Newswise — EVANSTON - 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 (SESP) 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 the current issue of Psychoneuroendocrinology.

“Cortisol is naturally high in the morning to help perk you up, and it decreases into the evening,” said study lead author Emma Adam, professor of human development and social policy and faculty fellow at the Northwestern’s Institute for Policy Research. “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 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,” said Adam.

Adam’s team introduced the theory of “stress-related circadian dysregulation” (SCiD), which suggests that 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 health choices like getting regular exercise and 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, post-doctoral 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 SESP; Katie Dahlke, principal researcher at American Institutes for Research; and Kirsten Gilbert, post-doctoral research associate in the department of psychiatry at Washington University School of Medicine.