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Whitlock EP, Williams SB, Gold R, et al. Screening and Interventions for Childhood Overweight [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2005 Jul. (Evidence Syntheses, No. 36.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Screening and Interventions for Childhood Overweight [Internet].

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1Introduction

Scope And Purpose

This review examines the evidence for the benefits and harms of screening and earlier treatment of child and adolescent overweight in clinical settings. For simplicity, this review refers to children and adolescents collectively as children, unless sections pertain to a specific age group. This review's purpose is to summarize the current state of the evidence for primary care clinicians and identify key evidence gaps relating to clinical identification and treatment of childhood overweight. To facilitate the reading of this document, Appendix A lists all abbreviations used in the text, tables, figures, and appendixes.

Background

Burden of Illness

Obesity and overweight develop when there is a mismatch between energy intake and expenditure,1, 2 and are related to health risks and problems in children.3 The genetic survival advantage for individuals whose bodies use calories more slowly has become a disadvantage in a society where abundant food and inactivity predominate.4 Obesity and overweight are multi-factorial problems rooted in the interaction of the host (susceptibility due to genetics and learned behaviors), agent (energy imbalance), and environment (abundant food; reduced lifestyle activity; and economic, social, and cultural influences).1 Obesity/overweight has been declared an epidemic46 and a “public health crisis” among children in the United States and around the world7 due to alarming upward trends in its prevalence. Overweight in children (defined by experts as a body mass index [BMI] ≥ 95th percentile for age and sex)8, 9 aged two and older has at least doubled in the last 25 years (Figure 1). The age- and sex-specific mean BMI and the proportion of children with BMI ≥ 95th percentile increased markedly in children from the mid-1970s through the 1990s, with almost all of this increase occurring in children in the upper half of the BMI distribution.10 Thus, about 50% of children appear to have “obesity susceptibility genes” that have been acted upon by environmental changes in the last 25 years.11

Figure 1. Overweight Trends in Children and Adolescents.

Figure

Figure 1. Overweight Trends in Children and Adolescents.

Since increases in the mean BMI have occurred primarily due to increases in the upper half of the BMI distribution,12 weight-related health consequences will become increasingly common in children. Health consequences of childhood overweight and obesity have been reviewed recently and include pulmonary, orthopedic, gastroenterological, neurological, and endocrine conditions, as well as cardiovascular risk factors. 7, 1318 Tables 1 and 2 contain the limited prevalence data for key morbidities and risk factors available from recent summaries. Rarely, severe childhood obesity is associated with immediate morbidity from conditions such as slipped capital femoral epiphysis,19 while steatohepatitis and sleep apnea are somewhat more common.2024 Medical conditions new to this age group, such as Type 2 diabetes mellitus, 25 represent “adult” morbidities that are now seen more frequently among overweight adolescents.26, In a multi-ethnic sample from an obesity clinic, for example, 4% of children and adolescents (BMIs above the 95th percentile for age and sex) had undiagnosed diabetes. All with undiagnosed diabetes were either Hispanic or black adolescents.27 For most overweight/obese children, however, medical complications do not become clinically apparent for decades.13

Table 1. Overweight and Obesity-Associated Health Conditions in Children and Adolescents.

Table 1

Overweight and Obesity-Associated Health Conditions in Children and Adolescents.

Table 2. Overweight and Obesity-Associated Risk Factors in Children and Adolescents.

Table 2

Overweight and Obesity-Associated Risk Factors in Children and Adolescents.

