Teens experience changes in sleep as part of normal development during puberty. Adapting to the need for more sleep and shifting circadian rhythms can make the normal developmental transition in sleep patterns difficult.

A recent study found that violent environments can further impede sleep quality. A team led by Jennifer A. Heissel, Ph.D., and Emma Adam, Ph.D., from the School of Education and Social Policy at Northwestern University, found that adolescents who experience exposure to violent crimes within their community have sleep changes and elevation in stress hormones after the incident.

The study used sleep diaries from 80 adolescents with an average age of 15. The diaries revealed that on evenings after a violent crime, the teens fell asleep close to 30 minutes later than on other evenings. When controlling for weekend sleep bedtimes, the sleep was closer to 40 minutes later.

The adolescents also showed disrupted hormonal functions as measured by levels of cortisol — cortisol is considered to be a measure of stress. Community violence on an ongoing basis has been identified to result in symptoms of stress disorders among residents.

According to Adam, the findings "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.

"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," she said.

Reduced school performance is not the only consequence of poor quality of sleep. Reductions in sleep have been found to contribute to higher rates of physical injury among adolescents in a study of 1,559 middle school children.

Exposure to violence and subsequent sleep dysfunction may also be precursors to risk behavior. A longitudinal study of 20,716 inner-city African American adolescents ages 9 through 20 years over seven years found an association with sleep disturbances and risk behaviors.

Risk behaviors included carrying a weapon and worry. Sleep dysfunctions were also associated with seeing someone cut, stabbed or shot.

"For kids who have experienced some sort of violence, night time is troubling," Dr. Samuel L. Williams III, a psychiatrist who treats children with sleep problems, told The Baltimore Sun. "It is so dark it doesn't feel safe. Even if they do sleep it's a more restless sleep and that can be interrupted by nightmares."

Children are not the only ones affected by the violence in neighborhoods.

A cross-sectional study of 2,156 Hispanic adults age 18-64 were evaluated using questionnaires and sleep activity monitors. The study found that sleep duration and rates of insomnia were adversely influenced by neighborhood environment and threats of safety and violence. Reductions in sleep are also associated with chronic disease such as obesity, hypertension, diabetes and heart disease.

Living in an environment that is not only physically uncomfortable, but also emotionally stressful can take a toll on health. Children, adolescents and adults are harmed by living with the threat of physical violence.