Adolescence chapter 14chapter 15chapter 163

1. Adolescence
CHAPTER 14
CHAPTER 15
CHAPTER 16
361
W
ould you ride with an unskilled
driver? When my daughter
Bethany had her learner’s permit,
I tried to convey confidence. Not
until a terrified “Mom! Help!” did I grab the wheel to
avoid hitting a subway kiosk. I should have helped
sooner, but it is hard to know when children become
adults, able to manage without their mothers.
As an adolescent, Bethany was neither child nor
adult. A century ago, puberty began later: Soon after

2. puberty, many teenage girls married and boys found
work. Depending on customs and family income,
some married or entered the labor force even before
adolescence and some much later. Even today, in
some developing nations, by age 10 some boys are
working and some girls are betrothed.
It has been said that adolescence begins with
biology and ends with society. Today, adolescence
tends to begin earlier biologically and end later
sociologically than it once did. Growth is uneven in
both domains; some aspects of the brain mature at
puberty (emotional excitement) and some much
later (reflection). This led one observer to liken
adolescence to “starting turbo-charged engines
with an unskilled driver” (Dahl, 2004, p. 17).
In the next three chapters (covering ages 11–18),
we begin with biology (the growth increases of
puberty) and move toward society (the roles that

3. teenagers take on). Understanding adolescence is
more than an intellectual challenge: Those turbo-
charged engines need skilled guidance. Get ready
to grab the wheel.
PA R T V
Adolescence:
Biosocial Development
T
he body changes of early adolescence rival those of infancy in
speed and drama but differ in one crucial way: Adolescents are
aware. Even tiny changes (a blemish, a fingernail) matter when
a
person watches his or her own body transforming.
I once overheard a conversation among three teenagers,
including my
daughter Rachel. All three were past the awkward years, now
becoming
beautiful. They were discussing the imperfections of their
bodies. One
spoke of her fat stomach (what stomach? I could not see it),
another of her
long neck (hidden by her silky, shoulder-length hair), and my
Rachel com-
plained not only about a bent finger but also about her feet!

4. The reality that children grow into men and women is no shock
to any
adult. But for teenagers, heightened self-awareness often
triggers surprise
and even horror, joy, or despair. This chapter describes normal
biosocial
changes, including growing bodies, emerging sexuality, and
maturing brains,
and then two possible problems.
14
363
CHAPTER OUTLINE
c Puberty Begins
Hormones
When Will Puberty Start?
Too Early, Too Late
Nutrition
c The Transformations of Puberty
Growing Bigger and Stronger
Sexual Maturation
Brain Development
A CASE TO STUDY:

5. What Were You Thinking?
ISSUES AND APPLICATIONS:
Calculus at 8 A.M.?
c Possible Problems
Sex Too Soon
Drug Use and Abuse
Learning from Experience
That’s What Friends Are For Jennifer’s
preparations for her prom include pedi-
cure and hairstyle, courtesy of her good
friends Khushbu and Meredith. In every
generation and society the world over,
teenagers help their same-sex friends
prepare for the display rituals involved in
coming of age, but the specifics vary by
cohort and culture. M
IK
E
K
IN

6. G
/
A
P
P
H
O
T
O
Puberty Begins
Puberty refers to the years of rapid physical growth and sexual
maturation that
end childhood, eventually producing a person of adult size,
shape, and sexual
potential. The forces of puberty are unleashed by a cascade of
hormones that
produce external signs as well as the heightened emotions and
sexual desires that
many adolescents experience. The process normally starts
between ages 8 and 14.
The biological changes follow a common sequence (see Table
14.1).
For girls, puberty begins with growth of the nipples and initial
pubic hair, then
a peak growth spurt, widening of the hips, the first menstrual
period (menarche),
final pubic-hair pattern, and full breast development. The
current average age of

