Strauss RS, Pollack HA. Epidemic Increase in Childhood Overweight, 1986-1998. JAMA. 2001;286(22):2845-2848. doi:10.1001/jama.286.22.2845
Author Affiliations: Department of Pediatrics, UMDNJ-Robert Wood Johnson School of Medicine, New Brunswick, NJ (Dr Strauss) and Department of Health Management and Policy, School of Public Health, University of Michigan, Ann Arbor (Dr Pollack).
Context Overweight is the most common health problem facing US children. Data
for adults suggest that overweight prevalence has increased by more than 50%
in the last 10 years. Data for children also suggest that the prevalence of
overweight continues to increase rapidly.
Objective To investigate recent changes in the prevalence of overweight within
a nationally representative sample of children.
Design, Setting, and Participants The National Longitudinal Survey of Youth, a prospective cohort study
conducted from 1986 to 1998 among 8270 children aged 4 to 12 years (24 174
growth points were analyzed).
Main Outcome Measures Prevalence of overweight children, defined as body mass index (BMI)
greater than the 95th percentile for age and sex, and prevalence of overweight
and at-risk children, defined as BMI greater than the 85th percentile for
age and sex. The roles of race/ethnicity, sex, income, and region of residence
were also examined.
Results Between 1986 and 1998, overweight increased significantly and steadily
among African American (P<.001), Hispanic (P<.001), and white (P = .03)
children. By 1998, overweight prevalence increased to 21.5% among African
Americans, 21.8% among Hispanics, and 12.3% among non-Hispanic whites. In
addition, overweight children were heavier in 1998 compared with 1986 (P<.001). After adjusting for confounding variables,
overweight increased fastest among minorities and southerners, creating large
demographic differences in the prevalence of childhood overweight by 1998.
The number of children with BMI greater than the 85th percentile increased
significantly from 1986 to 1998 among African American and Hispanic children
(P<.001 for both) and nonsignificantly among white
children (P = .77).
Conclusions Childhood overweight continues to increase rapidly in the United States,
particularly among African Americans and Hispanics. Culturally competent treatment
strategies as well as other policy interventions are required to increase
physical activity and encourage healthy eating patterns among children.
The prevalence of overweight is increasing dramatically in the United
States. Results from the Behavioral Risk Factor Surveillance System suggest
that obesity prevalence has increased by more than 50% among adults between
1991-1999.1,2 The prevalence of
childhood overweight is also increasing at an accelerating rate.3
The most recent data from the 1988-1991 National Health and Nutrition Examination
Survey III (NHANES III) demonstrate that the number of overweight children
has increased among all age, race, and sex groups since the NHANES II, 1963-1970.4 Preliminary data from the most recent NHANES study
(NHANES IV, 1999) indicate that overweight continues to increase.5
Data from the 1988-1991 NHANES III cohort suggest that approximately
14% of US children are overweight.6 More recent
data suggest that overweight is more common among specific population subgroups.
The prevalence of overweight in the Practice Partner Research Network, a network
of primary care practices across the country, was 18% to 20%, while the prevalence
of "at-risk" children was 34% to 36%.7 Similarly,
among third- and sixth-grade children in New York City, the prevalence of
overweight was 15% to 22%.8
To monitor overweight trends in children from 1986-1998, we analyzed
data from the National Longitudinal Survey of Youth (NLSY). The NLSY study
design allows for an accurate determination of changes in overweight rates,
since a common survey design was followed for the duration of the study.
The study population consists of 4- to 12-year-old children born to
women enrolled in the NLSY. The NLSY consists of a national sample of young
adults who were interviewed yearly or biyearly from 1979-1998, as well as
a supplemental sample of Hispanics, African Americans, and poor whites. The
NLSY was originally designed to study variations in labor market behaviors
and experiences. However, over time, the study expanded its mission and now
provides a comprehensive assessment of factors that influence social, emotional,
and cognitive development of children born to mothers enrolled in the NLSY.
The weighted sample of children is nationally representative of young children
born to mothers who were 23 to 39 years old. Data on NLSY children were collected
prospectively every 2 years. Detailed information on region of residence and
family income were updated every 1 to 2 years during in-home interviews. Missing
demographic data were obtained from the previous response. Complete demographic
and socioeconomic data were available in approximately 93% of the eligible
cohort.9- 11 Details
of NLSY assessment methodology, attrition, and other matters are described
in detail elsewhere.9- 11
Growth data were available for 8270 unique children. Because multiple
observations of many children were obtained over the 1986-1998 time frame,
24 300 growth observations were available for analysis (Table 1). Weights and heights were measured by the in-home interviewer
using a portable scale and tape measure. Height was measured for 81% of the
sample, and weight was measured for 76%. In the remaining subjects, parental
reports were used. Body mass index (BMI) z scores
were calculated using the LMS method.12,13
The BMI z-score measurements 6 or more SDs from the
reference median were excluded (n = 126) as likely measurement errors, reporting
errors, or signs of extreme medical condition.
Overweight was defined as BMI greater than the 95th percentile for age
and sex derived from a fixed reference distribution. We used the most recent
Centers for Disease Control and Prevention (CDC) National Center for Health
Statistics (NCHS) growth curves.10 The percentage
of children with BMIs above the 85th percentile for age and sex were also
analyzed to assess the total number of children who are considered overweight
and at risk for overweight. These cutoff values are in accordance with recommendations
of an expert panel on childhood obesity14 as
well as previous studies.4 There was no significant
difference in the rate of increase of overweight among children with reported
and measured heights and weights (P = .85).
