Locus coeruleus integrity is related to an exploitation-based decision-making bias in older adulthood

Optimal decision-making balances exploration for new information against exploitation of known rewards, a process mediated by the locus coeruleus and its norepinephrine projections. We predicted that an exploitation-bias that emerges in older adulthood would be associated with lower microstructural integrity of the locus coeruleus. Leveraging in vivo histological methods from quantitative MRI-magnetic transfer saturation-we provide evidence that older age is associated with lower locus coeruleus integrity. Critically, we demonstrate that an exploitation bias in older adulthood, assessed with a foraging task, is sensitive and specific to lower locus coeruleus integrity. Because the locus coeruleus is uniquely vulnerable to Alzheimer's disease pathology, our findings suggest that aging, and a presymptomatic trajectory of Alzheimer's related decline, may fundamentally alter decision-making abilities in later life.

Iron Deposition and Distribution Across the Hippocampus Is Associated with Pattern Separation and Pattern Completion in Older Adults at Risk for Alzheimer's Disease

Elevated iron deposition in the brain has been observed in older adult humans and persons with Alzheimer's disease (AD), and has been associated with lower cognitive performance. We investigated the impact of iron deposition, and its topographical distribution across hippocampal subfields and segments (anterior, posterior) measured along its longitudinal axis, on episodic memory in a sample of cognitively unimpaired older adults at elevated familial risk for AD (N = 172, 120 females, 52 males; mean age = 68.8 ± 5.4 years). MRI-based quantitative susceptibility maps were acquired to derive estimates of hippocampal iron deposition. The Mnemonic Similarity Task was used to measure pattern separation and pattern completion, two hippocampally mediated episodic memory processes. Greater hippocampal iron load was associated with lower pattern separation and higher pattern completion scores, both indicators of poorer episodic memory. Examination of iron levels within hippocampal subfields across its long axis revealed topographic specificity. Among the subfields and segments investigated here, iron deposition in the posterior hippocampal CA1 was the most robustly and negatively associated with the fidelity memory representations. This association remained after controlling for hippocampal volume and was observed in the context of normal performance on standard neuropsychological memory measures. These findings reveal that the impact of iron load on episodic memory performance is not uniform across the hippocampus. Both iron deposition levels as well as its spatial distribution, must be taken into account when examining the relationship between hippocampal iron and episodic memory in older adults at elevated risk for AD.

Neurobehavioral mechanisms influencing the association between generativity, the desire to promote well-being of younger generations, and purpose in life in older adults at risk for Alzheimer's disease

OBJECTIVES

Generativity, the desire and action to improve the well-being of younger generations, is associated with purpose in life among older adults. However, the neurobehavioral factors supporting the relationship between generativity and purpose in life remain unknown. This study aims to identify the functional neuroanatomy of generativity and mechanisms linking generativity with purpose in life in at-risk older adults.

METHODS

Fifty-eight older adults (mean age = 70.8, SD = 5.03, 45 females) with a family history of Alzheimer's disease (AD) were recruited from the PREVENT-AD cohort. Participants underwent brain imaging and completed questionnaires assessing generativity, social support, and purpose in life. Mediation models examined whether social support mediated the association between generativity and purpose in life. Seed-to-voxel analyses investigated the association between generativity and resting-state functional connectivity (rsFC) to the ventromedial prefrontal cortex (vmPFC) and ventral striatum (VS), and whether this rsFC moderated the relationship between generativity and purpose in life.

RESULTS

Affectionate social support mediated the association between generative desire and purpose in life. Generative desire was associated with rsFC between VS and precuneus, and, vmPFC and right dorsolateral prefrontal cortex (rdlPFC). The vmPFC-rdlPFC rsFC moderated the association between generative desire and purpose in life.

DISCUSSION

These findings provide insight into how the brain supports complex social behavior and, separately, purpose in life in at-risk aging. Affectionate social support may be a putative target process to enhance purpose in life in older adults. This knowledge contributes to future developments of personalized interventions that promote healthy aging.

