Effects of omega-3 fatty acids on cognitive performance: a meta … · Effects of omega-3 fatty acids on cognitive performance: a meta-analysis Graham Mazereeuw a,b, Krista L. Lanctôta,b,c,

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Neurobiology of Aging 33 (2012) 1482.e17–1482.e29

Effects of omega-3 fatty acids on cognitive performance:a meta-analysis

Graham Mazereeuwa,b, Krista L. Lanctôta,b,c, Sarah A. Chaua,b, Walter Swardfagera,b,Nathan Herrmanna,c,*

a Sunnybrook Health Sciences Centre, Toronto, Ontario, Canadab Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada

c Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada

Received 9 August 2011; received in revised form 6 October 2011; accepted 12 December 2011

Abstract

Background: Higher intake of omega-3 fatty acids (n-3 FAs) is associated with a reduced risk of Alzheimer’s disease (AD) and milderforms of cognitive impairment (e.g. cognitive impairment no dementia [CIND]); however, findings from interventional trials are incon-sistent. This meta-analysis examined the neuropsychological benefit of n-3 FAs in randomized double-blind placebo-controlled studies(RCTs) including healthy, CIND, or AD subjects.Methods: Literature was searched using Medline, Embase, PsycInfo, Cochrane Library, Allied and Complementary Medicine Database(AMED), and Cumulative Index to Nursing and Allied Health Literature (CINAHL) up to September 2011. Treatment effects weresummarized across cognitive subdomains, and effect sizes were estimated using Hedge’s g and random effects modeling.Results: Ten RCTs were combined quantitatively. There was no effect of n-3 FAs on composite memory (g � 0.04 [95% CI: �0.06–0.14],N � 934/812, p � 0.452). When examined by domain, no overall benefit for immediate recall (0.04 [�0.05–0.13], N � 934/812, p � 0.358)was detected; however, an effect in CIND subjects (0.16 [0.01–0.31], N � 349/327, p � 0.034) was found. A benefit for attention andprocessing speed was also detected in CIND (0.30 [0.02–0.57], N � 107/86, p � 0.035), but not healthy subjects. Benefits for delayed recall,recognition memory, or working memory and executive function were not observed. Treatment did not benefit AD patients as measured bythe Mini-Mental State Examination (MMSE) or Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS–cog). No differencesin adverse events (AE), dropout, or dropout due to AE between groups were observed.Conclusions: These results suggest an effect of n-3 FAs within specific cognitive domains in CIND, but not in healthy or AD subjects.© 2012 Elsevier Inc. All rights reserved.

Keywords: Omega-3 fatty acids; Eicosapentaenoic acid; Docosahexaenoic acid; Cognitive decline; Alzheimer’s disease; Memory

www.elsevier.com/locate/neuaging

1. Introduction

As our population has aged, cognitive impairment asso-ciated with Alzheimer’s disease (AD) and other dementiashas become a considerable burden. It is currently estimatedthat 35.6 million people are living with dementia worldwide(Wimo and Prince, 2010). Many others experience signifi-

* Corresponding author at: Sunnybrook Health Sciences Centre, 2075Bayview Avenue, Room FG05, Toronto, ON, M4N 3M5, Canada. Tel: �116 480 6133; fax: �1 416 480 6022.

E-mail address: [email protected] (N. Herrmann).

0197-4580/$ – see front matter © 2012 Elsevier Inc. All rights reserved.10.1016/j.neurobiolaging.2011.12.014

cant cognitive deficits in the absence of the full dementiasyndrome, variably described as mild cognitive impairment(MCI) or cognitive impairment no dementia (CIND), withapproximately 12% of these individuals converting to de-mentia each year (Plassman et al., 2008). Despite thesealarming statistics, it is estimated that delaying the diseaseonset by as little as 1 year would spare almost 9.2 millionpeople worldwide from developing dementia by 2050(Wimo and Prince, 2010).

AD is initially characterized by amnesia and executivedysfunction and progresses to global deficits that ultimately
lead to total incapacity (Jicha and Markesbery, 2010). These
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1482.e18 G. Mazereeuw et al. / Neurobiology of Aging 33 (2012) 1482.e17–1482.e29

features are thought to result from aberrant protein aggre-gation as extracellular amyloid-� plaques and intracellulareurofibrillary tangles are associated with disrupted neu-otransmission and deterioration of synaptic integrity (Diaolo and Kim, 2011). Although milder forms of cognitive

mpairment may not share this hallmark neuropathology,here appears to be a common deficiency in several key lipidpecies in the brain and periphery of impaired patients.ross-sectional studies have consistently reported lower

evels of omega-3 fatty acids (n-3 FAs), especially docosa-exaenoic acid (DHA), in serum, erythrocyte membranes,nd postmortem brain tissue of patients with AD (Conquert al., 2000; Tully et al., 2003) and CIND (Huang, 2010;

halley et al., 2008), and evidence suggests that dietary n-3A intake is associated with superior performance on neu-opsychological testing (Kalmijn et al., 2004; Nurk et al.,007; Whalley et al., 2004). Prospective studies indicatehat higher intake of n-3 FAs is associated with lower ratesf cognitive decline and may be protective against the onsetf cognitive impairment and neurological morbidity (Dev-re et al., 2009; Morris et al., 2003; Roberts et al., 2010; vanelder et al., 2007).Several clinical trials (Boston et al., 2004; Chiu et al.,

008; Dangour et al., 2010; Freund-Levi et al., 2006; John-on et al., 2008; Kotani et al., 2006; Quinn et al., 2010; Sinnt al., 2011; Suzuki et al., 2001; Vakhapova et al., 2010; vane Rest et al., 2008; Yehuda et al., 1996; Yurko-Mauro etl., 2010) have investigated the cognitive benefit of n-3 FAherapy in both impaired and nonimpaired patients; how-ver, mixed results have been reported, possibly because ofample heterogeneity or methodological inconsistencies.he effects of n-3 FAs on specific neuropsychological do-ains have not been investigated previously in a quantita-

ive synthesis. This meta-analysis reports the cognitive ben-fits of n-3 FA treatment within specific neuropsychologicalomains across cognitively normal elderly subjects, thoseith CIND, and patients with AD.

