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Andersen RE, Crespo CJ, Bartlett SJ, Cheskin LJ, Pratt M. Relationship of Physical Activity and Television Watching With Body Weight and Level of Fatness Among Children: Results From the Third National Health and Nutrition Examination Survey. JAMA. 1998;279(12):938–942. doi:10.1001/jama.279.12.938
From the Divisions of Geriatric Medicine and Gerontology (Dr Andersen) and Gastroenterology (Drs Bartlett and Cheskin), Johns Hopkins University School of Medicine, Baltimore, Md; Department of Health and Fitness, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md (Dr Crespo); and the Physical Activity and Health Branch, Centers for Disease Control and Prevention, Atlanta, Ga (Dr Pratt). Dr Crespo is now with the American University Department of Health and Fitness, Washington, DC.
Context.— Physical inactivity contributes to weight gain in adults, but whether
this relationship is true for children of different ethnic groups is not well
Objective.— To assess participation in vigorous activity and television watching
habits and their relationship to body weight and fatness in US children.
Design.— Nationally representative cross-sectional survey with an in-person interview
and medical examination.
Setting and Participants.— Between 1988 and 1994, 4063 children aged 8 through 16 years were examined
as part of the National Health and Nutrition Examination Survey III. Mexican
Americans and non-Hispanic blacks were oversampled to produce reliable estimates
for these groups.
Main Outcome Measures.— Episodes of weekly vigorous activity and daily hours of television watched,
and their relationship to body mass index and body fatness.
Results.— Eighty percent of US children reported performing 3 or more bouts of
vigorous activity each week. This rate was lower in non-Hispanic black and
Mexican American girls (69% and 73%, respectively). Twenty percent of US children
participated in 2 or fewer bouts of vigorous activity per week, and the rate
was higher in girls (26%) than in boys (17%). Overall, 26% of US children
watched 4 or more hours of television per day and 67% watched at least 2 hours
per day. Non-Hispanic black children had the highest rates of watching 4 or
more hours of television per day (42%). Boys and girls who watch 4 or more
hours of television each day had greater body fat (P<.001)
and had a greater body mass index (P<.001) than
those who watched less than 2 hours per day.
Conclusions.— Many US children watch a great deal of television and are inadequately
vigorously active. Vigorous activity levels are lowest among girls, non-Hispanic
blacks, and Mexican Americans. Intervention strategies to promote lifelong
physical activity among US children are needed to stem the adverse health
consequences of inactivity.
THE PREVALENCE of overweight continues to increase in the US adult population.1-3 In the 12 years between
the Second National Health and Nutrition Examination Survey (NHANES II, 1976
through 1980) and NHANES III (1988 through 1991), the prevalence of overweight
in US adults increased from 25% to 33%.2 The
prevalence of overweight also increased by similar magnitudes among all sex
and age groups of children and adolescents.1
Obesity in children has been associated with subsequent morbidity and mortality
in adulthood.4 These trends have persisted
despite our nation's intense preoccupation with weight.5
Similarly, the prevalence of obesity in England has doubled in the past
decade, yet daily energy intake and fat consumption have actually been reduced
in that country during this time period.6 A
change in the volume of daily physical activity may account for this apparent
discrepancy. Increasingly, leisure time activities are more sedentary, with
television watching, video games, and personal computing among the most popular
pastimes. Further, people in industrialized countries are expending less energy
in activities of daily living, and at work.6,7
Several studies suggest that an active lifestyle during childhood and
adolescence can play an important role in optimizing growth and development.7,8 The Centers for Disease Control and
Prevention recently recommended that comprehensive school and community programs
be developed to promote physical activity among children and adolescents.9 The goals of these programs are to increase knowledge
about activity and exercise, develop behavioral and motor skills that promote
lifelong activity, and encourage physical activity outside of physical education
Using data from NHANES III, this article provides estimates of daily
television watching habits and weekly bouts of vigorous physical activity
in a nationally representative sample of US children aged 8 through 16 years.
We also examined the relationship between body mass index (BMI), body fatness,
and bouts of vigorous activity and television watching.
The NHANES III was conducted by the Centers for Disease Control and
Prevention, National Center for Health Statistics. The plan and operation
of NHANES III have been described elsewhere.10,11
Briefly, the survey was designed to produce a nationally representative sample
of the US population. One of its main goals was to estimate the national prevalence
of selected health conditions and risk factors.
