Sleep duration, sleep problems, and perceived stress are associated with hippocampal subfield volumes in later life: findings from The Irish Longitudinal Study on Ageing.

STUDY OBJECTIVES: This study examines the cross-sectional and 2-year follow-up relationships between sleep and stress and total hippocampal volume and hippocampal subfield volumes among older adults. METHODS: Four hundred seventeen adults (aged 68.8 ± 7.3; 54% women) from the Irish Longitudinal Study on Ageing completed an interview, a questionnaire, and multiparametric brain magnetic resonance imaging. The relationships between self-reported sleep duration, sleep problems, perceived stress, and total hippocampal volume were examined by using ordinary least squares regressions. Linear mixed-effects models were used to investigate the relationships between sleep duration, sleep problems, perceived stress, changes in these measures over 2-years, and hippocampal subfield volumes. RESULTS: No cross-sectional and follow-up associations between sleep and total hippocampal volume and between stress and total hippocampal volume were found. By contrast, Long sleep (≥9-10 h/night) was associated with smaller volumes of molecular layer, hippocampal tail, presubiculum, and subiculum. The co-occurrence of Short sleep (≤6 h) and perceived stress was associated with smaller cornu ammonis 1, molecular layer, subiculum, and tail. Sleep problems independently and in conjunction with higher stress, and increase in sleep problems over 2 years were associated with smaller volumes of these same subfields. CONCLUSION: Our study highlights the importance of concurrently assessing suboptimal sleep and stress for phenotyping individuals at risk of hippocampal subfield atrophy.

The Association Between Hair Cortisol, Hair Cortisone, and Cognitive Function in a Population-Based Cohort of Older Adults: Results From The Irish Longitudinal Study on Ageing.

Experimental evidence to date largely supports an association between the stress hormone cortisol and cognitive performance. Older adults, in particular, may be vulnerable to the neurotoxic effects of prolonged increases in cortisol; however, the assessment of chronic hormone levels has previously been challenging. Hair cortisol analysis has advantages over other cortisol metrics for this purpose as it facilitates the assessment of total hormone secretion over several months. Cortisol and cortisone were measured in the scalp hair of 1,876 older adults from The Irish Longitudinal Study on Ageing. Participants underwent a battery of cognitive tests assessing global function, memory, executive function, and processing speed. After adjustment for hair characteristics, demographics, metabolic risk factors, cardiovascular conditions, and depression, regression analysis revealed an inverse relationship of hair glucocorticoids to immediate (cortisol: ß = -.12, p = .032; cortisone: ß = -.021, p = .036) and delayed (cortisol: ß = -.13, p = .003; cortisone: ß = -.23, p = .006) word recall performance. They were also associated with more errors on the Mini-Mental State Examination (cortisol: incidence rate ratio (IRR) = 1.06, p = .008; cortisone: IRR = 1.14, p = .002) and Montreal Cognitive Assessment (cortisone: IRR = 1.06, p = .015). Higher hair glucocorticoids are inversely associated with memory and global cognition in a population-based sample of older adults. Future work should explore the prognostic significance of these findings.