CHICAGO, Aug. 29 (Xinhua) -- A new study found that violent crime changes youth's sleep patterns immediately following the crime and changes patterns of the stress hormone cortisol the following day.
Researchers at Northwestern University (NU), New York University, and DePaul University came to the conclusion after studying that both the situations may disrupt academic performance of students.
The study has been published in the latest issue of the journal Child Development.
Researchers tracked the sleep and stress hormones of 82 youth aged 11 to 18 in a large Midwestern city who attended public schools that were racially, ethnically, and socioeconomically diverse.
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 all the violent crimes reported to the police in the city during the study, including which youth had a violent crime occur in his or her neighborhood.
For each youth, researchers compared the students' sleep on the nights following a violent crime to their sleep on nights when there were no violent crimes committed nearby.
They also compared students' stress hormones (cortisol) on days following a violent crime to their stress hormones on days when there were no violent crimes committed nearby.
Findings are: Youth went to sleep later on nights when a violent crime occurred near their home, often resulting in fewer total hours of sleep.
Besides, the increase in youth's cortisol levels the morning after a crime occurred nearby was larger than on mornings following no crime the previous day, indicating the body's anticipation of more stress the day following a crime.
Moreover, the changes in sleep and cortisol were largest when the crime committed the previous day was homicide; were moderate when it was assault and sexual assault; and were nonexistent when it was robbery.
"Both sleep and cortisol are connected to the ability to learn and perform academic tasks; our study identifies a pathway by which violent crime may get under the skin to affect academic performance," said Jennifer A. Heissel, a NU PhD graduate in human development and sociology who led the study.
The results of the research have provided "a link between violent crime and several mechanisms known to affect cognitive performance, and may also help explain why some low-income youth living in high-risk neighborhoods sleep less than higher-income youth," said Emma Adam, a NU human development and social policy professor who co-authored the study.
Research in the past has found a link between violent crimes and performance on tests, but researchers could not explain why crime affects academic performance.