Nocturnal sleep apnea/hypopnea is associated with lower memory performance in APOE ε4 carriers

The impact of brain-systemic oxygenation coupling in sleep-disordered breathing on cognitive function in elderly

BACKGROUND

Intermittent hypoxia, a consequence of sleep-disordered breathing (SDB), may contribute to an increased risk of cognitive decline. However, the association between SDB and cognition remains highly variable.

METHODS

Fifty-two community-dwelling healthy older adults (28 women) were recruited. All participants underwent neuropsychiatric evaluations, simultaneous ambulatory polysomnography (PSG), and near-infrared spectroscopy (NIRS) recordings. We quantified the average coherence between oxy-Hb and SpO2 signals during SDB events to determine whether it could predict cognitive outcomes in healthy older adults, where higher coherence indicates reduced protection against systemic hypoxia.

RESULTS

The mean (SD) coherence of oxy-Hb and SpO2 was 0.16 (0.07). Linear regression analysis showed a significant association between mean coherence and worse Stroop Color Word Test scores (t=-0.304, p = .004). In contrast, oxy-Hb reduction alone and conventional SDB parameters did not show a significant association with cognition.

CONCLUSION

This is the first report to demonstrate an association between a novel parameter of brain-systemic oxygenation coherence in SDB and cognition in older adults. A higher coherence rate of cortical oxy-Hb and systemic SpO2 during SDB may reflect a loss of compensatory mechanisms against systemic hypoxia and could help stratify older adults with a higher risk for cognitive decline.

Biomarkers of sleep-wake disturbance as predictors of cognitive decline and accelerated disease progression

INTRODUCTION

In older adults, where sleep disturbances and cognitive impairment are common, mounting evidence suggests a potential connection between sleep and cognitive function, highlighting the significance of utilizing sleep as a biomarker for early detection of cognitive impairment to improve clinical outcomes in a noninvasive, cost-effective manner.

AREAS COVERED

This review describes the relationship between sleep and cognitive function in older adults, encompassing both subjective and objective measures of sleep quality, duration, architecture, and sleep-disordered breathing. The authors consider the directionality of the associations observed in prospective and cross-sectional studies, exploring whether sleep disturbances precede cognitive decline or vice versa. Furthermore, they discuss the potential bidirectional relationships between sleep and Alzheimer's disease (AD) risks in older adults while also examining the neurodegenerative pathways of this relationship.

EXPERT OPINION

Routine sleep monitoring in primary care settings has the potential to bolster early detection and treatment of sleep disturbance, and by extension, reduce the risk of dementia. Improving sleep assessment tools, such as wearables, provide scalable alternatives to traditional methods like polysomnography, potentially enabling widespread monitoring of sleep characteristics. Standardized measurement and inclusive participant recruitment are needed to enhance generalizability, while longitudinal studies are essential to understand the interaction between sleep and AD pathology.

Older adults at greater risk for Alzheimer's disease show stronger associations between sleep apnea severity in REM sleep and verbal memory

BACKGROUND

Obstructive sleep apnea (OSA) increases risk for cognitive decline and Alzheimer's disease (AD). While the underlying mechanisms remain unclear, hypoxemia during OSA has been implicated in cognitive impairment. OSA during rapid eye movement (REM) sleep is usually more severe than in non-rapid eye movement (NREM) sleep, but the relative effect of oxyhemoglobin desaturation during REM versus NREM sleep on memory is not completely characterized. Here, we examined the impact of OSA, as well as the moderating effects of AD risk factors, on verbal memory in a sample of middle-aged and older adults with heightened AD risk.

METHODS

Eighty-one adults (mean age:61.7 ± 6.0 years, 62% females, 32% apolipoprotein E ε4 allele (APOE4) carriers, and 70% with parental history of AD) underwent clinical polysomnography including assessment of OSA. OSA features were derived in total, NREM, and REM sleep. REM-NREM ratios of OSA features were also calculated. Verbal memory was assessed with the Rey Auditory Verbal Learning Test (RAVLT). Multiple regression models evaluated the relationships between OSA features and RAVLT scores while adjusting for sex, age, time between assessments, education years, body mass index (BMI), and APOE4 status or parental history of AD. The significant main effects of OSA features on RAVLT performance and the moderating effects of AD risk factors (i.e., sex, age, APOE4 status, and parental history of AD) were examined.

RESULTS

Apnea-hypopnea index (AHI), respiratory disturbance index (RDI), and oxyhemoglobin desaturation index (ODI) during REM sleep were negatively associated with RAVLT total learning and long-delay recall. Further, greater REM-NREM ratios of AHI, RDI, and ODI (i.e., more events in REM than NREM) were related to worse total learning and recall. We found specifically that the negative association between REM ODI and total learning was driven by adults 60 + years old. In addition, the negative relationships between REM-NREM ODI ratio and total learning, and REM-NREM RDI ratio and long-delay recall were driven by APOE4 carriers.

CONCLUSION

Greater OSA severity, particularly during REM sleep, negatively affects verbal memory, especially for people with greater AD risk. These findings underscore the potential importance of proactive screening and treatment of REM OSA even if overall AHI appears low.

Obstructive sleep apnea and cognitive functioning in the older general population: The moderating effect of age, sex, ApoE4, and obesity

Research on the relationship between obstructive sleep apnea and cognitive functioning has yielded conflicting results, particularly in the older population, and moderators of this association have rarely been studied. Here we investigated the cross-sectional association between obstructive sleep apnea and cognitive functioning as well as the moderating effect of age, sex, apolipoprotein E4, and obesity on this association among community-dwelling older people. We analysed data from 496 participants (71.4 ± 4.4 years; 45.6% men) of the HypnoLaus study who underwent polysomnography and a battery of neuropsychological tests. The sample was categorised as no-to-mild obstructive sleep apnea (apnea-hypopnea index 0-14.9/h; reference), moderate obstructive sleep apnea (apnea-hypopnea index 15.0-29.9/h), or severe obstructive sleep apnea (apnea-hypopnea index ≥30/h). Regression and moderation analyses were performed with adjustment for confounders. Apolipoprotein E4 and obesity moderated the association between severe obstructive sleep apnea and processing speed, whereas no moderating effects were found for age and sex. In apolipoprotein E4 carriers only, severe obstructive sleep apnea was associated with lower performance in Stroop condition 1 (B = 3.13, p = 0.024). In obese participants only, severe obstructive sleep apnea was associated with lower performance in Stroop condition 1 (B = 3.02, p = 0.025) and Stroop condition 2 (B = 3.30, p = 0.034). Severe obstructive sleep apnea was also associated with lower executive function in the whole sample according to Stroop condition 3 (B = 3.44, p = 0.020) and Stroop interference score (B = 0.24, p = 0.006). Our findings support associations of severe obstructive sleep apnea (but not moderate obstructive sleep apnea) with lower performance in processing speed and executive function in the older general population. Apolipoprotein E4 and obesity appear to be vulnerability factors that strengthen the association between severe obstructive sleep apnea and lower performance in processing speed.

Impact of PTSD and Obstructive Sleep Apnea on Cognition in Older Adult Veterans

Background: Posttraumatic stress disorder (PTSD) and obstructive sleep apnea (OSA) are highly prevalent and comorbid among older adult male veterans. Both PTSD and OSA are independently associated with cognitive deficits in older adults, but little research regarding the impact of comorbid PTSD and OSA among older adults exists. Purpose: The current study aimed to examine the independent and interactive effects of PTSD and OSA on cognitive functioning in older adult veterans. Study Sample: Older adult male veterans with (n = 106) and without PTSD (n = 69), ranging in age from 55 to 89 (M = 63.35). Data Collection: Participants underwent polysomnography evaluation to assess severity of OSA symptoms and comprehensive neuropsychological evaluation to assess cognitive functioning in 3 domains: attention and processing speed, learning and memory, and executive functioning. Results: Multiple regression analyses showed that the interaction between PTSD and OSA did not predict cognitive performance. However, PTSD significantly predicted poorer attention and processing speed, and increased OSA severity predicted poorer learning and memory. Conclusions: While PTSD and OSA did not have a synergistic detrimental impact on cognition, each independently predicted poorer cognitive functioning within certain domains, suggesting that older adults with these comorbid conditions may experience a wider array of cognitive difficulties.

