Conventional wisdom says that hardship can make us old before our time.
In fact, a new study suggests that violence leaves long-term scars on children's bodies — not just in bruises on the skin, but also altering their DNA, causing changes that are equivalent to seven to 10 years of premature aging.
Scientists measured this cellular aging by studying the ends of children's chromosomes, called telomeres, according to Idan Shalev, lead author of a study in today's Molecular Psychiatry.
Telomeres are special DNA sequences that act like the plastic tips on shoelaces, which prevent the DNA in chromosomes from unraveling. They get shorter each time a cell divides, until a cell can't divide anymore and it dies.
Several factors have been found to shorten telomeres, including smoking, radiation and psychological stresses such as early life maltreatment and taking care of a chronically ill person.
In this study, researchers examined whether exposure to violence could make children's telomeres shorten faster than normal. They interviewed the mothers of 236 children at ages 5, 7 and 10, asking whether the youngsters had been exposed to domestic violence between the mother and her partner; physical maltreatment by an adult; or bullying. Researchers measured the children's telomeres — in cells obtained by swabbing the insides of their cheeks — at ages 5 and 10.
Telomeres shortened faster in kids exposed to two or more types of violence, says Shalev, a post-doctoral researcher at the Duke Institute for Genome Sciences & Policy in Durham, N.C. Unless that pattern changes, the study suggests, these kids could be expected to develop diseases of aging, such as heart attacks or memory loss, seven to 10 years earlier than their peers.
Shalev says there is hope for these kids. His study found that, in rare cases, telomeres can lengthen. Better nutrition, exercise and stress reduction are three things that may be able to lengthen telomeres, he says.
The study confirms a small-but-growing number of studies suggesting that early childhood adversity imprints itself in our chromosomes, says Charles Nelson, a professor of pediatrics and neuroscience at Harvard Medical School.
In a 2011 study, Nelson and colleagues found shorter telomeres in Romanian children who had spent more time in institutions, compared with children sent to foster care.
"We know that toxic stress is bad for you," says Nathan Fox, a professor of human development at the University of Maryland and co-author of the 2011 paper. "This paper provides a mechanism by which this type of stress gets 'under the skin' and into the genes."