Dynamics of the human stress system in depression
| PhD ceremony: | dr. S.H. (Sanne) Booij |
| When: | November 09, 2015 |
| Start: | 16:15 |
| Supervisors: | prof. dr. A.J. (Tineke) Oldehinkel, prof. dr. P. (Peter) de Jonge |
| Co-supervisor: | dr. E.H. Bos |
| Where: | Academy building RUG / Student Information & Administration |
| Faculty: | Medical Sciences / UMCG |
Depression is a stress-related disorder, often with a chronic course. Studies into the biology of depression have often focused on a major component of the stress system, the hypothalamic-pituitary-adrenal (HPA) axis, which increases release of the hormone cortisol upon activation by stress.
Studies into the amount of cortisol in depressed versus non-depressed individuals show inconsistent results. A possible explanation is that researchers insufficiently accounted for fluctuations in cortisol production during the day and that functioning of the HPA axis may change over time. Studies described in this thesis suggest that the cortisol stress response is increased in individuals with acute depressive problems, but decreases in individuals with a longer history of depressive problems. In addition, our studies also suggest that the presence of a relationship between depression and increased cortisol levels at the group level does not imply that depressed individuals can be categorized according to their cortisol levels. Therefore, we conclude that cortisol is currently not a good biomarker for depression.
In this thesis, we also examined whether a possible antidepressant effect of physical activity on depressive symptoms is explained by changes in functioning of the HPA axis. Regular exercise appeared to decrease depressive symptoms as expected, but changes in the cortisol stress response did not appear to underlie this effect. In addition, it was found that daily physical activity leads to an increase in positive emotions in almost everyone, while the effect on negative emotions differs between individuals.