If parents are very strict with their children, then they need to stop, as a new study has found that tough parenting can alter how the body reads the DNA of these children.

The study, presented at ECNP Congress in Vienna, indicated that these changes could effectively become "hard-wired" to the DNA of those children who perceive their parents as harsh, increasing their biological risk for depression in adolescence and later life.

"We discovered that perceived harsh parenting, with physical punishment and psychological manipulation, can introduce an additional set of instructions on how a gene is read to become hard-wired into DNA," said researcher Evelien Van Assche, now working at the University of Munster.

"We have some indications that these changes themselves can predispose the growing child to depression. This does not happen to the same extent if the children have had a supportive upbringing," Assche added.

For the study, the team selected 21 adolescents who reported good parenting and compared them with 23 adolescents who reported harsh parenting.

All adolescents were between 12 and 16 years old, with a mean of 14 years for both groups. For both groups, 11 adolescents were boys meaning that the two groups were comparable, with a similar age and a similar boy-girl distribution.

Many who had experienced harsh parenting showed initial, sub-clinical signs of depression. The researchers then measured the range of methylation at more than 450,000 places in the DNA of each subject and found that this was significantly increased in those who reported a harsh upbringing.

Methylation is a normal process that occurs when a small chemical molecule is added to the DNA, changing how the instructions written in your DNA are read: for example, methylation may increase or decrease the amount of an enzyme produced by a gene.

Increased variation in methylation is known to be associated with depression.