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Study explains link between academic performance and violence

Sleep disruption following violent incidents and increased levels of cortisol affect ability to learn

EVANSTON - Numerous studies have shown a relationship between high-crime communities and the academic performance of children who live within them. 

Now, new Northwestern University research suggests sleep disruption following violent incidents and increased amounts of the stress hormone cortisol offer a biological explanation for why children who live in neighborhoods with higher rates of violent crime struggle more in school.  

“Both sleep and cortisol are connected to the ability to learn and perform academic tasks,” said study lead author Jenni Heissel, who recently received her Ph.D. in human development and social policy from the School of Education and Social Policy. “Our study identifies a pathway by which violent crime may get under the skin to affect academic performance.”

The study, conducted by researchers at Northwestern, New York University and DePaul University, found violent crime changes the sleep patterns of children living nearby, which increases the amount of cortisol, the stress hormone, in the children’s bodies the day immediately following the violent incident. Both sleep disruption and increased cortisol have demonstrated a negative impact on academic performance.

“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,” Heissel said. 

Researchers tracked the sleep and stress hormones of 82 young people, ages 11 to 18, in a large Midwestern city who attended racially, ethnically and socioeconomically diverse public schools.

The students filled out daily diaries over four days, wore activity-tracking watches that measured sleep and had their saliva tested three times a day to check for cortisol. Researchers also collected information on violent crimes reported to police in the city during the study, including which students had violent crimes occur in their neighborhoods. 

Researchers compared the students’ sleep on nights following a violent crime to their sleep on nights when there were no violent crimes committed nearby. They also compared students’ cortisol on days following a violent crime to their stress hormones on days when there were no violent crimes committed nearby.

Among the findings: Students went to sleep later on nights when a violent crime occurred near their home, often resulting in fewer total hours of sleep. In addition, the increase in youth’s cortisol levels the morning after a nearby crime occurred the day before was larger than on mornings following no crime the previous day, a pattern that previous research suggests might reflect the body’s anticipation of more stress the day following a crime. The changes in sleep and cortisol were largest when the crime committed the previous day was homicide, they were moderate for assault and sexual assault and nonexistent for robbery.

“The results of our research have several implications for policy,” suggested study co-author Emma Adam, professor of human development and social policy at SESP. 

“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.”

The study was supported by Northwestern’s Institute for Policy Research and the National Institutes of Health.

The study was published in Child Development under the title Violence and Vigilance: The Acute Effects of Community Violent Crime on Sleep and Cortisol by Heissel, JA (Northwestern University), Sharkey, PT (New York University), Torrats-Espinosa, G (New York University), Grant, K (DePaul University) and Adam, EK (Northwestern University).

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