Purpose. The study sought to determine if race/ethnicity, age, gender, and poverty index influence the development of overweight (OW) or obesity (OB) in children 6–11 years of age and whether a desirable time to intervene could be established.
Methods. A descriptive and comparative analysis was conducted using data from the 1999–2008 National Health and Nutrition Examination Survey.
Results. Advancing age was the single largest predictor of OW or OB followed by race/ethnicity.
Practice Implications. Culturally sensitive interventions targeting children in their early elementary school years could reduce the consequences of OW and OB in childhood.
Trends in overweight (OW) and obesity (OB) in U.S. children suggest the escalating problem of excess weight has now reached epidemic proportions (Ogden, Carroll, Curtin, Lamb, & Flegal, 2010). Data collected as a part of the National Health and Nutrition Examination Survey (NHANES) dating back to the 1980s provide a picture of an increasing prevalence of OW and OB among U.S. children and adolescents. More recently, the 2007–2008 NHANES revealed that 31.7% of 2- to 19-year-old U.S. children are at or have exceeded the 85th percentile for body mass index (BMI) based on age and sex, with 11.9% of these children meeting or exceeding the 97th percentile for BMI by age (Ogden et al., 2010).
To place these current numbers in context, it helps to examine the changes in OW and OB over time using the NHANES data. The NHANES revealed 10% of U.S. children and adolescents between 1988 and 1994 were OW or OB, and by 1999–2000 the number increased to more than 14% (Hedley et al., 2004). From 1999 to 2004, OW and OB rates were at 35% in the 2- to 19-year-old group (Hedley et al., 2004). By the 2003–2004 survey periods, OW among U.S. children was reported at 31.9%, with 16.9% falling into the obese category (Ogden, Carroll, & Flegal, 2008). In the NHANES data from 2007 to 2008, nearly one third of U.S. children were OW or OB using age- and sex-specific BMI (Ogden et al., 2010).
Children who live with OW or OB face shorter life expectancy and risk having a life of physical or emotional limitations (Daniels, 2006; Isomaa et al., 2001; Lederman et al., 2004; Molnar, 2004). The future outlook for children with unchecked OW or OB may be apparent in the rates of cardiovascular disease, stroke, and diabetes—conditions that contribute to morbidity and premature death across the life span (Robertson, Brunner, & Sheiham, 1999). Over the past 20 years, studies suggest that OW and OB in the U.S. general population parallels the rate of metabolic syndrome (Molnar, 2004), a condition that includes hyperinsulinemia/insulin resistance, hypertension, and dyslipedemia (Molnar, 2004). Metabolic syndrome is thought to be predictive of type-2 diabetes mellitus and cardiovascular disease (Isomaa et al., 2001; Speiser et al., 2005). In one longitudinal study, childhood OB, insulin resistance, and hypertension were associated with an increased risk of premature death (Franks et al., 2010). In addition, childhood OB has been associated with certain cancers, fatty liver disease, sleep apnea, asthma, joint disorders, and mental health issues (Barlow, 2007; Fennoy, 2010).
While the physical limitations of OW and OB are serious, equally concerning are the psychosocial alterations that may accompany the condition. As children live with OW and OB, levels of self-esteem suffer (Wang & Veugelers, 2008) and quality of life is adversely influenced (Williams, Wake, Hesketh, Maher, & Waters, 2005). Therefore, it may be useful to consider the factors that contribute to the epidemic of OW and OB.
Two common lifestyle behaviors—diets high in saturated fats and sugars, and too little physical activity—are implicated as factors contributing to OW and OB. Although poor diet and inactivity are modifiable risk factors (Mokdad, Marks, Stroup, & Geberding, 2004), changing behaviors to reduce the risk is difficult when parents and families of children who are OW or OB do not recognize the risk for their children (Hill & Wyatt, 2006; Rich et al., 2005). A study conducted by Etelson, Brand, Patrick, and Shirali (2003) found that only 10.5% of the 83 parents in their study perceived their OW child's weight accurately. In fact, some parents consider a baby healthy only when the baby is overweight, such as the Mexican American families who believe a fat baby is a healthy baby (Garcia, 2005).
