Their DNA proves what language has long suggested.

Flickr/Sarah G...

We often say that kids who get bullied on the playground or who live in violent homes are forced to grow up faster, but the idiom reveals a kernel of truth.

Children who've gone through violent experiences are more likely to have older DNA, a study from Duke University has discovered:

The findings suggest a mechanism linking cumulative childhood stress to telomere maintenance and accelerated aging, even at a young age. It appears to be an important way that childhood stress may get "under the skin" at the fundamental level of our cells.

Telomeres play an important role in the DNA aging process. Capping the ends of chromosomes, telomeres prevent DNA from unraveling. They also get shorter as cells divide, meaning that the gradual loss of telomeres over time is a decent proxy for a person's actual age.

Now, it appears that in addition to unhealthy behaviors like smoking, childhood violence may also play a role in accelerating telomere loss. Significant telomere loss has been connected to diseases of old age like dementia and heart disease.

Duke researchers examined data from a longitudinal study that began tracking 1,100 British families in the 1990s. Between DNA samples taken early on from the families' children and interviews conducted with the youths' mothers, scientists were able to figure out which kids were subjected to physical harm. Children who had been exposed to two or more kinds of violence showed much more telomere loss than the study's other children.