The research included 432 adolescents who were 11 to 17 years old and who are part of the larger ongoing Adolescent Health and Development in Context study, a longitudinal research project looking at the impact of social and other factors on health. That project is led by Christopher Browning, a sociology professor at Ohio State who is also a co-author of the cortisol and depression study.

For the cortisol study, the researchers measured depression with a nine-item questionnaire that the participants filled out. They were asked to rate their experience in a variety of areas, including how often they feel that their life has been a failure or that people have been unfriendly to them.

In most cases, the researchers examined a 3-centimeter hair sample – enough to assess cortisol levels for the previous three months.

After adjusting the results for a variety of potential factors that could contribute to depressive symptoms and to cortisol levels, the researchers found the surprising trend that both low and high cortisol had a statistically significant relationship to depression.

Nearly one in eight adolescents have experienced a major depressive episode, according to 2016 data, and the proportion of young people facing depression has steadily increased in the last decade. Suicide is the second leading cause of death among adolescents.

But children and teens can struggle to describe their symptoms, and parents and others can miss warning signs if they mistake serious mental health problems for the normal turbulence of puberty, Ford said.

“It’d be really ideal to have an objective measurement, because using subjective measures of stress is problematic, particularly with children and teens,” she said.

Testing is simple, and relatively cheap (on the order of about $35), but it won’t be something to consider for widespread use until researchers better understand what values are normal and what values are out of range and cause for concern, Ford said.

It’s possible that cortisol testing could serve not just as a detection tool, but as a way to watch over time to see if therapy and medication are helping someone with depression, or if the mental illness is intensifying and putting the adolescent at risk of suicide, she said.

Next, Ford would like to conduct a longer, larger study looking at adolescent depression and cortisol levels over time.

Samantha Boch of Nationwide Children’s Hospital also worked on the study.

The National Institutes of Health supported the research.

For help, contact the National Suicide Prevention Lifeline at 1-800-273-8255/TALK (or 1-888-628-9454 for Spanish speakers). To reach someone at Ohio’s 24/7 Crisis Text Line, send 4HOPE to 741741.