We all know that hunger is a problem in America, but it can be difficult for many of us to fully grasp its effects, especially when it comes to children.

Almost 50 million Americans are food insecure, and 15 million of them are children. Technically, the term “food insecure” means lacking adequate access to a sufficient and healthy diet. While that doesn’t always translate directly to simple hunger, it does mean that parents are often unsure of the source of their children’s next meal.

Food insecurity is not good for anyone’s health, but scientists are finding that the impacts on children can be particularly harsh. A new study published in the journal Health Affairs using data gathered during the Great Recession (December 2007 to June 2009) suggests that young children who didn’t have access to enough food during this time were significantly affected—in ways that can have lasting impacts.

In their study, Rice University sociologists Rachel Kimbro and Justin Denney examined the impacts of food insecurity on kindergartners and first graders and found that food insecure children had increased behavioral problems and worse overall health than those from families where food was plentiful. These results, Kimbro and Denney report, “are troubling.”

So are the statistics. During this period, food insecurity spiked, reaching the highest levels ever recorded—21 percent—in 2009. But things haven’t improved radically since then. Just last year, that number remained at 19 percent for households with children.

The health impacts of hunger on kids are dramatic. Food insecure children are twice as likely to experience health problems overall, nearly one and a half times more likely to have asthma, and more likely to have iron-deficiency anemia (which can affect children’s motor skills) and developmental delays. They also experience more headaches, stomach aches, and colds.

Poor nutrition can also increase children’s sensitivity to environmental toxins— contaminants like lead and air pollution which impact learning ability.

All of this obviously means increased healthcare costs, says Deborah Frank, Boston School of Medicine professor of pediatrics and director of Boston Medical Center’s Grow Clinic for Children and principal investigator of Children’s Health Watch. And, she says, “The younger the child, the more likely the family is to be food insecure.” That, she adds, is “really terrifying because the developing brain is particularly sensitive in the first thousand days of life.”

When Food Becomes Scarce

Kimbro and Denney’s study looked specifically at what happens to young children when their households stopped having enough food. They found that on top of a lack of adequate calories and nutrition, the shift itself also created household stress, which had profound impacts on children’s health and well-being.

“We found consistent negative impacts of the transitions on teachers’ reports of children’s externalizing behaviors, self-control, and interpersonal skills and on parents’ reports of children’s overall health status,” wrote Kimbro and Denney in their study.

“One of the things that surprised us is that we expected similar outcomes with kids who were food insecure in both kindergarten and first grade and those who transitioned into food insecurity,” Kimbro told Civil Eats. But it turns out the latter group—those who were jolted by the shift—“were more at risk and even worse off than kids who were insecure at both time points.”

University of California San Francisco associate professor of Medicine and of Epidemiology and Biostatistics Hilary Seligman explains that food insecurity affects children’s behavior through “three different pathways.” One is the shift to a lower quality diet, which has obvious health implications, particularly obesity and chronic diseases like diabetes. Another is by changing eating behaviors, something that can have life-long impacts on both physical and mental health.