Race/ethnicity may also contribute to higher risks of OW or OB in children. Race has traditionally been used to describe the shared biological characteristics of a population, such as skin color, genes, or other features. Ethnicity is typically used to categorize cultural characteristics, such as shared language, ancestry, religious traditions, dietary preferences, and history. The term race/ethnicity is used in this study, as race and ethnicity are classified together in the NHANES (Centers for Disease Control and Prevention [CDC], n.d.).
Healthy People 2010 identified OW and OB as a leading health indicator and called for interventions to address the problem in children and adolescents. The CDC reports that more than 54 million children attend schools every day in the United States. The fact that school attendance represents the single largest time commitment in the lives of children between 5 and 17 years of age makes addressing childhood OB in public schools opportune. Since 1987, the Division of Adolescent and School Health (DASH) Program of the CDC has provided programs that focused on instruction and demonstration of healthy behaviors in U.S. school systems through the Coordinated School Health Program (U.S. Department of Health and Human Services, 2010a). Despite efforts to reduce the proportion of children and adolescents who are overweight or obese, the United States has made little progress toward meeting the goal (Ogden & Carroll, 2010). Healthy People 2020 objectives for Early and Middle School populations call for a 10% improvement in the number of teachers with health and physical education preparation at the undergraduate or graduate level in school systems (U.S. Department of Health and Human Services, 2010b). Knowing where to focus the efforts of these additional resources may help improve long-term outcomes as students learn to change behaviors at an early age.
Children begin their formal school experience around the age of 6, when they are faced with academic and social learning opportunities and challenges. With so many hours spent in schools, the school plays an important role in the child's health and development both socially and academically (U.S. Department of Health and Human Services, 2010a). Consistent with the DASH position, educators and the National Association of School Boards of Education state that school academic achievement and health are interrelated (Wechsler, McKenna, Lee, & Dietz, 2004). Addressing OW and OB takes on greater importance as children begin their formal education because of the health implications and risks and the need for focused academic success. Providing a priori evidence to support the Healthy People 2020 recommendations is equally important in view of the need for efficient and effective school health practices.
According to Swinburn, Gill, and Kumanyika (2005), the groundswell of attention directed toward OB in U.S. media and health publications is a reflection of the nation's growing concern for OB-related illnesses. As a result of this intense attention, private and governmental agencies grasp for programs of prevention without taking time to test their effectiveness (Swinburn et al., 2005). An example of this rush to solve the OB epidemic can be seen in the initiatives included in the Child Nutrition and WIC Reauthorization Act of 2004. In this Act, schools were charged with the responsibility to establish healthy diets, nutrition education, and physical activity programs, yet no guidelines were offered for program development, monitoring, evaluation, or reporting (The Child Nutrition and WIC Reauthorization Act of 2004, S. 2507, 2004). Therefore, it is important to not only examine the problem of OW and OB in children, as we have done in the current study, but also to offer criteria that may contribute to the evidence needed to inform future studies and programs.
The purpose of the current study was to examine the prevalence of OW and OB of children in the 6- to 7-, 8- to 9-, and 10- to 11-year age ranges using NHANES data from 1999 to 2008. The study examined the variables of gender, age, race/ethnicity, and poverty index ratio (PIR) to discover patterns of OW and OB within and among the groups, and to determine whether or not the data point toward a definitive time period when changes in OW or OB are more evident and when interventions might be more effectively applied.
