INSTITUTE FOR POLICY RESEARCH

A lack of variation in the stress hormone cortisol from morning to evening is tied to a wide range of negative health conditions, including inflammation and immune system dysfunction, new Northwestern University research suggests.

In the first comprehensive review of the relationship between daily cortisol fluctuations and health, researchers at the School of Education and Social Policy combined data from 80 different studies to show that while cortisol levels matter, a lack of variation from morning to evening may be even more telling.   

The researchers found that people with flatter daily cortisol slopes—meaning cortisol levels changed less from morning to evening—experienced poorer health, according to the study in Psychoneuroendocrinology.

“Cortisol is naturally high in the morning to help perk you up, and it decreases into the evening,” said IPR developmental psychologist Emma Adam. “The loss of this cycle—or the lack of variation of cortisol—is what is associated with negative health outcomes in our study.”

The researchers found 10 out of 12 different health conditions they examined were associated with the loss of variation in cortisol levels.

“While inflammation and the immune system dysfunction had the strongest associations, fatigue, cancer, depression, and obesity were all worse in people who had less variation in their cortisol,” Adam said.

Adam’s team introduced the theory of “stress-related circadian dysregulation (SCiD),” which suggests that flatter or less variable daily cortisol rhythms emerge from exposure to chronic stress, and may indicate a more general disruption in circadian rhythms that are associated with poor health.  

Adam and her collaborators have previously shown that flatter cortisol rhythms are linked to chronic stress of various forms, ranging from family conflict to experiences of loneliness and discrimination.

They suggest that focusing on restoring daily rhythms is an important goal when trying to improve health.

“It’s the righting of rhythms that are important, more so than the righting of levels,” the researchers wrote. “We want cortisol high when it’s supposed to be high and low when it’s supposed to be low,” added Adam.

Good choices like getting regular exercise, enough sleep, and following the same sleep schedule each night are important steps towards restoring strong daily cortisol rhythms.

Adam’s study co-authors include Meghan Quinn, postdoctoral fellow in the Department of Psychology and Human Development at Vanderbilt University; Royette Tavernier, assistant professor of psychology at Wesleyan University; Mollie McQuillan, doctoral candidate in the School of Education and Social Policy; Katie Dahlke, principal researcher at American Institutes for Research; and Kirsten Gilbert, postdoctoral research associate in the department of psychiatry at the Washington University School of Medicine.

Emma Adam is professor of human development and social policy and an IPR fellow.

This article was originally published by the School of Education and Social Policy.