Quantitative Erythrocyte Omega-3 EPA Plus DHA Levels are Related to Higher Regional Cerebral Blood Flow on Brain SPECT

Abstract

Background: The interrelationships between omega-3 fatty acids status, brain perfusion, and cognition are not well understood.

Objective: To evaluate if SPECT brain imaging of cerebral perfusion and cognition varies as a function of omega-3 fatty acid levels.

Methods: A random sample of 166 study participants was drawn from a psychiatric referral clinical for which erythrocyte quantification of omega-3 eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) (the Omega-3 Index) was available. Quantitative brain SPECT was done on 128 regions based on a standard anatomical Atlas. Persons with erythrocyte EPA+DHA concentrations were dichotomized based on membership in top 50th percentile versus bottom 50th percentile categories. Two-sample t-tests were done to identify statistically significant differences in perfusion between the percentile groups. Partial correlations were modeled between EPA+DHA concentration and SPECT regions. Neurocognitive status was assessed using computerized testing (WebNeuro) and was separately correlated to cerebral perfusion on brain SPECT imaging and omega-3 EPA+DHA levels.

Results: Partial correlation analyses showed statistically significant relationships between higher omega-3 levels and cerebral perfusion were in the right parahippocampal gyrus (r = 0.20, p = 0.03), right precuneus (r = 0.20, p = 0.03), and vermis subregion 6 (p = 0.21, p = 0.03). Omega-3 Index levels separately correlated to the feeling subsection of the WebNeuro (r = 0.25, p = 0.01).

Conclusion: Quantitative omega-3 EPA+DHA erythrocyte concentrations are independently correlated with brain perfusion on SPECT imaging and neurocognitive tests. These results have implications for the role of omega-3 fatty acids toward contributing to cognitive reserve.

Keywords

Brain SPECT cognitive omega-3

INTRODUCTION

Alzheimer’s disease (AD) is the most common cause of dementia and remains an incurable disorder, with no successful curative drug trials in over three decades [1, 2]. However, the etiology of AD is increasingly recognized as multifactorial with potential subtypes [3]. The term “mixed dementia” specifically refers to the frequent co-existence of AD pathology with vascular risk factors such as hypertension and type 2 diabetes [4]. This phenomenon suggests the existence of risk factors for dementia that may be preventable or modifiable.

These initial observations have led to the development of dementia prevention concepts that focus on targeting modifiable risk factors [5]. Of particularly recent interest is an emphasis on dietary approaches for preventing cognitive decline. Specifically, consumption of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) either in foods or from dietary supplements, is thought to represent a promising risk reduction strategy for dementia prevention.

Multiple studies spanning various methodologies have suggested that supplementing diets with EPA and DHA may reduce risk of cognitive decline. Specifically, these omega-3 s have anti-amyloid, anti-tau, and anti-inflammatory actions in the brains of animal models [6]. Also, EPA+DHA enhance the functioning of the recently discovered glymphatic system, a cerebrospinal fluid mediated mechanism for removing toxins from the brain such as amyloid [7]. Analysis of a 2-year randomized trial with B vitamins (folate+B6+B12) found that higher baseline EPA+DHA status correlated with reduction of cognitive decline as measured by the Clinical Dementia Rating scale [8]. Interestingly, these data also showed that folate-B6-B12 did not significantly reduce cognitive decline in the setting of low baseline EPA+DHA concentration but did reduce decline when their baseline levels were relatively high. The mechanisms by which EPA and DHA support cognitive function include their structural and functional contributions to cell membranes, their importance for synaptic connectivity, and contributions to attenuating the anti-inflammatory response in the brain and other organs [9]. A recent study showed that another mechanism by which EPA and DHA can promote improved brain function is increased amyloid breakdown through potentiating actions of insulin degrading enzyme [10]. This enzyme is competitively inhibited by hyperinsulinemia in type 2 diabetes [11], a disease that may be favorably impacted by EPA+DHA supplementation [12].

Treatment trials have also tested the influence of EPA+DHA on cognition. One double blind placebo controlled study in 44 cognitively normal elderly individuals found that supplementation with 2,200 mg of EPA and DHA for 26 weeks resulted in improvement on neuropsychological test assessment of memory [13]. However, a systematic review of three randomized clinical trials of EPA+DHA supplementation in persons with mild to moderate AD did not find any benefit for reversing the progression of the disorder [14]. This contrast in findings suggests that the benefits of these omega-3 fatty acids are best studied in a preventive capacity in prodromal stages, before the burden of AD or mixed pathologies becomes too burdensome to address. For this reason, we sought in this study to better understand the relationship between EPA+DHA status, cerebral perfusion and cognitive performance.

METHODS

Subjects

This study was conducted on a randomly selected sample of 166 subjects drawn from the Amen Clinics (Newport Beach, Costa Mesa, Fairfield, and Brisbane, CA; Tacoma and Bellevue, WA; Reston, VA; Atlanta, GA; New York, NY). Diagnoses were made by board certified or eligible psychiatrists, using all available data, including detailed clinical history, mental status examination. and DSM-IV or V criteria, consistent with the current standard of care. De-identified data was obtained for analysis from a research database containing brain SPECT data and related subject information under approval by an accredited institutional review board, IntegReview (IRB# 004; http://www.integreview.com/).

Functional perfusion neuroimaging

All subjects underwent perfusion neuroimaging with single photon emission computed tomography (SPECT) in accordance with Society for Nuclear Medicine Guidelines, as previously described [15 –17]. All scans were acquired on a high-resolution Picker (Phillips) Prism XP 3000 triple-headed gamma camera with fan beam collimators with data collected in 128×128 matrices, yielding 120 images per scan with each image separated by three degrees spanning 360 degrees. First level processing of images from raw data was performed using the software package Odyssey FX V8.90 developed by Picker Image System for Phillips/GE SPECT cameras. A low pass filter (Butterworth filter) was applied with a high cutoff (0.25 cycles per pixel). For baseline, or resting state scans, patients sit in a dimly lit room with eyes open and low ambient noise. Approximately 30 minutes after the injection, subjects are scanned for 30 minutes. For concentration or on-task scans, study subjects returned on a separate day when the subject is injected while performing the Conner’s Continuous Performance Test (C-CPT). Patients were injected three minutes after starting the C-CPT and then perform the task for another 10 minutes. Scanning was then done approximately 30 minutes after injection. During image acquisition, Chang attenuation correction was performed [18]. Transaxial slices oriented horizontal to the AC-PC line were created along with coronal and sagittal images (6.6 mm apart, unsmoothed). Three dimensional reformats were generated for review based on Odyssey image visualization software.