7. menarche among well-nourished girls is about 12 years, 8
months (Malina et al.,
2004), although, as you will soon see, variation in timing is
quite normal.
For boys, the usual sequence is growth of the testes, initial
pubic hair, growth
of the penis, first ejaculation of seminal fluid (spermarche),
facial hair, peak
growth spurt, voice deepening, and final pubic-hair growth
(Biro et al., 2001;
Herman-Giddens et al., 2001). The modal age of spermarche is
just under 13
years, the same as for menarche.
Typically, physical growth and maturation are complete four
years after the first
signs appear, although some individuals (usually late
developers) add height, and
most (especially early developers) gain more fat and muscle in
their late teens or
early 20s.
Hormones
Just described are the visible changes of puberty. An invisible
event begins the
entire process, namely a marked increase in certain hormones,
which are natural
puberty The time between the first onrush
of hormones and full adult physical devel-
opment. Puberty usually lasts three to five

8. years. Many more years are required to
achieve psychosocial maturity.
menarche A girl’s first menstrual period,
signaling that she has begun ovulation.
Pregnancy is biologically possible, but ovu-
lation and menstruation are often irregular
for years after menarche.
spermarche A boy’s first ejaculation of
sperm. Erections can occur as early as
infancy, but ejaculation signals sperm pro-
duction. Spermache occurs during sleep
(in a “wet dream”) or via direct stimulation.
hormone An organic chemical substance
that is produced by one body tissue and
conveyed via the bloodstream to another
to affect some physiological function. Vari-
ous hormones influence thoughts, urges,
emotions, and behavior.

9. 364 C H A P T E R 14 ■ Adolescence: Biosocial Development
TABLE 14.1
AT ABOUT THIS TIME: The Sequence of Puberty
Approximate
Girls Average Age* Boys
Ovaries increase production of
estrogen and progesterone†
Uterus and vagina begin to grow
larger
Breast “bud” stage
Pubic hair begins to appear; weight
spurt begins
Peak height spurt
Peak muscle and organ growth (also,
hips become noticeably wider)
Menarche (first menstrual period)
First ovulation
Voice lowers

10. Final pubic-hair pattern
Full breast growth
9
91⁄2
10
11
111⁄2
12
121⁄2
13
14
15
16
18
Testes increase production of
testosterone†
Testes and scrotum grow larger
Pubic hair begins to appear

11. Penis growth begins
Spermarche (first ejaculation); weight
spurt begins
Peak height spurt
Peak muscle and organ growth (also,
shoulders become noticeably broader)
Voice lowers; visible facial hair
Final pubic-hair pattern
*Average ages are rough approximations, with many perfectly
normal, healthy adolescents as much as three years
ahead of or behind these ages.
†Estrogens and testosterone influence sexual characteristics,
including reproduction. Charted here are the in-
creases produced by the gonads (sex glands). The ovaries
produce estrogens and the testes produce androgens,
especially testosterone. Adrenal glands produce some of both
kinds of hormones (not shown).
chemicals in the bloodstream that affect every body cell.
Hormones regulate
hunger, sleep, moods, stress, sexual desire, and much more.

12. At least 23 hormones affect human growth and maturation,
several of which in-
crease markedly in the months before the first signs of puberty.
Technically, those
first straggly pubic hairs are “a late event” in the process
(Cameron, 2004, p. 116).
You learned in Chapter 8 that the production of many hormones
is regulated
deep within the brain, where biochemical signals from the
hypothalamus signal
another brain structure, the pituitary. The pituitary produces
hormones that
stimulate the adrenal glands, small glands located above the
kidneys at either
side of the lower back. The adrenal glands produce more
hormones. This HPA
axis (hypothalamus-pituitary-adrenal) is the route followed by
hormones that reg-
ulate stress, growth, sleep, appetite, and sexual excitement as
well as puberty (see
Figure 14.1).
Sex Hormones
At adolescence, the pituitary also activates the gonads, or sex
glands (ovaries in
females; testes, or testicles, in males). One hormone in
particular, GnRH
(gonadotropin-releasing hormone), causes the gonads to enlarge
and dramatically
increase their production of sex hormones, chiefly estradiol in
girls and testos-
terone in boys. These hormones affect the entire body shape and
function.

