Circadian rhythmicity and subjective wellbeing of carers under chronic stress

While acute stress tends to be associated with release of cortisol which is adaptive and assists with the capacity to meet life's challenges, prolonged stress has been linked to negative effects. Indeed, chronic stress may be associated with maladaptive physiological changes. There is increasing evidence of a bodily cost from chronic stress, termed allostatic load, due to the wear and tear on body systems, such as the hypothalamic-pituitaryadrenal axis (HPA), from chronic adjustment in the face of ongoing demand. Such changes are considered likely to compromise the ongoing capacity for homeostasis and health. It appears that this physiological disturbance may be linked to corresponding disruption to both immune functioning and circadian, or daily, body rhythms. Circadian patterns within body systems allow synchronisation of behavioural needs and their physiological prerequisites. Circadian cortisol patterns allow predictive homeostasis with respect to regular daily challenges such as a morning peak to support the change from rest to meeting the challenges of a new day. Under chronic stress, however, the resetting of daily pattern of HPA activity may occur, with lowering of the typical morning rise a potential physiological strategy to down-regulate excessive cortisol levels. However, in the longer term such changes are considered to be likely to have negative consequences for health. While diurnal patterns of the stress hormone cortisol have been the focus of much research to date, the hormone melatonin is considered to be an excellent marker of circadian rhythmicity and is beginning to be taken into account in studies of chronic stress. While such indications tend to support the notion of stress as the perception of a threat to bodily homeostasis, an alternative view is that of Lazarus and Folkman, that stress results from the sense that one's wellbeing is at threat. Recent definitions of subjective wellbeing (SWB) describe it as a global assessment of psychological functioning which is made up of both an affective and cognitive assessment of satisfaction with one's life circumstances. The maintenance of SWB has been proposed to involve the protection of an underlying mood state within a narrow adaptive range. These efforts toward SWB homeostasis, however, are only thought to be effective up to an individual stress threshold, beyond which failure of SWB, and lack of resilience to external events, will likely result. SWB in the dissatisfied range has been described as indicative of homeostatic failure and high risk of depression. It has recently been proposed that this sense of personal wellbeing may, in fact, represent the reading of an underlying biological state, or core affect. Despite recent indications that SWB may represent the subjective experience of the underlying physiology necessary for adaptive mood and positive engagement with the world, the links between possible circadian dysregulation and SWB under conditions of chronic stress have not been explored. Unpaid family caregiving has been called a prototypical chronic stressor. Primary carers, who provide the bulk of the care required, are particularly likely to experience chronic adversity and subsequent health and wellbeing decrements. To date, studies of the circadian effects on carers' immunity and cortisol rhythmicity have produced mixed results. The diurnal patterns of melatonin and core body temperature have not been investigated among primary carers. The current study sought to examine the biopsychosocial effects of chronic stress among informal family carers by examining the links between circadian rhythmicity, immunity and SWB. It was predicted that primary carers would exhibit reduced levels of immunity as well as circadian dysregulation of melatonin, cortisol, and core body temperature in the form of reduced amplitude of the diurnal pattern. A sample of 31 carers who had been in their caring role for a minimum of two years (max 40 years) were compared with 35 age and gendermatched non-carers. Participants collected saliva samples in the morning and evening for two consecutive days and kept a 7-day sleep diary while maintaining their regular routine. From the saliva samples, determinations were made for morning and evening cortisol and melatonin and for morning sIgA antibody levels. Participants also completed psychological scales to measure stress, distress, hassles, uplifts, coping strategies, subjective wellbeing, social functioning and circadian preference. A subset of 20 participants also collected core body temperature data using a rectal temperature sensor for 24 hours. All data collection took place within one week of late spring. The results showed substantially poorer outcomes for carers across all psychological measures compared to non-carers. In particular, carers were differentiated by high levels of stress and low SWB and social functioning. However, they did not show reduced sIgA levels or indicate dysregulation of cortisol or core body temperature rhythms. However, the findings did provide evidence of disturbed melatonin patterns among carers, with higher morning values and blunted amplitude. Furthermore, treatment of the data according to SWB levels, showed that carers were more likely to report dissatisfaction with life and that individuals in the dissatisfied SWB range exhibited cortisol dysregulation in the form of lower morning values and blunted amplitude. The current study provides support for the view that poor quality sleep and circadian dysregulation of melatonin are likely consequences of chronic carer stress. Further, the current results also indicate that failure of SWB maintenance appears to be associated with disturbed cortisol rhythmicity. Taken together, the current findings point to sleep disturbance as a potentially critical component of chronic stress effects. This study also lends support to the notion that SWB may represent the subjective reading of a physiological state associated with cortisol synchrony and biological readiness to engage with the world. Further investigation of chronic stress effects may have the potential to suggest interventions, both short-term such as administration of melatonin or its agonists, and long-term, toward addressing chronic disadvantage and provision of adequate support to those experiencing chronic adversity. Moreover, better understanding of the links between SWB and circadian rhythmicity, as a possible physical underpinning, has the potential to improve knowledge of the physiological basis of quality of life