Overweight is associated with a higher prevalence of intermediate metabolic consequences and risk factors, such as insulin resistance, elevated blood lipids, increased blood pressure, and impaired glucose tolerance.2732 In cohort studies, such as the Muscatine and Bogalusa Heart studies, these conditions are strongly correlated cross-sectionally with adiposity.13 Among 2,430 adolescents aged 12 to 19 in the National Health and Nutrition Examination Survey (NHANES) III, the overall prevalence of metabolic syndrome (at least three of: elevated blood pressure, low HDL-cholesterol, high triglycerides, high fasting glucose, abdominal obesity) was 4.2%–6.1% of males and 2.1% of females (p=0.01).29 Prevalence varied with BMI, occurring in 28.7% of overweight adolescents (BMI ≥ 95th percentile), 6.8% of “at risk for overweight” adolescents (BMI 85th to 95th percentile), and 0.1% of those with BMI <85th percentile.

Perhaps the most significant short-term morbidities for overweight/obese children are psychosocial, including issues of social marginalization, self-esteem, and quality of life.3336 In a recent study, 10- to 11-year-old children rated same-sex obese children the least likeable, compared with children with various physical disabilities or normal healthy children.37 This finding replicates research conducted over 40 years ago, and suggests that prejudice against obese children has not improved, and may have increased. Children referred for evaluation of severe overweight (mean BMI 34.7) are significantly more likely to report impaired quality of life (odds ratio [OR] 5.5, 95% confidence interval [CI] 3.4–8.7) than are healthy children, or those with cancer (OR 1.3, 95% CI 0.8–2.3).38 While self-esteem is not necessarily affected in overweight children,34 it may be reduced in overweight adolescents.35 Adolescents with BMI > 95th percentile for sex and age are less likely to be nominated as one of their schoolmates' five best friends than normal weight adolescents, despite listing similar numbers of friends themselves.36 Psychiatric conditions are not clearly increased in the general population of overweight children.16

Risk factors for developing childhood overweight have also been recently reviewed7, 39 and include parental fatness, low parental education, social deprivation, and, perhaps, infant feeding patterns, early or more rapid puberty, extremes of birth weight, gestational diabetes, and various social and environmental factors, such as childhood diet or time spent in sedentary behaviors. Racial/ethnic disparities may be largely explained by socioeconomic circumstances and parental education.7

Cost of Obesity and Overweight

The direct health costs of childhood overweight can only be estimated, particularly since their major impact is likely to be felt in the next generation of adults.7 Adult obese patients are calculated to incur more health care costs than smokers or drinkers.40 Obesity appears to reduce life expectancy, particularly when occurring in young adults,41 and may soon exact the highest toll of all causes of preventable mortality.42 One recent study estimated that hospital costs for obesity-related disorders in children and adolescents have more than tripled in the last two decades, based in part on the doubling of child hospital episodes for obesity-related asthma, diabetes, sleep apnea, and gall bladder disease and on lengthened hospital stays for obese children.43 Preventing current or future excess costs associated with obesity may be difficult if third party reimbursement for evaluation and treatment remains limited,44 or if reimbursement hinges on the designation of overweight as a disease condition.

Condition Definition and Measurement

Defining obesity (excess body fat) in children is challenging. While gross obesity is obvious to all, differentiation of the mild case from the normal individual can be difficult, even for experts. Fatness forms a continuous spectrum from under-nutrition to “normal” fatness to gross obesity.45 There remains no universally accepted definition for obesity in children that differentiates those with normal or healthy fat from those in whom fatness is unhealthy.45 Epidemiological studies, obesity research, and clinical care of obese children have been hampered by this lack of clear and universally accepted diagnostic criteria.46 “Overweight” and “obesity” are used in the literature based on a wide variety of definitions referenced to “normal” values from various reference datasets.1 However, these values are not “norms,” but rather references for comparison of growth patterns to those of a larger population. Thus, such references are not standards that reflect health, risk, or disease states, but rather they describe the distribution in the population studied.