13. Estrogens (including estradiol) are considered female hormones,
and andro-
gens (including testosterone) are considered male hormones, but
the adrenal
glands produce both in everyone. Unlike those produced by the
adrenal glands,
the hormones produced by the gonads are sex-specific. After a
decrease during
childhood, testosterone skyrockets in boys—up to 20 times the
pre-pubescent
level (Roche & Sun, 2003). For girls, estradiol increases to
about 8 times the
childhood level (Malina et al., 2004).
The activated gonads eventually produce gametes (sperm and
ova), whose mat-
uration and release are heralded by spermarche or menarche,
signifying that the
young person has the biological potential to become a parent.
(Peak fertility comes
years later, but ovulation and ejaculation signify the possibility
of pregnancy.)
Sudden Emotions
Remember that the HPA axis leads from brain to body to
behavior. The behaviors
that adolescents are best known for are emotional and sexual —
moodiness and
lust that overtake the formerly predictable, seemingly asexual,
child. Hormones
influence this. To be specific:
■ Testosterone at high or accelerating levels stimulates rapid
arousal of emo-
tions, especially anger.

14. ■ Hormonal bursts lead to quick emotional extremes (despair,
ecstasy).
■ For many boys, the increase in androgens causes sexual
thoughts and a desire
to masturbate.
■ For many girls, the fluctuating estrogens increase happiness
in the middle of
the menstrual cycle (at ovulation) and sadness or anger at the
end.
pituitary A gland in the brain that responds
to a signal from the hypothalamus by pro-
ducing many hormones, including those
that regulate growth and control other
glands, among them the adrenal and sex
glands.
adrenal glands Two glands, located above
the kidneys, that produce hormones
(including the “stress hormones” epineph-
rine [adrenaline] and norepinephrine).
HPA axis The hypothalamus-pituitary-adrenal
axis, a route followed by many kinds of

15. hormones to trigger the changes of
puberty and to regulate stress, growth,
sleep, appetite, sexual excitement, and
various other bodily changes.
gonads The paired sex glands (ovaries in
females, testicles in males). The gonads
produce hormones and gametes.
estradiol A sex hormone, considered the
chief estrogen. Females produce more
estradiol than males do.
testosterone A sex hormone, the best
known of the androgens (male hormones);
secreted in far greater amounts by males
than by females.
Puberty Begins 365
Hypothalamus
Hormones
Pituitary Adrenal glands

16. HPA axis
Growth spurt
Primary sex characteristics
Secondary sex characteristics
Gonads
(ovaries or
testicles)
Increase
in many
hormones,
including
testosterone
and estrogen
Growth
hormone
(GH)
Gonadotropin-
releasinghormone < >
FIGURE 14.1

17. Biological Sequence of Puberty Puberty
begins with a hormonal signal from the hypo-
thalamus to the pituitary gland. The pituitary,
in turn, signals the adrenal glands and the
ovaries or testes to produce more of their
hormones.
Although adults experience these same hormonal effects, during
puberty hor-
mones are more erratic and powerful, less familiar and
controllable, and they come
in bursts, not a steady flow (Cameron, 2004; Susman & Rogol,
2004). Further,
when adults experience hormonal changes (especially during
pregnancy and birth),
cognitive maturation helps control the effects.
Hormones sometimes make adolescents seek sexual activity and
sometimes
arouse excitement, pleasure, and frustration. But human
thoughts and emotions
not only result from physiological and neurological processes—
they also cause
them (Damasio, 2003). An adolescent’s reactions to how other
people respond to
breasts, beards, and body shapes evoke emotions that, in turn,
affect hormones—
just as hormones affect emotions—with the particular emotional

