Early human capital, the COVID-19 food-insecurity shock, and adult mental health: a 22-year cohort study in Ethiopia, India, and Peru

Mental health challenges often begin to take root before a person turns twenty-five, yet most of what we know about their origins comes from wealthy nations. In lower- and middle-income countries, where the majority of the world's young people live, the story is far less clear. Scientists have long understood that a child's early years shape their future. Just as a strong foundation supports a building, early nutrition and health build what experts call human capital—the physical and mental resources a person carries into adulthood. At the same time, we know that sudden, massive economic shocks, like a global pandemic, can tear at the fabric of daily life, causing immediate distress. What remains a mystery is how these two forces interact over decades. Does the strength built in infancy protect a young adult when a crisis hits years later? Or does the shock of a pandemic leave a mark that early advantages simply cannot erase?

A new study spanning twenty-two years in Ethiopia, India, and Peru seeks to answer these questions by following two groups of children from their first birthdays into their late twenties and late twenties. The researchers tracked the lives of thousands of individuals, measuring their growth as infants, their household conditions during the COVID-19 pandemic, and their mental health as adults. They wanted to see if the height a child achieved in their first year of life could predict their mental well-being decades later, and whether the food shortages many families faced during the pandemic would leave a lasting scar on their minds. The findings reveal a stark reality: while early physical growth is a powerful predictor of how tall an adult will be, it offers no shield against the mental health toll of a major economic crisis. Instead, the study shows that the hunger and worry experienced during the pandemic years continue to echo in the minds of young adults three to four years later, regardless of how well they were nourished as babies.

The research team, drawing on data from the Young Lives study, followed two birth cohorts: one group born around 2001 and another around 1994. By the time the study reached its final round in 2023 and 2024, the younger group was about twenty-two years old, and the older group was about twenty-nine. The scientists began by looking at the children's height-for-age z-scores from their first year of life. This measurement is a standard way to gauge early nutrition; a lower score indicates that a child was shorter than expected for their age, often due to poor diet or illness. The researchers checked if this early physical state predicted outcomes in adulthood, such as whether the person had a formal job with a written contract, how much schooling they completed, or their mental health.

The results were precise and clear regarding physical growth. A child who was taller than average for their age in infancy grew up to be taller as an adult. Specifically, for every standard deviation increase in height during infancy, the adult was about 1.6 centimeters taller. This confirms that early nutrition has a long reach into physical development. However, this early advantage did not translate into better mental health. The study found no link between how tall a child was as an infant and their levels of depression or anxiety as an adult. Similarly, early height did not predict whether a young adult would hold a formal job. The mental health of these young adults appeared to be governed by much more immediate circumstances than by the nutritional endowments of their infancy.

The story changed dramatically when the researchers looked at the pandemic. During the height of the COVID-19 crisis, the study team conducted phone surveys to ask families about their food security. They used a simple scale to measure how often households struggled to eat enough. The data showed that food insecurity was widespread, particularly in Ethiopia, where nearly one in five households reported moderate to severe hunger. When the researchers connected this pandemic-era hunger to the mental health scores measured three to four years later, a strong pattern emerged.

For every step up the scale of food insecurity—moving from "always eats enough" to "sometimes" or "often" does not eat enough—the level of depressive symptoms in adulthood increased significantly. The study calculated that each step on this scale raised the depression score by 0.41 points. In terms of probability, this shift meant that for every step up in food insecurity, the chance of a young adult having clinically relevant anxiety rose by 1.9 percentage points, and the chance of clinically relevant depression rose by 1.0 percentage point. These effects were robust, holding true even after the researchers accounted for other factors like the person's sex, their parents' education, and the number of shocks their family had faced over the years.

Crucially, the study tested the idea that early human capital might act as a buffer. The hypothesis was that a child who entered the pandemic with better health and nutrition might be more resilient to the stress of hunger. The data did not support this. The researchers found that early height-for-age did not moderate the impact of the food shock. Whether a person had been well-nourished as an infant or not, the link between pandemic hunger and adult mental distress remained the same. The "resilience" that early advantages might provide did not show up in these results. The gradient of distress traveled with the persistence of hardship; those who were hungry during the pandemic were more likely to be hungry as adults, and those who were distressed during the pandemic were more likely to be distressed years later.

The study also explored whether these effects varied by country or by the age at which the young people were hit by the crisis. The results suggested that the impact of food insecurity was not uniform. In India, the link between pandemic hunger and later depression was the strongest, while in Ethiopia, the link was essentially non-existent. In Peru, the effect was intermediate. Similarly, the researchers looked at the two birth cohorts. The older group, who were about twenty-six years old during the pandemic, showed a steeper rise in symptoms for every step of food insecurity compared to the younger group, who were about nineteen. However, the authors caution that these differences between countries and age groups are based on smaller numbers of participants and should be viewed as exploratory rather than definitive. They noted that the patterns were clear enough to be statistically significant but required further study to understand the specific cultural or economic reasons behind them.

The researchers were careful to rule out other explanations for their findings. They checked if the results were simply because people who were already struggling were more likely to drop out of the study over the twenty-two years. Using statistical methods to adjust for this possibility, they found that the link between pandemic hunger and adult mental health remained strong. They also examined whether the association was just a reflection of a person's general tendency to report both hardship and distress. By looking at the data from the pandemic period itself, they determined that while a stable personality trait might explain some of the connection, it could not account for the entire effect. The observed increase in symptoms was larger than what would be expected if it were just a matter of reporting style.

In the end, the study paints a picture of a generation whose mental well-being was shaped less by the nutrition they received as babies and more by the economic stability of their young adulthood. The pandemic food shock acted as a powerful force, leaving a legacy of anxiety and depression that persisted years after the crisis had technically ended. The findings suggest that in low- and middle-income countries, protecting household food security during times of aggregate shock is central to safeguarding the mental health of young adults. While early investments in child nutrition are vital for physical growth, they are not a substitute for economic security in adulthood. The mental health of a twenty-two-year-old in 2024 was deeply connected to whether their family had enough to eat in 2020, a connection that early advantages could not break.