls indicated that those who reported that religion was of low or moderate importance to them had a much earlier sexual debut that their counterparts who said that religion was very important or extremely important to them (George Dalmida & others, 2018).

image12Psychologists are exploring ways to encourage adolescents to make less risky sexual decisions. Here an adolescent participates in an interactive video session developed by Julie Downs and her colleagues at the Department of Social and Decision Making Sciences at Carnegie Mellon University. The videos help adolescents evaluate their responses and decisions in high-risk sexual contexts. ©Michael Ray

Cognitive and personality factors are increasingly implicated in sexual risk taking in adolescence. Weak self-regulation (difficulty controlling one’s emotions and behavior) and impulsiveness are two such factors. Another longitudinal study found that weak self-regulation at 8 to 9 years of age and risk proneness (tendency to seek sensation Page 348and make poor decisions) at 12 to 13 years of age set the stage for sexual risk taking at 16 to 17 years of age (Crockett, Raffaelli, & Shen, 2006). Also, a meta-analysis indicated that the link between impulsivity and risky sexual behavior was likely to be more characteristic of adolescent females than males (Dir, Coskunpinar, & Cyders, 2014).

Contraceptive Use Too many sexually active adolescents still do not use contraceptives, use them inconsistently, or use contraceptive methods that are less effective than others (Chandra-Mouli & others, 2018; Diedrich, Klein, & Peipert, 2017; Fridy & others, 2018; Jaramillo & others, 2017). In 2015, 14 percent of sexually active adolescents did not use any contraceptive method the last time they had sexual intercourse (Kann & others, 2016a). Researchers have found that U.S. adolescents are less likely to use condoms than their European counterparts (Jorgensen & others, 2015).

developmental connection
Conditions, Diseases, and Disorders
What are some good strategies for protecting against HIV and other sexually transmitted infections? Connect to “Physical and Cognitive Development in Early Adulthood.”

Recently, a number of leading medical organizations and experts have recommended that adolescents use long-acting reversible contraception (LARC). These include the Society for Adolescent Health and Medicine (2017), the American Academy of Pediatrics and American College of Obstetrics and Gynecology (Allen & Barlow, 2017), and the World Health Organization (2017). LARC consists of the use of intrauterine devices (IUDs) and contraceptive implants, which have a much lower failure rate and are more effective in preventing unwanted pregnancy than birth control pills and condoms (Diedrich, Klein, & Peipert, 2017; Fridy & others, 2018; Society for Adolescent Health and Medicine, 2017).

Sexually Transmitted Infections Some forms of contraception, such as birth control pills or implants, do not protect against sexually transmitted infections, or STIs. Sexually transmitted infections (STIs) are contracted primarily through sexual contact, including oral-genital and anal-genital contact. Every year more than 3 million American adolescents (about one-fourth of those who are sexually experienced) acquire an STI (Centers for Disease Control and Prevention, 2018). In a single act of unprotected sex with an infected partner, a teenage girl has a 1 percent risk of getting HIV, a 30 percent risk of acquiring genital herpes, and a 50 percent chance of contracting gonorrhea (Glei, 1999). Yet another very widespread STI is chlamydia. We will consider these and other sexually transmitted infections in more detail later.

Adolescent Pregnancy Adolescent pregnancy is another problematic outcome of sexuality in adolescence and requires major efforts to reduce its occurrence (Brindis, 2017; Chandra-Mouli & others, 2018; Fridy & others, 2018; Marseille & others, 2018; Romero & others, 2017; Tevendale & others, 2017). In cross-cultural comparisons, the United States continues to have one of the highest adolescent pregnancy and childbearing rates in the industrialized world, despite a considerable decline during the 1990s. The U.S. adolescent pregnancy rate is eight times as high as that in the Netherlands. Although U.S. adolescents are no more sexually active than their counterparts in the Netherlands, their adolescent pregnancy rate is dramatically higher. In the United States, 82 percent of pregnancies in adolescents 15 to 19 years of age are unintended (Koh, 2014). A cross-cultural comparison found that among 21 countries, the United States had the highest adolescent pregnancy rate among 15- to 19-year-olds and Switzerland the lowest (Sedgh & others, 2015).

