A study conducted on 346 19-month-old twins by an international team led by Universite Laval professor of psychology Michel Boivin reveals that the genetic and environmental bases of hormonal response to stress depend on the context in which a child grows up.
This is the first time such an effect has been reported in young humans. The researchers explain the details of their findings in the latest edition of the Archives of General Psychiatry.
The study shows that, for children growing up in a favorable family environment, genetics account for 40% of the individual differences in cortisol response to unfamiliar situations. Cortisol is a stress hormone produced in new, unpredictable or uncontrollable contexts. In contrast, if children are raised in difficult family circumstances, the environment completely overrides the genetic effect as if it had established a programmed hormonal conditioning to stress.
The researchers already assumed that variability in cortisol production among individuals exposed to the same stressful conditions depended on both genetic and environmental factors. In order to estimate precisely these genetic and environmental contributions, they studied 130 identical twins who share 100% of their genes and 216 fraternal twins who share close to 50% of their genetic makeup. Each child, accompanied by its mother, was brought into a room, and then successively exposed to a clown and a noisy robot. “These are not traumatic events, but they are sufficient to cause behavioral changes in most children of that age,” explained Professor Boivin.