. Methods

.1. Data sources

All analyses were performed according to Preferred Re-orting Items for Systematic Reviews and Meta-AnalysesPRISMA) guidelines (Liberati et al., 2009). Literature wasearched using the Medical Literature Analysis and Re-rieval System Online (MEDLINE; National Library of

edicine, Bethesda, MD), Excerpta Medica Database (Em-ase; Elsevier, Amsterdam, the Netherlands), PsycINFOAmerican Psychological Association, Washington, DC),he Cochrane Library (the Cochrane Collaboration, Oxford,xfordshire, UK), Allied and Complementary Medicineatabase (AMED; the British Library, London, UK), andumulative Index to Nursing and Allied Health Literature

CINAHL; EBSCO Publishing, Glendale, CA) up to Sep-
ember 2011. The search was conducted using the key c
ords “Alzheimer’s disease,” “dementia,” “cognition,”cognitive” plus “docosahexaenoic acid,” “DHA,” “ome-a-3 fatty acid,” “fish oil,” “eicosapentaenoic acid,” andEPA.” The search was then repeated using the key wordss Medical Subject Headings (MeSH, The National Libraryf Medicine, Bethesda, MD). Reports that could not beetrieved online were sought through contact with studyuthors. Reference lists from selected studies were searchedor additional reports, and all relevant findings were addedo the selected pool.

.2. Study selection and eligibility criteria

Reports of original work investigating the treatment ef-ect of n-3 FAs as an intervention for cognitive benefit inognitively normal elderly adults (healthy), elderly adultsith memory complaints and objective cognitive decline

CIND), and patients with dementia or AD according totandardized criteria (such as the National Institute of Neu-ological and Communicative Disorders and Stroke/Alzhei-er’s Disease and Related Disorders Association orSM-IV [American Psychiatric Association, 2000]) were

ncluded in this review. Inclusion criteria required all stud-es to be randomized, double-blind, and placebo-controlledRCT) and the intervention with n-3 FAs to be in supple-ent form rather than dietary. Studies were not limited by

anguage but were limited to those with populations aged 50nd older and without diagnosed psychiatric comorbidity.ll studies were required to have presented measurable

esults of neuropsychological testing.

.3. Data extraction

Two independent reviewers examined each retrieved ar-icle. Final article selection was based on the amalgamationf individually selected reports, and all discrepancies re-arding inclusion were settled by consensus. The methodsnd results sections of each selected article were exami-ed, and baseline sample characteristics, intervention pro-ocols, and results of pre- and post-treatment neuropsycho-ogical evaluation (mean � SD) were extracted for bothreatment and placebo groups.

.4. Evaluation of reporting quality

Selected studies were analyzed for quality of reporting bywo independent raters using the PEDro Scale (Sherrington etl., 2000), an 11-item scale that has been supported as aomprehensive tool for assessing the methodological qual-ty and quality of reporting in randomized-controlled trialsArmijo Olivo et al., 2008). The PEDro scale was selected forts applicability to the design of the selected studies and for itsase of use. PEDro scores for each study were averaged andhen compared with the suggested cutoff score of 5 pointsMaher et al., 2003) for division between “high” and “low.”he strength of PEDro score correlation between raters was
alculated using Spearman’s rank correlation.

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2.5. Statistical analyses

Extracted results of neuropsychological testing were re-classified into cognitive domains as defined by Lezak et al.(2004). For meta-analysis, we considered all neuropsycho-logical data that could be classified under immediate recall,delayed recall, recognition, working memory and executivefunction, and attention and processing speed. Measures ofglobal cognitive function such as the Mini-Mental StateExamination (MMSE) (Folstein et al., 1975) and the Alz-heimer’s Disease Assessment Scale–Cognitive Subscale(ADAS–cog) (Rosen et al., 1984) were also meta-analyzedin a subsection of AD studies. A planned subgroup analysisexamined the effect of n-3 FA treatment on the domains ofimmediate and delayed verbal recall in studies includinghealthy subjects and high-functioning subjects with CINDor AD. Impaired subgroups were classified as “high-func-tioning” according to an MMSE score of 26 or higher, asthis represents the suggested boundary between “normal”and “impaired” on the MMSE (van Gorp et al., 1999).

Hedge’s g was used to represent effect sizes betweentreatment and placebo groups for continuous neuropsycho-logical outcomes in each study. Hedge’s g provides a stan-dardized estimate of effect size that is appropriate for com-bining multiple cognitive tests in populations of varyingsample sizes and has been used successfully in a similarmeta-analysis (Smith et al., 2010). Using standardized esti-mates, multiple assessments for a particular neuropsycho-logical domain could be collapsed into a single g value suchthat each study contributed only one effect size per domain.Effect sizes across studies for each domain were summa-rized using random effects modeling (Harris et al., 2008)and interpreted as suggested by Cohen (1988). When morethan one treatment arm was used for an included study, theeffect sizes for each arm were averaged into a single treat-ment effect. Random effects models assume that studies aredrawn from unequal populations and therefore account forvariable underlying effects in estimates of uncertainty. Ran-dom effects models were appropriate, as heterogeneity wasexpected because of variation between studies in the cog-nitive assessment tools. Effect sizes were calculated basedon the mean difference of change scores for the treatmentand placebo groups and their reported standard deviations.Where change scores were not reported for a neuropsycho-logical test, pre- and post-intervention values were used tocalculate the change score, and standard deviations wereestimated as prescribed by the Cochrane Handbook forSystematic Reviews of Interventions (Higgins and Green,2011). Dichotomous safety and tolerability outcomes suchas dropout, adverse events, and dropout due to adverseevents were summarized across studies by an overall rela-tive risk between treatment and placebo groups and randomeffects modeling.