Despite the negative comparisons of the United States with many other developed countries, there have been some encouraging trends in U.S. adolescent pregnancy rates. In 2015, the U.S. birth rate for 15- to 19-year-olds was 22.3 births per 1,000 females, the lowest rate ever recorded, which represents a dramatic decrease from the 61.8 births for the same age range in 1991 and down even 8 percent from 2014 (Martin & others, 2017) (see Figure 6). There also has been a substantial decrease in adolescent pregnancies across ethnic groups in recent years. Reasons for the decline include school/community health classes, increased contraceptive Page 349use, and fear of sexually transmitted infections such as AIDS.

image13 FIGURE 6 BIRTH RATES FOR U.S. 15- TO 19-YEAR-OLD GIRLS FROM 1980 TO 2015. Source: Martin, J. A. et al. “Births: Final data for 2015.” National Vital Statistics Reports, 66 (1), 2017, 1.

Ethnic variations characterize birth rates for U.S. adolescents. Latina adolescents are more likely than African American and non-Latina White adolescents to have a child (Martin & others, 2017). Latina and African American adolescent girls who have a child are also more likely to have a second child than are non-Latina White adolescent girls (Rosengard, 2009). And daughters of teenage mothers are at increased risk for teenage childbearing, thus perpetuating an intergenerational cycle (Meade, Kershaw, & Ickovics, 2008).

Adolescent pregnancy creates health risks for both the baby and the mother (Leftwich & Alves, 2017). Infants born to adolescent mothers are more likely to have low birth weights—a prominent factor in infant mortality—as well as neurological problems and childhood illness (Leftwich & Alves, 2017). A recent study assessed the reading and math achievement trajectories of children born to adolescent and non-adolescent mothers with different levels of education (Tang & others, 2016). In this study, higher levels of maternal education were linked to higher academic achievement through the eighth grade. Nonetheless, the achievement of children born to adolescent mothers never reached the levels of children born to adult mothers. Adolescent mothers are more likely to be depressed and to drop out of school than their peers are (Siegel & Brandon, 2014). Although many adolescent mothers resume their education later in life, they generally never catch up economically with women who postpone childbearing until their twenties. Also, a study of African American urban youth found that at 32 years of age, women who had become mothers as teenagers were more likely than non-teen mothers to be unemployed, live in poverty, depend on welfare, and not have completed college (Assini-Meytin & Green, 2015). In this study, at 32 years of age, men who had become fathers as teenagers were more likely than non-teen fathers to be unemployed.

A special concern is repeated adolescent pregnancy. In a recent national study, the percentage of teen births that were repeat births decreased from 2004 (21 percent) to 2015 (17 percent) (Dee & others, 2017). In a recent meta-analysis, use of effective contraception, especially LARC, and education-related factors (higher level of education and school continuation) resulted in a lower incidence of repeated teen pregnancy, while depression and a history of abortion were linked to a higher percentage of repeated teen pregnancy (Maravilla & others, 2017).

Researchers have found that adolescent mothers interact less effectively with their infants than do adult mothers (Leftwich & Alves, 2017). One study revealed that adolescent mothers spent more time negatively interacting and less time in play and positive interactions with their infants than did adult mothers (Riva Crugnola & others, 2014). Also, a recent intervention, “My Baby and Me,” that involved frequent, intensive home visitation coaching sessions with adolescent mothers across three years resulted in improved maternal behavior and child outcomes (Guttentag & others, 2014).

Although the consequences of America’s high rate of adolescent pregnancy are cause for great concern, it often is not pregnancy alone that leads to negative consequences for an adolescent mother and her offspring. Adolescent mothers are more likely to come from low-SES backgrounds (Mollborn, 2017). Many adolescent mothers also were not good students before they became pregnant (Malamitsi-Puchner & Boutsikou, 2006). However, not every adolescent female who bears a child lives a life of poverty and low achievement. Thus, although adolescent pregnancy is a high-risk circumstance, and adolescents who do not become pregnant generally fare better than those who do, some adolescent mothers do well in school and have positive outcomes (Schaffer & others, 2012).