Midlife physical activity engagement is associated with later-life brain health

The relationship between midlife physical activity (PA), and cognition and brain health in later life is poorly understood with conflicting results from previous research. Investigating the contribution of midlife PA to later-life cognition and brain health in high-risk populations will propel the development of health guidance for those most in need. The current study examined the association between midlife PA engagement and later-life cognition, grey matter characteristics and resting-state functional connectivity in older individuals at high-risk for Alzheimer's disease. The association between midlife PA and later-life cognitive function was not significant but was moderated by later-life PA. Meanwhile, greater midlife moderate-to-vigorous PA was associated with greater grey matter surface area in the left middle frontal gyrus. Moreover, greater midlife total PA was associated with diminished functional connectivity between bilateral middle frontal gyri and middle cingulum, supplementary motor areas, and greater functional connectivity between bilateral hippocampi and right cerebellum, Crus II. These results indicate the potentially independent contribution of midlife PA to later-life brain health.

The influence of generativity on purpose in life is mediated by social support and moderated by prefrontal functional connectivity in at-risk older adults

Objectives

Generativity, the desire and action to improve the well-being of younger generations, is positively associated with purpose in life among older adults. However, the neural basis of generativity and the neurobehavioral factors supporting the relationship between generativity and purpose in life remain unknown. This study aims to identify the functional neuroanatomy of generativity and mechanisms linking generativity with purpose in life in at-risk older adults.

Methods

Fifty-eight cognitively healthy older adults (mean age = 70.78, 45 females) with a family history of Alzheimer's disease were recruited from the PREVENT-AD aging cohort. Participants underwent brain imaging and completed questionnaires assessing generativity, social support, and purpose in life. Mediation models examined whether social support mediated the association between generativity and purpose in life. Seed-to-voxel analyses investigated the association between resting-state functional connectivity (rsFC) to the ventromedial prefrontal cortex (vmPFC) and ventral striatum (VS) and whether this rsFC moderated the relationship between generativity and purpose in life.

Results

Affectionate social support mediated the association between generative desire and purpose in life. Generative desire was associated with rsFC between VS and precuneus and vmPFC and right dorsolateral prefrontal cortex (rdlPFC). The vmPFC-rdlPFC connectivity moderated the association between generative desire and purpose in life.

Discussion

These findings provide insight into how the brain supports social behavior and, separately, purpose in life in at-risk aging. Affectionate social support may be a putative target process to enhance purpose and life in older adults. This knowledge contributes to future developments of personalized interventions that promote healthy aging.

Resting-state MRI functional connectivity as a neural correlate of multidomain lifestyle adherence in older adults at risk for Alzheimer's disease

Prior research has demonstrated the importance of a healthy lifestyle to protect brain health and diminish dementia risk in later life. While a multidomain lifestyle provides an ecological perspective to voluntary engagement, its association with brain health is still under-investigated. Therefore, understanding the neural mechanisms underlying multidomain lifestyle engagement, particularly in older adults at risk for Alzheimer's disease (AD), gives valuable insights into providing lifestyle advice and intervention for those in need. The current study included 139 healthy older adults with familial risk for AD from the Prevent-AD longitudinal aging cohort. Self-reported exercise engagement, cognitive activity engagement, healthy diet adherence, and social activity engagement were included to examine potential phenotypes of an individual's lifestyle adherence. Two adherence profiles were discovered using data-driven clustering methodology [i.e., Adherence to healthy lifestyle (AL) group and Non-adherence to healthy lifestyle group]. Resting-state functional connectivity matrices and grey matter brain features obtained from magnetic resonance imaging were used to classify the two groups using a support vector machine (SVM). The SVM classifier was 75% accurate in separating groups. The features that show consistently high importance to the classification model were functional connectivity mainly between nodes located in different prior-defined functional networks. Most nodes were located in the default mode network, dorsal attention network, and visual network. Our results provide preliminary evidence of neurobiological characteristics underlying multidomain healthy lifestyle choices.