Associations Between Amyloid Burden, Hypoxemia, Sleep Architecture, and Cognition in Obstructive Sleep Apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with an increased risk of amyloid-β (Aβ) burden, the hallmark of Alzheimer's disease, and cognitive decline.

OBJECTIVE

To determine the differential impacts of hypoxemia and slow-wave sleep disruption on brain amyloid burden, and to explore the effects of hypoxemia, slow-wave sleep disruption, and amyloid burden on cognition in individuals with and without OSA.

METHODS

Thirty-four individuals with confirmed OSA (mean±SD age 57.5±4.1 years; 19 males) and 12 healthy controls (58.5±4.2 years; 6 males) underwent a clinical polysomnogram, a NAV4694 positron emission tomography (PET) scan for Aβ burden, assessment of APOEɛ status and cognitive assessments. Linear hierarchical regressions were conducted to determine the contributions of demographic and sleep variables on amyloid burden and cognition.

RESULTS

Aβ burden was associated with nocturnal hypoxemia, and impaired verbal episodic memory, autobiographical memory and set shifting. Hypoxemia was correlated with impaired autobiographical memory, and only set shifting performance remained significantly associated with Aβ burden when controlling for sleep variables.

CONCLUSIONS

Nocturnal hypoxemia was related to brain Aβ burden in this sample of OSA participants. Aβ burden and hypoxemia had differential impacts on cognition. This study reveals aspects of sleep disturbance in OSA that are most strongly associated with brain Aβ burden and poor cognition, which are markers of early Alzheimer's disease. These findings add weight to the possibility that hypoxemia may be causally related to the development of dementia; however, whether it may be a therapeutic target for dementia prevention in OSA is yet to be determined.

Interaction between apolipoprotein E genotypes, excessive daytime sleepiness, and cognitive function in obstructive sleep apnea patients

BACKGROUND

Some studies show an association between the apolipoprotein E ε4 allele (ApoEε4) and obstructive sleep apnea syndrome (OSAS), and other studies, an association between ApoEε4 and excessive daytime sleepiness (EDS), but there are no data in the literature on the interaction between EDS, cognitive function, and ApoEε4 in patients with OSA.

OBJECTIVE

To examine the cognitive function of adults with and without EDS and with and without ApoEε4.

METHODS

A total of 21 male and female patients aged between 33 and 79 years, underwent a clinical interview, ApoE genotyping, neuropsychological evaluation, polysomnography, and the application of the Epworth Sleepiness Scale.

RESULTS

Excessive daytime sleepiness was associated with lower intelligence quotient (IQ; total performance) and worse immediate visual memory, regardless of the ApoE genotype. Patients carrying the ApoEε3/ε4 genotype had a worse performance in divided attention, constructional praxis, perceptual organization, and cognitive flexibility. A combination of the ε4 allele and EDS potentiates the negative effect on cognition, except for immediate visual memory. In this case, patients had a worse performance in terms of processing speed, selective attention, and visuomotor coordination.

CONCLUSIONS

Excessive daytime sleepiness and the ApoEε3/ε4 genotype are associated with worse cognitive performance in OSA patients. The combination of EDS and ε4 allele potentiates cognitive impairment.

Positive Airway Pressure and Cognitive Disorders in Adults With Obstructive Sleep Apnea: A Systematic Review of the Literature

BACKGROUND AND OBJECTIVES

Alzheimer disease (AD) and other forms of dementia represent a rising global public health crisis. Because effective treatments to prevent, cure, or slow progression of dementia are unavailable, identification of treatable risk factors that increase dementia risk such as obstructive sleep apnea (OSA) could offer promising means to modify dementia occurrence or severity. Here, we systematically reviewed the impact of positive airway pressure (PAP) therapy on the incidence of cognitive disorders and cognitive decline among middle-aged and older adults with OSA.

METHODS

We performed a systematic search of MEDLINE, EMBASE, Scopus, and CINAHL before May 2021 to identify articles that focused on associations between PAP therapy use and cognitive disorders. We included studies that examined the effects of PAP treatment on (1) the incidence of cognitive disorders among individuals ≥40 years of age diagnosed with OSA and (2) the progression of cognitive decline among people with preexisting cognitive disorders and OSA.

RESULTS

We identified 11 studies (3 clinical trials and 8 observational studies). In these studies, 96% participants had OSA (n = 60,840) and 9% had baseline cognitive impairment (mild cognitive impairment [MCI] or AD) (n=5,826). Of all study participants, 43,970 obtained PAP therapy, and 16,400 were untreated or in a placebo group. Nine out of 11 studies reported a protective effect of PAP therapy on MCI and AD incidence, e.g., delayed age at MCI onset, reduced MCI or AD incidence, slower cognitive decline, or progression to AD.

DISCUSSION

These findings suggest a role for OSA as a modifiable risk factor for cognitive decline. Identification of modifiable risk factors is imperative for alleviating the impact of cognitive disorders on aging adults and their family members. Future research should build on this review and focus on PAP interventions as a potential means to alleviate the incidence of cognitive disorders and cognitive decline, particularly among ethnoracial groups who have been underrepresented and underinvestigated in the extant literature.

Effects of exercise training on brain metabolism and cognitive functioning in sleep apnea

Impaired glucose metabolism reflects neuronal/synaptic dysfunction and cognitive function decline in patients with obstructive sleep apnea (OSA). The study investigated the extent to which exercise training (ET) improves cerebral metabolic glucose rate (CMRgl) and cognitive function in patients with OSA. Patients with moderate to severe OSA were randomly assigned to ET (3 times/week, n = 23) or no intervention (control, n = 24). Echocardiography and apolipoprotein ε4 (APOEε4) genotyping were obtained at baseline. Both groups underwent cardiopulmonary exercise testing, polysomnography, cognitive tests, brain magnetic resonance imaging, and ¹⁸F-fluoro-2-deoxy-d-Glucose positron emission tomography (¹⁸FDG-PET) at baseline and study end. Compared with control, exercise-trained group had improved exercise capacity, decreased apnea–hypopnea index (AHI), oxygen desaturation and arousal index; increased attention/executive functioning, increased CMRgl in the right frontal lobe (P < 0.05). After ET an inverse relationships occurred between CMRgl and obstructive AHI (r = − 0.43, P < 0.05) and apnea arousal index (r = − 0.53, P < 0.05), and between the changes in CMRgl and changes in mean O₂ saturation during sleep and non-rapid eye movement sleep (r = − 0.43, P < 0.05), desaturation during arousal (r = − 0.44, P < 0.05), and time to attention function testing (r = − 0.46, P < 0.05). ET improves OSA severity and CMRg in the frontal lobe, which helps explain the improvement in attention/executive functioning. Our study provides promising data that reinforce the growing idea that ET may be a valuable tool to prevent hypoxia associated with decreased brain metabolism and cognitive functioning in patients with moderate to severe OSA.

Trial registration: NCT02289625 (13/11/2014).

Sleep and Cognition: A Narrative Review Focused on Older Adults

Little is known regarding sleep's association with the traditional developmental course of late-life cognitive functioning. As the number of older adults increases worldwide, an enhanced understanding of age-related changes in sleep and cognition is necessary to slow decline and promote optimal aging. This review synthesizes the extant literature on sleep and cognitive function in healthy older adults, older adults with insomnia, and older adults with sleep apnea, incorporating information on the potential promising effects of treating poor sleep on cognitive outcomes in older adults. Unifying theories of the sleep-cognition association, possible mechanisms of action, and important unanswered questions are identified.

APOE ε4, Alzheimer's disease neuropathology and sleep disturbance, in individuals with and without dementia

Background

Apolipoprotein E epsilon 4 (APOE-ε4) carrier status is an established risk factor for Alzheimer’s disease (AD) dementia. It has also been linked with sleep disturbance in healthy older adults and increased insomnia risk. This association may be driven by the effect of APOE-ε4 on AD pathological change, itself associated with sleep abnormalities. To assess this relationship, we have evaluated post-mortem neuropathological findings in patients with and without cognitive impairment and AD pathology, who had extensive clinical assessment within 12 months of death.

