A question hiding inside a map
Look at a map of childhood obesity rates in the United States, then look at a map showing where children are most likely to earn more than their parents. The two pictures line up uncomfortably well. The American South, for instance, has both some of the country’s highest rates of obesity among schoolchildren and some of its lowest rates of upward economic mobility.
Is that overlap a coincidence, or is childhood weight actually shaping the economic trajectories of the next generation? A new paper published in the Journal of Population Economics takes on that question directly. The researchers report that children who were obese in adolescence end up, on average, about 20 percentile points lower than their parents in the adult income distribution. They are also less likely to live in neighborhoods that offer strong economic opportunities.
The research team and the puzzle they wanted to solve
Economists have long studied the ingredients of intergenerational mobility, meaning whether adult children earn more, less, or about the same as their parents. Family structure, early education, and neighborhood quality are all known to matter. Childhood health has also been linked to adult earnings in past work, but no study had closely examined how childhood obesity specifically affects movement up or down the economic ladder.
Maoyong Fan of Ball State University, Yanhong Jin of Rutgers University, and Man Zhang of Renmin University of China set out to fill that gap. The central challenge is that simply comparing obese and non-obese children would mix cause and effect. Many of the same conditions that raise a child’s risk of obesity, including low family income, food environments, and neighborhood stress, also independently limit future earnings.
To separate the effect of obesity itself from these overlapping factors, the team turned to genetics. Each person carries tiny variations in their DNA called single nucleotide polymorphisms, or SNPs. Researchers can add up many weight-related SNPs into what is known as a polygenic score, a summary measure of a person’s genetic predisposition toward higher body weight.
Cleaning up a genetic tool
A simple polygenic score for body mass index, or BMI, is an imperfect instrument because some genes that influence weight also influence other traits, such as educational attainment or cognitive ability. This overlap, known as pleiotropy, can muddy the analysis: if genes that predict weight also predict schooling, it becomes impossible to tell whether obesity or education is driving the adult outcome.
The researchers built a refined version of the BMI polygenic score. They took the raw score and statistically removed the portions that overlapped with polygenic scores for educational attainment, intelligence, and cognitive function. What remained was a measure closely tied to BMI but essentially uncorrelated with genetic markers of schooling or cognition. The authors then verified that this cleaned-up score was still a strong predictor of childhood obesity.
Following thousands of lives across two decades
For the data, the team used the National Longitudinal Study of Adolescent to Adult Health, known as Add Health. This long-running survey began in 1994, when participants were in grades 7 through 12, and has followed them through five waves, most recently when they were between 33 and 43 years old. It includes information on weight, family income, neighborhoods, schooling, health, and jobs, along with genetic data for a large subset of participants.
The researchers linked Add Health to the Opportunity Atlas, a dataset developed by economist Raj Chetty and colleagues that measures economic opportunity at the census-tract level. The final sample consisted of 2,842 white participants, a restriction the authors made because the polygenic scores available in Add Health are based largely on genetic studies of people of European ancestry.
To track mobility, the team compared each adult child’s household income percentile in mid-career with their parents’ income percentile back in the 1990s. They also compared the neighborhood opportunities where participants grew up with those where they lived as adults, using three measures: average household income rank, the probability of reaching the top 20 percent of the income distribution, and the probability of living in a neighborhood with a poverty rate below 10 percent.
What the numbers showed
Using the refined genetic score as a stand-in for childhood obesity, the researchers found that obese children ended up roughly 20 percentile points lower than their parents in the adult income distribution, compared with their normal-weight peers. Children who had been overweight, a slightly broader category, ended up about 14 percentile points lower.
The neighborhood results showed a similar pattern. Childhood obesity was linked to a 5.4-percentage-point drop in the average income rank of the neighborhood participants lived in as adults, a 4.4-percentage-point drop in the probability of living in a top-20-percent-income area, and a 17.6-percentage-point drop in the probability of living in a low-poverty neighborhood.
The effects were not spread evenly. They were larger for girls, for children raised in the South and Midwest, and for children from families below the median income. For low-income families, childhood obesity was associated with roughly a 54 percent decline in intergenerational income mobility, compared with about 28 percent for higher-income families.
The pathways from weight to wages
The authors then examined how childhood obesity might translate into lower adult income. They identified several connected steps. Obese children were significantly less likely to earn a college degree and completed fewer years of schooling. They were more likely to be obese as adults, to report poorer health, and by mid-career to experience physical limitations and conditions such as sleep apnea.
In the labor market, childhood obesity was linked to lower odds of reaching median income levels for college-educated workers, higher reported experiences of weight-related mistreatment on the job, and sorting into lower-paying service occupations rather than higher-paying management, business, science, and arts roles. Geographic mobility, meaning how far or often people moved, did not appear to be a meaningful channel. The issue was not whether people moved, but the quality of neighborhoods they ended up in.
Implications and caveats
For policymakers and employers, the findings point to childhood health as a factor in the economic opportunity discussion, alongside schools, neighborhoods, and family income. The authors describe what they call an income-health feedback loop, in which low-income families face higher childhood obesity rates, and childhood obesity in turn is linked to lower adult incomes.
Several caveats apply. The study’s sample is limited to white participants because of how the genetic data were built, so the findings may not generalize to other groups. Income in the adult survey is reported in ranges rather than exact dollars. And while the genetic instrument addresses many sources of bias, it cannot rule out every possible unknown pathway linking genes to outcomes.