Data and Tools Integration in the Canadian Open Neuroscience Platform

We present the Canadian Open Neuroscience Platform (CONP) portal to answer the research community's need for flexible data sharing resources and provide advanced tools for search and processing infrastructure capacity. This portal differs from previous data sharing projects as it integrates datasets originating from a number of already existing platforms or databases through DataLad, a file level data integrity and access layer. The portal is also an entry point for searching and accessing a large number of standardized and containerized software and links to a computing infrastructure. It leverages community standards to help document and facilitate reuse of both datasets and tools, and already shows a growing community adoption giving access to more than 60 neuroscience datasets and over 70 tools. The CONP portal demonstrates the feasibility and offers a model of a distributed data and tool management system across 17 institutions throughout Canada.

Open science datasets from PREVENT-AD, a longitudinal cohort of pre-symptomatic Alzheimer's disease

To move Alzheimer Disease (AD) research forward it is essential to collect data from large cohorts, but also make such data available to the global research community. We describe the creation of an open science dataset from the PREVENT-AD (PResymptomatic EValuation of Experimental or Novel Treatments for AD) cohort, composed of cognitively unimpaired older individuals with a parental or multiple-sibling history of AD. From 2011 to 2017, 386 participants were enrolled (mean age 63 years old ± 5) for sustained investigation among whom 349 have retrospectively agreed to share their data openly. Repositories are findable through the unified interface of the Canadian Open Neuroscience Platform and contain up to five years of longitudinal imaging data, cerebral fluid biochemistry, neurosensory capacities, cognitive, genetic, and medical information. Imaging data can be accessed openly at https://openpreventad.loris.ca while most of the other information, sensitive by nature, is accessible by qualified researchers at https://registeredpreventad.loris.ca. In addition to being a living resource for continued data acquisition, PREVENT-AD offers opportunities to facilitate understanding of AD pathogenesis.

INTREPAD: A randomized trial of naproxen to slow progress of presymptomatic Alzheimer disease

OBJECTIVE

To evaluate the safety and efficacy of low-dose naproxen for prevention of progression in presymptomatic Alzheimer disease (AD) among cognitively intact persons at risk.

METHODS

Investigation of Naproxen Treatment Effects in Pre-symptomatic Alzheimer's Disease (INTREPAD), a 2-year double-masked pharmaco-prevention trial, enrolled 195 AD family history-positive elderly (mean age 63 years) participants screened carefully to exclude cognitive disorder (NCT-02702817). These were randomized 1:1 to naproxen sodium 220 mg twice daily or placebo. Multimodal imaging, neurosensory, cognitive, and (in ∼50%) CSF biomarker evaluations were performed at baseline, 3, 12, and 24 months. A modified intent-to-treat analysis considered 160 participants who remained on-treatment through their first follow-up examination. The primary outcome was rate of change in a multimodal composite presymptomatic Alzheimer Progression Score (APS).

RESULTS

Naproxen-treated individuals showed a clear excess of adverse events. Among treatment groups combined, the APS increased by 0.102 points/year (SE 0.014; p < 10-12), but rate of change showed little difference by treatment assignment (0.019 points/year). The treatment-related rate ratio of 1.16 (95% confidence interval 0.64-1.96) suggested that naproxen does not reduce the rate of APS progression by more than 36%. Secondary analyses revealed no notable treatment effects on individual CSF, cognitive, or neurosensory biomarker indicators of progressive presymptomatic AD.

CONCLUSIONS

In cognitively intact individuals at risk, sustained treatment with naproxen sodium 220 mg twice daily increases frequency of adverse health effects but does not reduce apparent progression of presymptomatic AD.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that, for people who are cognitively intact, low-dose naproxen does not significantly reduce progression of a composite indicator of presymptomatic AD.

Odor identification as a biomarker of preclinical AD in older adults at risk

OBJECTIVE

To assess odor identification (OI) as an indicator of presymptomatic Alzheimer disease (AD) pathogenesis in cognitively normal aging individuals at increased risk of AD dementia.

METHODS

In 274 members of the PREVENT-AD cohort of healthy aging persons with a parental or multiple-sibling history of AD dementia, we assessed the cross-sectional association of OI with potential indicators of presymptomatic AD. Some 101 participants donated CSF, thus enabling assessment of AD pathology with the biomarkers total tau (t-tau), phospho-tau (P181-tau), and their ratios with β-amyloid (Aβ1-42). Adjusted analyses considered age, cognition, APOE ε4 status, education, and sex as covariates. We measured OI using the University of Pennsylvania Smell Identification Test and cognitive performance using the Repeatable Battery for Assessment of Neuropsychological Status. Standard kits provided assays of the AD biomarkers. Analyses used robust-fit linear regression models.

