The Relationship between Diet, Depression, and Alzheimer's Disease: A Narrative Review.

PURPOSE OF REVIEW: This narrative review evaluates the role of diet in the relationship between depression and Alzheimer's disease (AD). RECENT FINDINGS: AD and depression are often comorbid, and depression appears to independently increase the future risk of AD. Evidence suggests diet influences the risk of both conditions directly and indirectly. Diet impacts neurochemical and biological processes that may affect the development and progression of depression and cognitive dysfunction. The dietary components offering the greatest protection against depression and AD are yet to be determined. Current evidence highlights the importance of polyphenolic compounds, folate, B vitamins, and polyunsaturated fatty acids, along with adherence to dietary patterns like the Mediterranean diet, which includes multiple beneficial dietary factors. SUMMARY: The investigation of dietary factors in the prevention of depression and AD is a comparatively young field of research. Comprehensive highly characterised longitudinal datasets and advanced analytical approaches are required to further examine the complex relationship between diet, depression, and AD. There is a critical need for more research in this area to develop effective preventive strategies aimed at maintaining mental and physical health with advancing age.

Sleep discrepancy and cognitive function in community-dwelling older adults.

This was the first study to use cluster analysis to characterise sleep discrepancy (the discordance between self-reported and objective sleep) across multiple sleep parameters, in community-dwelling older adults. For sleep efficiency, negative discrepancy (the tendency to self-report worse sleep than objectively-measured) was associated with poorer memory, independent of insomnia severity, depressive symptoms and objective sleep. This suggests a unique role for sleep discrepancy as a possible risk factor for future cognitive decline, and warrants the need for further research.

Association of Basal Forebrain Atrophy With Cognitive Decline in Early Alzheimer Disease.

BACKGROUND AND OBJECTIVES: In early Alzheimer disease (AD), ß-amyloid (Aß) deposition is associated with volume loss in the basal forebrain (BF) and cognitive decline. However, the extent to which Aß-related BF atrophy manifests as cognitive decline is not understood. This study sought to characterize the relationship between BF atrophy and the decline in memory and attention in patients with early AD. METHODS: Participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study who completed Aß-PET imaging and repeated MRI and cognitive assessments were included. At baseline, participants were classified based on their clinical dementia stage and Aß status, yielding groups that were cognitively unimpaired (CU) Aß-, CU Aß+, and mild cognitive impairment (MCI) Aß+. Linear mixed-effects models were used to assess changes in volumetric measures of BF subregions and the hippocampus and changes in AIBL memory and attention composite scores for each group compared with CU Aß- participants. Associations between Aß burden, brain atrophy, and cognitive decline were evaluated and explored further using mediation analyses. RESULTS: The cohort included 476 participants (72.6 ± 5.9 years, 55.0% female) with longitudinal data from a median follow-up period of 6.1 years. Compared with the CU Aß- group (n = 308), both CU Aß+ (n = 107) and MCI Aß+ (n = 61) adults showed faster decline in BF and hippocampal volumes and in memory and attention (Cohen d = 0.73-1.74). Rates of atrophy in BF subregions and the hippocampus correlated with cognitive decline, and each individually mediated the impact of Aß burden on memory and attention decline. When all mediators were considered simultaneously, hippocampal atrophy primarily influenced the effect of Aß burden on memory decline (ß [SE] = -0.139 [0.032], proportion mediated [PM] = 28.0%) while the atrophy of the posterior nucleus basalis of Meynert in the BF (ß [SE] = -0.068 [0.029], PM = 13.1%) and hippocampus (ß [SE] = -0.121 [0.033], PM = 23.4%) distinctively influenced Aß-related attention decline. DISCUSSION: These findings highlight the significant role of BF atrophy in the complex pathway linking Aß to cognitive impairment in early stages of AD. Volumetric assessment of BF subregions could be essential in elucidating the relationships between the brain structure and behavior in AD.

The AUstralian multidomain Approach to Reduce dementia Risk by prOtecting brain health With lifestyle intervention study (AU-ARROW): A study protocol for a single-blind, multi-site, randomized controlled trial.

