By Charlene N. Rivera-Bonet | Waisman Science Writer
Adolescents who experience sustained childhood maltreatment show high, inflexible cortisol levels that persist throughout the day in different social contexts, a new study shows. This flattened cortisol rhythm may be a pathway for poorer physical and mental health in youth that experience abuse.
The new research from the lab of Seth Pollak, PhD, Vaughan Bascom Distinguished Professor of Psychology, Pediatrics, and Public Affairs, shows that childhood maltreatment changes the circadian rhythm component of the main stress response system, the hypothalamic-pituitary-adrenal (HPA) axis. The stress hormone released by this system, cortisol, typically rhythmic throughout the day, shows an elevated flattened pattern in adolescents with a history of maltreatment, which is exacerbated in their home environments and by stressful family relationships.
Cortisol levels typically fluctuate throughout the day. It has a rhythm with a purpose. In the mornings, when cortisol is at its highest, it serves to get an individual ready for the day. “You can think of it like a cup of coffee that gets you going,” says Elizabeth Shirtcliff, PhD, former postdoctoral fellow in Pollak’s lab, current research professor at the University of Oregon, and first author of the study. Cortisol levels then gradually decline throughout the day, which is important for tissue repair, memory formation, and other physiological needs.
But this rhythm is impacted by external factors. Cortisol levels during the day, or diurnal rhythms, are flexible, and can change in response to external stimuli, environmental disruptions and to meet the demands of a challenging situation. Flatter cortisol rhythms have been associated with poor health outcomes such as depression, inflammation, and obesity. “One of the great things about this biomarker [cortisol] is it’s both responsive and reflective to the environment, but then also has components of it which are stable, and have that long-term prediction of health,” Shirtcliff says.
The researchers looked at adolescents with substantial childhood maltreatment to learn how the chronic day-to-day wear of adversity impacts them physiologically, and if these effects of maltreatment remain across social contexts – home, school and a novel environment. Specifically, they determined if different social contexts shaped cortisol’s rhythm throughout the day. “We reasoned that if we looked at contexts that held different meaning for kids, that their diurnal rhythms might reflect that,” Shirtcliff explains.
The adolescents, aged 9-15, provided saliva samples for cortisol analysis while at home, school, or in the research laboratory. The lab represented a novel and social environment for the adolescents, with some stressful components such as tests and magnetic resonance imaging. The school provided a social, but familiar environment, while home was non-social and familiar.
Youth that had been maltreated demonstrated an elevated and flattened pattern of cortisol levels across all three contexts – home, school and lab. Although cortisol has a bad reputation for being a stress hormone, a rhythm of highs and lows is needed for optimal function. “What we see with flattened circadian rhythms is that, at the point in time of the day that cortisol should be high, it’s low. And at the point in time of the day that cortisol should be low, it’s high,” Shirtcliff says. Their results demonstrated that the effects of maltreatment on cortisol levels was the strongest at the home environment and overlapped with current interpersonal stress in the family. This supports the idea that long-term, negative relationships between parents and children can take a toll on an adolescents’ HPA axis in youth who have experienced maltreatment.
Examining these two groups of adolescents in different contexts also provides insight into how adolescents’ HPA axes operate when they are raised in more nurturing environments. “The critical finding here is that biology is flexible and adaptive to environmental demands. Had we just studied children in the laboratory, we would have missed all that was happening,” Pollak says.
The inflexibility in cortisol levels observed in the maltreated adolescents serves as an adaptation to the adolescents’ abusive environment and a protective mechanism that promotes vigilance. “They are adapting to that environment, shielding themselves from that stress,” Shirtcliff says. “And the cost of that adaptation is loss of flexibility across environmental contexts. So, the cost of adaptation is high in the context of maltreatment.”
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