Erythrocyte omega-3 quantification

As part of their standard care, the subjects chosen had blood omega-3 fatty acid levels quantified using previously described methods [19]. Briefly, a single drop of blood was collected on anti-oxidant treated filter paper and sent to the laboratory (OmegaQuant Analytics, LLD, Sioux Falls, SD) for analysis. Whole blood fatty acid (FA) composition was determined by direct transmethylation and analysis by gas liquid chromatography. FA composition is expressed as a percent of total blood FAs. The Omega-3 Index is the red blood cell EPA+DHA content and is routinely extrapolated from the whole blood analysis as described [19]. Other metrics derived from the analysis include the ratio of omega-6 arachidonic acid (AA) to EPA (AA to EPA) and the omega 6 to omega 3 ratio. [The omega-6 fatty acids include 18:2n6, 18:3n6, 20:2n6, 20:3n6, 20:4n6 (AA), 22:4n-6, and 22:5n6; and the omega-3 fatty acids include 18:3n3, 20:5n3 (EPA), 22:5n3, and 22:6n3 (DHA)]. Study subjects were not taking omega-3 fatty acid supplements neither were they on specialized prescribed diets emphasizing fish high in omega-3 fatty acid content such as salmon.

Neuropsychological assessment

Evaluation of neuropsychological function was conducted with the WebNeuro software program, as described in prior work [20]. WebNeuro is an internet based (http://dl.brainresource.com/download/webneuro.html) self-administered test battery assessing multiple domains. The neurocognitive aspects of the test include i) motor coordination, ii) processing speed as measured by reaction time, iii) sustained attention, iv) controlled attention, v) mental flexibility, vi) inhibition, vii) working memory, viii) recall memory, and ix) executive function. Affective assessment in the WebNeuro included examination of feelings of depression, anxiety, and emotional resilience.

Statistical analyses

All statistical analyses were done in Statistical Package for the Social Sciences (SPSS, version 24, IBM, Armonk, New York). Determining the relationship between the Omega-3 Index, brain perfusion on SPECT regions of interest (ROIs), and WebNeuro results was done in several steps. First, the Omega-3 Index, AA to EPA ratio, and omega 6 to omega 3 ratio were rank ordered by a median split using a group wise comparison. This resulted in two groups: top 50th percentile and bottom 50th percentile. Second, two sample t-tests with Bonferroni correction were done to identify statistically significant group differences in cerebral perfusion. Third, partial correlation analyses controlling for age, gender, and history of traumatic brain injury (TBI) and attention deficit hyperactivity disorder (ADHD) status were done between the omega-3 indices and the statistically significant different regions identified in step 2. Fourth, correlations between the statistically significant regions in step three and WebNeuro cognitive domains was conducted to determine relationships between brain perfusion regions of interest that vary as a function of EPA+DHA levels and neurocognitive evaluations. Finally, separate correlations were done between EPA+DHA levels and neurocognitive evaluations. All analyses controlled for age, gender, ADHD, and TBI status as these two comorbidities were the most common in our cohort.

RESULTS

Subjects’ characteristics for high versus low median split serum measured omega-3 concentration groups are shown in Table 1.

Table 1

Subject characteristics in high versus low median partition of erythrocyte omega-3 levels