Methods

This retrospective cohort study used UK Brain Banks Network data. Eligible subjects were aged over 50, with pre-mortem neuropsychiatry inventory scores of sleep disturbance (NPI-K), neurocognitive testing and functional cognitive status assessment (Clinical Dementia Rating scale). Neuropathological data included Thal phase, Braak stage and CERAD scores (measures of Aβ plaque distribution, tangle distribution and neuritic plaque density, respectively) combined to form the National Institute on Aging Alzheimer’s Association (NIA-AA) ABC score reflecting AD neuropathology. Participants with other significant intracerebral pathology or pathological features of non-AD dementia were excluded.

Multivariate linear regression was performed with NPIK Global Score (NPIK frequency score multiplied by severity score) as the dependent variable and APOE-ε4 heterozygosity or homozygosity as independent variables. Covariates included age, gender, APOE-ε2 status and ABC NPI measures reflecting depression and anxiety. Further models stratified by ABC score and functional cognitive status were also produced.

Results

Seven hundred twenty-eight records were identified. Two hundred two participants were included in the final analysis: mean (SD) age 84.0 (9.2) and MMSE 14.0 (11.8). Mean sleep disturbance scores were highest in ε4 homozygosity (n=11), 4.55 (5.4); intermediate in ε4 heterozygosity (n=95), 2.03 (4.0); and lowest in non-ε4 carriers (n=96), 1.36 (3.3). Within the full sample, controlling for pathological status, age, gender, depression, anxiety and CDR-SOB status, APOE-ε4 homozygosity was associated with sleep disturbance (β 2.53, p=0.034). APOE-ε4 heterozygosity was similarly associated in individuals without dementia (β 1.21, p=0.048).

Conclusion

These findings lend weight to the hypothesis that APOE-ε4 affects sleep by mechanisms independent of AD pathological change. Evaluation of those mechanisms would enhance understanding of sleep disturbance pathways and potentially provide treatment targets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00992-y.

The Role of Amyloid, Tau, and APOE Genotype on the Relationship Between Informant-Reported Sleep Disturbance and Alzheimer's Disease Risks

BACKGROUND

The association between sleep and Alzheimer's disease (AD) biomarkers are well-established, but little is known about how they interact to change the course of AD.

OBJECTIVE

To determine the potential interaction between sleep disturbance and Aβ, tau, and APOE4 on brain atrophy and cognitive decline.

METHODS

Sample included 351 participants (mean age 72.01 ± 6.67, 50.4%female) who were followed for approximately 5 years as part of the Alzheimer's Disease Neuroimaging Initiative. Informant-reported sleep disturbance (IRSD) was measured using the Neuropsychiatric Inventory (NPI). Changes in magnetic resonance imaging (MRI)-measured AD signature brain regions and cognitive performance and IRSD's interaction with cerebrospinal fluid amyloid-β (Aβ42) and p-Tau depositions and APOE4 status were examined using the linear mixed models.

RESULTS

Baseline IRSD was not significantly associated with the rate of atrophy after adjusting for covariates (age, sex, education, total NPI severity score, and sleep medications). However, there was a significant interaction between IRSD and AD biomarkers on faster atrophy rates in multiple brain regions, including the cortical and middle temporal volumes. Post-hoc analyses indicated that Aβ and p-Tau/Aβ predicted a faster decline in these regions/domains in IRSD, compared with biomarker-negative individuals with IRSD (ps≤0.001). There was a significant IRSD*APOE4 interaction for brain atrophy rate (ps≤0.02) but not for cognition.

CONCLUSION

IRSD may increase the future risk of AD by contributing to faster brain atrophy and cognitive decline when combined with the presence of AD biomarkers and APOE4. Early intervention for sleep disturbance could help reduce the risk of developing AD.

Neuropsychiatric Inventory-Questionnaire Assessed Nighttime Behaviors in Cognitively Asymptomatic Patients with Pathologically Confirmed Alzheimer's Disease Predict More Rapid Cognitive Deterioration

BACKGROUND

The temporal relationship between sleep, Alzheimer's disease (AD), and cognitive impairment remains to be further elucidated.

OBJECTIVE

First, we aim to determine whether the Neuropsychiatric Inventory-Questionnaire (NPI-Q) assessed nighttime behaviors prior to cognitive decline influence the rate of cognitive deterioration in pathologically confirmed AD, and second, to assess the possible interactions with APOE allele and cerebral amyloid angiopathy (CAA).

METHODS

The rate of cognitive decline between cognitively asymptomatic participants from the National Alzheimer Coordinating Center who eventually received a neuropathologic diagnosis of AD with (+NTB) or without (-NTB) nighttime behaviors were compared using independent samples t-test. Participants were stratified by APOE carrier and CAA status. Demographic and patient characteristics were assessed using descriptive statistics, and the independent samples t-test was used for continuous variables and chi-square test for categorical variables. The significance level was set at p≤0.05.

RESULTS

The rate of cognitive decline was greater in +NTB (n = 74; 3.30 points/year) than -NTB (n = 330; 2.45 points/year) (p = 0.016), even if there was no difference in cognitive status at onset. This difference was restricted to APOE ɛ4 carriers (p = 0.049) and positive CAA participants (p = 0.020). Significance was not reached in non-carriers (p = 0.186) and negative CAA (p = 0.364). APOE and CAA were not differentially distributed between the NTB groups.

CONCLUSION

NPI-Q assessed nighttime behaviors, a surrogate for sleep disturbances, are associated with more rapidly deteriorating cognition in patients with AD neuropathology who are also carriers of APOE ɛ4 or show CAA.

Neurocognitive Performance Improvement after Obstructive Sleep Apnea Treatment: State of the Art

Background: Obstructive Sleep Apnea (OSA) syndrome is a respiratory sleep disorder characterized by partial or complete episodes of upper airway collapse with reduction or complete cessation of airflow. Although the connection remains debated, several mechanisms such as intermittent hypoxemia, sleep deprivation, hypercapnia disruption of the hypothalamic–pituitary–adrenal axis have been associated with poor neurocognitive performance. Different treatments have been proposed to treat OSAS patients as continuous positive airway pressure (CPAP), mandibular advancement devices (MAD), surgery; however, the effect on neurocognitive functions is still debated. This article presents the effect of OSAS treatments on neurocognitive performance by reviewing the literature. Methods: We performed a comprehensive review of the English language over the past 20 years using the following keywords: neurocognitive performance and sleep apnea, neurocognitive improvement and CPAP, OSAS, and cognitive dysfunction. We included in the analysis papers that correlated OSA treatment with neurocognitive performance improvement. All validated tests used to measure different neurocognitive performance improvements were considered. Results: Seventy papers reported neurocognitive Performance improvement in OSA patients after CPAP therapy. Eighty percent of studies found improved executive functions such as verbal fluency or working memory, with partial neural recovery at long-term follow-up. One article compared the effect of MAD, CPAP treatment on cognitive disorders, reporting better improvement of CPAP and MAD than placebo in cognitive function. Conclusions: CPAP treatment seems to improve cognitive defects associated with OSA. Limited studies have evaluated the effects of the other therapies on cognitive function.

Cognition effectiveness of continuous positive airway pressure treatment in obstructive sleep apnea syndrome patients with cognitive impairment: a meta-analysis

Obstructive sleep apnea (OSA) is a common respiratory disorder characterized by recurrent pharyngeal collapses during sleep leading to intermittent hypoxia and sleep disruption. Cognitive challenges and high risks of cognitive impairment, including Alzheimer's disease (AD), are closely associated with OSA. Currently, continuous positive airway pressure (CPAP) is widely used in the treatment of OSA. However, whether CPAP benefits cognitive functions in patients with OSA remains elusive. Here, we identified published studies through a systematic review of PubMed, Cochrane Library, Embase, Wanfang Data, CBM, and CNKI from January 1, 1970, to July 1, 2020. 288 patients from 7 articles (one was excluded in the meta-analysis for it was a follow-up study) were included in the present study. It revealed that cognitive functions of OSA patients with mild cognitive impairment (MCI) or AD were mildly but significantly improved after CPAP treatment (SMD 0.49, 95% CI 0.11-0.86), especially long-term CPAP treatment (SMD 0.56, 95% CI 0.10-1.02, p = 0.02), as measured by Mini-Mental State Examination (MMSE) (SMD 0.49, 95%CI 0.11-0.86). However, no significant cognition benefits were detected by the Montreal Cognitive Assessment (SMD 0.43, 95% CI 0.85-1.72). In terms of heterogeneity, cognitive improvements by CPAP were detectable on OSA patients either at a younger age or over longer periods of CPAP treatment. Therefore, our findings highlight the partial efficiency of CPAP treatment in cognition improvement of OSA patients with MCI or AD.