INTRODUCTION: The Finnish Geriatric Intervention Study (FINGER) led to the global dementia risk reduction initiative: World-Wide FINGERS (WW-FINGERS). As part of WW-FINGERS, the Australian AU-ARROW study mirrors aspects of FINGER, as well as US-POINTER. METHOD: AU-ARROW is a randomized, single-blind, multisite, 2-year clinical trial (n = 600; aged 55-79). The multimodal lifestyle intervention group will engage in aerobic exercise, resistance training and stretching, dietary advice to encourage MIND diet adherence, BrainHQ cognitive training, and medical monitoring and health education. The Health Education and Coaching group will receive occasional health education sessions. The primary outcome measure is the change in a global composite cognitive score. Extra value will emanate from blood biomarker analysis, positron emission tomography (PET) imaging, brain magnetic resonance imaging (MRI), and retinal biomarker tests. DISCUSSION: The finalized AU-ARROW protocol is expected to allow development of an evidence-based innovative treatment plan to reduce cognitive decline and dementia risk, and effective transfer of research outcomes into Australian health policy. Highlights: Study protocol for a single-blind, randomized controlled trial, the AU-ARROW Study.The AU-ARROW Study is a member of the World-Wide FINGERS (WW-FINGERS) initiative.AU-ARROW's primary outcome measure is change in a global composite cognitive score.Extra significance from amyloid PET imaging, brain MRI, and retinal biomarker tests.Leading to development of an innovative treatment plan to reduce cognitive decline.

Suboptimal self-reported sleep efficiency and duration are associated with faster accumulation of brain amyloid beta in cognitively unimpaired older adults.

INTRODUCTION: This study investigated whether self-reported sleep quality is associated with brain amyloid beta (Aß) accumulation. METHODS: Linear mixed effect model analyses were conducted for 189 cognitively unimpaired (CU) older adults (mean ± standard deviation 74.0 ± 6.2; 53.2% female), with baseline self-reported sleep data, and positron emission tomography-determined brain Aß measured over a minimum of three time points (range 33.3-72.7 months). Analyses included random slopes and intercepts, interaction for apolipoprotein E (APOE) ε4 allele status, and time, adjusting for sex and baseline age. RESULTS: Sleep duration <6 hours, in APOE ε4 carriers, and sleep efficiency <65%, in the whole sample and APOE ε4 non-carriers, is associated with faster accumulation of brain Aß. DISCUSSION: These findings suggest a role for self-reported suboptimal sleep efficiency and duration in the accumulation of Alzheimer's disease (AD) neuropathology in CU individuals. Additionally, poor sleep efficiency represents a potential route via which individuals at lower genetic risk may progress to preclinical AD. Highlights: In cognitively unimpaired older adults self-report sleep is associated with brain amyloid beta (Aß) accumulation.Across sleep characteristics, this relationship differs by apolipoprotein E (APOE) genotype.Sleep duration <6 hours is associated with faster brain Aß accumulation in APOE ε4 carriers.Sleep efficiency < 65% is associated with faster brain Aß accumulation in APOE ε4 non-carriers.Personalized sleep interventions should be studied for potential to slow Aß accumulation.

The impact of exercise on blood-based biomarkers of Alzheimer's disease in cognitively unimpaired older adults.

