Sleep Characteristics and Risk of Stroke and Dementia: An Observational and Mendelian Randomization Study

Modifiable lifestyle factors influencing neurological and psychiatric disorders mediated by structural brain reserve: An observational and Mendelian randomization study

BACKGROUND

Modifiable lifestyle factors are implicated as risk factors for neurological and psychiatric disorders, but whether these associations are causal remains uncertain. We aimed to evaluate associations and ascertain causal relationships between modifiable lifestyle factors, neurological and psychiatric disorder risk, and brain structural magnetic resonance imaging (MRI) markers.

METHODS

We analyzed data from over 50,000 UK Biobank participants with self-reported lifestyle factors, including alcohol consumption, smoking, physical activity, diet, sleep, electronic device use, and sexual factors. Primary outcomes were stroke, all-cause dementia, Parkinson's disease (PD), Major depression disorder (MDD), Anxiety Disorders (ANX), and Bipolar Disorder (BIP), alongside MRI markers. Summary statistics were obtained from genome-wide association studies and Mendelian randomization (MR) analyses investigated bidirectional associations between lifestyle factors, neurological/psychiatric disorders, and MRI markers, with mediation assessed using multivariable Mendelian randomization (MVMR).

RESULTS

Cross-sectional analyses identified lifestyle factors were associated with neurological and psychiatric disorders and brain morphology. MR confirmed causal relationships, including lifetime smoking index on Stroke, PD, MDD, ANX and BIP; play computer games on BIP; leisure screen time on Stroke and MDD; automobile speeding propensity on MDD; sexual factors on MDD and BIP; sleep characteristics on BIP and MDD. Brain structure mediated several lifestyle-disorder associations, such as daytime dozing and dementia, lifetime smoking and PD and age first had sexual intercourse and PD.

CONCLUSION

Our results provide support for a causal effect of multiple lifestyle measures on the risk of neurological and psychiatric disorders, with brain structural morphology serving as a potential biological mediator in their associations.

The link between sleep duration and stroke risk

In this review paper, we explore the complex relationship between sleep duration and stroke risk, outlining the association of both insufficient sleep and excessive sleep with an increased risk of cerebrovascular diseases. We explore a U-shaped relationship between sleep duration and cardiovascular outcomes, including stroke. Our review explores findings from cohort studies, meta-analyses, and Mendelian randomization studies, highlighting the nuanced findings and identifying gaps in the current literature. We discussed the direct and indirect effects of sleep duration on stroke risk, considering factors such as atherosclerosis, atrial fibrillation, hypertension, and hyperlipidemia. We also discuss the methodological challenges inherent in current studies, such as the reliance on self-reported sleep measures and the need for more objective and comprehensive assessments. The paper emphasizes the importance of recognizing individual variations in optimal sleep duration and the potential confounding effects of sleep quality and other sleep-related disorders on stroke risk. Furthermore, we explore the potential mechanisms by which sleep duration may influence endothelial function, oxidative stress, and vascular compliance, suggesting areas for future investigation. The paper makes a compelling case for the inclusion of sleep duration as a key factor in stroke prevention strategies, recommending that healthcare professionals proactively assess and manage sleep patterns to mitigate stroke risk.

Excessive sleep is associated with worse cognition, cognitive decline, and dementia in mild cognitive impairment

INTRODUCTION

This study examines the link between daytime and nighttime excessive sleep and cognition, cognitive decline, and dementia in individuals with existing mild cognitive impairment (MCI).

METHODS

Using data from the Swedish longitudinal study Good Aging in Skåne, participants aged 60-102 years were retrospectively classified as MCI based on cognitive testing. The average follow-up time was 6.59 years. Mixed linear models assessed cross-sectional and longitudinal associations between excessive sleep patterns (napping ≥2 h or nighttime sleep ≥9 h) and multiple cognitive domains. Cox regressions estimated dementia risk for excessive sleep.

RESULTS

Of 4930 participants, 2052 (41%) had MCI. Excessive daytime napping and nighttime sleep were associated with worse cognition and cognitive decline. Excessive napping and nighttime sleep were also linked to higher dementia risk (hazard ratios: 1.75 and 1.86, respectively).

DISCUSSION

These findings suggest that excessive sleep in MCI is associated with further cognitive decline and dementia.

Highlights

Excessive daytime napping and nighttime sleep are linked cognitive decline for those with MCI.Excessive sleep during the day or at night heighten dementia risk.Worse test scores across multiple cognitive domains were observed for excessive daytime nappers.Excessive sleep in MCI may be a warning sign for further cognitive decline.

Review of recently published articles

Aysha Mendes provides a synopsis and brief review of a selection of recently published research articles that are of interest to community nurses.

Associations of sleep disorders with all-cause MCI/dementia and different types of dementia - clinical evidence, potential pathomechanisms and treatment options: A narrative review

Due to worldwide demographic change, the number of older persons in the population is increasing. Aging is accompanied by changes of sleep structure, deposition of beta-amyloid (Aß) and tau proteins and vascular changes and can turn into mild cognitive impairment (MCI) as well as dementia. Sleep disorders are discussed both as a risk factor for and as a consequence of MCI/dementia. Cross-sectional and longitudinal population-based as well as case-control studies revealed sleep disorders, especially sleep-disorderded breathing (SDB) and excessive or insufficient sleep durations, as risk factors for all-cause MCI/dementia. Regarding different dementia types, SDB was especially associated with vascular dementia while insomnia/insufficient sleep was related to an increased risk of Alzheimer's disease (AD). Scarce and still inconsistent evidence suggests that therapy of sleep disorders, especially continuous positive airway pressure (CPAP) in SDB, can improve cognition in patients with sleep disorders with and without comorbid dementia and delay onset of MCI/dementia in patients with sleep disorders without previous cognitive impairment. Regarding potential pathomechanisms via which sleep disorders lead to MCI/dementia, disturbed sleep, chronic sleep deficit and SDB can impair glymphatic clearance of beta-amyloid (Aß) and tau which lead to amyloid deposition and tau aggregation resulting in changes of brain structures responsible for cognition. Orexins are discussed to modulate sleep and Aß pathology. Their diurnal fluctuation is suppressed by sleep fragmentation and the expression suppressed at the point of hippocampal atrophy, contributing to the progression of dementia. Additionally, sleep disorders can lead to an increased vascular risk profile and vascular changes such as inflammation, endothelial dysfunction and atherosclerosis which can foster neurodegenerative pathology. There is ample evidence indicating that changes of sleep structure in aging persons can lead to dementia and also evidence that therapy of sleep disorder can improve cognition. Therefore, sleep disorders should be identified and treated early.