18. reaction not di-
rectly tied to specific hormones (Alsaker & Flammer, 2006).
This is clearer with an example. Suppose a 13-year-old girl
hears a lewd remark,
provoked by her developing breasts in a too-tight shirt. She
might feel a surge of
anger, fear, or embarrassment, but it is the remark, not her
hormones, that arouses
her. Her emotions might cause a rise in stress hormones and
sexual ones as well.
Evidence for a complex link between hormones and emotions
came from a
study of 56 adolescents who were late to begin puberty ( Schwab
et al., 2001).
Doctors prescribed treatment every 3 months: injections of
hormones (low,
medium, or high doses of testosterone or an estrogen)
alternating with injections
of a placebo (which had no hormones). Gradually, the outward
signs of puberty
appeared.
Every three months, other measures were taken: the level of sex
hormones
(measured via blood tests) and the emotions felt by the
adolescents (via a ques-
tionnaire). An emotional shift occurred, indirectly caused by the
hormones. Over
the two years, moods became more positive, not directly
because of hormones in
the body but presumably because the teenagers were happy with
their physical
development.

19. Surprisingly, happiness and sadness did not correlate with
shifting hormonal
levels. The teenagers did not seem emotionally aroused by the
level of hormones
in their systems—with one exception. Both boys and girls
reported more anger
when they had had moderate amounts of hormones, not the
highest
levels of testosterone (for the boys) or estrogens (for the girls)
(Sus-
man & Rogol, 2004).
When Will Puberty Start?
Hormones cascading into the bloodstream always trigger the
changes
of puberty. However, age of onset varies. Age 11 or 12 is most
likely,
but a rise in hormones is still considered normal in those as
young as
age 8 or as old as age 14. This variation is not random but is
affected
by genes, body fat, and stress (Ellis, 2004).
Genes
The genes on the sex chromosomes markedly affect the onset of
puberty. Among well-nourished children, at least one girl (XX)
in a
fifth-grade class has already developed breasts and begun to
grow to
adult height. Not until age 18 or so has her last male classmate
(XY)
sprouted facial hair and grown to man-size.

20. On average, girls are about two years ahead of boys in height.
However, hormonally and sexually girls are ahead by only a few
months, not by years (Malina et al., 2004), because the height
spurt
occurs about midway in female pubescence (before menarche)
but
is a late event (after spermarche) for boys.
Especially for Parents of Teenagers
Why would parents blame adolescent moods
on hormones?
366 C H A P T E R 14 ■ Adolescence: Biosocial Development
S
K
J
O
LD
P
H
O
T
O
G
R
A
P

21. H
S
/
T
H
E
I
M
A
G
E
W
O
R
K
S
Both 12 The ancestors of these two
Minnesota 12-year-olds came from northern
Europe and West Africa. Their genes have
dictated some differences between them,
including the timing of puberty, but these
differences are irrelevant to their friendship.

22. Genes influence the timing of puberty in other ways as well.
Monozygotic twins
are more alike than same-sex dizygotic twins (Roche & Sun,
2003). Ethnic varia-
tions in pubertal timing are partly genetic (see Figure 14.2). In
the United States,
African Americans tend to reach puberty earlier than do
European Americans or
Hispanic Americans (see Figure 14.3). Asian Americans average
several months
later (Herman-Giddens et al., 2001; Malina et al., 2004).
Ages in Europe also vary, probably for genetic reasons.
Northern European girls
are said to reach menarche at 13 years, 4 months, on average,
and southern Euro-
pean girls do so at an average age of 12 years, 5 months
(Alsaker & Flammer, 2006).
Body Fat
The genetic differences noted above are apparent only when
every child is well
fed. Puberty starts earlier in the cities of India and China than
in the remote
villages, probably because rural children are often hungry. In
Poland and Greece,
urban–rural differences are shown in that puberty occurs a year
earlier in Warsaw
Puberty Begins 367
11.8