This study involved a retrospective, quantitative, cross-sectional analysis of the prevalence of OW and OB among children participating in the NHANES. As a cross-sectional analysis, the sample represents individuals who were selected and had assessments completed by trained professionals at a single point in time. The NHANES data for this study were not longitudinal data, and each of the children assessed by the NHANES staff represents one of the 4,583 individuals. The researchers proposed that by looking at these national trends over time, even though it is cross-sectional, there is knowledge to be gained. The NHANES data are drawn using a complex, multistage probability sample of the U.S. civilian, noninstitutionalized population (CDC, n.d.). The sample for this study was drawn from the total population of 6- to 11-year-old children with only those of Mexican American, non-Hispanic Black, and non-Hispanic White ethnicity enrolled. Furthermore, the sample excluded all cases where any of the key variables were missing data.
The NHANES (http://www.cdc.gov/nhanes/) is an ongoing study that began in 1999 and currently has more than 30,000 participants. For the current study, the sample was drawn from the data in the 2-year interval, continuous ongoing survey periods, collected between 1999 and 2008. Included in the sample are data from the examination of 4,583 children between the ages of 6 and 11 years. The data from each of the 2-year survey intervals were merged into one file, with sample weights calculated according to NHANES published procedures (CDC, n.d.). These procedures were followed for analysis.
As a part of the NHANES procedures, assent and consent were obtained from participants/their guardians by the NHANES examiners, and there was no personal identifiable information on any of the 4,583 cases included in the sample population for the current study. Human subjects institutional review board approval was obtained for this study using secondary data.
The measure for determining OW or OB using the NHANES in the current study was the BMI, calculated using the formula: height (m2)/weight (kg). The BMI age and gender-specific cutoff values recommended by the International Obesity Task Force (IOTF; Cole, Bellizzi, Flegal, & Dietz, 2000) were used for defining OW and OB (see Table 1). The OW and OB categories are mutually exclusive categories, so each child with a BMI level that exceeded the cutoff point for age and gender was classified either as OW or OB. To calculate the percentage of OW and OB, the relevant population total was used as the denominator. While the term OB is under debate as a potential stigmatizing label for children who are OB (Hill & Wyatt, 2006), it is the recognized definition from the IOTF and was used in this study.
Table 1. International Obesity Task Force Cutoff Values for Body Mass Index (BMI) Classifying Overweight and Obesity by Gender and Age
Overweight is defined as BMI greater than the number shown below but less than the cutoff value for obese:
Obese is defined as BMI greater than:
Note: Data from the International Obesity Task Force cutoff values for obesity and overweight (Cole et al., 2000).
Once the age- and sex-specific BMI levels for OW and OB were identified, all other cases fell into the normal or underweight category, and the three-level variable was labeled BMI Status. The independent variables were race/ethnicity, gender, PIR, and age. Gender was categorized as male or female, and race/ethnicity as Mexican American, non-Hispanic Black, and non-Hispanic White. Poverty level was determined using the PIR, which was formed into a dichotomous variable for less than or equal to 1.0 for children of families living at or below poverty level and greater than 1.0 for those living above poverty level. Because of the small sample size within the other racial/ethnic groups, only the Mexican American, non-Hispanic Black, and non-Hispanic White populations were included in the analysis.
An earlier study of NHANES data, conducted by Ogden et al. (2006), reported limitations in analysis by age within the 6- to 11-year age groups because of the small sample size when race and gender were considered. For this reason, the researchers chose to group the children by 2-year age intervals, thereby increasing the sample size for each of the three age groups: 6–7 years, 8–9 years, and 10–11 years. This process resulted in a cross-sectional view of children between 6 and 11 years of age from 1999 to 2008.
SPSS, Version 16.0 with Complex Samples Add-On (SPSS Inc., Chicago, IL, USA) was used to examine frequencies for OW and OB within race/ethnic groups, gender, poverty levels, and 2-year age groups. Univariate, descriptive analysis was undertaken to examine the key variables with BMI status (normal, OW, and OB), race/ethnicity (three groups), age groups (three levels), and PIR (two levels). Gender was included as a dichotomous variable. Chi-square testing was used to assess whether race/ethnicity, age groups, gender, or PIR affected the BMI status of children in the study. Multilevel frequency distributions were conducted in addition to cross tabulations to obtain percentages using the 2-year age groups and BMI status. The use of percentages in this study forms the basis of the quantitative analysis bringing to light the trends across the survey periods and providing a means to describe the problem of OB and OW in relationship to this cross-sectional study.