Heterogeneity in comparisons for each neuropsycholog-
ical domain was calculated using a Q statistic in chi-square
analysis, and the impact of heterogeneity was calculatedusing an I2 index (Higgins and Thompson, 2002). A signif-cant Q statistic indicates diversity in underlying character-stics between studies. Heterogeneity was investigated usingubgroup analyses of impaired and healthy populations andsing meta-regression analyses (summarized using a � co-

efficient) comparing effect sizes to study characteristicssuch as duration of treatment, dose of DHA, mean age,percentage male, mean baseline MMSE, and presence ofcognitive impairment (Hardbord and Higgins, 2008). Riskof publication and small study bias was evaluated usingfunnel plots and Egger’s test (Egger et al., 1997). All anal-yses were performed using Stata (release 10.1, StataCorp,College Station, TX).

3. Results

3.1. Literature search results

The search strategy returned 1038 unique titles including3 reports that were hand-selected from reference lists ofrelevant articles. Of these titles, 442 articles were relevant ton-3 FAs and cognition, dementia, or AD. A total of 433records were excluded from the 442 relevant articles, 317 ofwhich were not double-blind, placebo-controlled RCTs us-ing n-3 FAs as an intervention, and the remaining 116 werereviews. In total, 10 records were identified as eligible forthis meta-analysis (Table 1), 3 that included cognitivelynormal elderly adults (Dangour et al., 2010; Johnson et al.,2008; van de Rest et al., 2008), 4 that included subjects withCIND (Kotani et al., 2006; Sinn et al., 2011; Vakhapova etal., 2010; Yurko-Mauro et al., 2010), and 3 that includedsubjects with AD (Chiu et al., 2008; Freund-Levi et al.,2006; Quinn et al., 2010). An eligible conference abstract(Shinto et al., 2008) reporting the effect of n-3 FAs andlipoic acid in AD was also retrieved and presented in thesummary of nonpooled outcomes.

The effects of n-3 FAs on AD patients were only as-sessed using the MMSE and ADAS–cog; however, imme-diate and delayed verbal recall subitems of the ADAS–cogin one study (Freund-Levi et al., 2006) were available to thesubgroup analysis of high-functioning subjects. All otherneuropsychological domains were assessed in healthy andCIND subjects only.

3.2. Quality of reporting evaluation

All of the included studies scored above the suggestedcutoff for high quality (5 points) according to the PEDroscale (Maher et al., 2003). Scores ranged from 6 to 10(Table 1) with a mean of 8.85. The PEDro scores for the 2raters were strongly correlated (� � 0.838, p � 0.001).

3.3. Composite memory

Seven studies investigated the effect of n-3 FAs onmemory in CIND and healthy subjects with 2 studies (Sinn
et al., 2011; van de Rest et al., 2008) evaluating 2 different


Table 1Summary of study characteristics for papers included in this meta-analysis

Author/Year Sample size Patient characteristics (Rx/Pb) Intervention (mg/d) Outcomes Methodologicalcharacteristics (Rx/Pb)

Chiu et al., 2008 Rx: 20Pb: 15

Diagnosis: 18 MCI; 17 ADCriteria: Peterson criteria;DSM-IVAge: 74�8.7/76.5�9.2Gender (%Male): 35/53.3MMSE: 25.8/23.8Years of education: 10.9�5.3/8.5�6.4

Treatment arms:1080 EPA � 720DHA; placebo (tid)Duration: 24 wks

Primary: ADAS–Cog;CIBIC-PlusSecondary: MMSE; HDRS

Attrition (%): 29.2/45.5ITT: YPEDro: 9

Dangour et al.,2010

Rx: 434Pb: 433

Diagnosis: healthyAge: 74.7�2.5/74.6�2.7Gender (%Male): 53.4/56.6MMSE: 29/29Years of education: -

Treatment arms:500 DHA � 200EPA; placebo (bid)Duration: 108 wks

Primary: CVLT (total anddelayed recall)Secondary: WMS (StoryRecall); Spatial Memory;Letter Search/Cancellation;Symbol Letter Modality;Reaction Time; WAIS-Digit Span; VerbalFluency


Freud-Levi et al.,2006

Rx: 89Pb: 85

Diagnosis: ADCriteria: DSM-IVAge: 72.6�9.0/72.9�8.6Gender (%Male): 43/54MMSE: 23.6�3.9/23.2�3.8Years of education: -

Treatment arms:430 DHA � 150EPA; placebo (qid)Duration: 27 wks

Primary: ADAS–Cog;MMSESecondary: CDRS-Global;CDRS-Sum of Boxes


Johnson et al., 2008 Rx1: 14Rx2: 11Rx3: 14Pb: 10

Diagnosis: healthy elderlywomenAge:68.5�1.3/66.7�1.9/68.6�1.3/68.0�1.2Gender (%Male): 0MMSE: 16.0�1.0/13.8�0.5/14.8�0.5/13.6�1.1Years of education: 16.0�1.0/13.8�0.5/14.8�0.5/13.6�1.1