APOE Genotype and Alzheimer's Disease: The Influence of Lifestyle and Environmental Factors

Alzheimer's disease (AD) is the most common neurodegenerative disorder with obscure pathogenesis and no disease-modifying therapy to date. AD is multifactorial disease that develops from the complex interplay of genetic factors and environmental exposures. The E4 allele of the gene encoding apolipoprotein E (APOE) is the most common genetic risk factor for AD, whereas the E2 allele acts in a protective manner. A growing amount of epidemiological evidence suggests that several lifestyle habits and environmental factors may interact with APOE alleles to synergistically affect the risk of AD development. Among them, physical exercise, dietary habits including fat intake and ketogenic diet, higher education, traumatic brain injury, cigarette smoking, coffee consumption, alcohol intake, and exposure to pesticides and sunlight have gained increasing attention. Although the current evidence is inconsistent, it seems that younger APOE4 carriers in preclinical stages may benefit mostly from preventive lifestyle interventions, whereas older APOE4 noncarriers with dementia may show the most pronounced effects. The large discrepancies between the epidemiological studies may be attributed to differences in the sample sizes, the demographic characteristics of the participants, including age and sex, the methodological design, and potential related exposures and comorbidities as possible cofounding factors. In this Review, we aim to discuss available evidence of the prominent APOE genotype-environment interactions in regard to cognitive decline with a focus on AD, providing an overview of the current landscape in this field and suggesting future directions.

Poor sleep correlates with biomarkers of neurodegeneration in mild traumatic brain injury patients: a CENC study

STUDY OBJECTIVES

Sleep disorders affect over half of mild traumatic brain injury (mTBI) patients. Despite evidence linking sleep and neurodegeneration, longitudinal TBI-related dementia studies have not considered sleep. We hypothesized that poor sleepers with mTBI would have elevated markers of neurodegeneration and lower cognitive function compared to mTBI good sleepers and controls. Our objective was to compare biomarkers of neurodegeneration and cognitive function with sleep quality in warfighters with chronic mTBI.

METHODS

In an observational warfighters cohort (n = 138 mTBI, 44 controls), the Pittsburgh Sleep Quality Index (PSQI) was compared with plasma biomarkers of neurodegeneration and cognitive scores collected an average of 8 years after injury.

RESULTS

In the mTBI cohort, poor sleepers (PSQI ≥ 10, n = 86) had elevated plasma neurofilament light (NfL, x̅ = 11.86 vs 7.91 pg/mL, p = 0.0007, d = 0.63) and lower executive function scores by the categorical fluency (x̅ = 18.0 vs 21.0, p = 0.0005, d = -0.65) and stop-go tests (x̅ = 30.1 vs 31.1, p = 0.024, d = -0.37). These findings were not observed in controls (n = 44). PSQI predicted NfL (beta = 0.22, p = 0.00002) and tau (beta = 0.14, p = 0.007), but not amyloid β42. Poor sleepers showed higher obstructive sleep apnea (OSA) risk by STOP-BANG scores (x̅ = 3.8 vs 2.7, p = 0.0005), raising the possibility that the PSQI might be partly secondary to OSA.

CONCLUSIONS

Poor sleep is linked to neurodegeneration and select measures of executive function in mTBI patients. This supports implementation of validated sleep measures in longitudinal studies investigating pathobiological mechanisms of TBI related neurodegeneration, which could have therapeutic implications.

Obstructive Sleep Apnea and Cognitive Decline: A Review of Potential Vulnerability and Protective Factors

Around 40% of dementia risk is attributable to modifiable risk factors such as physical inactivity, hypertension, diabetes and obesity. Recently, sleep disorders, including obstructive sleep apnea (OSA), have also been considered among these factors. However, despite several epidemiological studies investigating the link between OSA and cognitive decline, there is still no consensus on whether OSA increases the risk of dementia or not. Part of the heterogeneity observed in previous studies might be related to some individual characteristics that modulate the association between OSA and cognitive decline. In this narrative review, we present these individual characteristics, namely, age, sex, menopause, obesity, diabetes mellitus, hypertension, cardiovascular diseases, smoking, excessive alcohol consumption, depression, air pollution, Apolipoprotein E ε4 allele, physical activity, and cognitive reserve. To date, large cohort studies of OSA and cognitive decline tended to statistically control for the effects of these variables, but whether they interact with OSA to predict cognitive decline remains to be elucidated. Being able to better predict who is at risk of cognitive decline when they have OSA would improve clinical management and treatment decisions, particularly when patients present relatively mild OSA.

Sleep symptomatology is associated with greater subjective cognitive concerns: Findings from the community-based Healthy Brain Project

STUDY OBJECTIVES

To examine if sleep symptomatology was associated with subjective cognitive concerns or objective cognitive performance in a dementia-free community-based sample.

METHODS

A total of 1421 middle-aged participants (mean±standard deviation = 57±7; 77% female) from the Healthy Brain Project completed the Pittsburgh Sleep Quality Index (PSQI), Insomnia Severity Index (ISI), and Epworth Sleepiness Scale (ESS) to measure sleep quality, insomnia symptom severity, and daytime sleepiness, respectively. Participants were classified as having no sleep symptomatology (normal scores on each sleep measure), moderate sleep symptomatology (abnormal scores on one sleep measure), or high sleep symptomatology (abnormal scores on at least two sleep measures), using established cut-off values. Analysis of covariance was used to compare objective cognitive function (Cogstate Brief Battery) and subjective cognitive concerns (Modified Cognitive Function Instrument) across groups.

RESULTS

Following adjustments for age, sex, education, mood, and vascular risk factors, persons classified as having high sleep symptomatology, versus none, displayed more subjective cognitive concerns (d=0.24) but no differences in objective cognitive performance (d=0.00-0.18). Subjective cognitive concerns modified the association between sleep symptomatology and psychomotor function. The strength of the relationship between high sleep symptomatology (versus none) and psychomotor function was significantly greater in persons with high as compared with low cognitive concerns (β±SE =-0.37±0.16; p=0.02).

CONCLUSIONS

More severe sleep symptomatology was associated with greater subjective cognitive concerns. Persons reporting high levels of sleep symptomatology may be more likely to display poorer objective cognitive function in the presence of subjective cognitive concerns.

The Sleep Side of Aging and Alzheimer's Disease

As we age, sleep patterns undergo significant modifications in micro and macrostructure, worsening cognition and quality of life. These are associated with remarkable brain changes, like deterioration in synaptic plasticity, gray and white matter, and significant modifications in hormone levels. Sleep alterations are also a core component of mild cognitive impairment (MCI) and Alzheimer's Disease (AD). AD night time is characterized by a gradual decrease in slow-wave activity and a substantial reduction of REM sleep. Sleep abnormalities can accelerate AD pathophysiology, promoting the accumulation of amyloid-β (Aβ) and phosphorylated tau. Thus, interventions that target sleep disturbances in elderly people and MCI patients have been suggested as a possible strategy to prevent or decelerate conversion to dementia. Although cognitive-behavioral therapy and pharmacological medications are still first-line treatments, despite being scarcely effective, new interventions have been proposed, such as sensory stimulation and Noninvasive Brain Stimulation (NiBS). The present review outlines the current state of the art of the relationship between sleep modifications in healthy aging and the neurobiological mechanisms underlying age-related changes. Furthermore, we provide a critical analysis showing how sleep abnormalities influence the prognosis of AD pathology by intensifying Aβ and tau protein accumulation. We discuss potential therapeutic strategies to target sleep disruptions and conclude that there is an urgent need for testing new therapeutic sleep interventions.