Of the 4,583 children 6–11 years of age included in the study, unweighted counts and percentages for gender, age groups, race/ethnicity, and PIR are reported in Table 2. Race/ethnicity data reflect the oversampling of Mexican American and non-Hispanic Black children in the NHANES. Chi-square results showed that PIR was not a significant predictor ([2, n= 4,583]= 1.0443, p= .5932) of the outcome variable, so PIR was eliminated from the analysis model and was used as a descriptor forthe sample. The effect of gender on BMI status approached significance (p= .06), with the variables of race/ethnicity and age groups strongly significant (p < .01).
Table 2. 1999–2008 National Health and Nutrition Examination Survey 6- to 11-Year-Old Sample Demographics
The sample size of 4,583 includes only data for the three major racial/ethnic groups used for analysis in this study. Excluded from the n are cases with missing data and other racial/ethnic groups.
b Rounded to the next tenth.
6- to 7-year-olds
8- to 9-year-olds
10- to 11-year-olds
Family poverty level
Poverty level or below
Above poverty level
The percentages of OW and OB were examined across the five survey periods (10 years). Data displayed in Figure 1 reflect a statistically significant BMI increase (p < .01) across the three 2-year age groups. Significantly lower BMIs were found in the 6- to 7-year age group (p < .01) in comparison to the 10- to 11-year age group. Over the 10 years of the NHANES study, trends revealed a significant climb in percentages of children who were OW in the 6- to 7-year age groups, leveling off by 2005–2006 and in 2007–2008. The 10- to 11-year age groups remained high until after 2004 where the percentages decreased. All age groups decreased equally over the 2 years after the 2004 survey period. In the OB category, all age groups were similar in percentages of OB in the 1999–2000 survey period, but dramatic increases were evident in the 10- to 11-year age group until the survey period of 2003–2004, after which, 10- to 11-year-old percentages of OB decreased. On the other hand, children in the younger age groups demonstrated decreasing percentages until after the 2004 survey period, where the two groups showed increases in percentages of OB, although the 8- to 9-year-olds' rate of increase was greater than that of the youngest group.
Examining the percentages of the three age groups by survey year using Figure 1 shows the relationship between the 6- to 7- and 8- to 9-year age groups in both the OW and OB categories. While the 10- to 11-year age group has a similar pattern in OW, with OB, the 10- to 11-year-old group deviated from the younger two groups. Examining the percentages of OW and OB by 2-year age group, gender, and race/ethnicity provides a more in-depth look at the trends. Across gender and race/ethnicity, the percentage of OW and OB was lowest in the 6- to 7-year age group, followed by subsequent increase in both the 8- to 9-year age group and 10- to 11-year age group (see Table 3).
Table 3. Percent OW and OB by 2-Year Age Group, Gender, and Race/Ethnicity
Age groupings and gender
Mexican American (n= 1,579)
Non-Hispanic Black (n= 1,566)
Non-Hispanic White (n= 1,438)
Note: OW, overweight—meets the IOTF cutoff points for body mass index 25 kg/m2; OB, obese—meets the IOTF cutoff points for body mass index 30 kg/m2; IOTF, International Obesity Task Force.
6- to 7-year-olds
8- to 9-year-olds
10- to 11-year-olds
The 6- to 7-year age group had the lowest total percentage in almost all areas. Within the 6- to 7-year age group, the highest percentages of OW (18.7) and OB (18.1) were among Mexican American males. Of the females, the non-Hispanic Black females were highest in percentage of OW (20.5), whereas the Mexican American females were highest in percent OB (16.2). The non-Hispanic Black males were lowest in OW (9.6), whereas the non-Hispanic White males were lowest in percent OB (8.2; see Table 3).