Physical activity is a promising preventative strategy for Alzheimer's disease: it is associated with lower dementia risk, better cognition, greater brain volume and lower brain beta-amyloid. Blood-based biomarkers have emerged as a low-cost, non-invasive strategy for detecting preclinical Alzheimer's disease, however, there is limited literature examining the effect of exercise (a structured form of physical activity) on blood-based biomarkers. The current study investigated the influence of a 6-month exercise intervention on levels of plasma beta-amyloid (Aß42, Aß40, Aß42/40), phosphorylated tau (p-tau181), glial fibrillary acidic protein (GFAP) and neurofilament light (NfL) chain in cognitively unimpaired older adults, and as a secondary aim, whether blood-based biomarkers related to cognition. Ninety-nine community-dwelling older adults (69.1 ± 5.2) were allocated to an inactive control, or to moderate or high intensity exercise groups where they cycled twice weekly for six months. At baseline and six months (post-intervention), fasted blood was collected and analysed using single molecule array (SIMOA) assays, and cognition was assessed. Results demonstrated no change in levels of any plasma biomarker from pre- to post-intervention. At baseline, higher NfL was associated with poorer cognition (ß = -0.33, SE = 0.13, adjusted p = .042). Exploratory analyses indicated higher cardiorespiratory fitness was associated with higher NfL and GFAP levels in apolipoprotein E (APOE) ε4 non-carriers compared to ε4 carriers (NfL, ß = -0.43, SE = 0.19, p = .029; GFAP, ß = -0.41, SE = 0.20, p = .044), though this association was mediated by body mass index (BMI). These results highlight the importance of considering BMI in analysis of blood-based biomarkers, especially when investigating differences between APOE ε4 carriers and non-carriers. Our results also indicate that longer follow-up periods may be required to observe exercise-induced change in blood-based biomarkers.

The Role of Diet and Gut Microbiota in Alzheimer's Disease.

Alzheimer's disease (AD), the most prevalent form of dementia, is characterized by the accumulation of amyloid-beta (Aß) plaques and hyperphosphorylated tau tangles. Currently, Alzheimer's disease (AD) impacts 50 million individuals, with projections anticipating an increase to 152 million by the year 2050. Despite the increasing global prevalence of AD, its underlying pathology remains poorly understood, posing challenges for early diagnosis and treatment. Recent research suggests a link between gut dysbiosis and the aggregation of Aß, the development of tau proteins, and the occurrence of neuroinflammation and oxidative stress are associated with AD. However, investigations into the gut-brain axis (GBA) in the context of AD progression and pathology have yielded inconsistent findings. This review aims to enhance our understanding of microbial diversity at the species level and the role of these species in AD pathology. Additionally, this review addresses the influence of confounding elements, including diet, probiotics, and prebiotics, on AD throughout different stages (preclinical, mild cognitive impairment (MCI), and AD) of its progression.

Physical activity and brain amyloid beta: A longitudinal analysis of cognitively unimpaired older adults.

INTRODUCTION: The current study evaluated the relationship between habitual physical activity (PA) levels and brain amyloid beta (Aß) over 15 years in a cohort of cognitively unimpaired older adults. METHODS: PA and Aß measures were collected over multiple timepoints from 731 cognitively unimpaired older adults participating in the Australian Imaging, Biomarkers and Lifestyle (AIBL) Study of Aging. Regression modeling examined cross-sectional and longitudinal relationships between PA and brain Aß. Moderation analyses examined apolipoprotein E (APOE) ε4 carriage impact on the PA-Aß relationship. RESULTS: PA was not associated with brain Aß at baseline (ß = -0.001, p = 0.72) or over time (ß = -0.26, p = 0.24). APOE ε4 status did not moderate the PA-Aß relationship over time (ß = 0.12, p = 0.73). Brain Aß levels did not predict PA trajectory (ß = -54.26, p = 0.59). DISCUSSION: Our study did not identify a relationship between habitual PA and brain Aß levels. HIGHLIGHTS: Physical activity levels did not predict brain amyloid beta (Aß) levels over time in cognitively unimpaired older adults (≥60 years of age). Apolipoprotein E (APOE) ε4 carrier status did not moderate the physical activity-brain Aß relationship over time. Physical activity trajectories were not impacted by brain Aß levels.

The effect of acute exercise on objectively measured sleep and cognition in older adults.

