Inflammatory signs for teenage depression differ between boys and girls – study

Researchers hope the findings will ultimately lead to the development of more targeted treatments for different biological sexes.

When inflammation occurs in the body proteins called cytokines are released into the blood.

Higher levels of cytokines are associated with depression in adults, studies have shown, but little is known about this relationship in adolescence.

The research, led by the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King’s College London, investigated differences in the relationship between inflammatory proteins and depression.

It found that different cytokines were involved in depression risk and severity in boys and girls.

Dr Zuzanna Zajkowska, postdoctoral researcher at King’s IoPPN and first author of the study, said: “This is the first study to show differences between boys and girls in the patterns of inflammation that are linked to the risk and development of adolescent depression.

“We found that the severity of depressive symptoms was associated with increased levels of the cytokine interleukin-2 in boys, but interleukin-6 in girls.

“We know more adolescent girls develop depression than boys and that the disorder takes a different course depending on sex, so we hope that our findings will enable us to better understand why there are these differences and ultimately help develop more targeted treatments for different biological sexes.”

To assess inflammation, the scientists measured blood cytokine levels in 75 adolescent boys and 75 adolescent girls (aged 14-16) from Brazil.

The teenagers were in three groups with equal numbers: those at low-risk for depression and not depressed, those at high risk of depression and not depressed, and those currently experiencing major depressive disorder (MDD).

The findings suggest there are differences between the individual inflammatory proteins associated with depression in adolescents.

Higher levels of the cytokine called interleukin-2 (IL-2) were associated with increased risk for depression and the severity of depressive symptoms in boys, but not in girls.

Higher levels of the cytokine IL-6 were associated with severity of depression in girls, but not boys.

According to the study, in boys the levels of IL-2 were higher in the high-risk than the low-risk group and even higher in the group diagnosed with depression.

This suggests that in boys IL-2 levels in the blood could help indicate the onset of future depression.

The risk of depression was assessed using a composite risk score based on 11 variables developed as part of the IDEA (Identifying Depression Early in Adolescence) project.

The teenagers completed several questionnaires, self-reporting their emotional difficulties, relationships, experiences and mood.

They also completed a clinical assessment with a child and adolescent psychiatrist.

Senior author on the study was Professor Valeria Mondelli, clinical professor of psychoneuroimmunology at King’s IoPPN and theme lead for psychosis and mood disorders at the NIHR Maudsley BRC.

She said: “Our findings suggest that inflammation and biological sex may have combined contribution to the risk for depression.

“We know that adolescence is a key time when many mental disorders first develop, and by identifying which inflammatory proteins are linked to depression and how this is different between boys and girls we hope that our findings can pave the way to understanding what happens at this critical time in life.

“Our research highlights the importance of considering the combined impact of biology, psychology and social factors to understand the mechanisms underlying depression.”

The research, published in Journal of Affective Disorders,  was part of the IDEA project funded by MQ Mental Health Research.

The project is investigating how cultural, social, genetic and environmental factors lead to the development of depression in 10 to 24-year-olds across the UK, Brazil, Nigeria, Nepal, New Zealand and the US.