Examination of children in the 8- to 9-year age group revealed little difference in the Mexican American males' BMI status percentage (21.6 and 21.0), but the non-Hispanic Black percent OW doubled over the early age group. Additionally, percentages of OW and OB in non-Hispanic White males increased significantly (p < .01) over the younger age group as did the percentages of OW and OB for females in both non-Hispanic White and non-Hispanic Black groups. The percentage of 8- to 9-year-old Mexican American females in the OW category paralleled that of the non-Hispanic White females.
In the 10- to 11-year age groups, across all race/ethnicities, Mexican American males were the highest in percent OW (28.7) and non-Hispanic White males lowest in OW (20.5) and OB (12.9). Mexican American and non-Hispanic Black females had higher percentages of OW and OB as compared with non-Hispanic White females. The highest OW percentages in the age group among the females were in the Mexican American females with 28% OW. The highest percentages of OB among females occurred in the non-Hispanic Black females with 25.6%. All three racial/ethnic groups in the 10- to 11-year age groups had higher percentages of OW and OB compared with their younger counterparts.
The results of these analyses of NHANES cross-sectional data indicate that OW and OB is a concern for males and females of all age groups, gender, and race/ethnicities considered in this study. While the youngest children (6–7 years old) had the lowest percentages of OW or OB, the combined percentages were staggering even in this young group. Race/ethnicity and class or PIR have been implicated in studies examining the problem of childhood OB in the past, but in this study, only race/ethnicity, age, and, to a lesser degree, gender were significant. Although the work of other investigators have found that social class plays a role in childhood OB (O'Dea, 2003, 2008), the comparable variable used in this study was PIR, and it was not found to be a significant factor contributing to BMI status in the 6- to 11-years 2-year age groups.
The percentages of OW and OB increased among the older age groups (8–11 years old), being most prevalent among Mexican American males and non-Hispanic Black females. By the 10- to 11-year age groups, non-Hispanic Black females had the highest percentage of OB, while the Mexican American females had the highest rate of OW across all 2-year age groups. These findings support the work of Caprio and colleagues (2008) and O'Dea (2008), indicating there is a need to consider race/ethnicity in tailoring behavioral interventions.
Although the findings in this study indicate that OW and OB are problems for children in all of the age groups under consideration, clear differences were seen by age. A similar study of OW using NHANES 1999–2004 data by Ogden and colleagues (2006) was consistent with these findings in suggesting that differences by racial/ethnic groups existed for both genders in the child and adolescent groups, and the increase in OW occurred across all ages from childhood to adolescence. The present study found Mexican American males and non-Hispanic Black females had the highest levels of OW and OB, supporting Ogden and colleagues' findings. In a study by Ogden and colleagues, differences in point estimates appeared larger in some subgroups and were considered less precise because of the smaller sample size when the subgroups were considered. To address the issues of sample size, this study attempted to increase the subgroup size by creating 2-year age groupings, thus effectively doubling the available population for each group.
Other studies have suggested that BMI may vary by race/ethnicity with non-Hispanic Black and Mexican Americans or Hispanics having a greater risk for OW and OB than the non-Hispanic White population. The current study concurs with these findings in general and additionally suggests that there are increases in OW and OB with age across all gender and racial/ethnic groupings. This suggests that early intervention, especially in the 6- to 7-year age range, may be helpful in preventing weight gain as age increases. These collective findings indicate a need to examine weight-related indicators in conjunction with considerations of race/ethnicity or culture (Wang & Wang, 2002).