	Low Omega-3 Index		High Omega-3 Index
	Mean	Count	Mean	Count
Age	31^a		46^b
Sex
Male		55^a		42^b
Female		28^a		41^b
Omega 3 Index (EPA+DHA as a % of total erythrocyte fatty acids)	3.76^a		6.40^b
Omega3 to Omega6 ratio	10.40^a		6.18^b
AA to EPA ratio	27.55^a		12.65^b
Time lag in days between omega 3 measurement and SPECT scan	63^a		117^a
WebNeuro Brain Health Score	4.08^a		4.23^a
WebNeuro Thinking Overall	4.7^a		4.8^a
WebNeuro Self-Regulation Overall	3.3^a		3.4^a
WebNeuro Feelings score	3.9^a		4.9^b
WebNeuro Emotions score	4.3^a		3.8^a
T_Concentration_Vermis_9 Normalized (ROI) AAL Atlas	64.214^a		66.283^a
T_Concentration_Vermis_8 Normalized (ROI) AAL Atlas	54.279^a		55.740^a
T_Concentration_Vermis_7 Normalized (ROI) AAL Atlas	56.099^a		57.253^a
T_Concentration_Vermis_6 Normalized (ROI) AAL Atlas	61.697^a		63.113^a
T_Concentration_Vermis_4_5 Normalized (ROI) AAL Atlas	59.868^a		61.654^a
T_Concentration_Vermis_3 Normalized (ROI) AAL Atlas	55.245^a		56.978^a
T_Concentration_Vermis_10 Normalized (ROI) AAL Atlas	59.444^a		62.436^a
T_Concentration_Vermis_1_2 Normalized (ROI) AAL Atlas	52.374^a		54.422^a
T_Concentration_Thalamus_R Normalized (ROI) AAL Atlas	58.699^a		61.303^b
T_Concentration_Thalamus_L Normalized (ROI) AAL Atlas	59.304^a		61.586^a
T_Concentration_Temporal_Sup_Post_R Normalized (ROI) AAL Atlas	51.724^a		52.812^a
T_Concentration_Temporal_Sup_Post_L Normalized (ROI) AAL Atlas	54.390^a		55.997^a
T_Concentration_Temporal_Sup_Mid_R Normalized (ROI) AAL Atlas	53.220^a		54.862^a
T_Concentration_Temporal_Sup_Mid_L Normalized (ROI) AAL Atlas	56.218^a		58.010^a
T_Concentration_Temporal_Sup_Ant_R Normalized (ROI) AAL Atlas	50.629^a		51.047^a
T_Concentration_Temporal_Sup_Ant_L Normalized (ROI) AAL Atlas	53.864^a		54.830^a
T_Concentration_Temporal_Pole_Sup_R Normalized (ROI) AAL Atlas	43.012^a		42.218^a
T_Concentration_Temporal_Pole_Sup_L Normalized (ROI) AAL Atlas	45.812^a		44.890^a
T_Concentration_Temporal_Pole_Mid_R Normalized (ROI) AAL Atlas	35.985^a		34.882^a
T_Concentration_Temporal_Pole_Mid_L Normalized (ROI) AAL Atlas	37.521^a		35.467^b
T_Concentration_Temporal_Mid_Post_R Normalized (ROI) AAL Atlas	47.921^a		47.602^a
T_Concentration_Temporal_Mid_Post_L Normalized (ROI) AAL Atlas	51.838^a		52.562^a
T_Concentration_Temporal_Mid_Mid_R Normalized (ROI) AAL Atlas	49.099^a		49.538^a
T_Concentration_Temporal_Mid_Mid_L Normalized (ROI) AAL Atlas	51.799^a		52.338^a
T_Concentration_Temporal_Mid_Ant_R Normalized (ROI) AAL Atlas	46.107^a		46.268^a
T_Concentration_Temporal_Mid_Ant_L Normalized (ROI) AAL Atlas	50.315^a		50.395^a
T_Concentration_Temporal_Inf_Post_R Normalized (ROI) AAL Atlas	42.672^a		42.030^a
T_Concentration_Temporal_Inf_Post_L Normalized (ROI) AAL Atlas	46.386^a		46.289^a
T_Concentration_Temporal_Inf_Mid_R Normalized (ROI) AAL Atlas	40.101^a		39.252^a
T_Concentration_Temporal_Inf_Mid_L Normalized (ROI) AAL Atlas	43.235^a		42.707^a
T_Concentration_Temporal_Inf_Ant_R Normalized (ROI) AAL Atlas	35.592^a		34.028^a
T_Concentration_Temporal_Inf_Ant_L Normalized (ROI) AAL Atlas	39.368^a		37.887^a
T_Concentration_SupraMarginal_R Normalized (ROI) AAL Atlas	47.688^a		47.508^a
T_Concentration_SupraMarginal_L Normalized (ROI) AAL Atlas	52.347^a		52.551^a
T_Concentration_Supp_Motor_Area_R Normalized (ROI) AAL Atlas	47.765^a		48.558^a
T_Concentration_Supp_Motor_Area_L Normalized (ROI) AAL Atlas	47.123^a		47.759^a
T_Concentration_Rolandic_Oper_R Normalized (ROI) AAL Atlas	54.291^a		54.989^a
T_Concentration_Rolandic_Oper_L Normalized (ROI) AAL Atlas	56.240^a		57.245^a
T_Concentration_Rectus_R Normalized (ROI) AAL Atlas	53.121^a		51.832^a
T_Concentration_Rectus_L Normalized (ROI) AAL Atlas	53.551^a		51.814^a
T_Concentration_Putamen_R Normalized (ROI) AAL Atlas	64.477^a		66.862^b
T_Concentration_Putamen_L Normalized (ROI) AAL Atlas	62.515^a		65.242^b
T_Concentration_Precuneus_R Normalized (ROI) AAL Atlas	51.469^a		52.402^a
T_Concentration_Precuneus_L Normalized (ROI) AAL Atlas	50.144^a		50.255^a
T_Concentration_Precentral_R Normalized (ROI) AAL Atlas	44.070^a		43.911^a
T_Concentration_Precentral_L Normalized (ROI) AAL Atlas	47.936^a		48.315^a
T_Concentration_Postcentral_R Normalized (ROI) AAL Atlas	42.271^a		41.547^a
T_Concentration_Postcentral_L Normalized (ROI) AAL Atlas	46.938^a		46.527^a
T_Concentration_Parietal_Sup_R Normalized (ROI) AAL Atlas	34.013^a		31.759^b
T_Concentration_Parietal_Sup_L Normalized (ROI) AAL Atlas	39.925^a		38.659^a
T_Concentration_Parietal_Inf_R Normalized (ROI) AAL Atlas	43.577^a		42.984^a
T_Concentration_Parietal_Inf_L Normalized (ROI) AAL Atlas	49.635^a		49.334^a
T_Concentration_ParaHippocampal_R Normalized (ROI) AAL Atlas	50.396^a		51.385^a
T_Concentration_ParaHippocampal_L Normalized (ROI) AAL Atlas	45.825^a		46.258^a
T_Concentration_Paracentral_Lobule_R Normalized (ROI) AAL Atlas	44.326^a		44.461^a
T_Concentration_Paracentral_Lobule_L Normalized (ROI) AAL Atlas	42.263^a		42.260^a
