Association of Sleep Duration with Obesity among US High School Students

Division of Adolescent and School Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Mailstop K-33, Atlanta, GA 30341, USA.
Journal of obesity 02/2012; 2012:476914. DOI: 10.1155/2012/476914
Source: PubMed
ABSTRACT
Increasing attention is being focused on sleep duration as a potential modifiable risk factor associated with obesity in children and adolescents. We analyzed data from the national Youth Risk Behavior Survey to describe the association of obesity (self-report BMI ≥95th percentile) with self-reported sleep duration on an average school night, among a representative sample of US high school students. Using logistic regression to control for demographic and behavioral confounders, among female students, compared to 7 hours of sleep, both shortened (≤4 hours of sleep; adjusted odds ratio (95% confidence interval), AOR = 1.50 (1.05-2.15)) and prolonged (≥9 hours of sleep; AOR = 1.54 (1.13-2.10)) sleep durations were associated with increased likelihood of obesity. Among male students, there was no significant association between obesity and sleep duration. Better understanding of factors underlying the association between sleep duration and obesity is needed before recommending alteration of sleep time as a means of addressing the obesity epidemic among adolescents.

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Available from: Geraldine S Perry, Dec 03, 2014
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Journal of Obesity
Volume 2012, Article ID 476914, 9 pages
doi:10.1155/2012/476914
Research Article
Association of Sleep Duration with Obesity among
US High School Students
Richard Lowry,
1
Danice K. Eaton,
1
Kathryn Foti,
1
Lela McKnight-Eily,
2
Geraldine Perry,
2
and Deborah A. Galuska
3
1
Division of Adolescent and School Health, National Center for Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Mailstop K-33, Atlanta, GA 30341, USA
2
Divi sion of Adult and Community Health, National Center for Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta, GA 30341, USA
3
Divi sion of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta, GA 30341, USA
Correspondence should be addressed to Richard Lowry, rxl1@cdc.gov
Received 6 September 2011; Accepted 20 November 2011
Academic Editor: Terry Huang
Copyright © 2012 Richard Lowry et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Increasing attention is being focused on sleep duration as a potential modifiable risk factor associated with obesity in children and
adolescents. We analyzed data from the national Youth Risk Behavior Survey to describe the association of obesity (self-report BMI
95th percentile) with self-reported sleep duration on an average school night, among a representative s ample of US high school
students. Using logistic regression to control for demographic and b ehavioral confounders, among female students, compared
to 7 hours of sleep, both shortened (
4 hours of sleep; adjusted odds ratio (95% confidence interval), AOR = 1.50 (1.05–2.15))
and prolonged (
9 hours of sleep; AOR = 1.54 (1.13–2.10)) sleep durations were associated with increased likelihood of obesity.
Among male students, there was no significant association between obesity and sleep duration. Better understanding of factors
underlying the association between sleep duration and obesity is needed before recommending alteration of sleep time as a means
of addressing the obesity epidemic among adolescents.
1. Introduction
During the past century, the average amount of time that
Americans sleep has decreased by approximately 20 percent
[1]. According to sleep duration guidelines suggested by the
National Sleep Foundation, insucient sleep, defined as <8
hours for children and <7 hours for adults on a weeknight, is
experienced by 45% of children ages 11–17 years and 37% of
adults [2, 3]. It is currently estimated that 50 to 70 million
Americans chronically suer from disorders of sleep and
wakefulness which adversely aect daily functioning, health,
and longevity [4]. The cumulative eects of chronic sleep
deprivation and sleep disorders have been associated with
increased mortality and increased risk for a wide range of
chronic diseases including depression, hypertension, stroke,
type 2 diabetes, heart disease, and obesity [4, 5].
The relationship between sleep and obesity has become
a topic of great interest as obesity rates reach record levels
and chronic sleep deprivation aects increasing numbers
of adolescents and adults in the United States [47]. The
two most commonly reported associations between sleep
duration and obesity are (1) a U-shaped curve where the
lowest obesity risk is found at about 7-8 hours of sleep
per night, with the odds of obesity rising for shorter and
longer sleep duration, leading to the optimal dose theory
of habitual sleep duration and (2) a negative linear pattern
where the longest sleep durations are associated with the least
likelihood and the shortest sleep durations are associated
with the g reatest likelihood of obesity, leading to the more
sleep is better theory of habitual sleep duration [5].
Although there are few proposed mechanisms for how
longer sleep duration might predispose toward obesity, there
is experimental evidence for metabolic pathways whereby
shortened sleep duration might lead to increased obesity.
Sleep restr iction in healthy adults has been shown to result
in decreased leptin le vels and increased ghrelin levels, w hich
Page 1
2 Journal of Obesity
result in decreased satiety and increased appetite, respectively
[8, 9]. Alterations in these hormone levels may lead to
increases in subsequent caloric intake and weight gain. Sleep
restriction also has been shown to alter carbohydrate metab-
olism, resulting in increased insulin resistance and impaired
glucose tolerance, which may also aect weight status [8,
10, 11]. Another recognized link between obesity and sleep
deprivation is obstructive sleep apnea, a condition which
may be caused by obesity and which results in sleep disrup-
tion. An analysis of 20 years of data on obesity-associated
diseases among children ages 6–17 years found that hospital
discharges for sleep apnea have increased more than 400%
[12].
