The study’s lead author, Idan Shalev, in the department of psychology and neuroscience at Duke University, says that he and his colleagues were interested in seeing whether the long-term negative effect of violence on children’s later health and behavior might be related to the early aging of their cells. So they took DNA samples from each child at age 5 and again at age 10 and studied their telomeres, the repetitive sequence of DNA that caps chromosomes at each end. Over time, telomeres get shorter, since each time a cell divides, a bit of the telomere is lost. Once the telomeres reach a certain length, the cell starts to die, leading some experts to believe that telomeres are a master regulator, or chronological clock, that documents a cell’s aging.

In recent years, studies have shown that stress can whittle away at telomeres, aging cells before their time. Indeed, the current study showed that children who were exposed to two or more kinds of violence showed more erosion of their telomeres between ages 5 and 10 than those who led less stressful lives. What’s more, each of the types of violence Shalev and his group studied had an effect on shortening telomeres, but exposure to multiple types of violence had a cumulative effect.