Income Gradient in Children s Physical Activity: Diminished Returns in Black Families

Research Article

J Pediatr & Child Health Care. 2022; 7(1): 1052.

Income Gradient in Children’s Physical Activity: Diminished Returns in Black Families

Assari S1,2,3* and Najand B1

¹Marginalization-Related Diminished Returns (MDRs) Research Center, Charles R Drew University of Medicine and Science, Los Angeles, California, USA

²Department of Family Medicine, Charles R Drew University of Medicine and Science, Los Angeles, California, USA

²Department of Urban Public Health, Charles R Drew University of Medicine and Science, Los Angeles, California, USA

*Corresponding author: Shervin Assari, Marginalization-Related Diminished Returns (MDRs) Research Center, Charles R Drew University of Medicine and Science, 1731 E 120th St, Los Angeles, California, USA, Tel: 1-734-363-2678; Email: [email protected]

Received: January 05, 2022; Accepted: February 15, 2022; Published: February 22, 2022


Background: While socioeconomic status (SES) indicators, such as family income, are among the primary drivers of individual health behaviors, the effects of these indicators on health behaviors may be weaker for racial/ethnic minorities, as described by the Marginalization related Diminished Returns (MDRs) phenomenon.

Objectives: Built on the MDRs framework, this study used a national sample of 9 and 10 year old children with the following two aims: First, to test the association between household income and physical activity, and second, to test racial/ethnic variation in these associations.

Methods: This cross-sectional study used the Adolescent Brain Cognitive Development (ABCD) baseline data. Participants included 9358 individuals who were either Black or White. Age, sex, racial/ethnicity, family structure (parental marital status), and frequency of physical activity were measured. Linear regression was used for data analysis.

Results: Overall, high family income showed a positive association with physical activity in the overall population. We documented a statistically significant interaction between race/ethnicity and household income on frequency of physical activity, showing weaker effects of family income on children’s physical activity in Black than White families.

Conclusion: We observed that household SES indicators, such as family income, have a larger effect on increasing children’s physical activity in White than Black families. Due to the existing MDRs, defined as weaker effects of family SES for racial/ethnic minority than White families, Black children from high SES families engage in less healthy behaviors than their White counterparts. MDRs sustain racial/ethnic disparities across class and SES lines.

Keywords: Educational attainment, physical activity, exercise, socioeconomic status, population groups


Theory and empirical data provided by several scholars such as Marmot [1,2], Hayward [3-5], Link and Phelan [6], Ross and Miroswky [7-9], Lantz and House [10], Williams [11], Braveman [12], and others [13] have shown that socioeconomic status (SES) indicators such as family income promote population health and wellbeing. SES is one mechanism through which education and income exerts a positive impact on health, improving health behaviors such as physical activity and exercise [14-21]. Healthy behaviors such as physical activity lower the risk of obesity, diabetes, heart disease, and mortality [14,22,23].

Recently, the Marginalization-related Diminished Returns (MDRs) phenomenon [24,25] has indicated that SES effects tend to be weaker for racial/ethnic minorities than non-Latino White families [26,27], in part because racial/ethnic minorities are still segregated and their high SES does not provide the very same access to options and opportunities that can enhance healthy behaviors of diverse racial/ ethnic groups. In summary, MDRs [24,25] refer to racism-related weaker effects of educational attainment and household income on behavioral and health outcomes of racial/ethnic minorities than their non-Latino White counterparts [28-34]. Similar MDRs are shown for a variety of other indicators of health, including exercise, diet [27], smoking [35-39], obesity [40,41], heart disease [42], disability [43], chronic disease [44], hospitalization [45], mortality [46-49]. While stress, labor market discrimination, segregation, food access, neighborhood quality, and various aspects of the social environment are all potential mechanisms, one of the proximal mediators of the MDRs might be dietary behaviors. We expect that pro-health diet to be less influenced by educational attainment and income in racial/ ethnic minority families because they face many barriers in their lives given racism and social stratification [50-52]. In addition, because racial/ethnic minorities live in marginalized communities and are more likely to be under the influence of parents who had spent their childhood in poverty, their family SES may not have had large effects on their physical activity. Multiple scholars have described the MDRs phenomenon as a product of both race/ethnicity and SES. Kaufman has discussed the poor overlap between SES across racial/ ethnic groups that result in residual and unmeasured confounding as well as not-comparability of SES across racial/ethnic groups [53]. Navarro has described this as race/ethnicity and SES, rather than race/ethnicity or SES effects due to the complex interplay between race/ethnicity and SES [54-56]. Ceci has mentioned that the Have- Nots (ethnic minorities) may gain health less than the Haves (non- Latino Whites) from the same resources (SES indicators) due to their lower readiness to uptake and navigate the complex social systems [57]. Most recently, a study showed that SES indicators better reduce cardiometabolic risk of White than Black families [58].

