In the first study of its kind, the research team collected saliva samples from 1,507 Syrian refugee children, aged 6 to 19, living in informal settlements in Lebanon. They analysed DNA methylation (DNAm), an epigenetic process where chemical tags are added to DNA at various sites in the genome (the complete set of genes). These DNAm changes can turn genes on or off without changing the DNA code.

Questionnaires, completed by both the children and their caregivers, were used to measure exposure to the war-related events experienced by the child.

Surrey — in collaboration with University College London, Institute for Development, Research, Advocacy and Applied Care, Lebanon, St Georges University Lebanon, and a leading international NGO — found that children who had been exposed to war events showed DNA m changes at several sites and regions in the genome. Some of these changes were linked to genes involved in critical functions like neurotransmission (how nerve cells communicate) and intracellular transport (how materials move within cells).

These specific changes are not known to be present in other forms of trauma, like poverty or bullying, suggesting that war may trigger unique biological responses in the body.

This research is funded by the National Institutes of Health (NIH).

Professor Michael Pluess, lead author of the study from the School of Psychology at the University of Surrey, said:

“While it’s common knowledge that war has an adverse impact on the mental health of children, our study has found evidence of the biological mechanisms underlying this effect. We also found that war is linked to slower epigenetic ageing — which could mean that war could be impacting the development of children.

“All told, our study paints a clearer picture of the tragic cost of war, beyond the mental stress, for the many millions of children caught in the middle of it.”

This paper is part of the BIOPATH study, a cohort study which began in 2017. BIOPATH is the first large-scale study of its kind among refugee children, setting the stage for a deeper understanding of how trauma impacts mental health development.

Additionally, the researchers also looked into how the biological effects of war differ between boys and girls. They found that girls who experienced war events showed more significant DNA m changes than boys, particularly in genes linked to stress response and brain development. While both boys and girls were affected, girls showed a stronger biological response to war exposure, suggesting that they may be more vulnerable to the long-term effects of trauma at a molecular level.

DNA m is a natural process where small chemical groups, called methyl groups, are added to certain parts of our DNA. These groups act like switches, turning genes on or off or adjusting how strongly they are expressed. Importantly, this doesn’t change the actual DNA sequence itself.

DNA m plays a key role in normal development and can be influenced by things like diet, stress, and exposure to trauma. When someone experiences extreme events, such as war, it can lead to changes in DNA m, which might affect their long-term physical and mental health. Scientists study these changes to understand how stressful experiences can leave lasting biological marks on the body.

The study has been published in JAMA Psychiatry.