T_Concentration_Pallidum_R Normalized (ROI) AAL Atlas	62.205^a		64.874^b
T_Concentration_Pallidum_L Normalized (ROI) AAL Atlas	57.663^a		60.652^b
T_Concentration_Olfactory_R Normalized (ROI) AAL Atlas	54.715^a		54.814^a
T_Concentration_Olfactory_L Normalized (ROI) AAL Atlas	52.813^a		53.094^a
T_Concentration_Occipital_Sup_R Normalized (ROI) AAL Atlas	44.087^a		42.949^a
T_Concentration_Occipital_Sup_L Normalized (ROI) AAL Atlas	44.435^a		43.598^a
T_Concentration_Occipital_Mid_R Normalized (ROI) AAL Atlas	41.603^a		40.391^a
T_Concentration_Occipital_Mid_L Normalized (ROI) AAL Atlas	45.373^a		45.482^a
T_Concentration_Occipital_Inf_R Normalized (ROI) AAL Atlas	37.405^a		36.041^a
T_Concentration_Occipital_Inf_L Normalized (ROI) AAL Atlas	44.269^a		44.142^a
T_Concentration_Lingual_R Normalized (ROI) AAL Atlas	54.396^a		56.070^a
T_Concentration_Lingual_L Normalized (ROI) AAL Atlas	55.339^a		57.328^b
T_Concentration_Insula_R Normalized (ROI) AAL Atlas	59.763^a		60.163^a
T_Concentration_Insula_L Normalized (ROI) AAL Atlas	57.530^a		58.910^a
T_Concentration_Hippocampus_R Normalized (ROI) AAL Atlas	51.737^a		54.018^b
T_Concentration_Hippocampus_L Normalized (ROI) AAL Atlas	50.701^a		52.460^a
T_Concentration_Heschl_R Normalized (ROI) AAL Atlas	60.082^a		61.773^a
T_Concentration_Heschl_L Normalized (ROI) AAL Atlas	57.903^a		60.259^b
T_Concentration_Fusiform_R Normalized (ROI) AAL Atlas	51.618^a		52.121^a
T_Concentration_Fusiform_L Normalized (ROI) AAL Atlas	52.238^a		52.840^a
T_Concentration_Frontal_Sup_R Normalized (ROI) AAL Atlas	45.004^a		44.449^a
T_Concentration_Frontal_Sup_Orb_R Normalized (ROI) AAL Atlas	47.859^a		45.532^b
T_Concentration_Frontal_Sup_Orb_L Normalized (ROI) AAL Atlas	49.101^a		47.413^a
T_Concentration_Frontal_Sup_Medial_R Normalized (ROI) AAL Atlas	48.013^a		46.644^a
T_Concentration_Frontal_Sup_Medial_L Normalized (ROI) AAL Atlas	49.812^a		48.235^a
T_Concentration_Frontal_Sup_L Normalized (ROI) AAL Atlas	45.386^a		44.610^a
T_Concentration_Frontal_Mid_R Normalized (ROI) AAL Atlas	46.917^a		46.308^a
T_Concentration_Frontal_Mid_Orb_R_10 Normalized (ROI) AAL Atlas	44.621^a		40.990^b
T_Concentration_Frontal_Mid_Orb_R Normalized (ROI) AAL Atlas	55.399^a		55.183^a
T_Concentration_Frontal_Mid_Orb_L_9 Normalized (ROI) AAL Atlas	47.415^a		44.756^b
T_Concentration_Frontal_Mid_Orb_L Normalized (ROI) AAL Atlas	57.121^a		55.825^a
T_Concentration_Frontal_Mid_L Normalized (ROI) AAL Atlas	49.500^a		49.227^a
T_Concentration_Frontal_Inf_Tri_R Normalized (ROI) AAL Atlas	47.669^a		46.701^a
T_Concentration_Frontal_Inf_Tri_L Normalized (ROI) AAL Atlas	52.325^a		52.171^a
T_Concentration_Frontal_Inf_Orb_R Normalized (ROI) AAL Atlas	46.866^a		43.934^b
T_Concentration_Frontal_Inf_Orb_L Normalized (ROI) AAL Atlas	49.397^a		47.257^b
T_Concentration_Frontal_Inf_Oper_R Normalized (ROI) AAL Atlas	51.360^a		50.366^a
T_Concentration_Frontal_Inf_Oper_L Normalized (ROI) AAL Atlas	53.520^a		53.245^a
T_Concentration_Cuneus_R Normalized (ROI) AAL Atlas	51.052^a		51.115^a
T_Concentration_Cuneus_L Normalized (ROI) AAL Atlas	51.495^a		51.443^a
T_Concentration_Cingulum_Post_R Normalized (ROI) AAL Atlas	51.039^a		52.831^a
T_Concentration_Cingulum_Post_L Normalized (ROI) AAL Atlas	56.088^a		57.806^a
T_Concentration_Cingulum_Mid_R Normalized (ROI) AAL Atlas	56.451^a		57.474^a
T_Concentration_Cingulum_Mid_L Normalized (ROI) AAL Atlas	58.096^a		59.389^a
T_Concentration_Cingulum_Ant_R Normalized (ROI) AAL Atlas	52.935^a		53.994^a
T_Concentration_Cingulum_Ant_L Normalized (ROI) AAL Atlas	56.492^a		57.494^a
T_Concentration_Cerebellum_Crus2_R Normalized (ROI) AAL Atlas	31.820^a		31.748^a
T_Concentration_Cerebellum_Crus2_L Normalized (ROI) AAL Atlas	36.478^a		36.560^a
T_Concentration_Cerebellum_Crus1_R Normalized (ROI) AAL Atlas	44.556^a		43.928^a
T_Concentration_Cerebellum_Crus1_L Normalized (ROI) AAL Atlas	51.241^a		50.691^a
T_Concentration_Cerebellum_9_R Normalized (ROI) AAL Atlas	48.914^a		49.684^a
T_Concentration_Cerebellum_9_L Normalized (ROI) AAL Atlas	48.216^a		49.083^a
T_Concentration_Cerebellum_8_R Normalized (ROI) AAL Atlas	38.471^a		38.710^a
T_Concentration_Cerebellum_8_L Normalized (ROI) AAL Atlas	41.941^a		41.964^a
T_Concentration_Cerebellum_7b_R Normalized (ROI) AAL Atlas	29.396^a		29.123^a
T_Concentration_Cerebellum_7b_L Normalized (ROI) AAL Atlas	36.730^a		36.505^a
T_Concentration_Cerebellum_6_R Normalized (ROI) AAL Atlas	61.006^a		62.912^a
T_Concentration_Cerebellum_6_L Normalized (ROI) AAL Atlas	62.657^a		64.963^a
T_Concentration_Cerebellum_4_5_R Normalized (ROI) AAL Atlas	56.369^a		57.887^a
T_Concentration_Cerebellum_4_5_L Normalized (ROI) AAL Atlas	55.918^a		57.582^a
T_Concentration_Cerebellum_3_R Normalized (ROI) AAL Atlas	51.624^a		52.645^a
T_Concentration_Cerebellum_3_L Normalized (ROI) AAL Atlas	52.423^a		54.582^b
T_Concentration_Cerebellum_10_R Normalized (ROI) AAL Atlas	34.752^a		34.674^a
T_Concentration_Cerebellum_10_L Normalized (ROI) AAL Atlas	38.189^a		38.576^a