Nocturnal Hypoxemia Is Associated with Altered Parahippocampal Functional Brain Connectivity in Older Adults at Risk for Dementia

BACKGROUND

Obstructive sleep apnea is associated with an increased risk of developing mild cognitive impairment and dementia. Intermittent nocturnal hypoxemia in obstructive sleep apnea is associated with brain changes in key regions that underpin memory.

OBJECTIVE

To determine whether older adults with severe nocturnal hypoxemia would exhibit reduced functional connectivity within these regions, with associated deficits in memory.

METHODS

Seventy-two participants 51 years and over underwent polysomnography with continuous blood oxygen saturation recorded via oximetry. The oxygen desaturation index (ODI, 3% dips in oxygen levels per hour) was the primary outcome measure. ODI was split into tertiles, with analyses comparing the lowest and highest tertiles (N = 48). Thirty-five of the 48 participants from these two tertiles had mild cognitive impairment. Participants also underwent resting-state fMRI and comprehensive neuropsychological, medical, and psychiatric assessment.

RESULTS

The highest ODI tertile group demonstrated significantly reduced connectivity between the left and right parahippocampal cortex, relative to the lowest ODI tertile group (t(42) = -3.26, p = 0.041, beta = -1.99).The highest ODI tertile group also had poorer working memory performance. In the highest ODI tertile group only, higher left-right parahippocampal functional connectivity was associated with poorer visual memory recall (between-groups z = -2.93, p = 0.0034).

CONCLUSIONS

Older adults with severe nocturnal hypoxemia demonstrate impaired functional connectivity in medial temporal structures, key regions involved in sleep memory processing and implicated in dementia pathophysiology. Oxygen desaturation and functional connectivity in these individuals each relate to cognitive performance. Research is now required to further elucidate these findings.

Sleep-disordered breathing and the risk of Alzheimer's disease

Sleep-disordered breathing is highly prevalent in the elderly population. Obstructive sleep apnea (OSA) represents the most common sleep disorder among the adult and elderly population. Recently, OSA diagnosis has been associated with an increased risk of developing cognitive decline and dementia, including vascular dementia and Alzheimer's disease (AD). Subsequently, there have been studies on AD biomarkers investigating cerebrospinal fluid, blood, neuroimaging, and nuclear medicine biomarkers in patients with OSA. Furthermore, studies have attempted to assess the possible effects of continuous positive airway pressure (CPAP) treatment on the cognitive trajectory and AD biomarkers in patients with OSA. This review summarizes the findings of studies on each AD biomarker (cognitive, biofluid, neuroimaging, and nuclear medicine imaging) in patients with OSA, also accounting for the related effects of CPAP treatment. In addition, the hypothetical model connecting OSA to AD in a bi-directional interplay is analyzed. Finally, the sex-based differences in prevalence and clinical symptoms of OSA between men and women have been investigated in relation to AD risk. Further studies investigating AD biomarkers changes in patients with OSA and the effect of CPAP treatment should be auspicated in future for identifying strategies to prevent the development of AD.

Sleep Fragmentation and Cognitive Trajectories After Critical Illness

BACKGROUND

ICU survivors can experience both cognitive dysfunction and persistent sleep disturbances after hospitalization. Sleep disturbances have been linked with cognitive impairment in various patient populations, and the apolipoprotein E (APOE) genotype has been linked to sleep-related impairments in cognition.

RESEARCH QUESTION

Is there an association between sleep, long-term cognition, and APOE status in ICU survivors?

STUDY DESIGN AND METHODS

We enrolled 150 patients from five centers who had been mechanically ventilated for at least 3 days; 102 patients survived to ICU discharge. Actigraphy and cognitive testing were undertaken at 7 days, 6 months, and 12 months after ICU discharge, and sleep duration, quality, and timing were estimated by actigraphy. APOE single nucleotide polymorphisms were assessed for each patient.

RESULTS

Actigraphy-estimated sleep fragmentation, but not total sleep time or interdaily stability (estimate of circadian rhythmicity), was associated with worse cognitive impairment at 7 days of ICU discharge. No actigraphy-estimated variable of sleep estimation at 7 days post-ICU discharge predicted cognitive impairment or persistent sleep abnormalities at 6 and 12 months of follow-up in subsequently assessed survivors. Possessing the APOE ε4 allele was not significantly associated with sleep disturbances and its presence did not modify the risk of sleep-related cognitive impairment at follow-up.

INTERPRETATION

Sleep fragmentation estimated by actigraphy was associated with worse cognitive performance in hospital, but not at later time intervals. Further research is needed to better delineate the relationship between persistent sleep disturbances and cognition in larger numbers of ICU survivors.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT02086877; URL: www.clinicaltrials.gov.

Association between insomnia and cognitive performance, gray matter volume, and white matter microstructure in cognitively unimpaired adults

BACKGROUND

Mounting evidence links poor sleep quality with a higher risk of late-life dementia. However, the structural and cognitive correlates of insomnia are still not well understood. The study aims were to characterize the cognitive performance and brain structural pattern of cognitively unimpaired adults at increased risk for Alzheimer's disease (AD) with insomnia.

METHODS

This cross-sectional study included 1683 cognitively unimpaired middle/late-middle-aged adults from the ALFA (ALzheimer and FAmilies) study who underwent neuropsychological assessment, T1-weighted structural imaging (n = 366), and diffusion-weighted imaging (n = 334). The World Health Organization's World Mental Health Survey Initiative version of the Composite International Diagnostic Interview was used to define the presence or absence of insomnia. Multivariable regression models were used to evaluate differences in cognitive performance between individuals with and without insomnia, as well as potential interactions between insomnia and the APOE genotype. Voxel-based morphometry and tract-based spatial statistics were used to assess between-group differences and potential interactions between insomnia and the APOE genotype in gray matter volume and white matter diffusion metrics.

RESULTS

Insomnia was reported by 615 out of 1683 participants (36.5%), including 137 out of 366 (37.4%) with T1-weighted structural imaging available and 119 out of 334 (35.6%) with diffusion-weighted imaging. Individuals with insomnia (n = 615) performed worse in executive function tests than non-insomniacs and displayed lower gray matter volume in left orbitofrontal and right middle temporal cortex, bilateral precuneus, posterior cingulate cortex and thalamus, higher gray matter volume in the left caudate nucleus, and widespread reduction of mean and axial diffusivity in right hemisphere white matter tracts. Insomnia interacted with the APOE genotype, with APOE-ε4 carriers displaying lower gray matter volumes when insomnia was present, but higher volumes when insomnia was not present, in several gray matter regions, including the left angular gyrus, the bilateral superior frontal gyri, the thalami, and the right hippocampus.

CONCLUSIONS

Insomnia in cognitively unimpaired adults at increased risk for AD is associated to poorer performance in some executive functions and volume changes in cortical and subcortical gray matter, including key areas involved in Alzheimer's disease, as well as decreased white matter diffusivity.

Associations Between the Apnea-Hypopnea Index During REM and NREM Sleep and Cognitive Functioning in a Cohort of Middle-Aged Adults

STUDY OBJECTIVES

Prior research has linked obstructive sleep apnea (OSA) to varied cognitive deficits. Additionally, OSA in rapid eye movement (REM) versus non-rapid eye movement (NREM) sleep has been shown to be a stronger predictor of outcomes such as hypertension. The present study aimed to investigate whether OSA-as characterized by the apnea-hypopnea index (AHI)-during REM and NREM sleep is associated with performance on a range of cognitive tasks. We also investigated whether the presence/absence of the apolipoprotein E4 allele (APOE4) modifies the associations between AHI during REM and NREM sleep and cognitive performance.

METHODS

A cross-sectional sample of 1,250 observations from 755 community-dwelling adults (mean [standard deviation] age, 62.3 [8.2] years) participating in the Wisconsin Sleep Cohort study was carried out by means of overnight polysomnography, paper-and-pencil cognitive tasks, and genetic data. Linear mixed effects models with repeated measures estimated associations of AHI during REM and NREM sleep with cognitive outcomes, stratified by APOE4 status (carrier versus noncarrier).

RESULTS

No significant associations were found between REM AHI and cognitive outcomes for either APOE4 carriers and non-carriers. Higher NREM AHI was associated with worse memory retention among APOE4 carriers; among noncarriers of APOE4, higher NREM AHI was associated with worse performance on a test of psychomotor speed, but better performance on two tests of executive function.