RESULTS

Reduced OI was associated with lower cognitive score and older age, as well as increased ratios of CSF t-tau and P181-tau to Aβ1-42 (all p < 0.02). However, the observed associations of OI with age and cognition were unapparent in adjusted models that restricted observations to CSF donors and included AD biomarkers. OI showed little association with CSF Aβ1-42 alone except in APOE ε4 carriers having lowest-quartile Aβ1-42 levels.

CONCLUSIONS

These findings from healthy high-risk older individuals suggest that OI reflects degree of preclinical AD pathology, while its relationships with age and cognition result from the association of these latter variables with such pathology. Diminished OI may be a practical and affordable biomarker of AD pathology.

Kinetics of 13C-DHA before and during fish-oil supplementation in healthy older individuals

BACKGROUND

Docosahexaenoic acid (DHA) kinetics appear to change with intake, which is an effect that we studied in an older population by using uniformly carbon-13-labeled DHA ((13)C-DHA).

OBJECTIVE

We evaluated the influence of a fish-oil supplement over 5 mo on the kinetics of (13)C-DHA in older persons.

DESIGN

Thirty-four healthy, cognitively normal participants (12 men, 22 women) aged between 52 and 90 y were recruited. Two identical kinetic studies were performed, each with the use of a single oral dose of 40 mg (13)C-DHA. The first kinetic study was performed before participants started taking a 5-mo supplementation that provided 1.4 g DHA/d plus 1.8 g eicosapentaenoic acid (EPA)/d (baseline); the second study was performed during the final month of supplementation (supplement). In both kinetic studies, blood and breath samples were collected ≤8 h and weekly over 4 wk to analyze (13)C enrichment.

RESULTS

The time × supplement interaction for (13)C-DHA in the plasma was not significant, but there were separate time and supplement effects (P < 0.0001). The area under the curve for plasma (13)C-DHA was 60% lower while subjects were taking the supplement than at baseline (P < 0.0001). The uniformly carbon-13-labeled EPA concentration was 2.6 times as high 1 d posttracer while patients were taking the supplement as it was at baseline. The mean (±SEM) plasma (13)C-DHA half-life was 4.5 ± 0.4 d at baseline compared with 3.0 ± 0.2 d while taking the supplement (P < 0.0001). Compared with baseline, the mean whole-body half-life was 61% lower while subjects were taking the supplement. The loss of (13)C-DHA through β-oxidation to carbon dioxide labeled with carbon-13 increased from 0.085% of dose/h at baseline to 0.208% of dose/h while subjects were taking the supplement.

CONCLUSIONS

In older persons, a supplement of 3.2 g EPA + DHA/d increased β-oxidation of (13)C-DHA and shortened the plasma (13)C-DHA half-life. Therefore, when circulating concentrations of EPA and DHA are increased, more DHA is available for β-oxidation. This trial was registered at clinicaltrials.gov as NCT01577004.

Effects of vegetable oils on biochemical and biophysical properties of membrane retinal pigment epithelium cells

The aim of this study was to investigate the effect of vegetable oil enrichment of retinal pigment epithelial (RPE) cells on their biochemical and biophysical properties. For this, RPE cells were incubated with 4 different vegetables oils (olive oil, corn oil, argan oil, and camelina oil). The cytotoxicity of these vegetable oils was assessed in vivo on 8-week-old mice and in vitro by using the neutral red and YO-PRO-1 tests. Membrane fluidity was evaluated by fluorescence anisotropy using the fluorescent probe diphenylhexatriene, and membrane fatty acid composition was assessed by gas chromatography. None of the oils tested displayed cytotoxic effects. In vitro, omega-3 rich oils improved membrane fluidity by 47% compared with the control cells. The omega-3 PUFA content within membranes decreased by 38% to 55% when cells were incubated separately with olive oil, corn oil, or argan oil, and increased when cells were incubated with a mixture of those oils, or with camelina oil alone (50% and 103% increase, respectively). Our results show that the fatty acids in vegetable oil incorporate into retinal cells and increase the plasma membrane fluidity.