Treatment arms:800 DHA (Rx1);12 lutein (Rx2);800 DHA � 12lutein (Rx3);placebo (qd)Duration: 16 wks

Verbal Fluency; WechslerDigit Span; Shopping ListTask; Word List MemoryTest; Memory in RealityApartment Test; NES2Pattern Comparison Test;Stroop Test; NES2 MoodScales* Primary outcome wasserum lipids and macularpigmentation

Attrition (%): 14.0 (total)ITT: NPEDro: 9

Kotani et al., 2006 Rx: 12Pb: 9

Diagnosis: MCICriteria: Peterson criteriaAge: 66.9�9.0/69.7�5.2Gender (%Male): 75/33MMSE: -Years of education: -

Treatment arms:40 ARA and DHA;placebo (six timesdaily)Duration: 12.8 wks

Primary: RBANS-Japanese Attrition (%): -ITT: NPEDro: 6

Quinn et al., 2010 Rx: 238Pb: 164

Diagnosis: ADCriteria: MMSE 14-26Age: 76�9.3/76�7.8Gender (%Male): 53/40.2MMSE: 20.9�3.6/20.3�3.7Years of education: 14�2.9/14�2.7

Treatment arms:550 DHA; placebo(tid)Duration: 81 wks

Primary: ADAS–Cog;CDRS-sum of boxesSecondary: MMSE;ADCS–ADL; NPI; Qualityof Life Alzheimer’sDisease Scale

Attrition (%): 28.1/24.4ITT: YPEDro: 9.5

Sinn et al., 2011 Rx EPA:17Rx DHA:18Pb: 15

Diagnosis: MCICriteria: MMSE � 22; VerbalPaired Associates Task,DemTect score � 1.5 SD belowpopulation mean.Age: 74.22 DHA/74.88 EPA/73 PbGender (%Male): 72/82/47MMSE:27.83�1.92/25.94�3.31/27.73�2.22Years of education: -

Treatment arms:1550 mg DHA �400 mg EPA;1670 mg EPA �160 mg DHA;placeboDuration: 27 wks

Memory FunctioningQuestionnaire; RAVLT;WAIS-Digit Span; Letter-Number Sequencing; TrailMaking Test; StroopColor-Word Test; VerbalFluency

Attrition (%): 0.0%DHA/5.5%EPA/16.6 PbITT: NPEDro: 9.0

(continued on next page)

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doses of DHA in individual treatment groups. All outcomestesting memory were pooled to produce a composite treat-ment effect for each study. Treatment did not significantlybenefit composite memory in the combined populationsacross these studies (Table 2). Subdivision of these studiesby diagnosis did not reveal an effect in either healthy orCIND subgroups (Fig. 1, Table 2). No significant heteroge-neity (Table 2) or publication bias (Egger’s test: coeffici-ent � �0.22 [95% CI: �1.17–0.73], p � 0.579) wasdetected across these studies.

Treatment effect size was not associated with study du-ration, dose of DHA, mean age of study subjects, percentagemale, baseline MMSE score, or presence of cognitive im-pairment in meta-regression analysis (Table 3).

3.4. Immediate recall

Seven studies, 2 including 2 dose groups (Sinn et al.,2011; van de Rest et al., 2008), investigated the effect of n-3FAs on immediate recall in CIND and healthy subjects.Overall, treatment did not significantly benefit immediate

Table 1(continued)

Author/Year Sample size Patient characteristics (Rx/Pb)

Vakhapova et al.,2010

Rx: 60Pb: 62

Diagnosis: elderly with memorycomplaintCriteria: � 25 MemoryComplaint Questionnaire ScaleAge: 72.9�8.2/73.0�8.3Gender (%Male): 48/53MMSE: 28.4�1.2/28.7�1.1Years of education: 13.5�3.7/13.3�3.6

van de Rest et al.,2008

Rx1: 96Rx2: 100Pb: 106

Diagnosis: cognitively-healthyelderlyAge:69.9�3.4/69.5�3.2/70.1�3.7Gender (%Male): 55/55/56MMSE: 28/28/28Years of education: -

Yurko-Mauro et al.,2010

Rx: 242Pb: 243

Diagnosis: elderly with memorycomplaintCriteria: DSM-IV ARCDAge: 70.0�9.3/70.0�8.7Gender (%Male): 44/40MMSE: 28.3�1.3/28.2�1.3Years of education: 14.5�2.5/14.7�2.6

Key: ARA, arachidonic acid; EPA, eicosapentaenoic acid; DHA, docosaheAlzheimer’s Disease Cooperative Study–Activities of Daily Living; ADCChange; ADCS–ADL PI, Alzheimer’s Disease Cooperative Study–Activitlogical Test Automated Battery; PAL, Paired Associate Learning; PRM, Paof Cambridge; SWM, Spatial Working Memory; CDR, Clinical DemenCaregiver Input; CVLT, California Verbal Learning Test; GDS, GeriatMini-Mental Status Examination; NPI, Neuropsychological Inventory; RARecognition Trial; RBANS, Repeatable Battery for the Assessment of NeurMemory Scale; qd, once daily; bid, twice daily; tid, three times daily; qid

recall in the combined populations across these studies (

(Table 2); however, a significant effect was seen in studiesof CIND subjects (Fig. 1, Table 2). There was no significantheterogeneity (Table 2) or publication bias (Egger’s test:coefficient � 0.44 [95% CI: �1.38–2.25], p � 0.565)detected across these studies.