Serious, extensive efforts are needed to help pregnant adolescents and young mothers enhance their educational and occupational opportunities (Carroll, 2018; Craft, Brandt, & Prince, 2016; Mueller & others, 2017; Romero & others, 2017). Adolescent mothers also need help obtaining competent child care and planning for the future.

Adolescents can benefit from age-appropriate family-life education (Barfield, Warner, & Kappeler, 2017; Mueller & others, 2017). Family and consumer science educators teach life skills, such as effective decision making, to adolescents. To read about the work of one family and consumer science educator, see Connecting with Careers . And to learn more about ways to reduce adolescent pregnancy, see Connecting Development to Life .

image14 What are some consequences of adolescent pregnancy? ©Geoff Manasse/Getty ImagesPage 350

connecting with careers
Lynn Blankinship, Family and Consumer Science Educator
Lynn Blankinship is a family and consumer science educator with an undergraduate degree in this field from the University of Arizona. She has taught for more than 20 years, the last 14 at Tucson High Magnet School.

Blankinship has been honored as the Tucson Federation of Teachers Educator of the Year and the Arizona Teacher of the Year. Blankinship especially enjoys teaching life skills to adolescents. One of her favorite activities is having students care for an automated baby that imitates the needs of real babies. She says that this program has a profound impact on students because the baby must be cared for around the clock for the duration of the assignment. Blankinship also coordinates real-world work experiences and training for students in several child-care facilities in the Tucson area.

For more information about what family and consumer science educators do, see the Careers in Life-Span Development appendix.

image15Lynn Blankinship (center) teaches life skills to students. Courtesy of Lynn Blankinship

connecting development to life
Reducing Adolescent Pregnancy
One strategy for reducing adolescent pregnancy, called the Teen Outreach Program (TOP), focuses on engaging adolescents in volunteer community service and stimulates discussions that help adolescents appreciate the lessons they learn through volunteerism.

Girls Inc. has four programs that are intended to increase adolescent girls’ motivation to avoid pregnancy until they are mature enough to make responsible decisions about motherhood (Roth & others, 1998). Growing Together, a series of five two-hour workshops for mothers and adolescents, and Will Power/Won’t Power, a series of six two-hour sessions that focus on assertiveness training, are for 12- to 14-year-old girls. For older adolescent girls, Taking Care of Business provides nine sessions that emphasize career planning as well as information about sexuality, reproduction, and contraception. Health Bridge coordinates health and education services—girls can participate in this program as one of their club activities. Girls who participated in these programs were less likely to get pregnant than girls who did not participate (Girls Inc., 1991).

In 2010, the U.S. government launched the Teen Pregnancy Prevention (TPP) program under the direction of the newly created Office of Adolescent Health (Koh, 2014). Currently, a number of studies are being funded by the program in an effort to find ways to reduce the rate of adolescent pregnancy.

The sources and the accuracy of adolescents’ sexual information are linked to adolescent pregnancy. Adolescents can get information about sex from many sources, including parents, siblings, schools, peers, magazines, television, and the Internet. A special concern is the accuracy of sexual information to which adolescents have access on the Internet.

Currently, a major controversy in sex education is whether schools should have an abstinence-only program or a program that emphasizes contraceptive knowledge (Erkut & others, 2013; MacKenzie, Hedge, & Enslin, 2017). Recent research reviews have concluded that abstinence-only programs do not delay the initiation of sexual intercourse and do not reduce HIV risk behaviors (Denford & others, 2017; Jaramillo & others, 2017; Santelli & others, 2017).

Despite the evidence that favors comprehensive sex education, there recently has been an increase in government funding for abstinence-only programs (Donovan, 2017). Also, in some states (Texas and Mississippi, for example), many students still either get abstinence-only or no sex education at all (Campbell, 2016; Pollock, 2017).

Recently, there also has been an increased emphasis in abstinence-only-until-marriage (AOUM) policies and programs. However, a major problem with such policies and programs is that a very large majority of individuals engage in sexual intercourse at some point in adolescence or emerging adulthood while the age of marriage continues to go up (27 for females, 29 for males in the United States) (Society for Adolescent Medicine, 2017).