Assuming that excess fat is the cause of adverse health consequences in children, ideal obesity measures should measure adiposity (total body fat expressed as a percent of total body weight) using valid and reliable body composition measures.46 Body composition measurement in children is more complicated than in adults by virtue of developmental changes and normal variations in body composition between children due to sex, race/ethnicity, and other factors.4751 Clinically feasible, reliable, and acceptable measures of adiposity or body fat distribution are not currently available for children52, 53 (Appendix B). Instead, clinical measures of overweight based on height and weight are most commonly used (Appendix C).46, 54 BMI, measured as kilograms of weight divided by height in meters squared (kg/m2), is widely recommended by experts as a simple and convenient measure of overweight for use during childhood,55 particularly in adolescents.6, 9 As a proxy for obesity, however, BMI has some acknowledged limitations in accurately defining excess fat for all populations and individuals,10 including the inability to distinguish between increased relative weight due to fat-free mass from that due to fat.55, 56 This has particular implications for non-white children due to differences in body composition, such as greater fat-free mass due to heavier bones or more muscle, and differences in growth patterns in children of different racial/ethnic groups.50, 57

Nonetheless, BMI is currently the preferred measure of overweight in children and adolescents in the U.S. and around the world.58, 59 BMI has major advantages compared with other currently available clinical measures, including: 1) ease and reliability of measurement; 2) the most comprehensive base of normative data available for clinical measurement interpretation and for ongoing epidemiological surveillance; 3) correlating as well or better with direct measures of body fat than other competing clinical measures (e.g., triceps skinfold); 4) correlating as well or better with adult measures (tracking) than competing clinical measures (e.g., triceps skinfold, waist-to-hip ratio, Ponderal Index [weight/height cubed]); 5) sensitivity to behavioral or environmental changes (evidenced by recent population BMI increases); and 6) having the most comprehensive research base relating it to morbidity and mortality.

Typical BMI growth curves show increasing BMI levels up to about one year of age, followed by decreasing BMI levels to a nadir between ages three and seven (the “adiposity rebound” or more accurately, BMI rebound), followed by increasing BMI throughout childhood and adolescence.60 The slope and shape of BMI curves are sex-specific and the percentile ranking of absolute BMI values varies by age.61 Threshold BMI percentiles to define overweight have been proposed by expert consensus: BMI between the 85th and 95th percentiles for age and sex is considered at risk of overweight, while BMI at or above the 95th percentile is considered overweight (and by some authors, obese).8, 9

A critical question is under what circumstances these BMI cutoffs should serve as a clinical overweight standard (a measure that embodies a target)62 for individual children. An accurate determination in the individual child is needed if interventions based on BMI screening programs are to be considered.63

While a number of studies have found that BMI cutoffs at the upper end of the distribution are reasonably specific for classifying the fattest children,64, 65 this body of literature comprises studies using different BMI cutoff definitions and varying criterion measures of body fat, many of which are not directly comparable or are of questionable validity (Table B-1 in Appendix B).53, 63, 66 There is very little evidence on the sensitivity and specificity of BMI as a screening tool for overweight or obesity, using valid reference standards composed of large U.S. samples representing boys and girls of all ages and races, with the broad range of body composition that would be seen in clinical practice. Thus, researchers have focused instead on the validity of BMI cutpoints as a pragmatic measure of risk for adult overweight and as an indicator of future morbidity or mortality.15, 59

Prior USPSTF Recommendations

In 1996, the U.S. Preventive Services Task Force (USPSTF) recommended periodic measurement of height and weight for all patients (B recommendation).67 Comparison of height and weight measures against appropriate age and sex norms to determine further evaluation, intervention, or referral was recommended using BMI (> 85th percentile) in adolescents, and using weight and height (or length as appropriate) plotted on growth charts or compared to average weight tables for age, sex, and height in younger children. The USPSTF has not previously made separate recommendations about screening criteria or specific interventions for overweight or obesity in childhood populations. To assist the USPSTF in making its recommendation, the Oregon Evidence-based Practice Center undertook a systematic review of the evidence concerning screening and interventions for overweight in childhood populations. We combined the findings of prior fair- or good-quality68 systematic evidence reviews with fair- to good-quality studies not covered in these reviews or published subsequently.

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