CONCLUSIONS

Sleep state-specific (REM, NREM) OSA may be differentially associated with varying dimensions of cognitive deficits in middle-aged to older adults, and such associations are likely to be modified by genetic factors, include APOE polymorphisms.

Therapeutic effects of CPAP on cognitive impairments associated with OSA

Obstructive sleep apnea (OSA) is the most common type of sleep apnea and caused by upper airway obstructions. Clinically, patients with OSA characteristically experience intermittent nocturnal hypoxemia and impaired sleep quality. Cognitive impairments are commonly seen in patients with an OSA diagnosis. A literature search on OSA, cognitive impairments and CPAP was performed with various electronic databases including Medline, EMBASE and Google Scholar. The chosen evidence was limited to human subject studies only, and reports on either central sleep apnea or non-classified sleep apnea were excluded. Available evidence has been systemically reviewed to ascertain what types of cognitive impairments are related to OSA as well as the pathological connections. In addition, effectiveness of continuous positive airway pressure (CPAP) was analyzed as a standard therapy for improving cognitive performance in patients with OSA. The review contributed in: (1) delineating OSA as a risk factor of cognitive impairments; (2) enumerating cognitive impairments seen in patients with OSA; (3) substantiating the relation between OSA and cognitive impairments from the pathological perspective of AD biomarkers; and (4) revealing duration of CPAP is crucial for its therapeutic effects on improving cognitive performance in patients with OSA.

Biomarkers of dementia in obstructive sleep apnea

Epidemiologic and mechanistic evidence is increasingly supporting the notion that obstructive sleep apnea is a risk factor for dementia. Hence, the identification of patients at risk of cognitive decline due to obstructive sleep apnea may significantly improve preventive strategies and treatment decision-making. Cerebrospinal fluid and blood biomarkers obtained through genomic, proteomic and metabolomic approaches are improving the ability to predict incident dementia. Therefore, fluid biomarkers have the potential to predict vulnerability to neurodegeneration in individuals with obstructive sleep apnea, as well as deepen our understanding of pathophysiological processes linking obstructive sleep apnea and dementia. Many fluid biomarkers linked to Alzheimer's disease and vascular dementia show abnormal levels in individuals with obstructive sleep apnea, suggesting that these conditions share common underlying mechanisms, including amyloid and tau protein neuropathology, inflammation, oxidative stress, and metabolic disturbances. Markers of these processes include amyloid-β, tau proteins, inflammatory cytokines, acute-phase proteins, antioxydants and oxidized products, homocysteine and clusterin (apolipoprotein J). Thus, these biomarkers may have the ability to identify adults with obstructive sleep apnea at high risk of dementia and provide an opportunity for therapeutic intervention. Large cohort studies are necessary to establish a specific fluid biomarker panel linking obstructive sleep apnea to dementia risk.

When a patient with depression is feeling sleepy, be aware of sleep apnoea

A 67-year-old man was referred to an outpatient clinic of geriatric psychiatry because of persistent symptoms of depression and anxiety, accompanied by sleepiness. The latter had been evaluated multiple times in the general practice over several years; each time it was considered to be a symptom of depression. After referral, the patient was diagnosed with severe obstructive sleep apnoea (OSA), comorbid to a depressive and anxiety disorder. Retrospectively, we conclude that affective symptoms accompanying OSA and sleepiness were wrongfully interpreted as depression, but after having led to problems at work, they have triggered psychiatric comorbidity. Treatment of OSA in addition to the psychiatric disorders resulted in a full recovery over time. The delayed diagnosis of OSA has certainly diminished the patient’s quality of life and might have precipitated the depressive disorder. Moreover, OSA poses patients at an increased risk of cardiovascular disease, hypertension, stroke and traffic accidents.

Greater Cognitive Deficits with Sleep-disordered Breathing among Individuals with Genetic Susceptibility to Alzheimer Disease. The Multi-Ethnic Study of Atherosclerosis

RATIONALE

There are conflicting findings regarding the link between sleep apnea and cognitive dysfunction.

OBJECTIVES

Investigate associations between indicators of sleep-disordered breathing (SDB) and cognitive function in the Multi-Ethnic Study of Atherosclerosis and assess effect modification by the apolipoprotein ε-4 (APOE-ε4) allele.

METHODS

A diverse population (N = 1,752) underwent type 2 in-home polysomnography, which included measurement of percentage sleep time less than 90% oxyhemoglobin saturation (%Sat < 90%) and apnea-hypopnea index (AHI). Epworth Sleepiness Scale score (ESS) and sleep apnea syndrome (SAS; AHI ≥ 5 and ESS > 10) were also analyzed. Cognitive outcomes included the Cognitive Abilities Screening Instrument; Digit Symbol Coding (DSC) test; and Digit Span Tests (DST) Forward and Backward.

RESULTS

Participants were 45.4% men, aged 68.1 years (SD, 9.1 yr) with a median AHI of 9.0 and mean ESS of 6.0. Approximately 9.7% had SAS, and 26.8% had at least one copy of the APOE-ε4 allele. In adjusted analyses, a 1-SD increase in %Sat < 90% and ESS score were associated with a poorer attention and memory assessed by the DST Forward score (β = -0.12 [SE, 0.06] and β = -0.13 [SE, 0.06], respectively; P ≤ 0.05). SAS and higher ESS scores were also associated with poorer attention and processing speed as measured by the DSC (β = -0.69 [SE, 0.35] and β = -1.42 [SE, 0.35], respectively; P < 0.05). The presence of APOE-ε4 allele modified the associations of %Sat < 90% with DST forward and of ESS with DSC (P_interaction ≤ 0.05).

CONCLUSIONS

Overnight hypoxemia and sleepiness were associated with cognition. The average effect estimates were small, similar to effect estimates for several other individual dementia risk factors. Associations were strongest in APOE-ε4 risk allele carriers. Our results (1) suggest that SDB be considered among a group of modifiable dementia risk factors, and (2) highlight the potential vulnerability of APOE-ε4 risk allele carriers with SDB.

Disturbed sleep and diabetes: A potential nexus of dementia risk

Type 2 diabetes (T2D) and sleep disturbance (e.g., insomnia, sleep-disordered breathing) are prevalent conditions among older adults that are associated with cognitive decline and dementia, including Alzheimer's disease (AD). Importantly, disturbed sleep is associated with alterations in insulin sensitivity and glucose metabolism, and may increase the risk of T2D, and T2D-related complications (e.g., pain, nocturia) can negatively affect sleep. Despite these associations, little is known about how interactions between T2D and sleep disturbance might alter cognitive trajectories or the pathological changes that underlie dementia. Here, we review links among T2D, sleep disturbance, cognitive decline and dementia-including preclinical and clinical AD-and identify gaps in the literature, that if addressed, could have significant implications for the prevention of poor cognitive outcomes.

Sleep and Cognition in Older Adults

Increased age is associated with normative declines in both sleep and cognitive functioning. Although there are some inconsistencies in the literature, negative sleep changes are associated with worse cognitive functioning. This negative relationship holds true across normal-sleeping older adults, older adults with insomnia, older adults with sleep disordered breathing, cognitively healthy older adults, and older adults with dementia. There are mixed results regarding potential benefits of sleep treatments on cognitive functions; however, this line of research deserves added attention because the potential mechanisms of action are likely distinct from other interventions to improve cognition.

APOE Genotype and Nonrespiratory Sleep Parameters in Cognitively Intact Older Adults

Study Objectives

The apolipoprotein E (APOE) Ɛ4 allele increases Alzheimer's disease (AD) risk and has been linked to a greater risk of sleep-disordered breathing. We investigated the association of APOE genotype with nonrespiratory sleep parameters.

Methods

We studied 1264 cognitively normal participants in the Baltimore Longitudinal Study of Aging (mean = 57.5 ± 16.1 years, range 19.9-92.0, 48.2% women, 19.8% African American) with APOE genotyping and self-reported sleep duration (≥9, 7 or 8, ≤6 hours), difficulty falling/staying asleep, and napping. We compared Ɛ4 carriers with all noncarriers and compared persons at reduced (Ɛ2/Ɛ2 or Ɛ2/Ɛ3) or elevated AD risk (≥1 Ɛ4 allele) with those neutral for AD risk (Ɛ3/Ɛ3).

