As presented at the American Psychosomatic Society Annual Meeting, held March 5-8 in Phoenix, Arizona, research scientists from the Department of Clinical and Theoretical Psychobiology at the University of Trier, Germany now found that the heritability of HPA and heart rate responses to psychosocial stress increases when the same stressful situation is repeated several times.

In this study, 58 twin pairs (33 monozygotic and 25 dizygotic) aged 16 to 24 years were exposed three times to a mental stressor by Ilona Federenko and coworkers. In this stressful situation, known as the “Trier Social Stress Test: TSST”, all participants had to give a free speech in front of an audience and resolve a mental calculation task. The TSST was repeated three times in one week intervals.

Interestingly, monozygotic twin pair’s stress responses (cortisol, ACTH, heart rate) got more and more similar across sessions, while the similarity of the dizygotic twins stress responses did not change across the three TSST exposures. Thus, the impact of genetic factors was most pronounced at the third TSST exposure and lowest at the initial exposure to this stressful situation. Possibly, situational factors are dominant and mask existing genetic influences when an individual is exposed to one single stressful situation.

Furthermore, it was observed that the impact of genetic factors on the cortisol response to stress was highest directly after the stress exposure, and considerably lower before the stressor and at more distant time points after the TSST. It is possible that the impact of genetic factors involved in regulating the cortisol reponse is increased under stress conditions - alternatively, some genes might exclusively exert their influence under stressful conditions.

In sum, the present study shows that the heritability of cortisol, ACTH, and heart rate responses to stress increases after repeated exposure to stress. Furthermore, an increased heritability can be observed during stimulated compared to unstimulated conditions in this sample.