Based on the information you read earlier about risk factors in adolescent sexual behavior, which segments of the adolescent population would benefit most from the types of sex education programs described here?

Page 351

Review Connect Reflect
LG2 Describe the changes involved in puberty, as well as changes in the brain and sexuality during adolescence.

Review
· What are some key aspects of puberty?

· What changes typically occur in the brain during adolescence?

· What are some important aspects of sexuality in adolescence?

Connect
· How might adolescent brain development be linked to adolescents’ decisions to engage in sexual activity or to abstain from it?

Reflect Your Own Personal Journey of Life
· Did you experience puberty earlier or later than your peers? How did this timing affect your development?

3 Issues in Adolescent Health
LG3 Identify adolescent problems related to health, substance use and abuse, and eating disorders.

Adolescent Health

Substance Use and Abuse

Eating Disorders

Many health experts argue that whether adolescents are healthy depends primarily on their own behavior. To improve adolescent health, adults should aim to (1) increase adolescents’ health-enhancing behaviors, such as eating nutritious foods, exercising, wearing seat belts, and getting adequate sleep; and (2) reduce adolescents’ health-compromising behaviors, such as drug abuse, violence, unprotected sexual intercourse, and dangerous driving.

ADOLESCENT HEALTH
Adolescence is a critical juncture in the adoption of behaviors that are relevant to health (Coore Desai, Reece, & Shakespeare-Pellington, 2017; Devenish, Hooley, & Mellor, 2017; Oldfield & others, 2018; Yap & others, 2017). Many of the behaviors that are linked to poor health habits and early death in adults begin during adolescence (Blake, 2017; Donatelle & Ketcham, 2018). Conversely, the early formation of healthy behavior patterns, such as regular exercise and a preference for foods low in fat and cholesterol, not only has immediate health benefits but helps in adulthood to delay or prevent disability and mortality from heart disease, stroke, diabetes, and cancer (Hales, 2018; Powers & Dodd, 2017).

Nutrition and Exercise Concerns are growing about adolescents’ nutrition and exercise habits (Donatelle, 2019; Powers & Dodd, 2017; Schiff, 2017, 2019; Smith & Collene, 2019). National data indicated that the percentage of overweight U.S. 12- to 19-year-olds increased from 11 percent in the early 1990s to nearly 20.5 percent in 2014 (Centers for Disease Control and Prevention, 2016). In another study, 12.4 percent of U.S. kindergarten children were obese, but by 14 years of age, 20.8 percent were obese (Cunningham, Kramer, & Narayan, 2014).

A special concern in American culture is the amount of fat we consume. Many of today’s adolescents virtually live on fast-food meals, which are high in fat. A comparison of adolescents in 28 countries found that U.S. and British adolescents were more likely to eat fried food and less likely to eat fruits and vegetables than adolescents in most other countries that were studied (World Health Organization, 2000). The National Youth Risk Survey found that U.S. high school students showed a linear decrease in their intake of fruits and vegetables from 1999 through 2015 (Kann & others, 2016a).

Being obese in adolescence predicts obesity in emerging adulthood. For example, a longitudinal study of more than 8,000 adolescents found that obese adolescents were more likely to develop severe obesity in emerging adulthood than were overweight or normal-weight adolescents (The & others, 2010). In another longitudinal study, the percentage of overweight individuals increased from 20 percent at 14 years of age to 33 percent at 24 years of age (Patton & others, 2011).

image16 ©Shutterstock/Thirteen

Researchers have found that individuals become Page 352less active as they reach and progress through adolescence (Alberga & others, 2012). A national study of U.S. adolescents revealed that physical activity increased until 13 years of age in boys and girls but then declined through 18 years of age (Kahn & others, 2008). A recent national study also found that adolescent girls were much less likely to have engaged in 60 minutes or more of vigorous exercise per day in 5 of the last 7 days (61 percent) than were boys (42 percent) (YRBSS, 2016). Ethnic differences in exercise participation rates of U.S. adolescents also occur, and these rates vary by gender. In the national study just mentioned, non-Latino White boys exercised the most, African American and Latino girls the least (YRBSS, 2016).

