Diurnal Cortisol Slope Mediates the Association Between Affect and Memory Retrieval in Older Adults With Mild Cognitive Impairment: A Path-Analytical Study

Life-course stress, cognition, and diurnal cortisol in memory clinic patients without dementia

AIMS

To examine associations of life-course stress with cognition and diurnal cortisol patterns in older adulthood, as well as potential mediation effects of diurnal cortisol patterns and perceived stress on the association between life-course stress and cognition.

METHODS

127 participants without dementia were selected from a cohort of Swedish memory clinic patients. Cross-sectional associations between scores on two chronic stress questionnaires (perceived stress, stressful life events (SLEs)), five cognitive domains (overall cognition, memory, working memory, processing speed, perceptual reasoning), and two measures of diurnal cortisol patterns (total daily output, diurnal cortisol slope), as well as potential mediation effects of diurnal cortisol patterns and perceived stress on associations between life-course stress and cognition, were assessed using linear regressions.

RESULTS

Greater lifetime exposure to SLEs was associated with worse memory, working memory, and processing speed performance, but not with diurnal cortisol patterns. A greater number of SLEs in late childhood was associated with worse working memory and processing speed, while a greater number of SLEs in non-recent adulthood were associated with better overall cognition and perceptual reasoning. Greater perceived stress was associated with a flattened diurnal cortisol slope, but not with cognition. No evidence for interplay between self-reported and physiological stress markers was found in relation to cognition, although there appeared to be a significant positive indirect association between economic/legal SLEs and the diurnal cortisol slope via perceived stress.

CONCLUSIONS

The associations between SLEs and cognition depend on the period during which SLEs occur, but seem independent of late-life cortisol dysregulation.

Circadian Rhythm Changes in Healthy Aging and Mild Cognitive Impairment

Disruptions in circadian rhythms can occur in healthy aging; however, these changes are more severe and pervasive in individuals with age-related and neurodegenerative diseases, such as dementia. Circadian rhythm alterations are also present in preclinical stages of dementia, for example, in patients with mild cognitive impairments (MCI); thus, providing a unique window of opportunity for early intervention in neurodegenerative disorders. Nonetheless, there is a lack of studies examining the association between relevant changes in circadian rhythms and their relationship with cognitive dysfunctions in MCI individuals. In this review, circadian system alterations occurring in MCI patients are examined compared to healthy aging individuals while also considering their association with MCI neurocognitive alterations. The main findings are that abnormal circadian changes in rest-activity, core body temperature, melatonin, and cortisol rhythms appear in the MCI stage and that these circadian rhythm disruptions are associated with some of the neurocognitive deficits observed in MCI patients. In addition, preliminary evidence indicates that interventions aimed at restoring regular circadian rhythms may prevent or halt the progress of neurodegenerative diseases and mitigate their related cognitive impairments. Future longitudinal studies with repeated follow-up assessments are needed to establish the translational potential of these findings in clinical practice.

Physical Activity and Cortisol Regulation: A Meta-Analysis

Physical activity participation is associated with effective stress coping, indicated by decreases in both physiological stress reactivity and perceived stress. Quantifying the effect of physical activity on the diurnal regulation of one key physiological stress indicator, the stress hormone, cortisol, across studies may demonstrate the extent to which physical activity participation is associated with diurnal HPA axis regulation. We meta-analyzed studies examining relations between physical activity participation and indices of HPA axis regulation: the diurnal cortisol slope and the cortisol awakening response. We also examined moderators of the relation. The analysis revealed a small, non-zero negative averaged correlation between physical activity and the diurnal cortisol slope (r = -0.043, 95% CI [-0.080, -0.004]). Examination of sample sociodemographic differences, study design characteristics, cortisol measurement methods, and physical activity variables as moderators revealed few effects on the relation between physical activity and diurnal cortisol slope. We did not observe lower levels of variability in the mean cortisol awakening response at higher levels of physical activity participation, and moderator analyses showed little evidence of reductions in heterogeneity for this effect. We found some evidence of systematic publication bias. Findings suggest higher physical activity is associated with a steeper diurnal cortisol slope. However, the cortisol awakening response did not differ by physical activity level. Future studies testing the physical activity and cortisol regulation association should use standardized physical activity measures, follow guidelines for better quality cortisol sampling collection and analysis, and test relations in large-scale empirical studies to confirm the direction and causality of the effect.

Adrenal aging and its effects on the stress response and immunosenescence

Normal aging is linked to various endocrine gland changes, including changes in the adrenal glands. Aging is linked to alterations of the hypothalamic-pituitary-adrenal (HPA) axis, including an increase in cortisol levels, a disruption of the negative cortisol feedback, and attenuation of cortisol's diurnal pattern. In addition, secretion of aldosterone and adrenal androgens [dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS)] from the adrenal cortex decreases with aging. In this review, we describe normal adrenal function, the adrenal response to stress and immunomodulation in aging individuals as well as the effects of adrenal aging on body composition, metabolic profile, bone health and cognition.

Current Views on the Role of Stress in the Pathogenesis of Chronic Neurodegenerative Diseases

The review summarizes the results of studies on the cellular and molecular mechanisms mediating the impact of stress on the pathogenesis of neurodegenerative brain pathologies (Alzheimer's disease, Parkinson's disease, etc.) and presents current information on the role of stress in the hyperphosphorylation of tau protein, aggregation of beta-amyloid, and hyperactivation of the hypothalamic-pituitary-adrenal axis involved in the hyperproduction of factors that contribute to the pathogenetic role of stress in neurodegeneration. The data on the participation of microglia in the effects of stress on the pathogenesis of neurodegenerative diseases are presented.