The ketogenic diet increases brain glucose and ketone uptake in aged rats: a dual tracer PET and volumetric MRI study

Despite decades of study, it is still unclear whether regional brain glucose uptake is lower in the cognitively healthy elderly. Whether regional brain uptake of ketones (β-hydroxybutyrate and acetoacetate [AcAc]), the main alternative brain fuel to glucose, changes with age is unknown. We used a sequential, dual tracer positron emission tomography (PET) protocol to quantify brain (18)F-fluorodeoxyglucose ((18)F-FDG) and (11)C-AcAc uptake in two studies with healthy, male Sprague-Dawley rats: (i) Aged (21 months; 21M) versus young (4 months; 4M) rats, and (ii) The effect of a 14 day high-fat ketogenic diet (KD) on brain (18)F-FDG and (11)C-AcAc uptake in 24 month old rats (24M). Similar whole brain volumes assessed by magnetic resonance imaging, were observed in aged 21M versus 4M rats, but the lateral ventricles were 30% larger in the 21M rats (p=0.001). Whole brain cerebral metabolic rates of AcAc (CMR(AcAc)) and glucose (CMR(glc)) did not differ between 21M and 4M rats, but were 28% and 44% higher, respectively, in 24M-KD compared to 24M rats. The region-to-whole brain ratio of CMR(glc) was 37-41% lower in the cortex and 40-45% lower in the cerebellum compared to CMR(AcAc) in 4M and 21M rats. We conclude that a quantitative measure of uptake of the brain's two principal exogenous fuels was generally similar in healthy aged and young rats, that the % of distribution across brain regions differed between ketones and glucose, and that brain uptake of both fuels was stimulated by mild, experimental ketonemia.

Plasma and brain fatty acid profiles in mild cognitive impairment and Alzheimer's disease

Alzheimer's disease (AD) is generally associated with lower omega-3 fatty acid intake from fish but despite numerous studies, it is still unclear whether there are differences in omega-3 fatty acids in plasma or brain. In matched plasma and brain samples provided by the Memory and Aging Project, fatty acid profiles were quantified in several plasma lipid classes and in three brain cortical regions. Fatty acid data were expressed as % composition and as concentrations (mg/dL for plasma or mg/g for brain). Differences in plasma fatty acid profiles between AD, mild cognitive impairment (MCI), and those with no cognitive impairment (NCI) were most apparent in the plasma free fatty acids (lower oleic acid isomers and omega-6 fatty acids in AD) and phospholipids (lower omega-3 fatty acids in AD). In brain, % DHA was lower only in phosphatidylserine of mid-frontal cortex and superior temporal cortex in AD compared to NCI (-14% and -12%, respectively; both p < 0.05). The only significant correlation between plasma and brain fatty acids was between % DHA in plasma total lipids and % DHA in phosphatidylethanolamine of the angular gyrus, but only in the NCI group (+0.77, p < 0.05). We conclude that AD is associated with altered plasma status of both DHA and other fatty acids unrelated to DHA, and that the lipid class-dependent nature of these differences reflects a combination of differences in intake and metabolism.

Mild experimental ketosis increases brain uptake of 11C-acetoacetate and 18F-fluorodeoxyglucose: a dual-tracer PET imaging study in rats

