Study Links Changes in Kids’ Sleep, Cortisol to Community Violence

Violent crimes disrupt the sleep patterns of children who live near the incident, which increases cortisol (the stress hormone) in their bodies the next day, according to a new study.

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Sleep disruption and increased cortisol have demonstrated a negative impact on academic performance.

“Both sleep and cortisol are connected to the ability to learn and perform academic tasks,” said lead study author Jennifer Heissel, who recently received her Ph.D. in human development and social policy from Northwestern University.

“Past research has found a link between violent crimes and performance on tests, but researchers haven’t been able to say why crime affects academic performance,” she added. “Our study identifies a pathway by which violent crime may get under the skin to affect academic performance.”

Northwestern researchers, along with colleagues at DePaul and New York universities, studied the sleep patterns and cortisol levels of 82 children, ages 11-18, in a large Midwestern city who attended racially, ethnically and socioeconomically diverse public schools.

Researchers declined to identify the city, citing a confidentiality agreement they made with school officials, but did say the crime rate in this large Midwestern city was higher than the national average.

Students wore activity-tracking watches that measured sleep and had their saliva tested three times a day to check their cortisol levels: twice in the morning and once before they went to sleep.

“Cortisol naturally has a spike when you wake up,” Heissel said. “When you fall asleep, you hit your lowest level of cortisol and it builds up overnight and accumulates. When you wake up – to get you over that sleep hurdle – you have a big jump in cortisol. That’s normal. That’s supposed to happen.”

Researchers also collected information on violent crimes reported to the police during the study, as well as which students had violent crimes occurring in their neighborhoods.

Students’ sleep on nights when a violent crime occurred near their homes was compared to nights when no such incidents took place. Researchers also compared students’ cortisol levels on the day after a violent crime to days when no crimes occurred in the vicinity.

The study found children went to sleep later on the nights violent crimes occurred near their homes. The following morning, cortisol levels were higher in students than on days when no violent crimes occurred nearby.

The above normal cortisol levels “were a sign that they might be anticipating a stressful day,” Heissel said. “For instance, cortisol can be good if it helps you concentrate on a big test coming up. The problem is if kids are over-activated or stressed about the wrong things. ... It’s hard to study in school or take an academic test or listen to the teacher if you’re all amped up.”

Researchers found changes in sleep and cortisol levels were largest when a homicide was committed and nonexistent for robberies. 

“The results of our research have several implications for policy,” said study co-author Emma Adam, professor of human development and social policy at Northwestern University, in a statement. “They provide a link between violent crime and several mechanisms known to affect cognitive performance. 

“They also may help explain why some low-income youth living in high-risk neighborhoods sleep less than higher-income youth. And they suggest that although programs to reduce violent crime may be the best policy solution, schools could also provide students with programs or methods to cope with their response to stressful events like nearby violent crimes.”

Given the small size of the study, Heissel recommends larger studies be conducted to confirm the study’s findings.

“We think of this as a first insight into a potential mechanism connecting how community violence affects academic performance,” she said. “It’s more of a call to action for future research.”

Follow Kristen Thometz on Twitter: @kristenthometz

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