Recent reviews of cross-sectional and longitudinal stud-
ies that examined the association between sleep duration and
obesity found no consistent pattern of association among
adults, w ith studies that reported a U-shaped association,
studies that reported a neg ative linear association, and stud-
ies that reported no association [5, 8]. Unlike adult studies,
pediatric studies involving young children have consistently
found a negative linear association between sleep duration
and obesity [5, 8, 13]. Findings from studies involving
adolescents are less consistent and sometimes exhibit sex
dierences [13]. The purpose of this study was to describe
the association between habitual sleep duration and obesity
among a nationally representative sample of high school
students, controlling for demographic characteristics and be-
havioral confounders. Specifically, we sought to determine
whether the association was a negative linear association,
such as t ypically found in studies involving younger children,
or a U-shaped association such as sometimes reported in
studies of adults and whether that association varied by sex,
race/ethnicity, or grade.
2. Methods
2.1. Sample and Survey Administration. Since 1991, the bien-
nial, national Youth Risk Behavior Survey ( YRBS) has used
a three-stage cluster sample desig n to produce nationally
representative samples of students in grades 9–12 attending
public and private schools. Student participation in the
survey was anonymous and voluntary, and local parental
permission procedures were followed. Students completed a
self-administered questionnaire during a regular class peri-
od. Responses were recorded directly on computer-scannable
questionnaire booklets. A weighting factor was applied to
each record to adjust for nonresponse and the oversam-
pling of black and Hispanic students. Sampling strategies
and the psychometric properties of the questionnaire have
been reported previously [1417]. The Centers for D isease
Control a nd Prevention (CDC) Institutional Review Board
granted approval for the national YRBS.
Data on sleep duration was collected in the national
YRBS for the first time in 2007. To increase the sample size
of students reporting long or short sleep durations, we
combined data from the 2007 and 2009 national YRBS.
Individual students were not followed longitudinally, but
rather each survey represented an independently selected,
nationally representative, cross-sectional sample of public
and private school students. School response rates for both
surveys were 81%. Student response rates for 2007 and 2009
were 84% and 88%, respectively. Overall response rates
(defined as school response rate
× student response rate)
were 68% and 71%, respectively. A s mall number of surveys
(62 in 2007 and 50 in 2009) failed data edit checks leaving
final sample sizes of 14,041 and 16,410, respectively [14, 15].
Thus, a total of 30,451 students were surveyed and provided
usable data during 2007–2009.
2.2. Measures
2.2.1. Demographic Characteristics. Demogr aphic character-
istics included sex, race/ethnicity (non-Hispanic white, non-
Hispanic black, Hispanic, and others), and grade (9th, 10th,
11th, and 12th).
2.2.2. Sleep. Students were asked, “On an average school
night, how many hours of sleep do you get?” Response op-
tions were “4 or less hours, “5 hours, “6 hours, “7 hours,
“8 hours, “9 hours, or “10 or more hours. Consistent with
the guidelines of the National Sleep Foundation, students
who reported sleeping less than 8 hours on a school night
were considered to have insucient sleep [2].
2.2.3. Obesity. Self-reported height and weight (without
shoes on) were used to calculate body mass index (BMI),
expressed as body weight in kilograms divided by the square
of height in meters (kg/m
2
). Using reference data from
growth charts produced by CDC, students with a BMI greater
than or equal to the 95th percentile for sex and age (in
months) were considered to be obese [18]. The questionnaire
asked students to report their age in years as a whole number
between 13 and 17 with additional options for 12 or younger
(assigned a value of 12 years) and 18 or older (assigned a
value of 18 years). Half a year (6 months) was added to the
age since, for example, students who reported their age as
16 years would, on average, b e approximately 16 years and 6
months (198 months) old.
2.2.4. Behavioral Confounders. To identify potential con-
founding variables to control for in our final analyses, we
examined the literature for health-related behaviors which
might be associated with both obesity and sleep duration
[1929]. We identified 8 behaviors assessed in the YRBS
which might confound the association between sleep dura-
tion and obesity. We then tested whether each behavior was
associated with sleep duration and obesity in our sample
using logistic regression models that controlled for sex, race/
ethnicity, and grade. Five behaviors were significantly associ-
ated with both sleep duration and obesity and were included,
along with demographic variables, as potential confounders
in final models. These behaviors included feeling sad and
hopeless (prevalence, 95% CI: 27.2%, 26.2%–28.2%), being
a current smoker (19.7%, 18.3%–21.2%), drinking nondiet
soda or pop (31.3%, 29.6%–33.1%), using a computer or
playing video games for 3 or more hours on an average school
Page 2
Journal of Obesity 3
day (24.9%, 23.5%–26.4%), and being physically active for at
least 60 minutes daily (17.8%, 17.0%–18.6%).
2.3. Missing Data. Of the 30,451 observations in the com-
bined dataset, a total of 2,211 (7.3%) were missing data on
BMI, and 3,515 (11.5%) were missing data on sleep duration.