However, most of the existing literature is on diminished returns of parental education and own education than other SES indicators such as household income. Thus, there is a need to study the MDRs of a wider range of SES indicators such as household income. To better understand whether MDRs observed in the ABCD data for brain outcomes [59-65] might be in part due to MDRs in health behaviors such as physical activity, we conducted a secondary analysis of the ABCD data to determine the association between household income and physical activity and variation in this effect by race/ethnicity. We hypothesize a positive association between household income and exercise of individuals. We, however, expect, built on the MDRs framework, that this positive association would be weaker for Black and Latino than non-Latino White children. As a result, we expect higher exercise of non-Latino White families with high SES than racial/ethnic minority families with similar SES, indicating a diminished effect of household income on exercise in Black and Latino families (due to access shaped by segregation). Then at least some of the MDRs in exercise and diet [26,27] would partially explain the MDRs in brain development [59-65].

Materials and Methods

Design and setting

This study is a secondary analysis of the first two years (waves 1 and 2) of data (2016/2018 to 2018/2020) of the Adolescent Brain Cognitive Development (ABCD) study [66-70]. The ABCD is a stateof- the-art and national longitudinal study of children’s development in the United States [66,71].

Sampling and participants

In the ABCD study, participating children were 9/10-yearold at the time of recruitment which was between 2016 and 2018. Recruitment occurred across 21 study sites in multiple cities across 15 US states in US. The primary recruitment strategy was through school systems [72]. The original/overall study included 10,875 children at baseline.

Eligibility and analytical sample

From the 10,875 participants, we included children at wave 1 who were either Latino or non-Latino White or Black. Race/ethnicity was based on parents’ reports. We did not include other racial/ethnic groups such as Asian, Native American, Mixed, Other, or unknown racial/ethnic groups. Participants were only included if they had data on SES, race/ethnicity, physical activity, and covariates (n=9358).

Study variables

Primary outcome: The ABCD study has used multiple measures of physical activity [73] including a three-item measure. The outcome in this variable was the frequency of physical activity and exercise. This variable was the average of the following three items: (1) During the past 7 days, on how many days were you physically active for a total of at least 60 minutes per day? (Add up all the time you spent in any kind of physical activity that increased your heart rate and made you breathe hard some of the time); (2) On how many of the past 7 days did you do exercises to strengthen or tone your muscles, such as push-ups, sit-ups, or weight lifting? and (3) In an average week when you are in school, on how many days do you go to physical education (PE) class? Response items for the first two questions were 0 = 0 days; 1 = 1 day; 2 = 2 days; 3 = 3 days; 4 = 4 days; 5 = 5 days; 6 = 6 days; 7 = 7 days. The response items for the last question were 0 = 0 days; 1 = 1 day; 2 = 2 days; 3 = 3 days; 4 = 4 days; 5 = 5 days. The total score ranged from 1 to 6. The measure was a quantitative score which showed a close to normal distribution. A higher score indicated more physical activity. This measure has acceptable validity and reliability and previously used in research [74].

Independent variable

Socioeconomic status: This study used household income as the SES indicator of interest. Household income was treated as a continuous measure. Annual family income had a range between 1 and 10 that referred to the following income levels: 1 = less than $5000; 2 = $5000; 3 = $12,000; 4 = $16,000; 5 = $25,000; 6 = $35,000; 7 = $50,000; 8 = $75,000; 9 = $100,000; 10 = $200,000+.


Race/Ethnicity: Race/ethnicity was composed of two categorical variables which were identified by the parents. All participants were non-Hispanic or Hispanic White or Black.


Demographic covariates included age, sex, and family structure. Parents reported the child’s age. Child age was a continuous variable calculated in months. The sex of the child was a dichotomous variable: 1 = male and 0 = female. Family structure was married or unmarried.

Data analysis

We used the SPSS 25.0 for data analysis. After ruling out multicollinearity between our variables and confirming a near to normal distribution of our outcome, we applied chi square and independent t test to compare race/ethnic groups for study variables. We used multivariable linear regression models with household income as the independent variable, physical activity as the outcome, and race/ethnicity as the moderator, and age, sex, and family structure. Overall, we ran four models. Model 1 and Model 2 were performed in the pooled sample. Model 1 did not include an interaction term but included all the confounders. Model 2, however, did include interaction terms between household income and race/ethnicity. All models also controlled for same confounders. Model 3 and Model 4 were run in Whites and Blacks, respectively. We reported the values b, SE, 95% CI, and p from our regression models.

Ethical considerations

This analysis was exempt from a full IRB review by Charles R Drew University of Medicine. The study of origin (ABCD) was approved by the Institutional Review Board (IRB) at the University of California, San Diego (UCSD). Assent and consent were received from children and their parents, respectively [71].


Overall, 9358 individuals entered this secondary analysis. Our participants were either White (n=7362) or Black (n=1996). Table 1 shows the summary of descriptive statistics overall and by race/ ethnicity.