Counting Lost Sleep

Research Uncovers Stress and Sleep Disparities Related to Race

By Bonnie Rubin

As Northwestern professor Emma Adam scrutinized her lab data, she noticed something curious about the adolescents in her study: their levels of cortisol—the body’s “fight or flight” stress hormone— differed along racial lines.

Everyone’s cortisol levels normally surge in the morning to help kick-start the day. By nightfall, cortisol wanes to prepare the body for sleep. But Adam’s data showed that relative to their white peers, the black teenagers’ cortisol levels were “flatter,” showing less change from morning to evening.

Examining other data, she found that black teens averaged 30 minutes less sleep per night than white teens—a sleep deficit with potentially adverse effects on daily functioning, school performance, and health.

These sets of data—revealing flatter or less variable cortisol levels and sleep disparities—led Adam to identify a new concept in social justice: sleep equity.

The banality of sleep belies its important role in human health and thriving. A highly evolved vigilance system, our sleep behavior corresponds to how safe and at ease we feel. When stress is thrown into the mix, it can change cortisol rhythms and sleep patterns. But not everyone experiences the same level of stress.

“Stress—and thus sleep—are unequally distributed in society,” says Adam, the Edwina S. Tarry Professor of Human Development and Social Policy at SESP. “African Americans in particular carry an unfair burden of stress due to structural inequalities and personal experiences of racism. Stress disparities in turn create sleep disparities that have very real implications for daily functioning and well-being.”

The idea of sleep equity—equalizing opportunities for healthy sleep across racially and socioeconomically diverse groups—is gaining traction. Adam’s research is part of a growing body of data showing that black people and other minority populations in the US sleep fewer hours on average than white people, and the sleep they do get is of poorer quality. When studies control for factors like education level and income, the gap narrows but doesn’t disappear.

In response to such findings, some authors and artists have argued that sleep, at once a luxury and a right, should be included in discussions of how to make amends for slavery, since many of the inequities that plague African Americans date back to the Atlantic slave trade and the Jim Crow segregation that followed. Black Power Naps, a New York–based performance-art exhibition, was an attempt by creators niv Acosta and Fannie Sosa to compensate for the “sleep gap” between white people and people of color. The Nap Ministry, a project founded by performance artist Tricia Hersey, explores the “liberating power of naps” for people of color through Instagram and pop-up collective napping opportunities in Chicago and Atlanta.

Not surprisingly, decent sleep can be elusive for those living in poorer, noisier neighborhoods with high crime rates. Working multiple jobs or overnight shifts can affect an entire household’s sleep patterns. And the stress of racial discrimination has been found to cut into sleep hours and feelings of restfulness.

“Sleep disparities are both caused by social inequalities and likely to perpetuate them,” says Jennifer Heissel (PhD17), one of Adam’s former lab members and now assistant professor at the Naval Postgraduate School.

Cortisol: The Body’s Alarm System

At the Contexts of Adolescent Stress and Thriving lab at Annenberg Hall, Adam traces how stress “gets under the skin” to cause health problems and affect children’s behavior and development, both academically and emotionally.

For more than a decade, Adam and her research team have focused on cortisol and its role as a biological energy regulator. During any kind of perceived threat—from a rattlesnake to a racist remark—cortisol increases sugars in the bloodstream, supplying energy to the muscles and brain. It also curbs functions that would be nonessential or detrimental in an emergency. In limited doses, cortisol is something the body needs, but the long-term activation of the stress-response system and overexposure to cortisol and other stress hormones can disrupt almost all the body’s functions.

In a 2007 study published in the Journal of Adolescent Health, Adam and four coauthors—including Amy DeSantis (PhD10), a senior research scientist at the Geisel School of Medicine at Dartmouth, and Leah Doane (PhD08), associate professor of psychology at Arizona State University—broke new ground when they showed racial disparities in cortisol levels. Later studies showed cortisol is affected by discrimination.

“The teenage years are a particularly sensitive time to be experiencing discrimination, perhaps because the body and brain are still developing,” says Adam.

Moreover, the effects may be cumulative. In another study, using data collected over two decades, Adam’s team found that the more discrimination people experience as teenagers and young adults, the more dysfunctional their cortisol rhythms are by age 32.

“Small changes in cortisol and sleep can add up over months and years,” Adam says. “There’s also an intergenerational pattern: a parent’s stress becomes a child’s stress, and a parent’s sleep schedule can spill over to affect a child’s sleep.”

Zip code also matters. In a study published in Child Development, Adam and coauthor Heissel found that young people’s sleep patterns and stress hormone levels change after a violent crime occurs in their neighborhood. Linking sleep, cortisol, and home-address data to a database of violent crimes in a large Midwestern city, they showed that cortisol levels skyrocket the morning after a local violent crime. Meanwhile, the greater the teens’ proximity to the crime scene, the more adverse the impact on their sleep.

Stress, Sleep, and School

“The disruption of both sleep and cortisol have been linked to poorer academic performance,” Heissel says. “Race-based stressors and their effect on stress hormones and sleep patterns are understudied contributors to the achievement gap.”

Research by cognitive psychologists backs up Heissel’s statements. According to a 2016 review article in Nature, stress at the time of learning might enhance how memories form, but it also makes it harder to retrieve past thoughts and can induce a shift from a flexible form of learning to rigid, habit-like behaviors.

“Stress effects are not limited to how much we learn or remember,” the Nature article authors wrote. “Stress also changes the nature (or quality) of memories, for instance, the strategies used during learning.”

Studies also suggest that cortisol blocks perceptual learning. Researchers at the University of California, Irvine, showed that short-term stress of as little as a few hours can impair brain-cell communication in areas associated with learning and memory.

Adam is now exploring interventions to reduce stress disparities, including mindfulness training, meditation, and nightly text messaging to cue dimmed lights and earlier bedtimes.

She’s also in the middle of the Biology, Identity, and Opportunity Study with SESP research project coordinator Ednah Nwafor. The five-year project, funded by a Lyle Spencer Research Award, helps students explore their races and cultures and promotes feelings of belonging and safety so they can better regulate stress hormones and get a good night’s rest.

“Sleep is an underappreciated factor in education and health disparities,” Adam says. “Racial inequality in school performance and completion is one of the biggest problems facing America today. Understanding the origins of these disparities is fundamental to beginning to reduce them.”

About Emma Adam

The Edwina S. Tarry Professor of Human Development and Social Policy at Northwestern, Emma Adam is a leading expert on the psychology and biology of stress and sleep in everyday settings. Most previous work on stress and sleep had been done in labs, but Adam developed methods allowing study participants to keep diaries of daily events and emotions as well as submit saliva samples for cortisol testing. She was able to demonstrate that naturally occurring negative feelings such as sadness, anger, and loneliness can lead to both acute and chronic changes in stress hormones. And she was the first to reveal ethnic and socioeconomic disparities in cortisol rhythms in adolescents, demonstrating that minority and lower-income children and youth who are exposed to discrimination have hormone patterns associated with lower daily energy levels and later health issues.