The NHANES III represents a 6-year study from 1988 through 1994 and
consists of two 3-year phases: phase I, 1988 through 1991; and phase II, 1991
through 1994. Although the entire 6-year survey constitutes a national survey,
the survey was designed so that each phase was also a nationally representative
sample. The NHANES III oversampled Mexican Americans, non-Hispanic blacks,
and young children to ensure weighted, reliable estimates for these groups.
Approximately 16 % of those interviewed ranged in age from 8 through 16 years.
Combined data from phases I and II are reported in this article.
The interview was conducted in the child's home and a detailed clinical
examination was performed in a mobile examination center. During the home
interview part of NHANES III, 5365 children were interviewed and the analytic
sample consisted of 4063 children aged 8 through 16 years who completed the
physical activity questionnaire and the body measurement component at the
mobile examination center. Children who were mentally retarded or had a proxy
answer questions for them were excluded from the analyses, as were those with
cerebral palsy, muscle weakness, or paralysis of the arms or legs.
Interviewing staff consisted of experienced persons, many of whom were
of Hispanic origin or bilingual in English and Spanish. Interview forms were
available in both languages. All staff attended yearly training sessions to
ensure maintenance of effective interviewing skills.
Information on self-reported race and ethnicity was used to classify
persons as non-Hispanic white, non-Hispanic black, or Mexican American (persons
of Mexican origin living in the United States). Age was defined as age in
years at the time of the household interview, which preceded the examination
by 2 to 3 weeks.
Participating children were asked how many times per week they "played
or exercised enough to make them sweat or breathe hard." These activities
did not exclude school-related involvements such as physical education. The
interview also included a question on the number of hours of television watched
the day before the interview was administered. Body composition was estimated
by calculating the BMI [the weight (in kilograms) divided by the height (in
meters, squared)], since it has been found to be significantly related to
the percentage of body fat and total body fat in boys and girls.12
We also calculated the sum of the subscapular and suprailiac skinfolds as
an index of trunk fat.
Statistical analyses were carried out using SAS13
and WesVarPC.14 For each survey, sampling weights
were calculated that took into account the unequal selection probabilities
resulting from the cluster design and from planned oversampling of certain
subgroups. All analyses incorporated the sampling weights. For variance estimation,
the balance repeated replication method in the software package WesVarPC14 was used. Statistical differences were determined
using 2-tailed t tests taking the sampling weights
and the complex sample design into account.14
Furthermore, the General Linear Model procedure in SAS13
was used to calculate the least square means to adjust for Tanner stages15 in estimating physical activity and hours of television
The cross-sectional prevalence estimates of the number of bouts of vigorous
activity per week for US children aged 8 through 16 years from 1988 through
1994 are shown in Table 1. Overall,
80% reported participating in play or exercise that made them sweat or breathe
hard 3 or more times per week; the rate was higher in boys (85%) than in girls
(74%). Among non-Hispanic white boys, 88% reported exercising vigorously 3
or more times per week, whereas 78% of non-Hispanic black boys and 80% of
Mexican American boys met this criterion; 72.6% of Mexican American girls
and 69% of non-Hispanic black girls reported performing 3 or more bouts of
vigorous activity each week, whereas only 12.2% of non-Hispanic white boys
reported fewer than 3 bouts of vigorous activity per week. Table 1 also presents prevalence rates of bouts of vigorous physical
activity among various age groups of US children. Boys and girls reported
similar patterns of vigorous play in both the 8 through 10 years and the 11
through 13 years age groups with the boys reporting slightly more physical
activity in each group. However, only 65% of girls aged 14 through 16 years
reported 3 or more bouts of vigorous activity per week, whereas 86% of age-matched
boys achieved this level. Few boys or girls reported 1 or less bouts of vigorous
activity per week, with the exception of 20.1% of 14- to 16-year-old girls
reporting this level of inactivity. Further analyses (data not shown) revealed
that 8.7% of the 14- to 16-year-old girls reported less than 1 bout of vigorous
activity per week.
The cross-sectional prevalence rate estimates of hours of television
watched per day among US children are presented in Table 2. Overall, 26% of American children reported watching 4 or
more hours of television per day; the rate was lower in girls (23%) than in
boys (29%). Forty-three percent of non-Hispanic black boys and girls reported
watching television for more than 4 hours per day. In contrast, non-Hispanic
white boys and girls had the lowest prevalence of watching television more
than 4 hours per day (25% of boys and 18% of girls).