T_Concentration_Caudate_R Normalized (ROI) AAL Atlas	53.691^a		55.248^a
T_Concentration_Caudate_L Normalized (ROI) AAL Atlas	51.051^a		51.536^a
T_Concentration_Calcarine_R Normalized (ROI) AAL Atlas	53.265^a		55.593^b
T_Concentration_Calcarine_L Normalized (ROI) AAL Atlas	51.675^a		52.872^a
T_Concentration_Angular_R Normalized (ROI) AAL Atlas	44.000^a		42.546^a
T_Concentration_Angular_L Normalized (ROI) AAL Atlas	48.549^a		48.611^a
T_Concentration_Amygdala_R Normalized (ROI) AAL Atlas	51.468^a		53.953^b
T_Concentration_Amygdala_L Normalized (ROI) AAL Atlas	50.488^a		52.349^a
T_Baseline_Vermis_9 Normalized (ROI) AAL Atlas	63.461^a		67.227^b
T_Baseline_Vermis_8 Normalized (ROI) AAL Atlas	54.471^a		56.530^a
T_Baseline_Vermis_7 Normalized (ROI) AAL Atlas	56.537^a		57.836^a
T_Baseline_Vermis_6 Normalized (ROI) AAL Atlas	61.425^a		64.267^b
T_Baseline_Vermis_4_5 Normalized (ROI) AAL Atlas	59.541^a		62.681^b
T_Baseline_Vermis_3 Normalized (ROI) AAL Atlas	54.648^a		57.614^b
T_Baseline_Vermis_10 Normalized (ROI) AAL Atlas	58.857^a		63.204^b
T_Baseline_Vermis_1_2 Normalized (ROI) AAL Atlas	51.483^a		55.401^b
T_Baseline_Thalamus_R Normalized (ROI) AAL Atlas	58.657^a		62.455^b
T_Baseline_Thalamus_L Normalized (ROI) AAL Atlas	58.911^a		63.019^b
T_Baseline_Temporal_Sup_Post_R Normalized (ROI) AAL Atlas	50.700^a		53.317^b
T_Baseline_Temporal_Sup_Post_L Normalized (ROI) AAL Atlas	53.943^a		56.579^b
T_Baseline_Temporal_Sup_Mid_R Normalized (ROI) AAL Atlas	52.587^a		55.173^b
T_Baseline_Temporal_Sup_Mid_L Normalized (ROI) AAL Atlas	55.696^a		58.740^b
T_Baseline_Temporal_Sup_Ant_R Normalized (ROI) AAL Atlas	50.049^a		51.316^a
T_Baseline_Temporal_Sup_Ant_L Normalized (ROI) AAL Atlas	53.287^a		55.402^b
T_Baseline_Temporal_Pole_Sup_R Normalized (ROI) AAL Atlas	42.564^a		41.817^a
T_Baseline_Temporal_Pole_Sup_L Normalized (ROI) AAL Atlas	45.378^a		44.861^a
T_Baseline_Temporal_Pole_Mid_R Normalized (ROI) AAL Atlas	36.098^a		34.253^b
T_Baseline_Temporal_Pole_Mid_L Normalized (ROI) AAL Atlas	37.374^a		35.028^b
T_Baseline_Temporal_Mid_Post_R Normalized (ROI) AAL Atlas	47.805^a		48.417^a
T_Baseline_Temporal_Mid_Post_L Normalized (ROI) AAL Atlas	51.739^a		53.503^b
T_Baseline_Temporal_Mid_Mid_R Normalized (ROI) AAL Atlas	48.313^a		49.211^a
T_Baseline_Temporal_Mid_Mid_L Normalized (ROI) AAL Atlas	51.086^a		52.761^b
T_Baseline_Temporal_Mid_Ant_R Normalized (ROI) AAL Atlas	45.684^a		45.761^a
T_Baseline_Temporal_Mid_Ant_L Normalized (ROI) AAL Atlas	49.507^a		50.293^a
T_Baseline_Temporal_Inf_Post_R Normalized (ROI) AAL Atlas	42.624^a		42.155^a
T_Baseline_Temporal_Inf_Post_L Normalized (ROI) AAL Atlas	46.770^a		46.572^a
T_Baseline_Temporal_Inf_Mid_R Normalized (ROI) AAL Atlas	39.940^a		39.171^a
T_Baseline_Temporal_Inf_Mid_L Normalized (ROI) AAL Atlas	43.050^a		43.211^a
T_Baseline_Temporal_Inf_Ant_R Normalized (ROI) AAL Atlas	35.411^a		33.480^b
T_Baseline_Temporal_Inf_Ant_L Normalized (ROI) AAL Atlas	38.966^a		37.154^a
T_Baseline_SupraMarginal_R Normalized (ROI) AAL Atlas	46.962^a		48.275^a
T_Baseline_SupraMarginal_L Normalized (ROI) AAL Atlas	52.097^a		53.248^a
T_Baseline_Supp_Motor_Area_R Normalized (ROI) AAL Atlas	47.577^a		49.409^b
T_Baseline_Supp_Motor_Area_L Normalized (ROI) AAL Atlas	46.914^a		48.131^a
T_Baseline_Rolandic_Oper_R Normalized (ROI) AAL Atlas	53.857^a		55.711^a
T_Baseline_Rolandic_Oper_L Normalized (ROI) AAL Atlas	55.862^a		57.984^a
T_Baseline_Rectus_R Normalized (ROI) AAL Atlas	52.421^a		51.993^a
T_Baseline_Rectus_L Normalized (ROI) AAL Atlas	53.161^a		52.016^a
T_Baseline_Putamen_R Normalized (ROI) AAL Atlas	63.334^a		67.441^b
T_Baseline_Putamen_L Normalized (ROI) AAL Atlas	61.662^a		66.058^b
T_Baseline_Precuneus_R Normalized (ROI) AAL Atlas	51.305^a		53.924^b
T_Baseline_Precuneus_L Normalized (ROI) AAL Atlas	49.981^a		51.779^a
T_Baseline_Precentral_R Normalized (ROI) AAL Atlas	43.849^a		44.384^a
T_Baseline_Precentral_L Normalized (ROI) AAL Atlas	47.858^a		48.724^a
T_Baseline_Postcentral_R Normalized (ROI) AAL Atlas	42.162^a		42.309^a
T_Baseline_Postcentral_L Normalized (ROI) AAL Atlas	46.912^a		47.429^a
T_Baseline_Parietal_Sup_R Normalized (ROI) AAL Atlas	34.153^a		32.765^a
T_Baseline_Parietal_Sup_L Normalized (ROI) AAL Atlas	40.592^a		39.704^a
T_Baseline_Parietal_Inf_R Normalized (ROI) AAL Atlas	43.406^a		43.818^a
T_Baseline_Parietal_Inf_L Normalized (ROI) AAL Atlas	49.775^a		50.453^a
T_Baseline_ParaHippocampal_R Normalized (ROI) AAL Atlas	50.086^a		51.831^b
T_Baseline_ParaHippocampal_L Normalized (ROI) AAL Atlas	45.441^a		47.010^b
T_Baseline_Paracentral_Lobule_R Normalized (ROI) AAL Atlas	44.197^a		45.899^a
T_Baseline_Paracentral_Lobule_L Normalized (ROI) AAL Atlas	42.371^a		43.503^a
T_Baseline_Pallidum_R Normalized (ROI) AAL Atlas	61.597^a		65.924^b
T_Baseline_Pallidum_L Normalized (ROI) AAL Atlas	56.739^a		61.007^b
T_Baseline_Olfactory_R Normalized (ROI) AAL Atlas	53.931^a		55.098^a
T_Baseline_Olfactory_L Normalized (ROI) AAL Atlas	52.705^a		53.241^a