Background: Exercise can improve cognition in aging, however it is unclear how exercise influences cognition, and sleep may partially explain this association. The current study aimed to investigate whether objectively measured sleep mediates the effect of an acute exercise intervention on cognition in older adults. Methods: Participants were 30 cognitively unimpaired, physically active older adults (69.2 ± 4.3 years) with poor sleep (determined via self-report). After a triple baseline cognitive assessment to account for any natural fluctuation in cognitive performance, participants completed either a single bout of 20-minutes of high intensity exercise on a cycle ergometer, or a control condition, in a cross-over trial design. Cognition was measured immediately post-intervention and the following day, and sleep (total sleep time, sleep onset latency, sleep efficiency, % of rapid eye movement sleep, light sleep and deep sleep) was characterized using WatchPAT™ at baseline (5 nights) and measured for one night after both exercise and control conditions. Results: Results showed no effect of the exercise intervention on cognition immediately post-intervention, nor an effect of acute exercise on any sleep variable. There was no mediating effect of sleep on associations between exercise and cognition. However, a change from baseline to post-intervention in light sleep and deep sleep did predict change in episodic memory at the ~24 h post-intervention cognitive assessment, regardless of intervention condition. Discussion: There was no effect of acute high intensity exercise on sleep or cognition in the current study. However, results suggest that associations between sleep and cognition may exist independently of exercise in our sample. Further research is required, and such studies may aid in informing the most effective lifestyle interventions for cognitive health.

The influence of baseline sleep on exercise-induced cognitive change in cognitively unimpaired older adults: A randomised clinical trial.

OBJECTIVES: Observational studies consistently demonstrate that physical activity is associated with elevated cognitive function, however, there remains significant heterogeneity in cognitive outcomes from randomized exercise interventions. Individual variation in sleep behaviours may be a source of variability in the effectiveness of exercise-induced cognitive change, however this has not yet been investigated. The current study aimed to (1) investigate the influence of a 6-month exercise intervention on sleep, assessed pre- and post-intervention and, (2) investigate whether baseline sleep measures moderate exercise-induced cognitive changes. METHODS: We utilised data from the Intense Physical Activity and Cognition (IPAC) study (n = 89), a 6-month moderate intensity and high intensity exercise intervention, in cognitively unimpaired community-dwelling older adults aged 60-80 (68.76 ± 5.32). Exercise was supervised and completed on a stationary exercise bicycle, and cognitive function was measured using a comprehensive neuropsychological battery administered pre- and post-intervention. Sleep was measured using the Pittsburgh sleep quality index. There was no effect of the exercise intervention on any sleep outcomes from pre- to post-intervention. RESULTS: There was a significant moderating effect of baseline sleep efficiency on both episodic memory and global cognition within the moderate intensity exercise group, such that those with poorer sleep efficiency at baseline showed greater exercise-induced improvements in episodic memory. CONCLUSIONS: These results suggest that those with poorer sleep may have the greatest exercise-induced cognitive benefits and that baseline sleep behaviours may be an important source of heterogeneity in previous exercise interventions targeting cognitive outcomes.

Longitudinal trajectories of basal forebrain volume in normal aging and Alzheimer's disease.

Dysfunction of the cholinergic basal forebrain (BF) system and amyloid-ß (Aß) deposition are early pathological features in Alzheimer's disease (AD). However, their association in early AD is not well-established. This study investigated the nature and magnitude of volume loss in the BF, over an extended period, in 516 older adults who completed Aß-PET and serial magnetic resonance imaging scans. Individuals were grouped at baseline according to the presence of cognitive impairment (CU, CI) and Aß status (Aß-, Aß+). Longitudinal volumetric changes in the BF and hippocampus were assessed across groups. The results indicated that high Aß levels correlated with faster volume loss in the BF and hippocampus, and the effect of Aß varied within BF subregions. Compared to CU Aß+ individuals, Aß-related loss among CI Aß+ adults was much greater in the predominantly cholinergic subregion of Ch4p, whereas no difference was observed for the Ch1/Ch2 region. The findings support early and substantial vulnerability of the BF and further reveal distinctive degeneration of BF subregions during early AD.

Elevated plasma sclerostin is associated with high brain amyloid-ß load in cognitively normal older adults.