Missing data on demographic characteristics ranged from
549 (1.8%) for race/ethnicity to 78 (0.3%) for sex, and
missing data on behavioral confounders ranged from 1,366
(4.5%) for current smoking to 502 (1.6%) for being physi-
cally active. Missing data were not imputed. A total of 23,579
students had complete data on all variables. Compared to
students with complete data on all variables, those with
missing data on at least 1 variable (n
= 6, 872) had similar
prevalence estimates for obesity (12.4% versus 12.3%, resp.)
and insucient sleep (69.2% versus 68.1%). Prevalence
estimates for sex, current smoking, drinking nondiet soda or
pop, time spent playing video games, and using a computer
for something other than schoolwork, and being physically
active also did not vary significantly between these two
groups. Compared to students with complete data, students
with some missing data were more likely to report very long
or short sleep durations, were more likely to be Hispanic or
other race/ethnicity, were more likely to be in lower grade
levels, and were more likely to report feeling sad or hopeless
(data not shown).
2.4. Analysis. All analyses were conducted using SUDAAN
[30] to account for the complex sample design. Prevalence
estimates in our analyses are unadjusted. Students who
reported sleeping
4 hours were considered to sleep 4 hours,
and students who reported sleeping
10hourswereconsid-
ered to sleep 10 hours. Using logistic regression, we tested for
the presence of linear and quadratic (U-shaped) associations
between obesity (dependent variable) and sleep duration
(independent variable), controlling for sex, race/ethnicity,
grade, and confounding behaviors. Finally, we calculated
crude and adjusted odds ratios with 95% confidence intervals
(CIs) for each level of sleep duration and each demographic
and behavioral variable entered into the final model. Associ-
ations were considered statistically significant at P<0.05.
3. Results
3.1. Sample Characteristics. The total sample size for the
combined 2007 and 2009 national YRBS datasets was 30,451.
Weighted prevalence estimates for demographic groups
included 51.4% male, 48.6% female, 59.4% white, 14.7%
black, 17.8% Hispanic, 8.1% other racial and ethnic minori-
ties, 28.5% 9th grade, 26.2% 10th grade, 23.5% 11th grade,
and 21.8% 12th grade students.
3.2. Sleep Duration. The distribution of sleep duration on
an average school night approximated a bell-shaped curve
among female and male students (Figure 1). Mean sleep
duration was shorter among female (6.7 hrs; 95% CI: 6.7-
6.8) than male (6.9 hrs; 95% CI: 6.8-6.9) students (t
= 8.78,
P<0.001). Approximately 7 of 10 (69.0%) students reported
0
5
10
15
20
25
30
35
56789
(%)
Hours of sleep
Male
Female
<
= 4 >= 10
Figure 1: Distribution of sleep duration on an average school night,
by sex—US high school students.
getting insucient (i.e., 7 hrs) sleep on an average school
night (Table 1 ). The prevalence of insucient sleep was
greater among female (71.6%) than male (66.6%) students
(t
= 8.05, P<0.001). Insucient sleep was more prevalent
among white (69.2%; t
= 2.42, P = 0.018) and black (70.5%;
t
= 3.24, P<0.002) than Hispanic (65.8%) s tudents. The
prevalence of insucient sleep increased with grade (59.1%,
9th; 68.2%, 10th; 74.1%, 11th; 76.8%, and 12th). All pairwise
comparisons by grade level were significant (t-test statistics
ranged from 2.70 to 17.78, all P<0.01).
3.3. Obesity. Approximately 12.4% of students were obese
(Table 1). The prevalence of obesity was greater among male
(15.7%) than female (8.9%) students (t
= 9.81, P<0.001).
Obesity was more prevalent among black (16.6%; t
= 6.46,
P<0.001) and Hispanic (15.7%; t
= 6.89, P<0.001) than
white (10.5%) students. The prevalence of obesity did not
vary significantly with grade.
3.4. Behavioral Confounders. We tested 8 behaviors assessed
in the YRBS which might confound the association between
sleep duration and obesity using logistic regression models
that controlled for sex, race/ethnicity, and grade (Table 2).
For this analysis, behavioral variables were coded dichoto-
mously using cut-points consistent with national guidelines,
health objectives, and surveillance categories [14, 31, 32].
Behaviors significantly associated with either insucient (
7
hours) or long (
9 hours) sleep duration and obesity were
identified as confounders and included along with demo-
graphic variables in final models. These 5 behaviors included
feeling sad and hopeless, being a current smoker, drinking
nondiet soda or pop, using a computer or playing video
games for 3 or more hours on an average school day, and
being physically active for at l east 60 minutes daily. Feeling
sad and hopeless was dierent from the other confounders
in that it was more likely to occur at both short (AOR
= 1.79)
and long (AOR
= 1.26) sleep durations.
3.5. Associat ion between Sleep Duration and Obesity. Using
logistic regression models which controlled for sex, race/
ethnicity, grade, and confounding behaviors, we detected a
significant quadratic (U-shaped) association (P
= 0.0330)
Page 3
4 Journal of Obesity
Table 1: Prevalence of insucient and long sleep duration and obesity—US high school students.