T_Baseline_Occipital_Sup_R Normalized (ROI) AAL Atlas	44.598^a		44.167^a
T_Baseline_Occipital_Sup_L Normalized (ROI) AAL Atlas	44.967^a		44.665^a
T_Baseline_Occipital_Mid_R Normalized (ROI) AAL Atlas	42.325^a		41.272^a
T_Baseline_Occipital_Mid_L Normalized (ROI) AAL Atlas	46.073^a		46.475^a
T_Baseline_Occipital_Inf_R Normalized (ROI) AAL Atlas	37.949^a		36.245^a
T_Baseline_Occipital_Inf_L Normalized (ROI) AAL Atlas	44.781^a		44.463^a
T_Baseline_Lingual_R Normalized (ROI) AAL Atlas	54.735^a		57.392^b
T_Baseline_Lingual_L Normalized (ROI) AAL Atlas	55.599^a		58.309^b
T_Baseline_Insula_R Normalized (ROI) AAL Atlas	58.723^a		60.496^a
T_Baseline_Insula_L Normalized (ROI) AAL Atlas	56.725^a		59.403^b
T_Baseline_Hippocampus_R Normalized (ROI) AAL Atlas	51.095^a		54.821^b
T_Baseline_Hippocampus_L Normalized (ROI) AAL Atlas	50.663^a		53.459^b
T_Baseline_Heschl_R Normalized (ROI) AAL Atlas	59.484^a		62.349^b
T_Baseline_Heschl_L Normalized (ROI) AAL Atlas	57.240^a		61.021^b
T_Baseline_Fusiform_R Normalized (ROI) AAL Atlas	51.457^a		52.863^a
T_Baseline_Fusiform_L Normalized (ROI) AAL Atlas	51.659^a		53.514^b
T_Baseline_Frontal_Sup_R Normalized (ROI) AAL Atlas	44.889^a		44.477^a
T_Baseline_Frontal_Sup_Orb_R Normalized (ROI) AAL Atlas	47.554^a		45.673^a
T_Baseline_Frontal_Sup_Orb_L Normalized (ROI) AAL Atlas	48.623^a		47.558^a
T_Baseline_Frontal_Sup_Medial_R Normalized (ROI) AAL Atlas	47.761^a		46.701^a
T_Baseline_Frontal_Sup_Medial_L Normalized (ROI) AAL Atlas	49.590^a		48.156^a
T_Baseline_Frontal_Sup_L Normalized (ROI) AAL Atlas	45.337^a		44.635^a
T_Baseline_Frontal_Mid_R Normalized (ROI) AAL Atlas	46.724^a		46.078^a
T_Baseline_Frontal_Mid_Orb_R_10 Normalized (ROI) AAL Atlas	44.396^a		40.821^b
T_Baseline_Frontal_Mid_Orb_R Normalized (ROI) AAL Atlas	54.547^a		55.289^a
T_Baseline_Frontal_Mid_Orb_L_9 Normalized (ROI) AAL Atlas	46.782^a		44.719^a
T_Baseline_Frontal_Mid_Orb_L Normalized (ROI) AAL Atlas	56.581^a		55.624^a
T_Baseline_Frontal_Mid_L Normalized (ROI) AAL Atlas	49.472^a		49.324^a
T_Baseline_Frontal_Inf_Tri_R Normalized (ROI) AAL Atlas	47.746^a		47.002^a
T_Baseline_Frontal_Inf_Tri_L Normalized (ROI) AAL Atlas	52.061^a		52.385^a
T_Baseline_Frontal_Inf_Orb_R Normalized (ROI) AAL Atlas	46.379^a		43.837^b
T_Baseline_Frontal_Inf_Orb_L Normalized (ROI) AAL Atlas	48.704^a		47.250^a
T_Baseline_Frontal_Inf_Oper_R Normalized (ROI) AAL Atlas	51.172^a		50.831^a
T_Baseline_Frontal_Inf_Oper_L Normalized (ROI) AAL Atlas	53.119^a		53.581^a
T_Baseline_Cuneus_R Normalized (ROI) AAL Atlas	51.349^a		52.424^a
T_Baseline_Cuneus_L Normalized (ROI) AAL Atlas	51.813^a		52.740^a
T_Baseline_Cingulum_Post_R Normalized (ROI) AAL Atlas	51.062^a		53.894^b
T_Baseline_Cingulum_Post_L Normalized (ROI) AAL Atlas	55.807^a		59.358^b
T_Baseline_Cingulum_Mid_R Normalized (ROI) AAL Atlas	56.033^a		58.246^b
T_Baseline_Cingulum_Mid_L Normalized (ROI) AAL Atlas	57.407^a		60.133^b
T_Baseline_Cingulum_Ant_R Normalized (ROI) AAL Atlas	51.933^a		54.454^b
T_Baseline_Cingulum_Ant_L Normalized (ROI) AAL Atlas	55.329^a		57.837^b
T_Baseline_Cerebellum_Crus2_R Normalized (ROI) AAL Atlas	31.976^a		31.082^a
T_Baseline_Cerebellum_Crus2_L Normalized (ROI) AAL Atlas	36.886^a		36.068^a
T_Baseline_Cerebellum_Crus1_R Normalized (ROI) AAL Atlas	44.442^a		43.997^a
T_Baseline_Cerebellum_Crus1_L Normalized (ROI) AAL Atlas	50.892^a		50.968^a
T_Baseline_Cerebellum_9_R Normalized (ROI) AAL Atlas	48.613^a		49.976^a
T_Baseline_Cerebellum_9_L Normalized (ROI) AAL Atlas	48.269^a		49.800^a
T_Baseline_Cerebellum_8_R Normalized (ROI) AAL Atlas	39.018^a		39.231^a
T_Baseline_Cerebellum_8_L Normalized (ROI) AAL Atlas	41.772^a		42.516^a
T_Baseline_Cerebellum_7b_R Normalized (ROI) AAL Atlas	30.316^a		29.762^a
T_Baseline_Cerebellum_7b_L Normalized (ROI) AAL Atlas	36.673^a		36.771^a
T_Baseline_Cerebellum_6_R Normalized (ROI) AAL Atlas	60.363^a		63.457^b
T_Baseline_Cerebellum_6_L Normalized (ROI) AAL Atlas	61.939^a		65.894^b
T_Baseline_Cerebellum_4_5_R Normalized (ROI) AAL Atlas	55.669^a		58.079^b
T_Baseline_Cerebellum_4_5_L Normalized (ROI) AAL Atlas	55.352^a		58.117^b
T_Baseline_Cerebellum_3_R Normalized (ROI) AAL Atlas	51.201^a		53.043^b
T_Baseline_Cerebellum_3_L Normalized (ROI) AAL Atlas	52.119^a		55.120_b
T_Baseline_Cerebellum_10_R Normalized (ROI) AAL Atlas	34.916^a		34.015^a
T_Baseline_Cerebellum_10_L Normalized (ROI) AAL Atlas	38.653^a		38.466^a
T_Baseline_Caudate_R Normalized (ROI) AAL Atlas	53.279^a		56.284^b
T_Baseline_Caudate_L Normalized (ROI) AAL Atlas	51.144^a		52.731^a
T_Baseline_Calcarine_R Normalized (ROI) AAL Atlas	53.805^a		56.773^b
T_Baseline_Calcarine_L Normalized (ROI) AAL Atlas	52.179^a		53.898^b
T_Baseline_Angular_R Normalized (ROI) AAL Atlas	43.667^a		43.401^a
T_Baseline_Angular_L Normalized (ROI) AAL Atlas	48.343^a		49.265^a
T_Baseline_Amygdala_R Normalized (ROI) AAL Atlas	50.655^a		54.155^b
T_Baseline_Amygdala_L Normalized (ROI) AAL Atlas	50.261^a		53.135^b