Osteoporosis and Alzheimer's disease (AD) mainly affect older individuals, and the possibility of an underlying link contributing to their shared epidemiological features has rarely been investigated. In the current study, we investigated the association between levels of plasma sclerostin (SOST), a protein primarily produced by bone, and brain amyloid-beta (Aß) load, a pathological hallmark of AD. The study enrolled participants meeting a set of screening inclusion and exclusion criteria and were stratified into Aß- (n = 65) and Aß+ (n = 35) according to their brain Aß load assessed using Aß-PET (positron emission tomography) imaging. Plasma SOST levels, apolipoprotein E gene (APOE) genotype and several putative AD blood-biomarkers including Aß40, Aß42, Aß42/Aß40, neurofilament light (NFL), glial fibrillary acidic protein (GFAP), total tau (t-tau) and phosphorylated tau (p-tau181 and p-tau231) were detected and compared. It was found that plasma SOST levels were significantly higher in the Aß+ group (71.49 ± 25.00 pmol/L) compared with the Aß- group (56.51 ± 22.14 pmol/L) (P < 0.01). Moreover, Spearman's correlation analysis showed that plasma SOST concentrations were positively correlated with brain Aß load (ρ = 0.321, P = 0.001). Importantly, plasma SOST combined with Aß42/Aß40 ratio significantly increased the area under the curve (AUC) when compared with using Aß42/Aß40 ratio alone (AUC = 0.768 vs 0.669, P = 0.027). In conclusion, plasma SOST levels are elevated in cognitively unimpaired older adults at high risk of AD and SOST could complement existing plasma biomarkers to assist in the detection of preclinical AD.

A Potential Role for Sirtuin-1 in Alzheimer's Disease: Reviewing the Biological and Environmental Evidence.

Sirtuin-1 (Sirt1), encoded by the SIRT1 gene, is a conserved Nicotinamide adenine dinucleotide (NAD+) dependent deacetylase enzyme, considered as the master regulator of metabolism in humans. Sirt1 contributes to a wide range of biological pathways via several mechanisms influenced by lifestyle, such as diet and exercise. The importance of a healthy lifestyle is of relevance to highly prevalent modern chronic diseases, such as Alzheimer's disease (AD). There is growing evidence at multiple levels for a role of Sirt1/SIRT1 in AD pathological mechanisms. As such, this review will explore the relevance of Sirt1 to AD pathological mechanisms, by describing the involvement of Sirt1/SIRT1 in the development of AD pathological hallmarks, through its impact on the metabolism of amyloid-ß and degradation of phosphorylated tau. We then explore the involvement of Sirt1/SIRT1 across different AD-relevant biological processes, including cholesterol metabolism, inflammation, circadian rhythm, and gut microbiome, before discussing the interplay between Sirt1 and AD-related lifestyle factors, such as diet, physical activity, and smoking, as well as depression, a common comorbidity. Genome-wide association studies have explored potential associations between SIRT1 and AD, as well as AD risk factors and co-morbidities. We summarize this evidence at the genetic level to highlight links between SIRT1 and AD, particularly associations with AD-related risk factors, such as heart disease. Finally, we review the current literature of potential interactions between SIRT1 genetic variants and lifestyle factors and how this evidence supports the need for further research to determine the relevance of these interactions with respect to AD and dementia.

Habitual dietary nitrate intake and cognition in the Australian Imaging, Biomarkers and Lifestyle Study of ageing: A prospective cohort study.