Demographic subgroup
Sleep duration
a
Insucient (7hours) Long(9 hours) Obese (BMI 95th percentile)
b
(N) % 95% CI % 95% CI (N) % 95% CI
Total (26,936) 69.0 67.8–70.3 7.6 7.1–8.1 (28,240) 12.4 11.713.2
Sex
Female (13,575) 71.6 70.3–72.8 6.2 5.6– 6.9 (14,096) 8.9 8.1
9.7
Male (13,297) 66.6 65.2–68.1 8.9 8.1– 9.7 (14,144) 15.7 14.5
17.0
Race/ethnicity
White (11,728) 69.2 67.7–70.7 6.7 6.1–7.3 (12,032) 10.5 9.5
11.7
Black (5,114) 70.5 68.7–72.3 8.7 7.6–10.0 (5,357) 16.6 15.3
18.1
Hispanic (7,296) 65.8 63.2–68.3 9.7 8.5–11.0 (7,863) 15.7 14.5
17.1
Other (2,357) 72.5 68.3–76.2 7.1 5.1– 9.9 (2,605) 11.4 9.8
13.3
Grade
9th (6,615) 59.1 57.4–60.7 12.5 11.2–13.8 (6,922) 12.7 11.7
13.9
10th (6,485) 68.2 66.3–70.1 7.1 6.2–8.0 (6,877) 12.0 10.9
13.1
11th (6,808) 74.1 72.2–76.0 5.4 4.8–6.2 (7,130) 12.2 11.1
13.4
12th (6,878) 76.8 74.9–78.7 4.3 3.7–5.1 (7,256) 12.8 11.4
14.4
N = unweighted sample size. CI = confidence interval.
a
On an average school night.
b
Based on self-reported height and weight, body mass index (BMI = weight [kg]/height [m]
2
) 95th percentile using growth charts developed by t he Centers
for Disease Control and Prevention for youth aged 2–20 years.
between sleep duration and obesity, but no evidence of a
linear association (P
= 0.4977) (Table 3 ). The unadjusted
prevalence of obesity was approximately 12% among stu-
dents who reported sleeping between 6 and 9 hours on an
average school night and increased slightly among students
who reported shorter (16.5% at
4 hrs) or longer (15.1% at
10 hrs) sleep duration.
Next, we tested whether the association between sleep
duration and obesity varied by sex, race/ethnicity, or g rade.
A significant interaction was detected for the quadratic (U-
shaped) association by sex (Wald F
= 9.84, P = 0.0024),
but not race/ethnicity (Wald F
= 0.51, P = 0.6763) or grade
(Wald F
= 1.40, P = 0.2480). Because of the significant inter-
action by sex, we r an separate analyses for females and males
(Table 3). We found no evidence of significant interactions
for a linear association by sex, race/ethnicit y, or grade.
Among female students, controlling for demograph-
ic characteristics and confounding behaviors we detected a
significant quadratic (U-shaped) association (P
= 0.0004)
between sleep duration and obesity, but no evidence of a
linear association (P
= 0.9653). The prevalence of obesity
was lowest (approximately 8%) among female students who
reported sleeping between 6 and 8 hours on an average
school night and increased among those w ho reported
shorter (14.6% at
4 hrs) or longer (14.1% at 10 hrs) sleep
duration (Table 3). Among male students, controlling for
demographic characteristics and confounding behaviors, we
did not detect a significant linear or quadratic association
between sleep duration and obesity (Ta b le 3 ).
Finally, because of the significant quadratic association
between sleep duration and obesity among females, we
compared crude odds ratios (ORs) and adjusted odds ratios
(AORs) for obesity by sleep duration among female students
(Table 4). We chose the sleep duration with the lowest
prevalence of obesity (7 hours) as the referent group. Com-
pared to females who slept 7 hours on an average school
night, those who slept fewer hours (OR
= 2.10, 4hrs;OR=
1.41, 5 hrs) and those who slept more hours (OR = 1.69,
9hrs; OR
= 2.00, 10 hrs) were more likely to be obese.
Controlling for demographic characteristics and confound-
ing behaviors attenuated, but did not eliminate, the statistical
significance of adjusted odds ratios for obesity at shorter
and longer sleep durations. Compared to female students
who slept 7 hours on an average school night, those who
slept
4hours(AOR= 1.50) and those who slept 9 hours
(AOR
= 1.55) were more likely to be obese. The AOR for
10 hours (AOR = 1.50) was similar in magnitude to the
odds ratio for 9 hours of sleep and probably fell short of
statistical significance because of small numbers of females
who slept
10 hours (n = 202). Combining sleep duration
categories of 9 hours and
10 hours, we found that females
who slept
9 hours were more likely to be obese (AOR = 1.54;
95% CI: 1.13–2.10) than females who slept 7 hours. Because
there was no statistical evidence for a significant linear or
quadratic association between sleep duration and obesity
(after controlling for potential confounders) among male
students, we did not compare crude and adjusted odds ratios
for obesity at dierent sleep durations among male students.