Treatment effect size was not associated with study du-ration, the dose of DHA, mean age of study subjects, per-centage male, or baseline MMSE score in meta-regressionanalysis (Table 3). However, there was a statistical trendtoward larger effect sizes in studies using CIND (� � 0.1995% CI: �0.03–0.42], p � 0.091) (Table 3).

.5. Delayed recall

Seven studies, 2 with 2 dose groups (Sinn et al., 2011;an de Rest et al., 2008), investigated the effect of n-3 FAsn delayed recall in CIND and healthy subjects. Overall,reatment did not significantly benefit delayed recall in theombined populations, and subdividing studies by diagnosisid not reveal an effect in healthy or CIND subgroups

ention (mg/d) Outcomes Methodologicalcharacteristics (Rx/Pb)

ent arms:S � 59 DHA75 EPA;o (tid)on: 15 wks

RAVLT (Hebrew version);RCFT; ADCS–CGIC;NexAde* No primary outcomeswere pre-determined

Attrition (%): 24.1/20.5ITT: NPEDro: 8

ent arms:PA � 847

(Rx1); 226176 DHA

placebo (qd)on: 26 wks

Primary: Word LearningTest; WAIS-Digit Span;Trail Making Test; StroopColor-Word Test; VerbalFluency Test

Attrition (%): 1.0/0/2.8ITT: YPEDro: 8

ent arms:HA; placebo

on: 24 wks

Primary: CANTAB PALSecondary: CANTAB(PRM, VRM, SOC,SWM); Frequency ofForgetting-10 scale;ADCS–ADL PI; MMSE;GDS


acid; ADAS–Cog, Alzheimer’s Disease Assessment Scale; ADCS–ADL,, Alzheimer’s Disease Cooperative Study–Clinical Global Impression ofaily Living Prevention Instrument; CANTAB, Cambridge Neuropsycho-

ecognition Memory; VRM, Verbal Recognition Memory; SOC, Stockingsing; CIBIC-Plus, Clinician Interview-Based Impression of Change plusression Scale; HDRS, Hamilton Rating Scale for Depression; MMSE,ey Auditory Verbal Learning Test; RCFT, Rey Complex Figure Test andlogical Status; WAIS, Wechsler Adult Intelligence Scale; WMS, Wechslerimes daily.

Interv

Treatm300 P� 19.placebDurati

Treatm1093 EDHAEPA �(Rx2);Durati

Treatm300 D(qd)Durati

xaenoicS–CGICies of Dttern Rtia Ratric DepVLT, Ropsycho; four t

Table 2). There was no significant heterogeneity (Table 2)

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or publication bias (Egger’s test: coefficient � �0.25 [95%CI: �0.90–0.38], p � 0.355) detected across these studies.


3.6. Recognition memory

Five studies, 2 with 2 dose groups (Sinn et al., 2011; vande Rest et al., 2008), investigated the effect of n-3 FAs onrecognition memory in CIND and healthy subjects. Overall,there was no effect of n-3 FAs on recognition memory in thecombined populations, and subdividing studies by diagnosisdid not reveal an effect in healthy or CIND subgroups

Table 2Summary of treatment effect sizes across neuropsychological domains insubanalysis of high-functioning subjects (CIND and AD)

Studies N (T/P) Treatment effec

g 95

Composite memoryCIND 4a 349/327 0.10 �Healthy 3a 585/485 0.00 �Overall 7 934/812 0.04 �

Immediate recallCIND 4a 349/327 0.16Healthy 3a 585/485 �0.03 �Overall 7 934/812 0.04 �

Delayed recallCIND 4a 349/327 0.03 �Healthy 3a 585/485 0.05 �Overall 7 934/812 0.04 �

RecognitionCIND 3a 337/318 �0.03 �Healthy 2a 210/116 0.03 �Overall 5 548/434 0.03 �

WM and EFCIND 2a 277/256 0.04 �Healthy 3 585/485 �0.04 �Overall 5 862/741 �0.02 �

A and PSCIND 3a 107/86 0.32Healthy 3a 585/485 �0.03 �Overall 6 692/571 0.02 �

MMSECIND 1 242/241 �0.06 �AD 3 344/261 0.05 �Overall 4 586/502 0.00 �

ADAS–cogAD 3 344/261 0.04 �

Immediate verbal recallImpaired 3 298/296 0.26 �Healthy 3a 585/485 �0.06 �Overall 6 883/781 0.07 �

Delayed verbal recallImpaired 3 298/296 0.30Healthy 3a 585/485 0.07 �Overall 6 883/781 0.13

Key: N (T/P), number of subjects in treatment/placebo group; g, Hedge’s gA and PS, attention and processing speed.

a reported 2 dose groups in treatment arm (Sinn et al., 2011; van de Re

(Table 2). No significant heterogeneity (Table 2) or publi- C

cation bias (Egger’s test: coefficient � �1.09 [95% CI:�4.50–2.31], p � 0.382) was detected across these studies.

Treatment effect size was not associated with study du-ation, dose of DHA, mean age of study subjects, percentageale, baseline MMSE score, or presence of cognitive im-

airment in meta-regression analysis (Table 3).