Brain glucose and ketone uptake was investigated in Fisher rats subjected to mild experimental ketonemia induced by a ketogenic diet (KD) or by 48 hours fasting (F). Two tracers were used, (11)C-acetoacetate ((11)C-AcAc) for ketones and (18)F-fluorodeoxyglucose for glucose, in a dual-tracer format for each animal. Thus, each animal was its own control, starting first on the normal diet, then undergoing 48 hours F, followed by 2 weeks on the KD. In separate rats on the same diet conditions, expression of the transporters of glucose and ketones (glucose transporter 1 (GLUT1) and monocarboxylic acid transporter (MCT1)) was measured in brain microvessel preparations. Compared to controls, uptake of (11)C-AcAc increased more than 2-fold while on the KD or after 48 hours F (P < 0.05). Similar trends were observed for (18)FDG uptake with a 1.9-2.6 times increase on the KD and F, respectively (P < 0.05). Compared to controls, MCT1 expression increased 2-fold on the KD (P < 0.05) but did not change during F. No significant difference was observed across groups for GLUT1 expression. Significant differences across the three groups were observed for plasma beta-hydroxybutyrate (beta-HB), AcAc, glucose, triglycerides, glycerol, and cholesterol (P < 0.05), but no significant differences were observed for free fatty acids, insulin, or lactate. Although the mechanism by which mild ketonemia increases brain glucose uptake remains unclear, the KD clearly increased both the blood-brain barrier expression of MCT1 and stimulated brain (11)C-AcAc uptake. The present dual-tracer positron emission tomography approach may be particularly interesting in neurodegenerative pathologies such as Alzheimer's disease where brain energy supply appears to decline critically.

Bezafibrate mildly stimulates ketogenesis and fatty acid metabolism in hypertriglyceridemic subjects

Our objective was to determine whether bezafibrate, a hypotriglyceridemic drug and peroxisome proliferator-activated receptor (PPAR)-alpha agonist, is ketogenic and increases fatty acid oxidation in humans. We measured fatty acid metabolism and ketone levels in 13 mildly hypertriglycemic adults (67 +/- 11 years old) during 2 metabolic study days lasting 6 h, 1 day before and 1 day after bezafibrate (400 mg of bezafibrate per day for 12 weeks). beta-Hydroxybutyrate, triglycerides, free fatty acids, fatty acid profiles, insulin, and glucose were measured in plasma, and fatty acid beta-oxidation was measured in breath after an oral 50-mg dose of the fatty acid tracer [U-(13)C]linoleic acid. As expected, 12 weeks on bezafibrate decreased plasma triglycerides by 35%. Bezafibrate tended to raise postprandial beta-hydroxybutyrate, an effect that was significant after normalization to the fasting baseline values (p = 0.03). beta-Oxidation of [U-(13)C]linoleic acid increased by 30% (p = 0.03) after treatment. On the metabolic study day after bezafibrate treatment, postprandial insulin decreased by 26% (p = 0.01), and glucose concentrations were lower 2 to 5 h postprandially. Thus, in hypertriglyceridemic individuals, bezafibrate is mildly ketogenic and significantly changes fatty acid metabolism, effects that may be linked to PPARalpha stimulation and to moderately improved glucose metabolism.

Maternal dietary fat determines metabolic profile and the magnitude of endocannabinoid inhibition of the stress response in neonatal rat offspring

Endocannabinoids (eCBs) are products of phospholipid (PL)-derived arachidonic acid (AA) that regulate hypothalamus-pituitary-adrenal axis activity. We hypothesized that differences in the quality and quantity of maternal dietary fat would modulate the PL AA content in the neonatal brain affecting stress responsiveness via differences in eCB production and activity in stress-activated brain areas. Pregnant rats were fed a 5% [control (C)] or 30% fat [high fat (HF)] diet rich in either n-6 (HF-n-6) or n-3 (HF-n-3) fat during the last week of gestation and lactation. Postnatal d 10 offspring were tested for metabolic hormones, AA (n-6) and eCB brain content, and hormonal effects of eCB receptor antagonism (AM251, 1 or 3 mg/kg ip) on stress responses. Like maternal diet, milk from HF-n-3 mothers had a reduced n-6/n-3 fat ratio compared with that of C and HF-n-6 mothers. Hypothalamic and hippocampal levels of PL AA were diet specific, reflecting the maternal milk and dietary n-6/n-3 ratio, with HF-n-3 offspring displaying reduced AA content relative to C and HF-n-6 offspring. Plasma corticosterone and insulin were elevated in HF-fed pups, whereas leptin was increased only in HF-n-6 pups. Basal eCB concentrations were also diet and brain region specific. In C pups, eCB receptor antagonist pretreatment increased stress-induced ACTH secretion, but not in the HF groups. Stress-induced corticosterone secretion was not sensitive to AM251 treatment in HF-n-3 pups. Thus, the nature of preweaning dietary fat differentially influences neonatal metabolic hormones, brain PL AA levels, and eCB, with functional consequences on hypothalamus-pituitary-adrenal axis modulation in developing rat pups.