4. Discussion
Nearly 7 out of 10 high school students reported sleeping
less than 8 hours on an average school night. This finding
is consistent with the high prevalence of insucient sleep
reported in other studies [2, 33]. In our study, the association
between sleep duration and obesity diered by sex, but
not by race/ethnicity or grade. Controlling for demographic
characteristics and behavioral confounders, we found
Page 4
Journal of Obesity 5
Table 2: Associations of insucient and long sleep duration, and obesity with other health-related behaviors—US high school students.
Health-related Behavior
Insucient sleep duration (
7hours)
a
Long sleep duration (9hours)
a
Obese (BMI 95th percentile)
b
AOR 95% CI P value AOR 95% CI P-value AOR 95% CI P value
Felt sad and hopeless
c
1.79 1.61–1.99 0.0000 1.26 1.08–1.46 0.0032 1.26 1.111.43 0.0006
Current smoker
d
1.63 1.45–1.84 0.0000 1.10 0.90–1.34 0.3604 1.31 1.15–1.50 0.0001
Drank nondiet soda
e
1.26 1.17–1.36 0.0000 1.14 0.96–1.34 0.1292 1.15 1.02–1.29 0.0237
Computer/video games
f
1.61 1.46–1.77 0.0000 1.10 0.91–1.33 0.2992 1.29 1.15–1.44 0.0000
Television viewing
g
1.02 0.93–1.11 0.6490 1.08 0.93–1.27 0.2999 1.48 1.33–1.64 0.0000
Physically active
h
0.82 0.75–0.90 0.0000 1.28 0.99–1.65 0.0571 0.63 0.55–0.72 0.0000
Ate fruits and vegetables
i
0.83 0.75–0.92 0.0008 1.50 1.27–1.76 0.0000 1.02 0.90–1.15 0.7393
Drank milk
j
0.86 0.77–0.97 0.0145 1.41 1.16–1.71 0.0008 1.10 0.95–1.28 0.1926
AOR = odds ratio adjusted for sex, race/ethnicity, and gra de. Referent for insucient (7 hours) and long (9 hours) sleep duration is 8 hours of sleep.
CI
= confidence interval.
a
On an average school night.
b
Based on self-reported height and weight, body mass index (BMI = weight [kg]/height [m]
2
) 95th percentile using growth charts developed by the Centers for Disease Control and Prevention for youth aged
2–20 years.
c
Almost every day for 2 or more weeks so that they stopped doing some usual activities.
d
Smoked cigarettes on at least 1 day during the 30 days before the sur vey.
e
Drank a can, bottle, or glass of soda or pop, not including diet soda or diet pop, at least one time per day during the 7 days before the survey.
f
Used a computer for something that was not school work or played video games for 3 or more hours per day on an average school day.
g
Watchedtelevisionfor3ormorehoursperdayonanaverageschoolday.
h
Were physically active doing any kind of physical activity that increased their heart rate and made them breathe hard some of the time for at least 60 minutes per day on all 7 days during the 7 days before the survey.
i
Ate fruits and vegetables 5 or more times per day during the 7 days before the survey.
j
Drank 3 or more glasses of milk per day during the 7 days before the survey.
Page 5
6 Journal of Obesity
Table 3: Linear and quadratic associations between obesity and sleep duration—US high school students.
Demographic
subgroup (N)
Prevalence of obesity
a
by sleep duration
b
4 hrs 5 hrs 6 hrs 7 hrs 8 hrs 9 hrs 10 hrs
P Va lue for tren d
c
%
95% CI
(N)
%
95% CI
(N)
%
95% CI
(N)
%
95% CI
(N)
%
95% CI
(N)
%
95% CI
(N)
%
95% CI
(N)
Linear Quadratic
Total Population (23,579)
16.5
14.2–19.2
(1,355)
13.9
12.4–15.5
(2,428)
11.5
10.5–12.5
(5,306)
12.2
10.9–13.6
(7,124)
12.1
10.9–13.4
(5,513)
12.4
10.4–14.7
(1,431)
15.1
10.6–21.1
(422)
.4977 .0330
Sex
Female (11,939)
14.6
11.3–18.7
(665)
10.3
8.6–12.4
(1,401)
8.3
7.2–9.5
(2,842)
7.5
6.3–9.0
(3,522)
8.3
7.0–9.9
(2,650)
12.1
9.3–15.6
(657)
14.1
8.8–21.8
(202)
.9653 .0004
Male (11,640)
18.4
14.6–23.0
(690)
18.4
16.1–21.1
(1,027)
15.1
13.3–17.1
(2,464)
16.2
14.0–18.8
(3,602)
15.3
13.2–17.6
(2,863)
12.5
9.8–15.9
(774)
15.9
9.8–24.7
(220)
.3432 .8428
CI = confidence interval. N = unweighted sample size.
a
Based on self-reported height and weight, body mass index (BMI = weight [kg]/height [m]
2
) 95th percentile using growth charts developed by the Centers
for Disease Control and Prevention for youth aged 2–20 years.
b
On an average school night.