Boys and girls reported similar patterns of television watching across
age groups (Table 2). The highest
prevalence of watching 4 or more hours of television per day occurred in 11-
to 13-year-old children. Both boys and girls in this age group also had the
lowest prevalence of watching 1 or less hours of television per day.
Figure 1 shows the Tanner-score
adjusted mean BMI (A) and the sum of the trunk skinfolds (B) in relation to
the number of bouts of vigorous activity completed weekly. Boys who reported
6 to 8 sessions of vigorous activity per week had the highest BMIs, whereas
those who reported 3 or fewer sessions of vigorous activity per week had the
lowest. In the girls, no clear trend occurred.
Figure 2 shows the Tanner-score
adjusted mean BMI (A) and the sum of the trunk skinfolds (B) in relation to
the number of daily hours of television watched. Boys and girls who watched
4 or more hours of television per day had the highest skinfold thicknesses
and highest BMIs; conversely, children who watched less than 1 hour of television
per day had the lowest BMIs.
We cross-tabulated thirds of daily television watching and thirds of
weekly bouts of vigorous activity to examine the interaction that these measures
may have on Tanner score–adjusted BMI and the sum of trunk skinfolds
(Figure 3). We observed that television
watching was more closely related to skinfolds and BMI than was vigorous activity.
Multivariate analyses revealed no interaction between television watching
and physical activity. Furthermore, significant effects were seen for television
watching but not for physical activity.
We found that US children are currently more active than their adult
counterparts, with almost 80% reporting 3 or more bouts of vigorous activity
each week.16 However, there are several worrisome
trends among adolescent females and ethnic minority groups. Of concern, 26%
of all girls and 31% of non-Hispanic black girls report 2 or fewer bouts of
vigorous activity per week. Our data reconfirm that vigorous activity among
ethnic minority children is lower than in non-Hispanic white children.17,18 Such information must be considered
when developing physical education curricula and community-based intervention
strategies aimed at increasing physical activity among different target populations.
One of the objectives of Healthy People 2000
is to increase vigorous physical activity to at least 3 days per week for
20 minutes or more per occasion in at least 75% of children and adolescents.19 Boys of all ages appear to be meeting this criterion.
However, a decrease in physical activity seems to occur as girls move from
the 11- to 13-year age group to the 14- to 16-year age group. Moreover, 20.1%
of girls aged 14 to 16 years reported 1 or fewer bouts of vigorous physical
activity each week. These data are consistent with the 1992 National Health
Interview Survey-Youth Risk Behavior Survey, which reported that 8.7 % of
15-year-old females reported no participation in moderate or vigorous activity,16 and that 18.5% of 17-year-old females were sedentary.
Malina20 has suggested that the adolescent
decline in physical activity that occurs after the growth spurt is probably
related to the social demands of adolescence, changing interests and the transition
from school to work or school to college. However, the level of physical activity
in our study may be optimistically high because children who lived in northern
states were surveyed during the summer when physical activity is known to
be at its peak. Furthermore, the question about physical activity did not
assess moderate activity or duration of vigorous activity, so a brief bout
of vigorous activity could have been reported as a single bout of exercise.
Because a sedentary lifestyle is considered a risk factor for coronary
artery disease,21 parents and health care professionals
need to encourage adolescent females in particular to maintain active lifestyles
throughout adolescence. The International Consensus Conference on Physical
Activity Guidelines for Adolescents recommends that "all adolescents . . .
be physically active daily, or nearly every day, as part of play, games, sports,
work, transportation, recreation, physical education, or planned exercise,
in the context of family, school, and community activities" and that "adolescents
engage in three or more sessions per week of activities that last 20 minutes
or more at a time and that require moderate to vigorous levels of exertion."22
We also found that non-Hispanic white children were the most active,
with 77% of girls and 88% of boys reporting 3 or more bouts of vigorous activity
per week. However, only 69% of non-Hispanic black girls and 73% of Mexican
American girls reached this threshold. Concerns about crime may present a
major barrier to some children becoming more physically active.7
In a survey of parents, 46% of US adults believed that their neighborhoods
were unsafe.23 Parents in minority populations
are twice as likely as non-Hispanic white parents to report that their neighborhoods
were unsafe. This information may partially explain the lower bouts of vigorous
activity and higher prevalence of television watching reported in non-Hispanic
black and Mexican American children. Successful implementation of policies
to address this problem may help to increase physical activity in these 2
groups. For example, neighborhood watch programs and increased policing in
high crime areas may help alleviate fears and foster an environment where
parents feel it is safe for their children to play. Furthermore, Healthy People 2000 calls for increased community availability and
accessibility of physical activity and fitness facilities.19
Thus, studies that specifically attempt to promote enjoyable, lifetime activities
among ethnic minorities should receive high priority in the public health
Troiano and colleagues1 reported that
the prevalence of overweight is increasing among boys and girls of all age
groups and suggested increasing physical activity as a means to address this
important health problem. Physical activity is inversely related to body weight,
body composition, and the waist-to-hip ratio in adults. Sedentary leisure
time activities such as television watching, playing video games, and personal
computing have contributed to the increasing prevalence of overweight in America.24-27 Our
report shows that television watching was associated with increased skinfold
thickness and BMI among US youth.