Because the NLSY oversampled African Americans and Hispanics, we used
NLSY sample weights to provide prevalence estimates corresponding to a nationally
representative sample. Data were analyzed using STATA 7.0 (Stata Corporation,
College Station, Tex). Since obesity is correlated within families, SEs in
descriptive statistics were adjusted to account for familial clustering cross-sectionally
and over time. Differences in proportions were compared by χ2
test. Prevalence results are presented for the weighted sample, while regression
results are presented for the unweighted sample, in accordance with NLSY study
To assess the relative rate of increase of overweight over the study
period, a cross-sectional, time-series multivariate logistic regression was
performed. Because the NLSY included repeated measures of the same individuals,
a generalized estimating equation specification was used, which included the
main effects, year interaction, and confounding variables (ie, race/ethnicity,
sex, urbanicity, region, income, maternal age, and child age). Standard errors
of each subgroup were calculated using the delta method, combining the SEs
for the estimated group-specific trend and for the base prevalence in each
Figure 1 indicates 1986-1998
trends in overweight children. As shown, the prevalence of overweight increased
significantly and steadily among African Americans, Hispanics, and non-Hispanic
whites. By 1998, overweight prevalence had increased by more than 120% among
African Americans and Hispanics, and by more than 50% among whites. By 1998,
21.5% of African American children and 21.8% of Hispanic children were overweight.
In contrast, 12.3% of white children were overweight. The relative weight
of overweight children also increased from 1986 to 1998 (% median [SD] BMI/age,
sex: 144% [1%] in 1986 vs 155% [1%] in 1998; P<.001),
suggesting that the severity as well as the prevalence of overweight increased
over the period.
Table 2 shows group-specific
increases for overweight. Overall, large differences in overweight prevalence
emerged between groups over the study period. To take one example, 1986 overweight
prevalence was virtually identical among upper-income white girls and among
lower-income African American andHispanic boys (6.6% vs 6.5%, P = .95). Yet by 1998, overweight prevalence had only slightly increased
to 8.7% among upper-income white girls (P = .45 compared
with 1986), while overweight prevalence had increased to 27.4% among lower-income
African American and Hispanic boys (P<.001 compared
with 1986). Overall, high income was protective of overweight among whites
(odds ratio [OR] for high vs low income, 0.78 [95% confidence interval (CI),
0.67-0.90]), equivocal among Hispanics (OR, 0.88 [95% CI, 0.57-1.34]), and
associated with increased rates of overweight among African Americans (OR,
1.39 [95% CI, 1.03-1.90]).
Regional differences also emerged over the study period. For example,
1986 child overweight prevalence was quite similar in southern and western
states (7.6% vs 9.4%, P = .39). By 1998, the overall
prevalence of overweight had increased to 10.8% in western states, and to
17.1% in southern states (P<.005).
The same general trends occur by applying a cutoff at the 85th percentile
of BMI (Figure 1, Table 2). Over the course of the study, the percentage of white
children with BMIs above the 85th percentile did not significantly increase
(Figure 1, Table 2). However, racial/ethnic, regional, and economic disparities
among children with BMIs above the 85th percentile increased from 1986 to
The prevalence of childhood overweight is rapidly increasing, with the
sharpest observed increases among boys, African Americans, Hispanics, and
those living in southern states. By 1998, more than 21% of African American
and Hispanic NLSY children were classified as overweight. These race/ethnic
trend disparities remained large and statistically significant after controlling
for family income and for other confounders. Increasing race/ethnic differences
in prevalence of childhood overweight are particularly disturbing, since these
may widen economic disparities15 and may increase
long-term race/ethnicity disparities in health outcomes.16
Although overweight increased rapidly among African Americans and Hispanics,
overweight prevalence increased by approximately 50% between 1986 and 1998
among non-Hispanic white children. This increase only appears modest when
compared with the triple-digit percentage increase in overweight in minority
The NLSY provides the most recent available data based on a single,
high-quality, nationally representative sample. Other studies documenting
the increase in childhood obesity have relied on comparisons of separate studies
that used diverse sampling techniques.3- 6
The NLSY study design allows for accurate determination of changes in overweight
prevalence, since a single sampling strategy and family sample frame was used
for the duration of the study.
A repeated cross-sectional sample over the same study period would be
preferable to the current NLSY cohort. Nevertheless, controlling for respondent
and maternal age effects had only small effects on estimated overweight prevalence.
In addition, the observed prevalence of overweight among NLSY children is
similar to that found in NHANES cohort data over periods when overlapping
prevalence estimates are available, supporting the validity of the NLSY estimates.
In this analysis, we defined overweight based on BMI from the new growth
curves released by the NCHS and the CDC. Because BMI cutoff levels with the
new growth curves are slightly higher than previous reference values, use
of previous standards would have produced even higher estimated prevalence
of overweight in this sample. For instance, the widely cited reference BMI
levels from the NHANES I study for 6- to 12-year-old children17
would have resulted in a net increase in estimated 1998 overweight prevalence
to 15.6% instead of the 13.3% we observed using the new NCHS/CDC standards.
Like many other preventable adverse health states, childhood overweight
reflects the convergence of many biological, economic, and social factors.
Overweight arises from multiple causes, some as intimate as the family dinner
table, others as seductive as television or the latest children's video game.
Provision of high-fat meals and snacks in school settings is both a powerful
temptation and a clear signal of accepted nutritional norms. Innovative strategies
have been evaluated to address each of these concerns.18- 20
No one intervention, by itself, is likely to produce large reductions in the
prevalence of obese or overweight children. Like adolescent smoking, teen
pregnancy, and youth violence, childhood overweight is prevalent because it
arises from deeply rooted behaviors and from social practices that are hardly
confined to children. Given the profound consequences of childhood inactivity,
poor nutrition, and overweight throughout the lifespan,21
urgency is warranted in responding to this epidemic.