c
Adjusted for sex, race/ethnicit y, grade, feeling sad and hopeless, current smoking, drinking nondiet soda or pop daily, using computers (non-school-related)
or playing video games 3 or more hours per day, and being physically active for at least 60 minutes 7 days per week.
a significant quadratic (U-shaped) association b etween sleep
duration on an average school night and obesity among
female students, but not among male students. No significant
linear associations were found among any demographic
subgroups. Among female students, the lowest obesity preva-
lence occurred at approximately 7 hours of sleep with greater
obesity prevalence occurring at shorter and longer sleep
durations. This ty pe of U-shaped association is often seen
between sleep duration and mortality, heart disease, type 2
diabetes, and obesity among adults [5]. Previous studies of
the association between sleep duration and obesity among
adults have sometimes found dierences by sex, with a
negative linear association among males and a U-shaped
association among females [8, 13]. One previous study
involving a nationally representative sample of middle and
high school students found dierences by sex, with a negative
linear association between sleep duration and obesity among
male students and no association among female students
[33]. Factors responsible for dierences in the findings from
that study compared to our study may include the addition
of 7th and 8th grade students to the Add Health Study
population [33]. Also, that study controlled for parental
education and physical activity and inactivity, but not for
depressive symptoms, smoking, or soda consumption [33].
While there is experimental evidence for metabolic
pathways whereby shortened sleep duration might lead to
obesity, there are currently no clearly delineated mechanisms
proposed for how longer sleep duration might lead to
the onset of obesity [5, 811]. Sleep restriction in healthy
adults has been shown to result in decreased leptin levels
which result in decreased satiety and increased ghrelin levels
which result in increased appetite [8, 9]. Alterations in these
hormone levels may subsequently lead to increased caloric
intake and weight gain among persons with shortened sleep
duration. A possible explanation for the association between
prolonged sleep duration and obesity among females in-
volves the dysfunctional sleep patterns often associated with
both obesity and depression. Prospective studies of children
and adolescents have found that obesity is associated with
later development of depressive symptoms, and juvenile
onset of depression increases risk for becoming overweight
in adulthood [34, 35]. More than 90% of children and
adolescents with major depressive disorder report subjec-
tive sleep complaints and obese children experience more
fragmented sleep, with frequent awakenings and episodes
of sleep apnea, compared to normal-weight children [12,
35]. It is possible that the dysfunctional sleep patterns
experienced by depressed and/or obese youth may, in some
cases, result in extended sleep durations in an attempt to
compensate for poor-quality and/or interrupted sleep. In
our study, having feelings of sadness and hopelessness was
more likely to occur at both short and long sleep durations.
Controlling for demographic and behavioral confounders
(including sadness/hopelessness) in our logistic regression
model attenuated, but did not eliminate, the increased odds
of being obese among female students w h o reported sleeping
either 4 or less hours or 9 or more hours (compared to 7
hours) on an average school night.
Age-dependent eects, such as the decreased sleep needs
of adults compared to young children, may account for
the dierent patterns of association (e.g., U-shaped among
adults versus negative linear among children) between sleep
duration and obesity [5]. For example, if there is an adverse
eect on obesity risk from long sleep duration in excess of
physiological needs, this could be evidenced among adults
who sleep as much as 10 or 12 hours per day. Young
Page 6
Journal of Obesity 7
Table 4: Odds ratios for obesity,
a
by sleep duration—US female high school students.
Independent variables (N = 11,939) % OR 95% CI AOR 95% CI
Sleep duration (hours)
b
4 (665) 14.6 2.10 1.472.99 1.50 1.052.15
5 (1,401) 10.3 1.41 1.06
1.88 1.17 0.87–1.58
6 (2,842) 8.3 1.10 0.87
1.39 1.00 0.78–1.27
7 (3,522) 7.5 1.00 (referent) 1.00 (referent)
8 (2,650) 8.3 1.11 0.87
1.42 1.11 0.86–1.43
9 (657) 12.1 1.69 1.17
2.42 1.55 1.07–2.25
10 (202) 14.1 2.00 1.213.30 1.50 0.91–2.49
Race/ethnicity
White (5,389) 6.8 1.00 (referent)
Black (2,391) 15.1 2.46 1.85–3.27
Hispanic (3,132) 11.8 1.81 1.44–2.27
Other (1,027) 8.0 1.17 0.79–1.75
Grade
9th (2,828) 9.0 0.89 0.70–1.12
10th (2,860) 8.7 0.87 0.70–1.09
11th (3,132) 8.5 0.86 0.66–1.13
12th (3,119) 9.4 1.00 (referent)
Felt sad and hopeless
c
Yes (4,266) 11.5 1.35 1.14–1.61
No (7,673) 7.5 1.00 (referent)
Current smoker
d
Yes (2,135) 12.2 1.63 1.35–1.97
No (9,804) 8.1 1.00 (referent)
Drank nondiet soda
e
Yes (3,303) 11.0 1.14 0.95–1.36
No (8,636) 8.2 1.00 (referent)
Computer/video games
f
Yes (2,438) 11.3 1.26 1.05–1.51
No (9,501) 8.3 1.00 (referent)
Physically active
g
Yes (1,272) 6.8 0.75 0.57–0.99
No (10,667) 9.2 1.00 (referent)
N = unweighted sample size. OR = unadjusted odds ratio. AOR = adjusted (for other variables in the model) odds ratio. CI = confidence interval.
