The stress of exposure to early-life violence can leave lasting marks on children so deep that it affects their DNA, according to the findings of a study by researchers at North Carolina's Duke University.
Chromosomes of children who were exposed to maternal violence, bullying or physical maltreatment by an adult showed signs of biological aging, researchers reported Tuesday in a study published by the journal Molecular Psychiatry.
The DNA of those children showed signs of "wear and tear" beyond that caused by chronological aging.
"They're definitely several years older than kids that didn't experience violence," said Idan Shalev, a post-doctoral researcher at Duke, who worked on the study.
Researchers examined the DNA of a group of kids when they were five, seven and 10 years old, and found shorter telomeres in the DNA of kids who were exposed to violence.
The children's experiences with violence included witnessing domestic disputes, being verbally or physically bullied and being abused by an adult.
Telomeres are DNA sequences found on the tips of chromosomes that keep DNA from unravelling, much like the plastic tips of shoelaces. When the telomeres are damaged or shortened, the number of times a cell can divide is limited.
Sybille Artz, a professor in the University of Victoria's School of Child and Youth Care, has conducted extensive research on children who have been exposed to family violence. She says they are at higher risk of facing emotional and mental-health impairments, as well as physical health impairments.
The longer a child is exposed to violence, the more at risk they become, Artz said, noting there is no such thing as "good violence."
"There seems to be a fairly strong convergence that emotional violence is probably as toxic as physical violence," she said.
The Duke research team wasn't able to tell if one particular form of violence, such as bullying, caused more damage than another, such as being exposed to domestic violence. But the researchers did discover that experiencing more than one form of violence had detrimental effects on the children.
"These findings are consistent with the theory that the effect of stress is seen most clearly when stress is measured in a cumulative way," the report said.
How, exactly, telomeres get damaged remains unknown, though Shalev said inflammation markers caused by stress can have negative effects on telomeres.
Research in the area is promising, however, including the discovery of an enzyme that can extend telomeres.
"There's some evidence from research on animals that it's possible to reverse the aging process," Shalev said.
"There is some evidence that we can slow down this acceleration of telomere erosion. So there is some hope for these kids."
In the meantime, the latest research sets the groundwork for prevention, Shalev said. By looking at telomeres, it's possible to tell someone's biological age, which can show if they're at increased risk for certain diseases.
The findings also present parents and policy-makers with motivation to take a firm stand on preventing violence, Shalev said.
"These children are aging at a different rate and we need to try to stop that in all kinds of different ways."
Exposing children to violence is an "unnecessary risk," Artz said.
"And it's a silly risk to take because it's entirely preventable," she said.