Ethnic disparities in adolescent body mass index in the United States: The role of parental socioeconomic status and economic contextual factors

Abstract

This paper examined the importance of household and economic contextual factors as determinants of ethnic disparities in adolescent body mass index (BMI). Individual-level data from the National Longitudinal Survey of Youth 1997 for the years 1997 through 2000 were combined with economic contextual data on food prices, outlet density and median household income. The Oaxaca–Blinder decomposition method was used to examine the factors that could help explain ethnic disparities in BMI. Ethnic differences in household demographic, parental socioeconomic status (SES), and economic contextual factors explained the majority of the male black–white (63%), male Hispanic–white (78%) and female Hispanic–white (62%) BMI gaps but less than one-half of the female black–white BMI gap (44%). We found that adding the economic contextual factors increased the explained portion of the ethnic BMI gap for both female and male adolescents: the economic contextual factors explained 28% and 38% of the black–white and Hispanic–white BMI gaps for males and 13% and 8% of the black–white and Hispanic–white BMI gaps for females, respectively. Parental SES was more important in explaining the Hispanic–white BMI gap than the black–white BMI gap for both genders, whereas neighborhood economic contextual factors were more important in explaining the male BMI gap than the female BMI gap for both black–white and Hispanic–white ethnic disparities. A significantly large portion of the ethnic BMI gap, however, remained unexplained between black and white female adolescents.

Introduction

In the United States, black and Hispanic adolescents are more prone to obesity as measured by age-gender adjusted body mass index (BMI) than their white counterparts. In 2007–2008, obesity prevalence among U.S. non-Hispanic white, non-Hispanic black and Hispanic adolescents, respectively, was 14.5%, 29.2% and 17.5% for females and 16.7%, 19.8% and 25.5% for males (Ogden, Carroll, Curtin, Lamb, & Flegal, 2010). This implies that the rates of obesity among black adolescents were approximately 100% higher among females and almost 20% higher among males compared to white adolescents. Among Hispanic adolescents, the obesity rates were approximately 20% higher among females and approximately 52% higher among males when compared to white adolescents. The ethnic disparity in adolescent obesity is a major source of concern for public health given that childhood obesity tracks into adulthood (Freedman et al., 2005) and obesity is associated with long-term negative health and labor market outcomes later in life (Han et al., 2009, USDHHS, 2001). The underlying causes of the ethnic disparities in obesity in the United States remain poorly understood although many previous studies have examined the related questions (Wang & Beydoun, 2007).

Disparities in household demographic and socioeconomic status (SES) characteristics are potential sources for the ethnic BMI gap. For example, in 2008, median household income among whites, blacks and Hispanics was $65,000, $39,879, and $40,466, respectively, and college degree attainment was similarly diverse at 29.9%, 19.3%, and 13.2%, respectively (U.S. Census Bureau, 2011b). The percentage of children living in poverty also differed substantially at 15.3%, 34.4% and 30.3% and the percentage living in families with female heads of household with no spouse present was 18.3%, 57.0% and 27.9%, respectively, for whites, blacks and Hispanics (U.S. Census Bureau, 2011a, U.S. Census Bureau, 2011b).

Associations between demographic characteristics such as ethnicity and family SES and obesity in U.S. children and adolescents have been described as important but complex (Beydoun and Wang, 2007, Gordon-Larsen et al., 2003, Shrewsbury and Wardle, 2008, Sobal and Stunkard, 1989, Wang et al., 2002, Wang and Zhang, 2006). For example, analyses of the National Health and Nutrition Examination Surveys (NHANES) data collected between 1971 and 2002 showed that not all sex-ethnic child groups from low-income families were at increased risk of being overweight or obese and an overall trend of a weakening association between family income and childhood obesity over time was observed (Wang & Zhang, 2006). Reviews of the literature reported that the association between obesity status and SES was weaker for children than for adults, and that the association was even weaker for children of ethnic minorities (McLaren, 2007, Sobal and Stunkard, 1989).

Data on U.S. adolescents (grades 7 through 12) enrolled in a nationally representative study of adolescent health showed a link between ethnic disparities in the prevalence of overweight and the ethnic disparities in family income and parental education, especially for girls (Gordon-Larsen, Adair & Popkin, 2003). The study showed that the racial/ethnic variation in overweight remained even when children had similar SES based on simulation analysis. Overall, these studies suggest that external factors outside of the household, such as economic and social environmental factors may have contributed significantly to the ethnic body weight disparities.

Recent studies showed that environmental or contextual factors were important determinants of adolescent obesity in addition to the influence of household characteristics in the United States (Auld and Powell, 2009, Chou et al., 2008, Powell, 2009). Further, neighborhoods with higher concentrations of low-income and/or ethnic minority populations were more likely to be obesogenic with higher concentrations of fast food restaurants and convenience stores and lower availability of supermarkets and physical activity-related facilities (Gordon-Larsen et al., 2006, Larson et al., 2009, Powell et al., 2006).

Several previous studies have contributed to our understanding of the extent to which both individual-level SES and the SES of the neighborhood contribute to the ethnic BMI gap among adults. Two recent studies both found that simultaneously controlling for individual-level SES, neighborhood SES and neighborhood racial composition was moderately important in reducing the adult black–white BMI difference (Boardman et al., 2005, Robert and Reither, 2004), particularly for women (Robert & Reither, 2004). However, similar contextual factors were found to be less important in another study that found that neighborhood SES and racial composition measures were associated with BMI outcomes but controlling for them did not reduce the ethnic BMI gap (Do et al., 2007). In a recent study that examined children, local area economic contextual factors such as food prices, food store and restaurant availability, and median household income were shown to be able to account for a significant part of the black–white BMI disparity (Powell & Chaloupka, 2011). Another recent study examined the importance of mothers’ perceptions of neighborhood safety as a possible explanation for ethnic differences in children’s BMI and reported that perceived police protection accounted for 12% of the explained black–white BMI gap and 15% of the explained Hispanic–white gap (Sen, Mennemeyer, & Gary, 2011).

Thus, previous studies have documented differential associations of parental SES with youths’ weight outcomes by ethnicity and suggest that despite differences in endowments of SES, differences in risk of overweight persist. Further, previous research on adults suggested that neighborhood SES contributed to part of the ethnic differences in weight although significant differences persisted. Indeed, given that black and Hispanic adolescents are more often in households with lower SES and at the same time more often surrounded by less healthy environments than their white counterparts, it is important to simultaneously determine the contribution of such environments toward the ethnic disparities in adolescent obesity.

We built on the previous research by simultaneously examining the importance of household-level SES, local area SES, and contextual factors related to the cost and availability of food and the availability of physical activity-related facilities as contributors to the ethnic BMI gap. This paper used the Oaxaca–Blinder decomposition method to systematically examine the degree to which the observed ethnic disparities in U.S. adolescent BMI were due to household demographic, parental SES, and economic contextual factors, including food prices, the availability of food stores, restaurants, commercial physical activity-related facilities, and median household income. Evidence linking ethnic disparities in contextual factors to ethnic disparities in adolescent obesity is of major interest to policymakers because changes to such external factors could serve as policy instruments for reducing such disparities in public health.