Results

In fully adjusted models, those with ≥1 Ɛ4 allele had a greater odds of being in a shorter sleep duration category compared to all noncarriers (odds ratio [OR] = 1.41, 95% confidence interval [CI] 1.06, 1.88) and Ɛ3/Ɛ3 carriers (OR = 1.43, 95% CI 1.06, 1.92). Compared to Ɛ3/Ɛ3 carriers, Ɛ2/Ɛ2 or Ɛ2/Ɛ3 carriers had a lower odds of reporting napping (OR = 0.64, 95% CI 0.43, 0.96). Among participants aged ≥50 years, sleep duration findings remained and Ɛ4 carriers had a greater odds of trouble falling/staying asleep than noncarriers (OR = 1.49, 95% CI 1.02, 2.17). We found some evidence for stronger associations of Ɛ4 with sleep duration among African Americans.

Conclusions

Self-reported sleep duration, napping, and trouble falling/staying asleep differ by APOE genotype. Studies are needed to examine whether APOE promotes AD by degrading sleep and to clarify the role of race in these associations.

Sleep characteristics and risk of dementia and Alzheimer's disease: The Atherosclerosis Risk in Communities Study

INTRODUCTION

This study tested the hypotheses that late-midlife obstructive sleep apnea (OSA) and short and long sleep duration are associated with dementia over 15 years of follow-up.

METHODS

A total of 1667 Atherosclerosis Risk in Communities Study participants underwent in-home polysomnography (1996-1998) and were followed for dementia. Dementia was defined by (1) hospitalization diagnosis codes (1996-2012) and (2) a comprehensive neurocognitive examination (2011-2013) with adjudication.

RESULTS

OSA and sleep duration were not associated with risk of incident dementia. When using adjudicated outcomes, severe OSA (≥30 vs. <5 apnea-hypopnea events/hour) was associated with higher risk of all-cause dementia (risk ratio [95% confidence interval], 2.35 [1.06-5.18]) and Alzheimer's disease dementia (1.66 [1.03-2.68]); associations were attenuated with cardiovascular risk factor adjustment. Sleeping <7 versus 8 to ≤9 hours was associated with higher risk of all-cause dementia (2.00 [1.03-3.86]).

DISCUSSION

When adjudicated outcome definitions were used, late-midlife OSA and short sleep duration were associated with all-cause and Alzheimer's disease dementia in later life.

A study protocol for an observational cohort investigating COGnitive outcomes and WELLness in survivors of critical illness: the COGWELL study

INTRODUCTION

Up to 9 out of 10 intensive care unit (ICU) survivors will suffer some degree of cognitive impairment at hospital discharge and approximately half will have decrements that persist for years. The mechanisms for this newly acquired brain injury are poorly understood. The purpose of this study is to describe the prevalence of sleep abnormalities and their association with cognitive impairment, examine a well-known genetic risk factor for dementia (Apolipoprotein E ε4) that may allow for genetic risk stratification of ICU survivors at greatest risk of cognitive impairment and determine if electroencephalography (EEG) is an independent predictor of long-term cognitive impairment and possibly a candidate intermediate end point for future clinical trials.

METHODS AND ANALYSIS

This is a multisite, prospective, observational cohort study. The setting for this trial will be medical and surgical ICUs of five large tertiary care referral centres. The participants will be adult patients admitted to a study ICU and invasively ventilated for ≥3 days . Participants will undergo follow-up within 7 days of ICU discharge, 6 months and 1 year. At each time point, patients will have an EEG, blood work (biomarkers; gene studies), sleep study (actigraphy), complete a number of questionnaires as well as undergo neuropsychological testing. The primary outcome of this study will be long-term cognitive function at 12 months follow-up as measured by the Repeatable Battery for the Assessment of Neuropsychological Status and Trails Making Test B.

ETHICS AND DISSEMINATION

The study has received the following approvals: University Health Network Research Ethics Committee (13-6425-BE), Sunnybrook Health Centre Research Ethics Committee (365-2013), Mount Sinai Research Ethics Committee (14-0194-E) and St. Michael's Hospital Research Ethics Committee (14-295). Results will be made available to critical care survivors, their caregivers, the funders, the critical care societies and other researchers.

TRIAL REGISTRATION NUMBER

NCT02086877; Pre-results.

Self-Reported Sleep Apnea and Dementia Risk: Findings from the Prevention of Alzheimer's Disease with Vitamin E and Selenium Trial

OBJECTIVES

To investigate the association between baseline sleep apnea and risk of incident dementia in the Prevention of Alzheimer's Disease with Vitamin E and Selenium (PREADViSE) study and to explore whether the association depends on apolipoprotein E (APOE) ɛ4 allele status.

DESIGN

Secondary analysis based on data collected during PREADViSE.

SETTING

Participants were assessed at 128 local clinical study sites during the clinical trial phase and later were followed by telephone from a centralized location.

PARTICIPANTS

Men enrolled in PREADViSE (without dementia or other active neurological conditions that affect cognition such as major psychiatric disorders, including depression; N = 7,547).

MEASUREMENTS

Participants were interviewed at baseline for sleep apnea. The Memory Impairment Screen (MIS) was administered to each participant annually. Subjects who failed this initial screen were tested with secondary screening tests. Medical history and medication use were determined, and the AD8 dementia screening instrument was used.

RESULTS

The effect of self-reported sleep apnea on dementia risk depended on APOE ɛ4 status. When the allele was absent, baseline self-reported sleep apnea was associated with a 66% higher risk of developing dementia (95% confidence interval = 2-170%), whereas self-reported sleep apnea conferred no additional risk for participants with an ɛ4 allele.

CONCLUSION

Sleep apnea may increase risk of dementia in the absence of APOE ɛ4. This may help inform prevention strategies for dementia or AD in older men with sleep apnea. Registration: PREADViSE is registered at ClinicalTrials.gov: NCT00040378.

Role of Oxidative Stress in the Neurocognitive Dysfunction of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is characterized by chronic nocturnal intermittent hypoxia and sleep fragmentations. Neurocognitive dysfunction, a significant and extraordinary complication of OSAS, influences patients' career, family, and social life and reduces quality of life to some extent. Previous researches revealed that repetitive hypoxia and reoxygenation caused mitochondria and endoplasmic reticulum dysfunction, overactivated NADPH oxidase, xanthine oxidase, and uncoupling nitric oxide synthase, induced an imbalance between prooxidants and antioxidants, and then got rise to a series of oxidative stress (OS) responses, such as protein oxidation, lipid peroxidation, and DNA oxidation along with inflammatory reaction. OS in brain could trigger neuron injury especially in the hippocampus and cerebral cortex regions. Those two regions are fairly susceptible to hypoxia and oxidative stress production which could consequently result in cognitive dysfunction. Apart from continuous positive airway pressure (CPAP), antioxidant may be a promising therapeutic method to improve partially reversible neurocognitive function. Understanding the role that OS played in the cognitive deficits is crucial for future research and therapeutic strategy development. In this paper, recent important literature concerning the relationship between oxidative stress and cognitive impairment in OSAS will be summarized and the results can provide a rewarding overview for future breakthrough in this field.

Depressive Symptoms in Patients with Obstructive Sleep Apnea

OBJECTIVES

Different studies have investigate depressive symptom degree within sleep disordered patients with obstructive sleep apnea (OSA). However, little is known and unclear about OSA in patients with depression symptom in the literature. The purpose of this study was to investigate patients with OSA would have a higher prevalence of depression symptom relative to control patients.

MATERIAL AND METHODS

72 patients with OSA (AHI ≥ 5) and 24 control subjects (AHI < 5) were assessed for depression symptom using the Beck Depression Inventory. Participants were underwent an overnight polysomnography assessment. An apnea-hypopnea index ≥ 5 events per hour was used as diagnosis for OSA. The associations between each total score on the Beck Depressive Inventory (BDI) and polysomnographic parameters were examined by correlation analysis.

RESULTS

We demonstrated that BDI scores has statistically significant correlation with the OSA in our present study according to similar previous studies (p= 0.008). Oxygen Desaturation Index (ODI) has correlated with BDI (r= 0.31).