Other issues may be associated with increased rates of OW and OB among children in the 6- to 11-year age group. Children in this age group are beginning their bodies' pubertal transformation, and it is possible that the mean age of puberty is changing. Either boys or girls may experience early pubertal changes, and those who do mature early are more prone to adiposity (Kindblom et al., 2006; Klump, Perkins, Burt, McGue, & Iacono, 2007). Children who reach puberty early may also be less likely to exercise or become active in sports activities; thus, further increases in percentage of OW may be expected in this young-maturing group (Davison, Werder, Trost, Baker, & Birch, 2007). A study of 1,239 girls in the United States concluded that the proportion of girls who had breast development at ages 7 and 8 was greater than girls born 10–30 years earlier (Biro et al., 2010). It would be helpful to examine age of menses in girls to determine if this early development may contribute to OW or OB.
This study was limited to the variables for race/ethnicity, age, PIR, and gender and, as such, may not include other variables that also contribute to OW and OB. Consideration of class or socioeconomic factors independent of PIR might provide further insight for the prevalence of OW and OB as other authors have postulated (O'Dea, 2008). The current study offers a closer look at the 6- to 11-year age group; the size of the sample, although enlarged with the use of the 2-year grouping by age, could still be improved if additional years of survey data are added in for trending by race/ethnicity, gender, and age.
Despite limitations, the current study offers an analysis of a large representative sample of more than 4,500 children ages 6–11 years. The study not only addresses the differences by age but also examines the differences by race/ethnicity. These data are particularly important because childhood OB is more prevalent in racial and ethnic minority groups, some of whom do not have adequate access to health education and services (ASPE, 2010). Additionally, when considering the trends over the five survey periods, the 2004 survey period appears to be a point where a downward trend began across the groups, particularly in the OW category for all children but also more noticeably in the OB category for the 10- to 11-year olds, which may be a hopeful sign that the legislation requiring schools to address the problem of OW and OB has had a desired impact (The Child Nutrition and WIC Reauthorization Act of 2004, S. 2507, 2004).
The results of this study support the literature showing varying degrees of OB and OW among different groups of children (Strauss & Pollack, 2001). The findings also point to early chronic illness risks for children who are OW or OB (Molnar, 2004) and must be considered if the epidemic of OW is to be countered with healthy lifestyle changes. When children are exposed to unhealthy lifestyles, supported by powerful media campaigns for products that increase their risk, counter campaigns must be just as powerful. Biological factors, behavior, and environment are interwoven complexities that affect the healthy weight of children and must be considered if the epidemic of OW is to be countered with healthy lifestyle changes (Brantley, Myers, & Roy, 2005; Huang & Goran, 2003; Lewis et al., 2006).
How might this information affect nursing practice?
The evidence from this study can serve as an alert to nurses caring for pediatric clients because OW and OB are becoming a serious healthcare emergency in the United States. Pediatric nurses can seize the opportunity to take the lead in preventing OW and OB in school-age children especially by focusing interventions with 6- to 7-year-olds as they enter elementary school.
School nurses are well prepared to be educators, advocates for clients, and collaborate with other healthcare professionals in preventing OW and OB among school-age children. The school system is home for many hours of the day for children, and approximately 70% of published school programs addressing OB are documented as effective (Doak, Visscher, Renders, & Seidell, 2006). Direct instruction and role modeling by school nurses or teachers about healthy eating and exercise could become a more prominent part of the general curriculum.
Public health and community nurses are positioned to serve in roles of educators, collaborators, and they can influence policy. Because there was a higher incidence of OW and OB among Mexican American and non-Hispanic Black children than non-Hispanic White children, race and ethnicity versus culture must be considered in planned interventions. Special cultural approaches need to be focused on the cultural uniqueness of each racial/ethnic group and on age- and gender-specific approaches targeting children in the 6- to 7-year age groups for prevention, and the 10- to 11-year age groups for healthy lifestyle and healthy weights. Knowing when to concentrate the resources to develop intensive interventions could benefit children of all racial and ethnic groups, and this study suggests the earlier the better.