Stress Hormones and Sleep Patterns Change After Violent Crimes

In 2015, the U.S. Department of Justice reported that the United States saw nearly 1.2 million violent crimes, including sexual assault, assault, robbery, and homicide.  New research has found that violent crimes change a young person’s sleep patterns on the night of the crime, as well as alter their cortisol (stress hormone) levels the following day, both of which may disrupt their academic performance in the following weeks.

The research came out of Northwestern University, DePaul University, and New York University.  Findings have been published in the journal, Child Development.

Jennifer A. Heissel, the lead author of the study and a Ph.D. graduate in human development and sociology, noted that prior studies connected test performance and violent crimes; however, researchers were unable to determine why the crime affected academic performance.  We know that cortisol and sleep are connected to learning, memory, and academic performance; however, this new research focuses on finding the pathway to specific types of violent crime that are affecting the youths’ academic performance.  Researchers found these pathways by looking at the causal factors involved with the hypothalamic-pituitary-adrenal (HPA) axis and sleep.  The HPA axis regulates the stress response.

For this study, scientists tracked the stress and sleep hormones in 82 kids between the ages of 11 and 18 years, all of whom lived in a Midwestern city and attended a public school.  The group was ethnically, racially, and socioeconomically diverse.  The participants wore activity watches that tracked their movements and measured their sleep.  They were also asked to fill out daily diaries over four days.  Additionally, scientists collected saliva to test three times a day to look at cortisol levels.  Outside of that, they collected data on police-reported violent crimes in the entire city during the study, with special attention given to the youth’s neighborhood.

Researchers analyzed the sleep patterns of each youth.  They compared sleep on the nights where there was a local violent crime to normal nights without any local crime.  Additionally, cortisol levels were compared on the following day after the violent crime was committed.  These were compared to the sleep hormones on days where no local violent crime was committed.

Findings showed that the kids went to sleep later on nights when violent crime was committed in their neighborhood.  This later sleep time resulted in fewer hours of quality sleep and an increase in cortisol levels the next morning.  The cortisol levels on the morning following the violent crime were much higher than the levels on mornings when no violent crime was committed.  This pattern was identified in previous research, which suggested the rise in cortisol was the body’s anticipation of something dangerous happening the day after the crime.  Sleep and cortisol level changes were most prominent when the violent crime committed was a homicide.  Changes were moderate for sexual assault and general assault.  No changes were noted with robbery.

Dr. Emma Adam, professor of human development and social policy, remarked that the results of this research have implications for policies.  Since findings link violent crime with negative changes in cognitive performance, they may help explain why youths in low-income neighborhoods are at higher risk of sleep loss than kids who live in higher income neighborhoods.  Reducing violent crime in these neighborhoods may be the best policy solution; however, schools could also create programs and methods that help students cope with stressful and traumatic events, such as dealing with nearby violent crimes.


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