BACKGROUND & AIMS: Dietary nitrate improves cardiovascular health via a nitric oxide (NO) pathway. NO is key to both cardiovascular and brain health. There is also a strong association between vascular risk factors and brain health. Dietary nitrate intake could therefore be associated with better cognitive function and reduced risk of cognitive decline. This is yet to be investigated. The aim of this study was to investigate the association between habitual intake of dietary nitrate from sources where nitrate is naturally present, and cognitive function, and cognitive decline, in the presence or absence of the apolipoprotein E (APOE) ε4 allele. METHODS: The study included 1254 older adult participants of the Australian Imaging, Biomarkers and Lifestyle Study of Ageing who were cognitively normal at baseline. Plant-derived, vegetable-derived, animal derived nitrate (not including meat where nitrate is an allowed additive), and total nitrate intakes were calculated from baseline food frequency questionnaires using comprehensive nitrate databases. Cognition was assessed at baseline and every 18 months over a follow-up period of 126 months using a comprehensive neuropsychological test battery. Multivariable-adjusted linear mixed effect models were used to examine the association between baseline nitrate intake and cognition over the 126 months (median [IQR] follow-up time of 36 [18-72] months), stratified by APOE ε4 carrier status. RESULTS: In non APOE ε4 carriers, for every 60 mg/day higher intake of plant-derived nitrate at baseline there was an associated higher language score [ß (95% CI): 0.10 (0.01, 0.19)] over 126 months, after multivariable adjustments. In APOE ε4 carriers, there was an associated better episodic recall memory [0.24 (0.08, 0.41)] and recognition memory [0.15 (0.01, 0.30)] scores. Similar associations were seen for the intakes of vegetable-derived and total nitrate. Additionally, in APOE ε4 carriers, for every 6 mg/day higher intake of animal-derived nitrate (excluding meat with nitrate as an allowed additive) at baseline there was an associated higher executive function score [ß (95% CI): 1.41 (0.42, 2.39)]. We did not find any evidence of an association between dietary nitrate intake and rate of cognitive decline. CONCLUSION: Our results suggest that habitual intake of dietary nitrate from sources where nitrate is naturally present impacts cognitive performance in an APOE genotype contingent manner. Further work is needed to validate our findings and understand potential mechanisms underlying the observed effects.

Plasma Glial Fibrillary Acidic Protein Is Associated with 18F-SMBT-1 PET: Two Putative Astrocyte Reactivity Biomarkers for Alzheimer's Disease.

BACKGROUND: Astrocyte reactivity is an early event along the Alzheimer's disease (AD) continuum. Plasma glial fibrillary acidic protein (GFAP), posited to reflect astrocyte reactivity, is elevated across the AD continuum from preclinical to dementia stages. Monoamine oxidase-B (MAO-B) is also elevated in reactive astrocytes observed using 18F-SMBT-1 PET in AD. OBJECTIVE: The objective of this study was to evaluate the association between the abovementioned astrocyte reactivity biomarkers. METHODS: Plasma GFAP and Aß were measured using the Simoa® platform in participants who underwent brain 18F-SMBT-1 and Aß-PET imaging, comprising 54 healthy control (13 Aß-PET+ and 41 Aß-PET-), 11 mild cognitively impaired (3 Aß-PET+ and 8 Aß-PET-) and 6 probable AD (5 Aß-PET+ and 1 Aß-PET-) individuals. Linear regressions were used to assess associations of interest. RESULTS: Plasma GFAP was associated with 18F-SMBT-1 signal in brain regions prone to early Aß deposition in AD, such as the supramarginal gyrus (SG), posterior cingulate (PC), lateral temporal (LT) and lateral occipital cortex (LO). After adjusting for age, sex, APOE ɛ4 genotype, and soluble Aß (plasma Aß42/40 ratio), plasma GFAP was associated with 18F-SMBT-1 signal in the SG, PC, LT, LO, and superior parietal cortex (SP). On adjusting for age, sex, APOE ɛ4 genotype and insoluble Aß (Aß-PET), plasma GFAP was associated with 18F-SMBT-1 signal in the SG. CONCLUSION: There is an association between plasma GFAP and regional 18F-SMBT-1 PET, and this association appears to be dependent on brain Aß load.

The relationship between objective physical activity and change in cognitive function.

INTRODUCTION: The current study investigated the association between objectively measured physical activity and cognition in older adults over approximately 8 years. METHODS: We utilized data from 199 cognitively unimpaired individuals from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study, aged ≥60. Actigraphy was used to measure physical activity (intensity, total activity, and energy expenditure) at baseline. Cognition was assessed using a comprehensive cognitive battery every 18-months. RESULTS: Higher baseline energy expenditure predicted better episodic recall memory and global cognition over the follow-up period (p = 0.031; p = 0.047, respectively). Those with higher physical activity intensity and greater total activity also had better global cognition over time (both p = 0.005). Finally, higher total physical activity predicted improved episodic recall memory over time (p = 0.022). DISCUSSION: These results suggest that physical activity can preserve cognition and that activity intensity may play an important role in this association. HIGHLIGHTS: Greater total physical activity predicts preserved episodic memory and global cognition. Moderate intensity physical activity (>3.7 metabolic equivalents of task [MET]) predicts preserved global cognition. Expending > 373 kilocalories per day may benefit episodic memory and global cognition.

