Most people know that children are affected by their parents' stress level. But a new study reveals that parental stress can even alter kids' DNA. The research, published in the journal Child Development, supports that the way a child is raised affects them on a biological level. "Maybe it's not nature or nurture, but nature AND nurture," says Jeremy Olson in the Minneapolis Star-Tribune. Here, a brief guide to this study:

How was this research conducted?
Geneticists surveyed hundreds of families in 1990 and 1991, when they had children at home who were infants or toddlers. They questioned mothers and fathers about problems like depression, family-expressed anger, and financial stress. They also took cheek swab DNA samples from 100 children of those families years later, when the children had grown into teenagers.

What did the researchers find?
There was a direct link between parents who reported high levels of stress in 1990 and 1991 and teenagers with differences in their genes, "including those [genes] related to anxiety levels, insulin suppression, and brain development," says Laura Kane in the Vancouver Sun.

What was different about those genes?
Some of them had distinct patterns of methylation, in which a chemical compound attaches to part of the DNA and changes the way the gene expresses itself. "Methylation acts like a light dimmer for genes," says geneticist Michael S. Kobor of the University of British Columbia, lead author of the study. "Each gene can be totally turned off, or totally turned on, or anywhere in between."

How were these kids affected psychologically?
The study didn't shed any light on how the adolescents behaved, or if these genetic changes affected their mental health. There were, however, some interesting differences between the fathers' stress and the mothers' stress. Maternal stress affected both boys and girls, but fathers' stress had a more profound effect on their daughters' DNA methylation. This supports earlier studies linking absent fathers with "earlier onset of puberty and difficult temperamental traits in girls — but not in boys," says Remy Melina at LiveScience.

Sources: Bioscience Technology, LiveScience, Minneapolis Star-Tribune, Vancouver Sun