a
Based on self-reported height and weight, body mass index (BMI = weight [kg]/height [m]
2
) 95th percentile using growth charts developed by the Centers
for Disease Control and Prevention for youth aged 2–20 years.
b
On an average school night.
c
Almost every day for 2 or more weeks so that they stopped doing some usual activities.
d
Smoked cigarettes on at least 1 day during the 30 days before the sur vey.
e
Drank a can, bottle, or glass of soda or pop, not including diet soda or diet pop, at least one time per day during the 7 days before the survey.
f
Used a computer for something that was not school work or played video games for 3 or more hours per day on an average school day.
g
Were physically active doing any k ind of physical activity that increase their heart rate and made them breathe hard some of the time for at least 60 minutes
per day on all 7 days during the 7 days before the survey.
children, with much longer physiological sleep needs, might
not show an adverse eect of “long sleep duration until 18
hours of sleep per day, which very few children would be
able to accrue [5]. Explanations for sex-related dierences
in the association between sleep duration and obesity may
include sex-related dierences in the physiology of puberty,
particularly w ith respect to body composition, for example,
the increasing adiposit y typically seen among females and
decreasing adiposity typically seen among males as they pass
through puberty [33]. Sex-related dierences in sleep physi-
ology, the psychosocial correlates of obesity and physiologic
pathways mediating the association between depression and
BMIhavebeennotedaswell[20, 33].
Our study has several strengths. The data are from na-
tionally representative samples of students in grades 9–12,
a population which includes older adolescents for whom
nationally representative data on sleep duration and obesity
are relatively limited. In our analyses, we were able to control
Page 7
8 Journal of Obesity
for a variety of health behaviors found to be associated both
with sleep duration and obesity, and which might therefore
confound their relationship. Final ly, by combining two large
national datasets, we obtained increased statistical power
enhancing our abilit y to char acterize the association between
sleep duration and obesity at the extremes of long and short
sleep duration and among demographic subgroups.
Many of the limitations of our study, such as the lack
of objective measures of sleep duration, are shared by other
published studies examining the association between sleep
duration and obesity [5, 8, 13]. We relied on a single self-
report for sleep duration on an average school night. Also,
data were not available on other potentially important factors
such as variation in sleep duration through the week, in-
cluding weekends, actual bedtime, and wake times, and sleep
quality, including the presence of snoring or breathing dif-
ficulties that might suggest undiagnosed obstructive sleep
apnea. In addition, we used BMI based on self-reported
height and weight to classify students with respect to obesity.
A national study of adolescents found the correlation (r
=
.92) of BMI and the specificity (0.996) of obesity status
(BMI
95th percentile) based on BMI calculated from self-
reported versus measured height and weig h t was very high
[36]. Although sensitivity (0.722) of obesity status based
on self-report was not as high, using self-reported height
and weight correctly classified 96% of teens with respect
to obesity, and girls were no more likely than boys to be
misclassified using self-reported height and weig ht [36].
Finally, our study is cross-sectional in design, and therefore
direction of causality cannot be inferred. Sleep duration
could aect weight gain, but obesity could also impact the
duration of sleep. Indeed, the association between short and
long sleep duration and obesity may not necessarily reflect
a causal relationship, but could be a marker indicating that
naturally short or long sleepers are at-risk populations for
obesity, chronic disease, and mortality [37].
5. Conclusion
The high prevalence of insucient sleep among adolescents,
with its deleterious eects on neurobehavioral function (i.e.,
mood, memor y, attention, and cognition) and associated in-
creases in motor vehicle accidents and impaired school per-
formance, provides a strong rationale to promote greater
duration and quality of sleep among teens [5, 38, 39]. How-
ever, with respec t to obesity prevention, the current literature
suggests that sex-related dierences (such as found in our
study) and other inconsistencies in the association between
sleep duration and obesity among children, adolescents,
and adults, coupled with the lack of clearly defined causal
pathways, make it premature to recommend alteration of
sleep patterns as an eective intervention to prevent the onset
of obesity in the general population or enhance weight loss
among the clinically obese [5]. There are currently no inter-
ventional or observational studies showing that weigh t loss
can be achieved in the general community or particular
subpopulations, through advice to change sleep duration.
Still, the consistent negative linear association between sleep
duration and obesity seen among younger children and the
positive impact of adequate sleep generally have led some
to suggest adequate sleep as an adjunct to other lifestyle
measures in the prevention of childhood obesity [37]. In the
absence of definitive evidence as to what constitutes “ade-
quate sleep for the purpose of promoting healthy weight,
one approach is to provide the appropriate circumstances
and environment for sleep and reduce external interference
with sleep through the maintenance of bedtime routines and
limiting television viewing and use of electronic devices near
bedtimes and in bedrooms [37, 40]. While there may be little
risk in taking such a pragmatic approach to the promotion
of adequate sleep as an adjunct strategy in the fight against
childhood obesity, it is clear that more needs to be known
about the association between sleep and obesity. In addition
to a better understanding of the mechanisms underlying the
association, further research is needed to determine the char-
acteristics of sleep patterns that may promote healthy weight
and whether behavioral programs aimed at changing sleep
duration as a means of weight control are safe and eective.
