Roxanne Schaakxs Major depressive disorder across the life span: the role of chronological and biological age

Date of PhD defense:    22 February 2018 
Institute: APH, VU Medical Center
Promotor: Prof.  Brenda Penninx
Prof. Aartjan Beekman
Co-promotor: dr. Hannie Comijs
During my PhD-trajectory at Amsterdam Public Health (APH, VU Medical Center), I studied whether there is an association between major depressive disorder and age. 
Major depressive disorder (MDD) is a serious psychiatric disorder with a high disease burden. Moreover, MDD has been associated with a higher likelihood for non-psychiatric chronic diseases to occur, such as cardiovascular diseases, diabetes, obesity and even premature mortality. It has been suggested that MDD in older age has a different presentation, different risk factors, and a different course compared to MDD in younger ages. With life expectancies increasing and more people reaching older age, it is important to tailor depression prevention, diagnosis and treatment to one's age.

Chronological age versus biological age
I studied the association between MDD and two types of age: chronological age (based on someone's date of birth) and biological age. The latter was defined as telomere length. Telomeres are situated at the ends of our chromosomes and protect our DNA from damage. Short telomeres are a risk factor for poor health. The shortening process is suggested to be accelerated in the presence of stress (e.g. depression). For both types of age I examined whether age was related to the presentation, risk factors, and course of MDD. Persons with and without MDD aged between 18 and 93 years were included in this study. These persons were participants in the Netherlands Study of Depression and Anxiety (NESDA) and the Netherlands Study of Depression in Older Persons (NESDO).

Major depressive disorder and age
My thesis has two clear conclusions. On the one hand, depression in older chronological age differs from depression in younger chronological age. It became apparent that MDD in older chronological age is more often characterized by somatic symptoms, such as sleeping problems and pain, and less mood symptoms such as feelings of anxiety. Characteristics of poor health, however, were more strongly related to the presence of MDD in younger adults. The two-year course of depression was more unfavourable for older persons. On the other hand, within older persons, I found no evidence for an association between MDD and biological age. Diagnosis and treatment of MDD currently is rather similar for younger and older adults. However, based on the findings in this thesis, it is worthwhile to tailor depression care according to someone's life phase.

Defending your thesis
Beforehand, I expected that I would feel my telomeres shrink (so to speak) during the defense. In practice, it turned out to actually be a fun experience. I would recommend everyone still working towards this moment to try and enjoy every minute of it – it is over before you know it!
Roxanne Schaakxs