Overall, we found high rates of television watching, with 26% of US
children (and 43% of non-Hispanic black children) watching 4 or more hours
per day. Strasburger28 has calculated that
the average high school graduate will likely spend 15000 to 18000 hours in
front of a television but only 12000 hours in school. Next to sleeping, television
watching occupies the greatest amount of leisure time during childhood.27 We found that skinfold thicknesses increased in both
boys and girls as the amount of television watched increased. This finding
is consistent with an earlier study that found a significant relationship
between television watching and the prevalence of obesity in children.26
We also found a relationship between television watching, physical activity,
and body composition. Children who watched more television and were less likely
to participate in vigorous activity tended to have higher BMIs. This is consistent
with the findings of Durant et al.29 Two studies
have reported strong inverse relationships between television watching and
physical activity after television was introduced into small communities in
Canada30 and Scotland.31
Additional research is needed to further identify types of physical activities
that could serve as alternative activities, especially for minority children,
among whom television watching is greatest. Studies among persons of low socioeconomic
status and among certain racial groups have demonstrated specific determinants
and activity preferences. This information has been used to effectively tailor
culturally appropriate physical activity promotion programs.
Currently, 45% of Mexican American and 49% of non-Hispanic black adult
women are overweight.2 Low levels of vigorous
activity and increased television watching most likely are contributing to
this trend. Overweight children are more likely to become overweight adults
than their leaner counterparts.32-34
It appears that overweight in adulthood can more accurately be predicted from
the body weight in late adolescence as opposed to younger ages.33,34
Furthermore, the risks of obesity in adulthood appear to be greater in persons
who were overweight during childhood and adolescent years.35,36
Thus, increased efforts must be placed on preventing excessive weight gain
in older children.
In our study, BMI and the sum of trunk skinfolds were similar in boys
and girls who were highly active compared with those who participated in little
activity. Conversely, children who watched the most television had more body
fat and greater BMIs than those who watched less than 2 hours per day. This
underscores the work of Epstein and colleagues,37
who reported that decreasing sedentary behaviors is a key ingredient to the
successful treatment of childhood obesity. Moreover, repeated exposure to
television commercials for food may prompt children to increase food consumption,
which ultimately leads to weight gain.38 Sedentary
activities that are regularly associated with eating also can become conditioned
cues for eating, such that a child who is not hungry and begins television
watching may find that the television watching cues eating.39
For young people, learning to be physically active may be a more potent
motivator for physical activity than the knowledge about why being physically
active is important.40,41 Health
care professionals, parents, and educators should encourage children and adolescents
to be active before, during, and after the school day. Recent guidelines for
the promotion of lifelong physical activity recommend that health care professionals
routinely assess levels of physical activity in their young patients. Physicians
can play a key role in encouraging sedentary children and their families to
adopt more active lifestyles.42,43
Inactive children and adolescents should be guided toward school or community
programs that encourage physical activity. Children and adolescents who regularly
participate in physical activity should be encouraged to continue and maintain
their active ways.
In summary, although many American children (80%) are regularly active,
rates of inactivity among adolescent girls, non-Hispanic blacks, and Mexican
Americans are cause for concern. One quarter of all US children watch 4 or
more hours of television each day, as do 43% of non-Hispanic blacks. Hours
of television watching is related to both BMI and skinfold thickness. Physicians
and other health care professionals should counsel children and their caregivers
on the importance of regular physical activity and decreasing sedentary activities.
Intervention strategies designed to promote lifetime physical activity represent
a major public health challenge and priority.