Confilct of Interests
The authors have no conflict of interests to declare.
Disclaimer
The findings and conclusions in this paper are those of the
authors and do not necessarily represent the ocial position
of the Centers for Disease Control and Prevention.
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  • Source
    • "Black participants had significantly shorter free night sleep than Hispanic participants and there was a similar trend for shorter free night sleep in Black compared to White participants. This is consistent with previous reports of shorter subjectively and objectively measured school night and total night sleep in Black compared to White adolescents and shorter subjectively measured sleep in Black compared to Hispanic adolescents (Lowry et al., 2012; Matthews, Hall, & Dahl, 2014; Moore et al., 2011; Organek et al., 2015). Other studies have reported longer self-reported sleep in Black compared to White adolescents and no differences between Black and Hispanic adolescents (Organek et al., 2015; Williams, Zimmerman, & Bell, 2013). "
    [Show abstract] [Hide abstract] ABSTRACT: Sleep is a complex behavior with numerous health implications. Identifying sociodemographic and behavioral characteristics of sleep is important for determining those at greatest risk for sleep-related health disparities. In this cross-sectional study, general linear models were used to examine sociodemographic and behavioral characteristics associated with sleep duration, chronotype, and social jet lag in adolescents. One hundred and fifteen participants completed Phase I (self-reported sleep measures), and 69 of these participants completed Phase II (actigraphy-estimated sleep measures). Black adolescents had shorter free night sleep than Hispanics. Youth with later chronotypes ate fewer fruits and vegetables, drank more soda, were less physically active, and took more daytime naps. Based on these findings, recommendations for individual support and school policies are provided.
    Full-text · Article · Sep 2015 · The Journal of School Nursing
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    • "This result is in line with another recently published Norwegian study among adolescents (aged 16–18 years) [52]. However, this latter study and studies among American adolescents have reported the opposite trend among sexes when considering sleep duration [3,23]. No relationship was detected between time in bed and overweight and/or obesity in the present study. "
    [Show abstract] [Hide abstract] ABSTRACT: Objective To investigate the prevalence of short time in bed (<8 h/day) and to examine the association between time in bed, overweight/obesity, health-risk behaviors and academic achievement in adolescents. Methods This study included a sample of adolescents (n = 2432) aged 15–17 years in the southern part of Norway (participation rate, 98.7%). A self-report questionnaire was used to assess time in bed, body mass index, dietary habits, physical activity habits, sedentary behavior, smoking and snuffing habits, and academic achievement. Results A total of 32.3% of the students reported short time in bed (<8 h/day) on an average school night. Several health-risk behaviors were associated with short sleep duration, including not being physically active for ⩾60 min for ⩾5 days/week (adjusted odds ratio, 1.33; 95% confidence interval, 1.05–1.68); using television/computer >2 h/day (1.63; 1.23–2.17); being a current smoker (2.46; 1.80–3.35) or snuffer (2.11; 1.57–2.85); having an irregular meal pattern (1.33; 1.05–1.68); intake of sweets/candy ⩾4 times/week (0.51; 0.32–0.83) and poor academic achievement (1.62; 1.26–2.09). All odds ratios were adjusted for sex, age and parental education. Conclusions In Norwegian adolescents, short time in bed is associated with several health-risk behaviors and poor academic achievement.
    Full-text · Article · Jun 2014 · Sleep Medicine
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    • "Adolescents go to bed late due to social and extracurricular activities occurring late in the evening (Roberts et al. 2010), technology distractions before bedtime (Calamaro et al. 2009) and delayed circadian timing associated with pubertal development (Carskadon et al. 1993). Insufficient sleep has negative effects on physical health (Lowry et al. 2012), cognition (Gruber et al. 2010) and emotions (Dahl 1999), and increases the risk of injuries (Pizza et al. 2010). Considering that insufficient sleep in adolescence has such far-reaching consequences, interventions aimed at advancing adolescent bedtime (i.e., shifting bedtime to an earlier time) to prevent insufficient sleep duration are needed. "
    [Show abstract] [Hide abstract] ABSTRACT: The aim of the study was to test the motivation and awareness variables of the I-change model as predictors of adolescent intention to go to bed earlier. Questionnaires regarding sleep related motivational and awareness variables were administered to 127 sleep restricted (determined by actigraphy) high school students (12–17 years old). The motivational variables positive attitudes towards sleep and parents setting wake time predicted higher intentions to go bed earlier. The awareness variable sleep related cues to action also predicted higher intentions to advance bedtime. Positive attitudes towards sleep partially mediated the effect of sleep related cues to action on intention to advance bedtime. Future sleep promotion programs should train adolescents to detect cues to go to bed earlier to increase their intentions to go to bed earlier. Adolescents should be assisted to develop positive attitudes towards sleep as to enhance their autonomous motivation to advance their bedtime.
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