Positive physical outcomes of exercise in adolescence include a lower rate of obesity, reduced triglyceride levels, lower blood pressure, and a lower incidence of type II diabetes (Barton & others, 2017; Powers & Howley, 2018; Son & others, 2017; Walton-Fisette & Wuest, 2018; Xie & others, 2017). Also, one study found that adolescents who were high in physical fitness had better connectivity between brain regions than adolescents who were low in physical fitness (Herting & others, 2014). Exercise in adolescence also is linked to other positive outcomes. Higher levels of exercise are related to fewer depressive symptoms in adolescents (Gosmann & others, 2015). In a recent study, a high-intensity exercise program reduced depressive symptoms and improved the moods of depressed adolescents (Carter & others, 2016). In another study, young adolescents who exercised regularly had higher academic achievement (Hashim, Freddy, & Rosmatunisah, 2012). And in a recent research review, among a number of cognitive factors, memory was the factor that most often was improved by exercise in adolescence (Li & others, 2017).

image17 What are some characteristics of adolescents’ exercise patterns? ©Tom Stewart/Corbis/Getty Images

Adolescents’ exercise is increasingly being found to be associated with parenting and peer relationships (Mason & others, 2017; Michaud & others, 2017). One study revealed that family meals during adolescence protected against becoming overweight or obese in adulthood (Berge & others, 2015). Another study revealed that female adolescents’ physical activity was linked to their male and female friends’ physical activity, while male adolescents’ physical activity was associated with their female friends’ physical activity (Sirard & others, 2013).

Researchers have found that screen time is associated with a number of adolescent health problems, including a lower rate of exercise and a higher rate of sedentary behavior (Pearson & others, 2017). In one research review, a higher level of screen-based sedentary behavior was associated with being overweight, having sleep problems, being depressed, and having lower levels of physical activity/fitness and psychological well-being (higher stress levels, for example (Costigan & others, 2013).

What types of interventions and activities have been successful in reducing overweight in adolescents and emerging adults? Research indicates that dietary changes and regular exercise are key components of weight reduction in adolescence and emerging adulthood (Fukerson & others, 2018; Lipsky & others, 2017; Martin & others, 2018; Powers & Howley, 2018). For example, a recent study found that a combination of regular exercise and a diet plan resulted in weight loss and enhanced executive function in adolescents (Xie & others, 2017).

Sleep Like nutrition and exercise, sleep is an important influence on well-being. Might changing sleep patterns in adolescence contribute to adolescents’ health-compromising behaviors? Recently there has been a surge of interest in adolescent sleep patterns (Hoyt & others, 2018; Meltzer, 2017; Palmer & others, 2018; Reddy & others, 2017; Seo & others, 2017; Wheaton & others, 2018). A longitudinal study in which adolescents completed a 24-hour diary every 14 days in ninth, tenth, and twelfth grades found that regardless of how much students studied each day, when the students sacrificed sleep time to study more than usual they had difficulty understanding what was taught in class and were more likely to struggle with class assignments the next day (Gillen-O’Neel, Huynh, & Fuligni, 2013). Also, a recent experimental study indicated that when adolescents’ sleep was restricted to five hours for five nights, then returned to ten hours for two nights, their sustained attention was negatively affected (especially in the early morning) and did not return to baseline levels during recovery (Agostini & others, 2017). Further, researchers have found that adolescents who get less than 7.7 hours of sleep per night on average have more emotional and peer-related problems, higher anxiety, and a higher level of suicidal ideation (Sarchiapone & others, 2014). And a recent national study of more than 10,000 13- to 18-year-olds revealed that later weeknight bedtime, shorter weekend bedtime delay, and both short and long periods of weekend oversleep were linked to increased rates of anxiety, mood, substance abuse, and behavioral disorders (Zhang & others, 2017). Further, in a four-year longitudinal study beginning at 12 years of age, poor sleep patterns (for example, shorter sleep duration and greater daytime sleepiness) at age 12 was associated with an increased likelihood Page 353of drinking alcohol and using marijuana at 16 years of age (Miller, Janssen, & Jackson, 2017). Also, recent Swedish studies revealed that adolescents with a shorter sleep duration were more likely to have more school absences, while shorter sleep duration and greater sleep deficits were linked to having a lower grade point average (Hysing & others, 2015, 2016).