Plasma Aß42/40 ratio, p-tau181, GFAP, and NfL across the Alzheimer's disease continuum: A cross-sectional and longitudinal study in the AIBL cohort.

INTRODUCTION: Plasma amyloid beta (Aß)1-42/Aß1-40 ratio, phosphorylated-tau181 (p-tau181), glial fibrillary acidic protein (GFAP), and neurofilament light (NfL) are putative blood biomarkers for Alzheimer's disease (AD). However, head-to-head cross-sectional and longitudinal comparisons of the aforementioned biomarkers across the AD continuum are lacking. METHODS: Plasma Aß1-42, Aß1-40, p-tau181, GFAP, and NfL were measured utilizing the Single Molecule Array (Simoa) platform and compared cross-sectionally across the AD continuum, wherein Aß-PET (positron emission tomography)-negative cognitively unimpaired (CU Aß-, n = 81) and mild cognitive impairment (MCI Aß-, n = 26) participants were compared with Aß-PET-positive participants across the AD continuum (CU Aß+, n = 39; MCI Aß+, n = 33; AD Aß+, n = 46) from the Australian Imaging, Biomarker & Lifestyle Flagship Study of Ageing (AIBL) cohort. Longitudinal plasma biomarker changes were also assessed in MCI (n = 27) and AD (n = 29) participants compared with CU (n = 120) participants. In addition, associations between baseline plasma biomarker levels and prospective cognitive decline and Aß-PET load were assessed over a 7 to 10-year duration. RESULTS: Lower plasma Aß1-42/Aß1-40 ratio and elevated p-tau181 and GFAP were observed in CU Aß+, MCI Aß+, and AD Aß+, whereas elevated plasma NfL was observed in MCI Aß+ and AD Aß+, compared with CU Aß- and MCI Aß-. Among the aforementioned plasma biomarkers, for models with and without AD risk factors (age, sex, and apolipoprotein E (APOE) ε4 carrier status), p-tau181 performed equivalent to or better than other biomarkers in predicting a brain Aß-/+ status across the AD continuum. However, for models with and without the AD risk factors, a biomarker panel of Aß1-42/Aß1-40, p-tau181, and GFAP performed equivalent to or better than any of the biomarkers alone in predicting brain Aß-/+ status across the AD continuum. Longitudinally, plasma Aß1-42/Aß1-40, p-tau181, and GFAP were altered in MCI compared with CU, and plasma GFAP and NfL were altered in AD compared with CU. In addition, lower plasma Aß1-42/Aß1-40 and higher p-tau181, GFAP, and NfL were associated with prospective cognitive decline and lower plasma Aß1-42/Aß1-40, and higher p-tau181 and GFAP were associated with increased Aß-PET load prospectively. DISCUSSION: These findings suggest that plasma biomarkers are altered cross-sectionally and longitudinally, along the AD continuum, and are prospectively associated with cognitive decline and brain Aß-PET load. In addition, although p-tau181 performed equivalent to or better than other biomarkers in predicting an Aß-/+ status across the AD continuum, a panel of biomarkers may have superior Aß-/+ status predictive capability across the AD continuum. HIGHLIGHTS: Area under the curve (AUC) of p-tau181 ≥ AUC of Aß42/40, GFAP, NfL in predicting PET Aß-/+ status (Aß-/+).  AUC of Aß42/40+p-tau181+GFAP panel ≥ AUC of Aß42/40/p-tau181/GFAP/NfL for Aß-/+.  Longitudinally, Aß42/40, p-tau181, and GFAP were altered in MCI versus CU.  Longitudinally, GFAP and NfL were altered in AD versus CU.  Aß42/40, p-tau181, GFAP, and NfL are associated with prospective cognitive decline.  Aß42/40, p-tau181, and GFAP are associated with increased PET Aß load prospectively.

The interaction between physical activity and sleep on cognitive function and brain beta-amyloid in older adults.

