A rough childhood doesn’t just make you grow up faster; it could actually make your body grow old early. In research studying how day-to-day circumstances affect our DNA, researchers have found evidence that social stresses from poverty could wear down children’s genes, making them vulnerable to cancer and age-related disorders at an earlier age.

Children in the study were ranked based on their poverty level, having depressed mothers, experiencing harsh parenting, and living in unstable family structures. “We selected 40 of the most and least advantaged kids,” Daniel Notterman, the study’s principal investigator, told Quartz. All were boys, and all African-American. The study drew its cohort from the Fragile Families and Child Wellbeing Study (FFCWS), a multiyear survey of 4,500 kids born in urban areas between 1998 and 2000.

When they compared the children, they found that the DNA from those in the economic bottom half looked slightly different from those at the top. The difference was in the repetitive sequence of genetic cipher called a telomere that caps off each strand of DNA. As humans age, each time their cells divide, a little bit of the telomere gets shaved away. Telomeres have been compared to the plastic bits that prevent the ends of shoestrings from fraying—and frayed DNA is bad for your health. ”Small telomeres can lead to aging or cancer,” says Rekha Rai, a biologist from Yale who studies telomere shortening and DNA damage.

The researchers found that the DNA from the children living in poverty and harsh conditions had telomeres that were 19% shorter than the more advantaged children. It was as if they had aged more.

Notterman and his team also found evidence that some people are more susceptible to this DNA damage than others. “This is one of the first studies to tangibly show that certain people are innately more sensitive to stress than other people,” says Notterman. This worked both ways: At the bottom of the social ladder, the telomeres of children with high genetic sensitivity were dramatically shorter. At the top, the sensitive kids had more resilient end caps.

Because the sample size was relatively small, Notterman says his group is now expanding their research to the other children in the FFCWS study, to see if the pattern holds. If it does, this research could start playing a role in debates about social welfare programs that seek to reduce these stresses on children. “At this stage, which is still early in our understanding, everything we’ve learned is consistent with policies that attempt to intervene early in a child’s life,” says Notterman.