.7. Working memory and executive function

Five studies, 2 with 2 dose groups (Sinn et al., 2011; vane Rest et al., 2008), investigated the effect of n-3 FAs onorking memory and executive function in CIND andealthy subjects. Overall, treatment did not appear to benefitorking memory and executive function in the combinedopulations, and the effect was not different in healthy or

and CIND subjects; the MMSE and ADAS–cog in AD patients; and

Heterogeneity

Z p Q d.f. p I2

25 1.17 0.241 0.31 3 0.989 0.0%14 0.02 0.982 0.56 2 0.905 0.0%14 0.75 0.452 1.68 6 0.989 0.0%

32 2.12 0.034 0.73 3 0.974 0.0%09 0.46 0.644 1.12 2 0.772 0.0%13 0.92 0.358 5.70 7 0.680 0.0%

18 0.42 0.672 0.79 3 0.940 0.0%16 0.82 0.413 1.11 2 0.775 0.0%13 0.91 0.364 1.93 7 0.983 0.0%

13 0.37 0.712 0.42 2 0.811 0.0%62 0.11 0.913 2.22 1 0.136 55.0%19 0.39 0.696 4.99 4 0.288 19.8%

21 0.47 0.639 0.29 1 0.590 0.0%08 0.69 0.493 0.26 2 0.880 0.0%08 0.29 0.772 1.15 4 0.886 0.0%

61 2.11 0.035 1.04 3 0.791 0.0%09 0.55 0.585 0.12 3 0.989 0.0%12 0.31 0.755 5.83 7 0.560 0.0%

12 0.62 0.538 0.00 0 n/a n/a12 0.56 0.574 0.18 2 0.915 0.0%12 0.01 0.995 0.87 3 0.832 0.0%

23 0.43 0.666 0.35 2 0.839 0.0%

62 1.41 0.158 4.57 2 0.102 56.3%08 0.87 0.384 1.46 2 0.481 0.0%26 0.75 0.456 10.85 5 0.054 53.9%

57 2.03 0.043 3.76 2 0.153 46.8%20 0.92 0.359 0.13 2 0.935 0.0%24 2.26 0.024 5.45 5 0.364 8.2%

nfidence interval; WM and EF, working memory and executive function;

, 2008).

healthy

t

% CI

0.06–0.0.14–0.0.06–0.

0.01–0.0.15–0.0.05–0.

0.12–0.0.07–0.0.05–0.

0.18–0.0.55–0.0.13–0.

0.13–0.0.16–0.0.11–0.

0.03–0.0.15–0.0.09–0.

0.23–0.0.12–0.0.12–0.

0.15–0.

0.10–0.0.20–0.0.12–0.

0.01–0.0.06–0.0.02–0.

; CI, co

IND subgroups when subdivided by diagnosis (Table 2).

1bC

rm(t


There was no significant heterogeneity (Table 2) or publi-cation bias (Egger’s test: coefficient � 0.60 [95% CI:�0.82–2.02], p � 0.272) detected across these studies.


3.8. Attention and processing speed

Six studies, 2 with 2 dose groups (Sinn et al., 2011; vande Rest et al., 2008), investigated the effect of n-3 FAs onattention and processing speed in CIND and healthy sub-jects. Overall, there was no effect of treatment on attention

.

.

.

.

.

.

Composite Memory - CINDKotaniSinnVakhapovaYurko-MauroSubtotal (I-squared = 0.0%, p = 0.983)

Composite Memory - HealthyDangourJohnsonvan de RestSubtotal (I-squared = 0.0%, p = 0.846)

Immediate Recall - CINDKotaniSinnVakhapovaYurko-MauroSubtotal (I-squared = 0.0%, p = 0.888)

Immediate Recall - HealthyDangourJohnsonvan de RestSubtotal (I-squared = 0.0%, p = 0.628)

Attention & Processing Speed - CINDKotaniSinnVakhapovaSubtotal (I-squared = 0.0%, p = 0.692)

Attention & Processing Speed - HealthyDangourJohnsonvan de RestSubtotal (I-squared = 0.0%, p = 0.959)

Study

2006201120102010

201020082008

2006201120102010

201020082008

200620112010

201020082008

Year

123560241

37514196

123560241

37514196

123560

37514196

Treatment

91562242

36910106

91562242

36910106

91562

36910106

Placebo

Placebo b

-2 -1

Fig. 1. The treatment effect of n-3 FAs on composite memory, immediaand CIND participants, separated by diagnosis. Effect sizes are calcul(x-axis) denote treatment benefit. Summary statistics: composite memoN � 585/485), immediate recall (CIND, z � 2.12, p � 0.034, N � 349speed (CIND, z � 2.13, p � 0.033, N � 107/86; Healthy, z � 0.52, pof each study); Placebo, N (placebo arm of each study). For interpretatiWeb version of this article.

and processing speed in the combined populations (Table

2); however, there was a significant effect in a subgroup ofCIND subjects when subdivided by diagnosis (Fig. 1, Table2). There was no significant heterogeneity (Table 2) de-tected across these studies, however, a trend toward risk ofpublication bias was indicated (Egger’s test: coefficient �.25 [95% CI: �0.30–2.80], p � 0.088). Adjustment forias did not change the treatment effect (g � �0.03 [95%I: �0.20–0.14], p � 0.731).

Treatment effect size was not associated with study du-ation, dose of DHA, mean age of study subjects, percentageale, or baseline MMSE score in meta-regression analysis

Table 3). The presence of cognitive impairment had arending effect on treatment effect size (� � 0.33 [95% CI:

0.11 (-0.75, 0.97)-0.02 (-0.62, 0.58)0.12 (-0.23, 0.47)0.10 (-0.08, 0.28)0.10 (-0.06, 0.25)

0.00 (-0.18, 0.18)-0.23 (-1.04, 0.58)0.02 (-0.22, 0.26)0.00 (-0.14, 0.14)

0.22 (-0.65, 1.09)0.17 (-0.43, 0.77)0.29 (-0.07, 0.65)0.13 (-0.05, 0.31)0.16 (0.01, 0.32)

-0.05 (-0.19, 0.09)-0.33 (-1.15, 0.49)0.04 (-0.20, 0.28)-0.03 (-0.15, 0.09)

