Abstract
This thesis focuses on the use of two new specimens – hair and fingernail – for measuring cortisol levels in stress, chronic fatigue syndrome, bipolar I disorder and unipolar, bipolar, atypical and non-atypical depression.To date, studies have only been able to obtain cross sectional measures of cortisol levels. These new specimens allow the assessment of cortisol levels over longer periods. The main component of the thesis is a series of case-control studies that used short-term (saliva), mid-term (fingernail) and long-term (hair) specimens for measuring cortisol levels in patients with the aforementioned disorders who were free from psychiatric comorbidity and psychotropic medication. Patients were age, gender and body mass index matched with a healthy control group. In the final, a longitudinal study, there was also a follow-up period where a series of salivary cortisol measurements and an additional hair sample were taken to describe long-term patterns of cortisol secretion in major depression, chronic fatigue syndrome and controls.
The systematic review presented in this thesis describes the characteristics of a normal and abnormal stress response as measured in hair, suggesting a new objective way of measuring stress. The normal stress response shows increased cortisol levels and the abnormal response decreased cortisol levels.
No significant chronic cortisol levels variations were found in any group. There was, however, a tendency for increased chronic cortisol levels in the bipolar depression I group. In contrast, chronic fatigue syndrome, atypical depression and the bipolar II depression, may all share the same acute and chronic cortisol status characterised by decreased cortisol levels in total daily cortisol output (as measured in saliva) and normocortisolaemia in hair. There was also a tendency for these cortisol patterns in the depressed, bipolar depression and bipolar depression II groups. It is proposed that chronic fatigue syndrome and these subtypes of depression may constitute a somatoform group of psychiatric disorders.
To date, only a small number of studies have measured fingernail cortisol in psychiatric disorders or conditions. Overall, fingernail and hair specimens showed dissimilar results in depressed participants. It appears that fingernail specimens provide a more sensitive measure of chronic cortisol alterations than hair. Fingernails’ results also suggest that some non-atypical subtypes of depression, such as melancholic and psychotic, may also have chronic increased cortisol levels in fingernails. These disorders, in addition to bipolar disorder I, may constitute a separate group of manic-depressive disorders based on this biomarker’s results.
Fingernail analysis also suggested that chronic cortisol alterations are not a reliable biomarker for bipolar I disorder.
Finally, the longitudinal measurement of hair and series of saliva samples showed a reduced long-term variability of cortisol secretion in chronic fatigue syndrome and major depression and suggested that this erratic pattern of cortisol secretion rather than changes in absolute cortisol levels may be an additional feature for these disorders.
| Date of Award | 1 Feb 2017 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Anthony Cleare (Supervisor), Allan Young (Supervisor) & Danilo Arnone (Supervisor) |