^*The subscripts denote presence or lack of statistical significance. For example, subscripts on values that both have a letter “a” denote lack statistical significance between that pair of values. A value with a subscript of letter “a” and one of letter “b” denotes a statistically significant difference. Multiple comparisons for cerebral perfusion are accounted for with a Bonferroni correction.

Persons with higher Omega-3 Index were older and more likely to be women (p < 0.05). These subjects also had lower AA/EPA and omega 6 to omega 3 ratios. Of the 166 subjects studied, 68 (41%) had a history of ADHD and 59 (36%) had a history of TBI but there was no difference in the rate of these co-morbidities as a function of Omega-3 Index. Baseline regions of interest with increased perfusion in the high Omega-3 Index group compared to low Omega-3 Index group included vermis subregions, thalamus, temporal subregions including the temporal pole, right supplementary motor area, bilateral putamen, right precuneus, bilateral hippocampus and parahippocampal gyrus, bilateral pallidum, bilateral lingual gyrus, Heschl’s gyrus, calcarine cortex, and amygdala. After controlling for age, gender, ADHD, and TBI status, the remaining statistically significant correlations between higher omega-3 levels and cerebral perfusion were in the right parahippocampal gyrus (r = 0.20, p = 0.03), right precuneus (r = 0.20, p = 0.03), and vermis subregion 6 (p = 0.21, p = 0.03). On concentration scans, increased perfusion was observed in the right thalamus, bilateral putamen, bilateral pallidum, left lingual gyrus, right hippocampus, right cerebellum 3L, left Heschl gyrus, and right calcarine cortex. None of these relationships was statistically significant when controlled for age, gender, ADHD, and TBI status. In terms of AA to EPA ratio, there were no statistically significant correlations between this metric and SPECT measured perfusion ROIs when controlling for age, gender, ADHD, and TBI status. Finally, increased omega 6 to omega 3 ratios were correlated to lower perfusion after accounting for age, gender, ADHD, and TBI status in the following regions: left Heschl gyrus (r = –0.23, p = 0.01), vermis subregion 8 (r = –0.23, p = 0.01), and right parahippocamal gyrus (r = –0.26, p = 0.01). Of the SPECT ROI regions that correlated with the Omega-3 Index, the right parahippocampal gyrus positively correlated with the thinking subsection of the WebNeuro (r = 0.19, p = 0.04), as did the left Heschl gyrus (r = 0.20, p = 0.03). These relationships are summarized in Fig. 1. Omega-3 Index levels separately correlated to the feeling subsection of the WebNeuro (r = 0.25, p = 0.01).