CONCLUSION

These findings show that the frequency depression symptom is higher among individuals with OSA. Patients with OSA should be screened cautiously for depressive disorders.

The Synergistic Relationship between Alzheimer's Disease and Sleep Disorders: An Update

Sleep disorders are frequently reported in Alzheimer's disease (AD), with a significant impact on patients and caregivers and a major risk factor for early institutionalization. Although changes in sleep organization are a hallmark of the normal aging processes, sleep macro- and micro-architectural alterations are more evident in patients affected by AD. Degeneration of neural pathways regulating sleep-wake patterns and sleep architecture may contribute to sleep alterations. In return, several recent studies suggested that common sleep disorders may precede clinical symptoms of dementia and represent risk factors for cognitive decline, through impairment of sleep-dependent memory consolidation processes. Thus, a close relationship between sleep disorders and AD has been largely hypothesized. Here, sleep alterations in AD and its pre-dementia stage, mild cognitive impairment, and their complex interactions are reviewed.

Sleep, Cognition and Dementia

The older patient population is growing rapidly around the world and in the USA. Almost half of seniors over age 65 who live at home are dissatisfied with their sleep, and nearly two-thirds of those residing in nursing home facilities suffer from sleep disorders. Chronic and pervasive sleep complaints and disturbances are frequently associated with excessive daytime sleepiness and may result in impaired cognition, diminished intellect, poor memory, confusion, and psychomotor retardation all of which may be misinterpreted as dementia. The key sleep disorders impacting patients with dementia include insomnia, hypersomnolence, circadian rhythm misalignment, sleep disordered breathing, motor disturbances of sleep such as periodic leg movement disorder of sleep and restless leg syndrome, and parasomnias, mostly in the form of rapid eye movement (REM) sleep behavior disorder (RBD). RBD is a pre-clinical marker for a class of neurodegenerative diseases, the "synucleinopathies", and requires formal polysomnographic evaluation. Untreated sleep disorders may exacerbate cognitive and behavioral symptoms in patients with dementia and are a source of considerable stress for bed partners and family members. When left untreated, sleep disturbances may also increase the risk of injury at night, compromise health-related quality of life, and precipitate and accelerate social and economic burdens for caregivers.

The Role of Sleep and Sleep Disorders in the Development, Diagnosis, and Management of Neurocognitive Disorders

It is becoming increasingly apparent that sleep plays an important role in the maintenance, disease prevention, repair, and restoration of both mind and body. The sleep and wake cycles are controlled by the pacemaker activity of the superchiasmic nucleus in the hypothalamus but can be disrupted by diseases of the nervous system causing disordered sleep. A lack of sleep has been associated with an increase in all-cause mortality. Likewise, sleep disturbances and sleep disorders may disrupt neuronal pathways and have an impact on neurological diseases. Sleep deprivation studies in normal subjects demonstrate that a lack of sleep can cause attention and working memory impairment. Moreover, untreated sleep disturbances and sleep disorders such as obstructive sleep apnoe (OSA) can also lead to cognitive impairment. Poor sleep and sleep disorders may present a significant risk factor for the development of dementia. In this review, the underlying mechanisms and the role of sleep and sleep disorders in the development of neurocognitive disorders [dementia and mild cognitive impairment (MCI)] and how the presence of sleep disorders could direct the process of diagnosis and management of neurocognitive disorders will be discussed.

Sleep-disordered breathing advances cognitive decline in the elderly

OBJECTIVE

To examine whether the presence of sleep-disordered breathing (SDB) is associated with an earlier age at mild cognitive impairment (MCI) or Alzheimer disease (AD)-dementia onset in participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. We also examined whether continuous positive airway pressure (CPAP) use is associated with delayed onset of cognitive decline.

METHODS

From the ADNI cohort, 3 subsets with progressively stringent criteria were created in a step-wise manner. Age at MCI or AD-dementia onset was the main outcome variable. Analyses were performed separately for each subset in untreated SDB+ vs SDB- and untreated SDB+ vs CPAP+ groups. Chi-square and t tests were performed to examine between-group differences. Survival analyses were performed using the Kaplan-Meier method, compared by the log-rank test, and assessed by multivariate Cox regression adjusting for potential confounders.

RESULTS

SDB+ patients had a younger age at MCI onset in all subsets (MC1: 72.63 vs 83.67; MC2: 72.15 vs 83.45; MC3: 77.40 vs 89.89; p < 0.01). SDB+ patients had a younger age at AD-dementia onset only in our most conservative subset (AC3: 83.46 vs 88.13; p < 0.05). In a combined outcome analysis, SDB+ patients had a younger age at onset to MCI or AD-dementia in all subsets. In subsets 1 and 2, CPAP use delayed the age at MCI onset (CMC1: 72.63 vs 82.10; CMC2: 72.11 vs 82.10; p < 0.01).

CONCLUSIONS

Consistent with our hypothesis, the presence of SDB was associated with an earlier age at cognitive decline. Our findings in CPAP+ participants suggest that CPAP treatment of SDB may delay progression of cognitive impairment.

No association between the ApoE ε2 and ε4 alleles and the risk of obstructive sleep apnea: A systematic review and meta-analysis

Apolipoprotein E (ApoE) gene ε2 and ε4 alleles have been reported to be associated with the risk of obstructive sleep apnea (OSA); however, the results are controversial. Thus, we performed a meta-analysis to obtain a more precise estimate of the associations by pooling sporadic, inconsistent and small-sample-size studies. Electronic databases such as PubMed and Embase were searched to identify eligible studies focusing on the association between ApoE polymorphisms and susceptibility to OSA before April 2014. The associations were assessed by odds ratio (ORs) with 95% confidence intervals (CIs). The Begg and Egger's test was used to evaluate publication bias. Ten eligible studies (1,696 cases/2,216 controls for the ε2 allele and 2,449 cases/5,592 controls for the ε4 allele) were included in the meta-analysis. An association between the ApoE ε2 and ε4 alleles and OSA was not found in the overall population (OR=0.97, 95% CI: 0.75-1.25; OR=1.09, 95% CI: 0.86-0.38 for ApoE ε2 and ε4, respectively). Significant heterogeneity (ε2: I²=36.6%, P=0.16; ε4: I²=69.7%, P=0.001) was observed across studies, however, heterogeneity could not be explained by variations in mean age, body mass index, apnea hypopnea index, gender, ethnic background, or the ApoE ε2 and ε4 alleles. No evidence of publication bias was found according to the Begg and Egger's test. In conclusion, our findings show that the ApoE ε2 and ε4 alleles have no significant associations with OSA susceptibility based on available data.

Sleep breathing disorders and cognitive function in the elderly: an 8-year follow-up study. the proof-synapse cohort

STUDY OBJECTIVES

Sleep breathing disorder (SBD) may be an important factor in age-related cognitive decline. In a cohort of healthy elderly subjects, we performed an 8-y longitudinal study to assess whether changes in cognitive function occur in untreated elderly patients with SBD and without dementia and the factors implicated in these changes.

DESIGN

A population-based longitudinal study.

SETTING

Clinical research settings.

PARTICIPANTS

A total of 559 participants of the PROOF study aged 67 y at the study entry and free from neurological disorders were examined.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Abnormal breathing events were defined by an apnea-hypopnea index (AHI) > 15. The raw cognitive data and averaged Z-scores for the attentional, executive, and memory functions were collected at the baseline and follow-up. At baseline, AHI > 15 was found in 54% of subjects with 18% having an AHI > 30. At follow-up, the presence of abnormal breathing events was associated with a slight but significant decline in the attentional domain (P = 0.01), which was more evident in the subjects with an AHI > 30 (P = 0.004). No significant changes over time were observed in the executive and memory functions. Several indices of chronic hypoxemia, defined either as a cumulative peripheral oxygen saturation (SpO2) < 90% or a minimal SpO2, accounted for portions of the variance in the decline in attention. All observed effects were small, accounting for 4-7% of variance in multivariate models.

CONCLUSION

In healthy elderly subjects, various components of sleep breathing disorder at baseline were associated with small changes in selected cognitive functions specific to the attention domain after controlling for multiple comorbidities, such as sleepiness, hypertension, diabetes, anxiety, and depression.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifiers NCT 00759304 and NCT 00766584.