BACKGROUND: Lifestyle factors such as physical activity and optimal sleep are associated with better cognition and lower levels of Alzheimer's disease (AD) biomarkers, including brain beta-amyloid (Aß) burden. OBJECTIVE: We utilised cross-sectional data from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study to determine whether self-reported physical activity (measured via the International Physical Activity Questionnaire) moderates the relationship between self-reported sleep (measured via the Pittsburgh Sleep Quality Index), cognition, and brain Aß. METHODS: Participants were 349 community-dwelling cognitively normal older adults (75.3 ± 5.7 years), all of whom underwent comprehensive cognitive assessment. Data from a subset of participants (n = 201) were used for analyses with brain Aß burden (measured by positron emission tomography) as the outcome. RESULT: Physical activity moderated the relationship between sleep duration and episodic memory (ß = -0.10, SE =0.03, p = .005), and sleep efficiency and episodic memory (ß = -0.09, SE =0.04, p = .011), such that greater amounts of physical activity mitigated the impact of suboptimal sleep duration and efficiency on episodic memory. Physical activity also moderated the relationship between sleep duration and brain Aß (ß = -0.13, SE =0.06, p = .031), and overall sleep quality and brain Aß (ß = 0.13, SE =0.06, p = .027). CONCLUSION: Our findings suggest that physical activity may play an important role in the relationship between sleep and cognitive function, and brain Aß.

Potential role of dietary nitrate in relation to cardiovascular and cerebrovascular health, cognition, cognitive decline and dementia: a review.

There is currently no effective treatment for dementia, of which Alzheimer's disease (AD) is the most common form. It is, therefore, imperative to focus on evidence-based preventive strategies to combat this extremely debilitating chronic disease. Nitric oxide (NO) is a key signalling molecule in the cardiovascular, cerebrovascular, and central nervous systems. Vegetables rich in nitrate, such as spinach and beetroot, are an important source of NO, with beneficial effects on validated markers of cardiovascular health and an association with a lower risk of cardiovascular disease. Given the link between cardiovascular disease risk factors and dementia, together with the important role of NO in vascular health and cognition, it is important to determine whether dietary nitrate could also improve cognitive function, markers of brain health, and lower risk of dementia. This review presents an overview of NO's role in the cardiovascular, cerebrovascular, and central nervous systems; an overview of the available evidence that nitrate, through effects on NO, improves cardiovascular health; and evaluates the current evidence regarding dietary nitrate's potential role in cerebrovascular health, cognitive function, and brain health assessed via biomarkers.

Plasma p-tau181/Aß1-42 ratio predicts Aß-PET status and correlates with CSF-p-tau181/Aß1-42 and future cognitive decline.

Background: In Alzheimer's disease (AD), plasma amyloid beta (Aß)1-42 and phosphorylated tau (p-tau) predict high amyloid status from Aß positron emission tomography (PET); however, the extent to which combination of these plasma assays can predict remains unknown. Methods: Prototype Simoa assays were used to measure plasma samples from participants who were either cognitively normal (CN) or had mild cognitive impairment (MCI)/AD in the Australian Imaging, Biomarkers and Lifestyle (AIBL) study. Results: The p-tau181/Aß1-42 ratio showed the best prediction of Aß-PET across all participants (area under the curve [AUC] = 0.905, 95% confidence interval [CI]: 0.86-0.95) and in CN (AUC = 0.873; 0.80-0.94), and symptomatic (AUC = 0.908; 0.82-1.00) adults. Plasma p-tau181/Aß1-42 ratio correlated with cerebrospinal fluid (CSF) p-tau181 (Elecsys, Spearman's ρ = 0.74, P < 0.0001) and predicted abnormal CSF Aß (AUC = 0.816; 0.74-0.89). The p-tau181/Aß1-42 ratio also predicted future rates of cognitive decline assessed by AIBL Preclinical Alzheimer Cognitive Composite or Clinical Dementia Rating Sum of Boxes (P < 0.0001). Discussion: Plasma p-tau181/Aß1-42 ratio predicted both Aß-PET status and cognitive decline, demonstrating potential as both a diagnostic aid and as a screening and prognostic assay for preclinical AD trials.