23. 11.6
12
12.2
12.4
12.6
12.8
13Age
(years)
Median Age of Menarche, by U.S. Ethnic Group
Median age at menarche
African American girls
Asian American girls
Mexican American girls
European American girls
Source: Chumlea et al., 2003.
FIGURE 14.2
Usually by Age 13 The median age of
menarche (when half the girls have begun to
menstruate) differs somewhat among ethnic

24. groups in the United States.
2
0
4
6
8
10
12
14Age
(years)
Timing of Menarche, by U.S. Ethnic Group
Timing of menarche
African American girls
Mexican American girls
European American girls
Earliest 10 percent Latest 10 percent
Source: Chumlea et al., 2003.
FIGURE 14.3

25. Almost Always by Age 14 This graph shows
the age of menarche for the earliest and lat-
est 10 percent of girls in three U.S. ethnic
groups. Note that, especially for the slow de-
velopers (those in the 90th percentile), ethnic
differences are very small.
Observation Quiz (see answer, page 368):
At first glance, ethnic differences seem
dramatic in Figure 14.2 but minimal in Figure
14.3. Why is this first glance deceptive?
than in Polish villages and 3 months earlier in Athens than in
the rest of Greece
(Malina et. al, 2004).
Worldwide, stocky individuals begin puberty before those with
thinner builds.
Some believe that hormones in the food supply cause earlier
puberty, and others
believe that hormones cause weight gain rather than vice versa
(Ellison, 2002).
Neither of these theories has been proven. Nonetheless, it is
apparent that
menarche occurs later in girls who have little body fat (because
they are under-

26. nourished or overexercised) and that most girls weigh at least
100 pounds (45
kilograms) before their first period (Berkey et al., 2000).
In both sexes, chronic malnutri tion delays puberty. This
probably explains why
puberty did not occur until about age 17 in the sixteenth
century. In the early
twentieth century, menarche occurred on average at age 15 in
Norway, Sweden,
and Finland (Tanner, 1990), compared with age 12 or 13 today.
These are examples of the secular trend, a term that refers to
earlier and
greater growth of children over the last two centuries as
nutrition and medical care
have improved. Over the twentieth century, each generation
experienced puberty
a few months earlier than did the preceding one (Alsaker &
Flammer, 2006).
The secular trend seems to have stopped in developed nations
(Roche & Sun,
2003). This has a specific application. Probably, after
considering the gender dif-
ferential (men are on average about 5 inches taller than women),
today’s young
adults will be about as tall as their parents unless chronic
illness or undernourish-
ment as a child is a factor.
Stress
The production of many hormones is directly connected to
stressful experiences
via the HPA axis (Sanchez et al., 2001). Because stress affects

27. reproductive
hormones, many young women experience irregular
menstruation when they leave
home for college or take trips abroad, and many couples find it
easier to become
pregnant on vacation than when they are working.
Stress affects pubertal hormones as well, paradoxically by
increasing (not
decreasing) them. Puberty tends to arrive earlier if a child’s
parents are sick,
addicted, or divorced, or when the neighborhood is violent and
impoverished
(Herman-Giddens et al., 2001; Hulanicka, 1999; Moffitt et al.,
1992).
Before concluding that stress causes early puberty, however,
you need to know
that not every scientist agrees that this is the case (Ellis, 2004).
Since puberty is
partly genetic, it could be that adults who reached puberty early
are likely to marry
and become parents young, which might make them more likely
to be under-
educated, depressed, angry, and divorced. Consequently, their
children would live
with conflicted, divorce-prone parents and thus experience early
puberty not be-
cause of the conflict but because of their genes.
However, at least one careful longitudinal study of 87 girls did
find a direct link
between stress and puberty (Ellis & Garber, 2000). Those girls
who fought with
their mothers and who lived with an unrelated man (stepfather
or mother’s