0.63 (-0.26, 1.52)0.16 (-0.44, 0.76)0.32 (-0.04, 0.68)0.32 (0.03, 0.61)

-0.04 (-0.18, 0.10)0.07 (-0.74, 0.88)-0.02 (-0.26, 0.22)-0.03 (-0.15, 0.09)

Hedge's g (95% CI)

3.086.3118.2872.33100.00

61.612.9635.43100.00

3.076.3318.1272.48100.00

71.392.1926.42100.00

10.6923.1266.20100.00

71.372.2226.41100.00

Weight%

0.11 (-0.75, 0.97)-0.02 (-0.62, 0.58)0.12 (-0.23, 0.47)0.10 (-0.08, 0.28)0.10 (-0.06, 0.25)

0.00 (-0.18, 0.18)-0.23 (-1.04, 0.58)0.02 (-0.22, 0.26)0.00 (-0.14, 0.14)

0.22 (-0.65, 1.09)0.17 (-0.43, 0.77)0.29 (-0.07, 0.65)0.13 (-0.05, 0.31)0.16 (0.01, 0.32)

-0.05 (-0.19, 0.09)-0.33 (-1.15, 0.49)0.04 (-0.20, 0.28)-0.03 (-0.15, 0.09)

0.63 (-0.26, 1.52)0.16 (-0.44, 0.76)0.32 (-0.04, 0.68)0.32 (0.03, 0.61)

-0.04 (-0.18, 0.10)0.07 (-0.74, 0.88)-0.02 (-0.26, 0.22)-0.03 (-0.15, 0.09)

Hedge's g (95% CI)

3.086.3118.2872.33100.00

61.612.9635.43100.00

3.076.3318.1272.48100.00

71.392.1926.42100.00

10.6923.1266.20100.00

71.372.2226.41100.00

Weight%

Treatment benefit

00 1 2

ll, and attention and processing speed across studies including healthying Hedge’s g and random effects meta-analysis, and positive valuesD, z � 1.25, p � 0.213, N � 349/327; Healthy, z � 0.00, p � 0.997,ealthy, z � 0.52, p � 0.600, N � 585/485), attention and processing

1, N � 585/485). CI, confidence interval; Treatment, N (treatment armhe references to color in this figure legend, the reader is referred to the

enefit

te recaated usry (CIN/327; H

� 0.60on of t

�0.04–0.70], p � 0.074) (Table 3).

p[g

rm(

3

3s

2voi(diHc(p

rss

w

(

3

2rsrenddt3hgoa�

rmp

3

ceaY(m

C

se grou


3.9. Global cognitive function

Four studies including CIND and AD subjects investi-gated the effect of n-3 FAs on global cognitive functionaccording to the MMSE, 3 of which also used the ADAS–cog. Overall, there was no effect of n-3 FAs on MMSEscore or on ADAS–cog score across these studies (Table 2).

Subdivision of these studies by diagnosis could not beperformed, as all of these studies used impaired populations.No publication bias was detected across studies in MMSE(Egger’s test: coefficient � 0.55 [95% CI: �2.65–3.74],

� 0.538) or ADAS–cog (Egger’s test: coefficient � 0.3995% CI: �3.93–4.70], p � 0.460) outcomes, and hetero-eneity was not significant (Table 2).

Treatment effect size was not associated with study du-ation, dose of DHA, mean age of study subjects, percentageale, or baseline MMSE score in meta-regression analysis

Table 3).

.10. Subgroup analyses

.10.1. Immediate verbal recall in high-functioningubjects

Six studies, 1 with 2 dose groups (van de Rest et al.,008), investigated the effect of n-3 FAs on immediateerbal recall in high-functioning subjects (healthy, CIND,r AD; with MMSE � 26). Treatment did not benefitmmediate verbal recall in the high-functioning subgroupFig. 2, Table 2). Subdivision of these studies by diagnosisid not result in any significant treatment effect across thempaired (AD and CIND) or healthy groups (Table 2).eterogeneity across these studies trended toward signifi-

ance (Table 2); however, no publication bias was detectedEgger’s test: coefficient � 0.58 [95% CI: �3.23–4.39],� 0.695).Treatment effect size was not associated with study du-

ation, dose of DHA, percentage male, baseline MMSEcore, or presence of cognitive impairment in meta-regres-

Table 3Results of meta-regression analyses between treatment effect size and sel

Domain Studies Duration

� (95% CI) p

omposite memory 7a 0.00 (�0.004–0.002) 0.617Immediate recall 7a 0.00 (�0.004–0.0001) 0.128Delayed recall 7a 0.00 (�0.003–0.002) 0.802RM 5a 0.03 (�0.04–0.10) 0.362WM and EF 5a 0.00 (�0.003–0.003) 0.722A and PS 6a 0.00 (�0.005–0.001) 0.239MMSE 4 0.00 (�0.01–0.01) 0.532ADAS–cog 3 0.00 (�0.09–0.08) 0.660IVR 6a 0.00 (�0.01–0.001) 0.132DVR 6a 0.00 (�0.005–0.002) 0.348

Key: BL MMSE, baseline MMSE score; % male, percentage male; RM, rePS, attention and processing speed; IVR, immediate verbal recall; DVR,

a Two studies (Sinn et al., 2011; van de Rest et al., 2008) reported 2 do

ion analysis (Table 3). Larger effect sizes were associated w

ith younger mean age (� � �0.05 [95% CI: �0.09–0.01], p � 0.034); however, this trend was driven by onestudy of considerably younger participants, and the associ-ation was not sustained once the outlying study was re-moved (� � �0.03 [95% CI: �0.10–0.03], p � 0.231)Table 3).

