A new study shows a humanitarian program focused on teaching youth affected by the Syrian war about the impacts of stress actually has a biological signature, in that it reduces levels of cortisol (dubbed the “stress hormone”) by a third.

The study, “Hair cortisol concentrations in war-affected adolescents: A prospective intervention trial,” which appears in the journal Psychoneuroendocrinology, is the first to show that a mental health intervention has impacts beyond self-reports of well-being and is the only one to date that has been able to track an objective indicator of intervention impact.

The study was conducted over an eight-week period in northern Jordan, where Mercy Corps, a global humanitarian and development organization, implemented programming for adolescents aged 12–18 who were heavily affected by the Syrian crisis. The study examined 733 youth, including Syrian refugees and Jordanians living in the same communities.

The researchers collected hair samples from the Syrian refugees and Jordanian counterparts to measure cortisol concentration, which functions as a “stress diary,” as levels of the hormone increase over time. They analyzed the hair cortisol as a marker of within- and between-person variation in adolescent responses to past trauma and current threats to well-being, in response to a brief intervention.

Through this study, the researchers found that hair cortisol can be used as an objective measure of the effectiveness of an intervention at reducing stress. These findings can help to explain why some highly traumatized kids and adults are less able to deal with stress. The researchers found that after exposure to high levels of trauma, cortisol production was dysregulated, so the physiological response to subsequent stress may be compromised in these individuals.

“This study was able to succeed because of the peer to peer partnerships established among academics from Jordan, U.S., Canada and the U.K. on one hand and the unique partnerships established with the refugee youth and families on the other,” notes first author Rana Dajani. Dajani is the 2017-2018 Rita E. Hauser Fellow at the Radcliffe Institute for Advanced Study at Harvard and associate professor of biology and biotechnology at the Hashemite University in Jordan. “Everyone was engaged to learn what makes a good intervention and what makes good rigorous research. Many of the research field team members were Syrians benefitting from the capacity building and critical thinking skills they gained.”

The study’s other co-authors include Principal Investigator Catherine Panter-Brick, professor of anthropology, health, and global affairs at Yale University; Kristin Hadfield, assistant professor in the Department of Biological and Experimental Psychology at Queen Mary University of London; Stan van Uum, professor in the Divisions of Clinical Pharmacology and Endocrinology and Metabolism at the Western University Schulich School of Medicine in Ontario; and Michael Greff, medical researcher at the Robarts Research Institute and Department of Paediatrics at Western University Schulich School of Medicine in Ontario.

The research was funded by Elrha’s Research for Health in Humanitarian Crises (R2HC) Programme, which is funded equally by the Wellcome Trust and the U.K. Government.