In a recent national survey of youth, only 27 percent of U.S. adolescents got eight or more hours of sleep on an average school night (Kann & others, 2016a). In this study, the percentage of adolescents getting this much sleep on an average school night decreased as they got older (see Figure 7). Also, in other research with more than 270,000 U.S. adolescents from 1991–2012, adolescents were getting less sleep in recent years than in the past (Keyes & others, 2015).

image18 FIGURE 7 DEVELOPMENTAL CHANGES IN U.S. ADOLESCENTS’ SLEEP PATTERNS ON AN AVERAGE SCHOOL NIGHT

The National Sleep Foundation (2006) conducted a U.S. survey of adolescent sleep patterns. Those who got inadequate sleep (eight hours or less) on school nights were more likely to feel tired or sleepy, to be cranky and irritable, to fall asleep in school, to be in a depressed mood, and to drink caffeinated beverages than their counterparts who got optimal sleep (nine or more hours). Also, a longitudinal study of more than 6,000 adolescents found that sleep problems were linked to subsequent suicidal thoughts and attempts in adolescence and early adulthood (Wong & Brower, 2012). Further, one study found that adolescents who got less than 7.7 hours of sleep per night on average had more emotional and peer-related problems, higher anxiety, and a higher level of suicidal ideation than their peers who got 7.7 hours of sleep or more (Sarchiapone & others, 2014).

Why are adolescents getting too little sleep? Among the reasons given are those involving electronic media, caffeine, and changes in the brain coupled with early school start times (Bartel, Scheeren, & Gradisar, 2018; Owens, 2014). In one study, adolescents averaged engaging in four electronic activities (in some cases, this involved simultaneous use of different devices) after 9 p.m. (Calamaro, Mason, & Ratcliffe, 2009). Engaging in these electronic activities in the evening can replace sleep time, and such media use may increase sleep-disrupting arousal (Cain & Gradisar, 2010). Also, a study of fourth- and seventh-graders found that sleeping near small screens (smartphones, for example), sleeping with a TV in the room, and more screen time were associated with shorter sleep duration in both children and adolescents (Falbe & others, 2015).

Caffeine intake by adolescents appears to be related to inadequate sleep (Owens, 2014). Greater caffeine intake as early as 12 years of age is linked to later sleep onset, shorter sleep duration, and increased daytime sleepiness (Carskadon & Tarokh, 2014). Further, researchers have yet to study the connection between adolescent sleep patterns and high levels of caffeine intake from energy drinks.

Mary Carskadon and her colleagues (2004, 2005, 2011a, b; Crowley & Carskadon, 2010; Tarokh & Carskadon, 2010) have conducted a number of research studies on adolescent sleep patterns. They found that when given the opportunity, adolescents will sleep an average of 9 hours and 25 minutes a night. Most get considerably less than nine hours of sleep, however, especially during the week. This shortfall creates a sleep deficit, which adolescents often attempt to make up on the weekend. The researchers also found that older adolescents tend to be sleepier during the day than younger adolescents. They theorized that this sleepiness was not due to academic work or social pressures. Rather, their research suggests that adolescents’ biological clocks undergo a shift as they get older, delaying their period of sleepiness by about one hour. A delay in the nightly release of the sleep-inducing hormone melatonin, which is produced in the brain’s pineal gland, seems to underlie this shift. Melatonin is secreted at about 9:30 p.m. in younger adolescents and approximately an hour later in older adolescents.

Carskadon concludes that early school starting times may cause grogginess, inattention in class, and poor performance on tests. Based on her research, school officials in Edina, Minnesota, decided to start classes at 8:30 a.m. rather than the usual 7:25 a.m. Since then there have been fewer referrals for discipline problems, and the number of students who report being ill or depressed has decreased. The school system reports that test scores have improved for high school students but not for middle school students. This finding supports Carskadon’s suspicion that early start times are likely to be more stressful for older than for younger adolescents.

image19In Mary Carskadon’s sleep laboratory at Brown University, an adolescent girl’s brain activity is being monitored. Carskadon (2005) says that in the morning, sleep-deprived adolescents’ “brains are telling them it’s night time . . . and the rest of the world is saying it’s time to go to school” (p. 19). ©Jim LoScalzo

One study found that just a 30-minute delay in school start time was linked to improvements in adolescents’ sleep, alertness, mood, and health (Owens, Belon, & Moss, 2010). In another study, early school start times were linked to a higher vehicle crash rate in adolescent Page 354drivers (Vorona & others, 2014). The American Academy of Pediatrics recommends that schools institute start times from 8:30 to 9:30 a.m. to improve adolescents’ academic performance and quality of life (Adolescent Sleep Working Group, AAP, 2014).