28. boyfriend) also had earlier puberty, even when genes and weight
were taken into
account. The longer a girl lived with a man who was not her
father, the earlier she
reached menarche.
Animal research also implicates stress. Mice, rats, and
opossums under stress
become pregnant at younger ages than do other members of
their species
(Warshofsky, 1999). Further, female mice reach puberty earlier
if, as infants, they
were raised with unrelated adult male mice (Caretta et al.,
1995).
The evidence for the stress hypothesis is sufficiently strong to
wonder why
stress would trigger puberty. Logically, conflicted or stepfather
families would
benefit if the opposite happened—if teenagers looked and acted
like children and
secular trend A term that refers to the ear-
lier and greater growth of children due to
improved nutrition and medical care over
the last two centuries.
368 C H A P T E R 14 ■ Adolescence: Biosocial Development
➤Response for Parents of Teenagers
(from page 366): If something causes

29. adolescents to shout “I hate you,” to slam
doors, or to cry inconsolably, parents may
decide that hormones are the problem.
This makes it easy to disclaim personal
responsibility for the teenager’s anger.
However, research on stress and hormones
suggests that this comforting attribution is
too simplistic.
➤Answer to Observation Quiz (from
page 367): The major reason is the vertical
axis, which covers a total of 11⁄2 years in
Figure 14.2 and 14 years in Figure 14.3. In
addition, the outliers (top and bottom 10
percent) in Figure 14.2 show less variation
than the median in Figure 14.3
could not reproduce. But that does not happen. One explanation
comes from evo-
lutionary theory:

30. Over the course of our natural selective history, ancestral
females growing up
in adverse family environments may have reliably increased
their reproductive
success by accelerating physical maturation and beginning
sexual activity and
reproduction at a relatively early age.
[Ellis & Garber, 2000, p. 486]
In other words, in past stressful times, adolescent parents could
replace them-
selves before they died, passing on family genes. Natural
selection favored genes
that adapted to wars, famine, and sickness by initiating early
puberty. Currently,
early sexuality and reproduction lead to social disruption, not
social survival, but
the human genome has been shaped over millennia. Although
many explanations
are possible for the link between stress and early puberty, the
evidence continues
to find the correlation (Romans et al., 2003).
Too Early, Too Late
For most adolescents, only one aspect of timing is important:
their friends’ sched-
ules. No one wants to be early or late, with early particularly
hard for girls, late for
boys. Why?
Think about the early-maturing girl. If she has visible breasts in
the fifth grade,
the boys tease her; they are awed by the sexual creature in their
midst. She must

31. fit her womanly body into a school chair designed for younger
children, and she
may hide her breasts in large T-shirts and bulky sweaters and
refuse to undress
for gym. Early-maturing girls tend to have lower self-esteem,
more depression,
and poorer body image than later-maturing girls (Compian et al,
2004; Mendle
et al., 2007).
Some early-maturing girls have boyfriends several years older,
which adds status
but more complications, including drug and alcohol use
(Weichold et al., 2003).
They are “isolated from their on-time-maturing peers [and] tend
to associate with
older adolescents. This increases their emotional distress” (Ge
et al., 2003, p. 437).
Cohort is crucial for boys. Early-maturing boys who were born
around 1930 often
became leaders in high school and beyond (M. C. Jones, 1965).
Early-maturing
boys also tend to be more successful as adults (Taga et al.,
2006). However, if
early-maturing boys live in stressful urban neighborhoods (with
poverty, drugs, and
violence) and if their parents are unusually strict, they are
likely to befriend
law-breaking, somewhat older boys (Ge et al., 2002). For both
sexes, early puberty
currently correlates with early romance, sex, and parenthood,
which lead to later
depression and other psychosocial problems (B. Brown, 2004;
Siebenbruner et al.,
2007).