Fig.1

Statistical relationships between erythrocyte omega-3 levels, brain perfusion, and cognition. This figure describes the statistically significant relationships between the Omega-3 index, regional perfusion on brain SPECT, and neurocognitive testing. The Omega-3 Index is derived from measurement of blood EPA+DHA. The r and p-values refer to outputs from partial correlation analyses adjusting for age, gender, ADHD, and TBI status.

DISCUSSION

In this study, we combined measurements of omega-3 fatty acid status (mainly the Omega-3 Index), quantitative neuroimaging with SPECT, and neurocognitive testing to advance understanding as to how EPA+DHA levels relate to brain function. What we observed was that higher EPA+DHA status as expressed by the Omega-3 Index is independently correlated with higher perfusion in brain regions important for cognitive function, including the parahippocampal gyrus and precuneus. Additionally, these regions exhibit their own correlations with neurocognitive function. Interestingly, the Omega-3 Index was independently associated with the feelings subsection of the WebNeuro test. Our findings suggest that higher EPA+DHA levels are related to multiple aspects of neurophysiology with brain perfusion imaging andcognition.

The concept that omega-3 fatty acids can have benefit for the brain was originally posited because of the relatively high content of DHA in cell membranes in the brain [21]. As successive human species have evolved larger skulls and thus larger brain volumes over time, this pattern has corresponded to historical increases in consumption of fish rich in omega-3 fatty acids [22]. While this pattern is unlikely to be entirely attributable to these dietary changes, prior literature shows EPA is also incorporated into brain cell membranes [23], though at smaller levels compared to DHA [21]. Higher dietary consumption of fish high in EPA+DHA was found to be correlated to larger gray matter volumes on voxel based morphometry of volumetric MRI in 260 elderly subjects aged 78 on average, including the hippocampus and precuneus [24]. This finding was replicated in a separate cohort of 1,111 postmenopausal women in which the Omega-3 Index was correlated to larger total brain and hippocampal volumes [25].

An additional mechanism by which EPA+DHA may improve regional brain volumes is by promoting increased cerebral blood flow. However, direct evidence for this effect has been lacking. One study using near infrared spectroscopy in 248 adults aged 60 on average showed no relationship between EPA+DHA intake and cerebral perfusion [26]. Evidence from animal studies, however, does support this hypothesis. One study showed improved cortical cerebral blood flow on ultra-high field MR imaging in a mouse model of AD receiving supplementation with omega-3 fatty acids [27]. Another study in this model being given DHA supplements while simultaneously on a standard Western diet found improved cerebral blood volume and decreased amyloidpathology [28].

The relationship between omega-3 fatty acid status and cognition is important, particularly with respect to potential implications for AD prevention. The OmegAD study demonstrated preservation of cognition as measured by ADAS-cog in 174 persons with mild to moderate AD randomized to 2.3 g of EPA+DHA supplements for six months versus placebo [29]. One study of 280 controls 30–54 years old found DHA levels were positively related to improved verbal reasoning, working memory, executive function and vocabulary [30]. The finding in our study that the strongest relationship with neurocognitive tests was with improved feeling subsection on the WebNeuro test can be connected to a prior meta-analysis showing benefit of omega-3 supplementation in major depressive disorder [31]. Because depression itself is a risk factor for AD [5], one mechanism by which EPA+DHA can conceivably reduce risk for AD is by modification of risk factors such as depression and vascular disease [32].

Strengths of our study include the precise measurement of blood omega-3 and omega-6 fatty acid levels. This advantage includes derivation of the Omega-3 Index— a direct indicator of the omega-3 status of red blood cell membranes that correlates with the omega-3 status of other tissues [33]. Availability of neurocognitive data allowed for correlations with this index and perfusion neuroimaging with SPECT. Limitations include the cross-sectional design, which prevents us from drawing causal relationships. Unmeasured confounding cannot be excluded. Consequently, the statistically significant relationships we discovered in this work are correlational and do not necessarily allow us to infer a causal mechanism between omega-3 fatty acids and brain perfusion. While differences in omega-3 concentrations were seen in persons with different average age and gender ratios, we separately controlled for these co-variates in all our analyses. We also controlled for ADHD and TBI status as these co-morbidities have been related to perfusion alternations in the brain[34, 35].

Overall, our study showed positive relationships between omega-3 EPA+DHA status, brain perfusion, and cognition. While this study was done in persons without dementia, the findings do have implications for risk of AD. Specifically, our study raises the possibility that higher omega-3 EPA+DHA fatty acid levels can improve underlying brain physiology that may in turn translate to better cognitive reserve [36]. Such concepts should be further elucidated in future interventional studies.

DISCLOSURE STATEMENT

Authors’ disclosures available online (http://j-alz.com/manuscript-disclosures/17-0281r1).

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