Higher plasma n-3 fatty acid status in the moderately healthy elderly in southern Québec: higher fish intake or aging-related change in n-3 fatty acid metabolism?

The elderly reportedly have a significantly higher % of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in plasma and red cell lipids. However, these observations are from a few small studies and the health status of the elderly in these studies is for the most part unclear. Since the elderly are susceptible to cardiovascular and neurological illnesses that seem to be related in part to lower intake of n-3 fatty acids it seems paradoxical that their blood levels of EPA and DHA would be higher than in young adults. We report here plasma fatty acid profiles and their response to supplementation with two types of fish oils from several of our recent studies in the moderately healthy elderly. We define the moderately healthy elderly as those who were in good physical condition, had no cognitive decline and, if present, in whom hypothyroidism, hyperlipidemia and/or hypertension were well-controlled. As shown previously, we confirm the higher % EPA and % total n-3 fatty acids (but not DHA) in fasting plasma and extend these findings to include higher plasma concentrations (mg/L) of n-3 fatty acids as well. The EPA-predominant supplement raised DHA only in the young, whereas the DHA-predominant supplement raised EPA more in the young than in the elderly. The moderately healthy elderly clearly have higher plasma n-3 fatty acids but whether this reflects differences in intake versus aging-related changes in n-3 fatty acid metabolism remains to be elucidated.

Unresolved issues in the link between docosahexaenoic acid and Alzheimer's disease

Lower consumption of docosahexaenoic acid (DHA) is commonly but not always associated with higher risk of cognitive decline and diagnosis of Alzheimer's disease (AD). We review here the available data relating DHA to AD, with emphasis on DHA content of plasma and brain. Our assessment of this literature is that low DHA is not consistently observed in AD plasma or brain. However, in dietary and population studies, low DHA intake is usually associated with low plasma DHA. Therefore, at present, there is no clear explanation of why the usual low DHA intake-low plasma DHA relationship appears not to exist in AD. Adding to the confusion, preliminary and inconclusive reports tentatively suggest that dietary DHA could potentially reduce cognitive deterioration in AD. These inconsistencies between dietary DHA, plasma/tissue DHA, and possible DHA efficacy in AD may be more methodological than biological, and may arise in part because only one study to date has reported both DHA intake and plasma DHA values in the same AD patients. Studies reporting DHA intake and plasma levels while also undertaking a DHA intervention in AD would presumably help resolve these issues.

Omega-3 fatty acids, energy substrates, and brain function during aging

The maintenance of optimal cognitive function is a central feature of healthy aging. Impairment in brain glucose uptake is common in aging associated cognitive deterioration, but little is known of how this problem arises or whether it can be corrected or bypassed. Several aspects of the challenge to providing the brain with an adequate supply of fuel during aging seem to relate to omega-3 fatty acids. For instance, low intake of omega-3 fatty acids, especially docosahexaenoic acid (DHA), is becoming increasingly associated with several forms of cognitive decline in the elderly, particularly Alzheimer's disease. Brain DHA level seems to be an important regulator of brain glucose uptake, possibly by affecting the activity of some but not all the glucose transporters. DHA synthesis from either alpha-linolenic acid (ALA) or eicosapentaenoic acid (EPA) is very low in humans begging the question of whether these DHA precursors are likely to be helpful in maintaining cognition during aging. We speculate that ALA and EPA may well have useful supporting roles in maintaining brain function during aging but not by their conversion to DHA. ALA is an efficient ketogenic fatty acid, while EPA promotes fatty acid oxidation. By helping to produce ketone bodies, the effects of ALA and EPA could well be useful in strategies intended to use ketones to bypass problems of impaired glucose access to the brain during aging. Hence, it may be time to consider whether the main omega-3 fatty acids have distinct but complementary roles in brain function.