A Mixed Method Approach to Post-Awakening Cortisol Research: Exploring Associations with Post-Awakening Melatonin, Primary Open-Angle Glaucoma and Experiences of Participation

The non-invasive, ecologically valid, measurement of post awakening cortisol secretion (PACS) in saliva tissue has greatly informed literature within the psychoneuroendocrinological discipline. Measured in the first 45 minutes of awakening, Indices of PACS include the rise in cortisol (cortisol awakening response: CAR) and total cortisol concentrations as measured by the area under the curve with reference to ground: AUCg. Via melanopsin containing retinal ganglion cells (mRGCs), upon awakening the hypothalamic suprachiasmatic nucleus (SCN) enhances cortisol secretion at wake, in response to light. The same projection of stimuli to the SCN also suppresses melatonin production, inducing sleep. The current work of this programme of research firstly investigated the relationship between post awakening cortisol secretion (PACS) and postawakening melatonin secretion (PAMS). Loss of mRGCs have been implicated in those with primary open-angle glaucoma (POAG). The second study therefore explored the relationship of PACS with primary open-angle glaucoma (POAG); a previously unstudied group. In the final study, an exploratory qualitative, investigation of individual experiences in participation in salivary cortisol research was conducted.

In study I, analysis of data from healthy males and females demonstrated for the first time the post awakening pattern of melatonin and its relationship with PACS. Results displayed a typical cortisol awakening response (CAR) profile, with a substantial increase in cortisol over the 45-minute post-awakening period. The decrease in post awakening melatonin secretion (PAMS) however was not statistically significant, as there was no main effect of sampling. Further, there were no associations between the hormone’s composites.

In study II, participants with POAG displayed the usual peak in cortisol following morning awakening over a two-day study period. This finding indicated preservation of the CAR amongst individuals with POAG. Overall post-awakening cortisol secretion of individuals with POAG was higher in comparison to a reference data (RD) group providing support for studies which have suggested an elevation of cortisol in those with high intraocular pressure. Furthermore, self-reported visual function in the POAG group, was negatively associated with the CAR, indicating that participants who reported a lower level of visual function displayed a greater rise in cortisol following awakening. In addition, on observation of the adherence data of the POAG group, findings also revealed that participants delayed the first morning sample (> 8 minutes) more often than the RD group. These findings indicated that participants with POAG experienced difficulties adhering to the sampling protocol in comparison to the RD group with no known visual difficulties. The findings of this study prompted questions surrounding the methodologies of PACS research. With successful measures of PACS taking place in a variety of sample groups, little is known about the overall experiences of being a participant in these studies. Furthermore, to achieve a successful first morning sample, a crucial element of this research is the assumption that participants have fundamentally the same understanding of “morning awakening”.

The aim of the final study was to understand the experiences of volunteers taking part in a PACS research study and to explore the understanding of the moment of morning awakening. A thematic analysis of the interview transcripts led to the development of three overarching themes. The first theme involved the motivations for taking part, for example, participants reported ‘a sense of duty to research’. The second overarching theme encapsulated the experiences of participation. Here, participants recounted on the study’s impact on sleep, personal apprehensions, heightened cognition, disruptions to morning routine and overall habituation after initial study day. The final theme identified the understanding of the moment of morning awakening. Participants discussed the difficulty in both explicitly describing and identifying the actual point of morning awakening. PACS research studies often take for granted the ‘self-collection’ instructions provided to participants. Through qualitative analyses of interviews study III emphasise the ambiguity of morning awakening and the difficulties participants experienced during the PACS study period and the requirement for PACS researchers to consider this when recruiting participants.

Overall, the unique contribution of this programme of research is threefold. Firstly, this was the first study to assay salivary melatonin in the UK and consider the relationship between PACS and PAMS in healthy participants. Secondly, the investigation of the patterns of PACS in those POAG in comparison with a RD group is also conducted for the first time. And finally, this programme of research uses a qualitative methodology for the first time to explore the experiences of participants taking part in PACS research studies. This gives rise to several methodological recommendations and informs current best practice methodology for PACS research:

i. At the participant recruitment stage, researchers should account for sleep differences in sleep patterns.

ii. Researchers should enter an active conversation surrounding the subjectivity in the understanding of the first point of morning wakefulness.

iii. A recommendation of a minimum repeated study days (3 days) is necessary to habituate to initial participant responses.