32. Late puberty may also be difficult, especially for boys. Ethnic
differences in age
of puberty can add to ethnic tensions in high school. Remember
that Asian Amer-
ican youth tend to experience later puberty. In one multiethnic
high school, the
“quiet Asian boys” were teased because they were shorter and
thinner than their
classmates, much to their dismay (Lei, 2003). This is a likely
explanation for the
greater peer discrimination experienced by the Chinese youth in
another school
(Greene et al., 2006; see Research Design). In a third
multiethnic high school,
Samoan students were small numerically but advanced in
puberty. As a result,
they were respected by their classmates of all backgrounds, able
to moderate ten-
sions between African and Mexican Americans (Staiger, 2006).
Interactions
among students in all three of these schools illustrate the
importance of physical
appearance for many adolescents. Puberty can enhance or
diminish a person’s
status with peers, depending partly on when it occurs.
Especially for Parents Worried About
Early Puberty Suppose your cousin’s 9-year-
old daughter has just had her first period, and
your cousin blames hormones in the food
supply for this “precocious” puberty. Should

33. you change your young daughter’s diet?
Puberty Begins 369
Research Design
Scientists: Melissa L. Greene, Niobe
Way, and Kerstin Pahl.
Publication: Developmental Psychology
(2006).
Participants: A total of 136 high school
students at a multiethnic high school in
New York City.
Design: Six times over the four years of
high school, students answered ques-
tionnaires about discrimination, ethnic
identity, depression, and self-esteem.
Major conclusion: For all four ethnic
groups (Black, Asian American, Puerto
Rican, and other Latino), perceived peer
discrimination had a greater impact on

34. self-esteem than did perceived adult
discrimination. The Asian Americans
averaged higher levels of perceived
discrimination than any other group;
the Black Americans were second.
Comment: This study is a welcome step
toward multifaceted, multiethnic, longi-
tudinal research on adolescents. More is
needed to provide, as the researchers
write, “a thorough examination of the
impact of experiences of discrimination
on well-being.”
Nutrition
All the changes of puberty depend on nutrition, yet many
adolescents are deficient
in necessary vitamins or minerals. A five-year longitudinal
study found that eating
habits get worse throughout the teen years (N. I. Larson et al.,
2006).
Diet Deficiencies

35. Fewer than half of all teenagers consume the recommended
daily dose of 15 mil-
ligrams of iron, found in green vegetables, eggs, and meat—all
spurned in favor of
chips, sweets, and fast food. Because menstruation depletes the
body of iron,
more adolescent girls are anemic than those in any other age or
gender group
(Belamarich & Ayoob, 2001). Adolescent boys also suffer from
anemia, especially
if they engage in physical labor or competitive sports, because
muscles need iron
(Blum & Nelson-Mmari, 2004).
Calcium is another example. About half of adult bone mass is
acquired from
ages 10 to 20, yet few adolescents consume enough calcium to
prevent osteoporo-
sis, which causes disability, injury, and death among older
adults. Milk drinking
has declined; most North American children once drank at least
a quart a day. In
2005 among ninth-graders, only 14 percent of U.S. girls and 24
percent of boys
drank even 24 ounces (3⁄4 liter) of milk a day. By twelfth grade,
the rates were 10
and 18 percent (MMWR, June 9, 2006).
Nutritional deficiencies result from the choices young
adolescents are allowed,
even enticed, to make. There is a direct link between deficient
diets and the
availability of vending machines in schools (Cullen & Zakeri,
2004). Fast-food
establishments cluster around high schools, if zoning permits,

36. and many such
places are hangouts for teenagers.
One reason is price. At least experimentally, 10- to 14-year-olds
choose healthy
foods if they are cheaper than unhealthy ones (Epstein et al.,
2006), but milk and
fruit juice are more expensive than fruit punch or soda, and
McDonald’s charges
more for a salad than a hamburger. Only 20 percent of high
school students in
2005 ate five or more servings of fruits or vegetables a day
(MMWR, June 9,
2006), worse than a decade ago (29 percent) (MMWR, August
14, 1998).
Body Image