Do sleep patterns change in emerging adulthood? Research indicates that they do (Galambos, Howard, & Maggs, 2011). One study revealed that more than 60 percent of college students were categorized as poor-quality sleepers (Lund & others, 2010). In this study, the weekday bedtimes and rise times of first-year college students were approximately 1 hour and 15 minutes later than those of seniors in high school (Lund & others, 2010). However, the first-year college students had later bedtimes and rise times than third- and fourth-year college students, indicating that at about 20 to 22 years of age, a reverse in the timing of bedtimes and rise times occurs. In another study, consistently low sleep duration in college students was associated with less effective attention the next day (Whiting & Murdock, 2016). Also, in a recent study of college students, a higher level of text messaging (greater number of daily texts, awareness of nighttime cell phone notifications, and compulsion to check nighttime notifications) was linked to a lower level of sleep quality (Murdock, Horissian, & Crichlow-Ball, 2017).

Leading Causes of Death in Adolescence The three leading causes of death in adolescence are unintentional injuries, homicide, and suicide (National Center for Health Statistics, 2018). Almost half of all deaths from 15 to 24 years of age are due to unintentional injuries, the majority of them involving motor vehicle accidents. Risky driving habits, such as speeding, tailgating, and driving under the influence of alcohol or other drugs, may be more important contributors to these accidents than lack of driving experience (White & others, 2018; Williams & others, 2018). In about 50 percent of motor vehicle fatalities involving adolescents, the driver has a blood alcohol level of 0.10 percent—twice the level at which a driver is designated as “under the influence” in some states. Of growing concern is the increasingly common practice of mixing alcohol and energy drinks, which is linked to a higher rate of driving while intoxicated (Wilson & others, 2018). A high rate of intoxication is also found in adolescents who die as pedestrians or while using vehicles other than automobiles.

Homicide is the second leading cause of death in adolescence, especially among African American males (National Center for Health Statistics, 2018). Also notable is the adolescent suicide rate, which has tripled since the 1950s. Suicide accounts for 6 percent of deaths in the 10-to-14 age group and 12 percent of deaths in the 15-to-19 age group. We will discuss suicide in more detail later.

SUBSTANCE USE AND ABUSE
Each year since 1975, Lloyd Johnston and his colleagues at the Institute of Social Research at the University of Michigan have monitored the drug use of America’s high school seniors in a wide range of public and private high schools. Since 1991, they also have surveyed drug use by eighth- and tenth-graders. In 2017, the study surveyed approximately 45,000 secondary school students in 380 public and private schools (Johnston & others, 2018).

In the University of Michigan study, drug use among U.S. secondary school students declined in the 1980s but began to increase in the early 1990s before declining again in the early part of the first decade of the 21st century. However, from 2006 through 2017, overall use of illicit drugs began increasing again, due mainly to an increase in marijuana use by adolescents. In 2006, 36.5 percent of twelfth-graders reported annual use of an illicit drug but in 2017 that figure had increased to 39.9 percent. However, if marijuana use is subtracted from the annual use figures, there has been a significant decline in drug use by adolescents. When marijuana use is deleted, in 2006, 19.2 percent of twelfth-graders used an illicit drug annually, but that figure showed a significant decline to 13.3 percent in 2017 (Johnston & others, 2018). Marijuana is the most widely used illicit drug by adolescents.

The United States continues to have one of the highest rates of adolescent drug use of any industrialized nation. Because of the increased legalization of marijuana use for adults in a number of states, youth are likely to have increased access to the drug and it is expected that marijuana use by adolescents will increase in the future.

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