.10.2. Delayed verbal recall in high-functioning subjectsSix studies, 1 with 2 dose groups (van de Rest et al.,

008), investigated the effect of n-3 FAs on delayed verbalecall in high-functioning subjects. There appeared to be amall, but significant, treatment effect on delayed verbalecall in these subjects (Fig. 2, Table 2). The treatmentffect was observed in a subgroup of impaired subjects butot in a subgroup of healthy subjects after subdivision byiagnosis (Table 2). There was no significant heterogeneityetected across these studies (Table 2). Significant publica-ion bias (Egger’s test: coefficient � 1.56 [95% CI: �0.44–.57], p � 0.097) was not indicated across these studies;owever, funnel plot asymmetry suggested further investi-ation of small study effects. The effect of n-3 FA treatmentn delayed verbal recall was no longer significant after trimnd fill procedures were carried out (g � 0.08 [95% CI:0.05–0.22], p � 0.235).Treatment effect size was not associated with study du-

ation, dose of DHA, mean age of study subjects, percentageale, baseline MMSE score, or presence of cognitive im-

airment in meta-regression analysis (Table 3).

.11. Safety and tolerability

Of the studies that reported safety and tolerability out-omes (Chiu et al., 2008; Dangour et al., 2010; Freund-Levit al., 2006; Johnson et al., 2008; Quinn et al., 2010; Sinn etl., 2011; Vakhapova et al., 2010; van de Rest et al., 2008;urko-Mauro et al., 2010), study dropout, adverse events

AEs), and dropout due to AE were similar between treat-ent and placebo groups (Table 4). Treatment compliance

udy characteristics

ose DHA Mean age

(95% CI) p � (95% CI) p

.00 (�0.0002–0.0002) 0.711 �0.01 (�0.04–0.02) 0.565

.00 (�0.0002–0.0002) 0.845 �0.02 (�0.07–0.03) 0.358

.00 (�0.0001–0.0003) 0.383 0.00 (�0.03–0.03) 0.758

.00 (�0.001–0.001) 0.661 0.01 (�0.07–0.10) 0.756

.00 (�0.001–0.001) 0.885 0.00 (�0.06–0.05) 0.933

.00 (�0.0004–0.0001) 0.417 �0.02 (�0.06–0.01) 0.132

.00 (�0.0004–0.0006) 0.474 0.02 (�0.08–0.12) 0.464

.00 (�0.02–0.02) 0.664 �0.15 (�3.89–3.60) 0.704

.00 (�0.0006–0.0004) 0.686 �0.05 (�0.09–0.01) 0.034

.00 (�0.0002–0.0004) 0.357 �0.02 (�0.06–0.02) 0.257

(continued on next page)

n memory; WM and EF, working memory and executive function; A andverbal recall; n/p, not performed.ps in the treatment arm.

ected st

D

�

0000000000

cognitiodelayed

as reported between 81% and 99% across both the treat-

�


ment and placebo groups. The most common AEs reportedacross these studies were gastrointestinal discomfort, diar-rhea, and headache, whereas other notable events includedrashes and infections. Only one study (Quinn et al., 2010)reported possible treatment-related serious adverse events(SAEs) (deep venous thrombosis, hospitalization, anddeath), but these did not differ between the treatment andplacebo groups.

3.12. Summary of nonpooled outcomes

Several important results extracted from the includedstudies could not be pooled for meta-analysis. One study(van de Rest et al., 2008) observed greater improvements inattention in ApoE-�4 carriers in both high-dose (1800 mg/d)and low-dose (400 mg/d) treatment groups compared withplacebo, whereas another study (Quinn et al., 2010) found asignificant treatment effect only in patients who did notcarry the ApoE-�4 allele. Chiu et al. reported an associationbetween n-3 FAs and improvements in global cognitiveperformance according to the Clinician Interview-BasedImpression of Change (CIBIC) and also found a significanteffect in a subgroup of CIND (MCI) patients using theADAS–cog. The rate of cognitive decline in the placebogroup of an AD trial (Freund-Levi et al., 2006) was signif-icantly attenuated by intervention with n-3 FA treatmentover 6 months, and a significant association between treat-ment and benefit to MMSE scores was seen in a subgroup ofpatients with baseline MMSE scores � 27. Another studyreported a significant benefit to MMSE scores in AD pa-tients treated with n-3 FAs and lipoic acid as well as animprovement on the Activities of Daily Living subscale ofthe ADAS–cog (ADCS–ADL) with n-3 FAs alone and incombination with lipoic acid (Shinto et al., 2008). No effectof n-3 FA treatment on the Clinical Dementia RatingScale—sum of boxes, ADCS–ADL, or the NeuropsychiatricInventory was reported in a study of AD patients (Quinn et

Table 3(continued)

% Male BL MMSE

� (95% CI) p � (95% CI)

0.01 (�0.03–0.01) 0.423 0.00 (�0.24–0.2�0.01�0.03–0.01) 0.305 �0.10 (�0.31–0.10.00 (�0.02–0.02) 0.710 0.01 (�0.20–0.20.01 (�0.05–0.06) 0.925 0.05 (�0.489–00.00 (�0.02–0.01) 0.614 �0.03 (�0.27–0.2

�0.01 (�0.08–0.06) 0.655 �0.07 (�0.31–0.10.01 (�0.07–0.10) 0.555 �0.01 (�0.09–0.0

�0.04 (�1.04–0.95) 0.668 �0.01 (�0.09–0.00.00 (�0.02–0.03) 0.625 0.00 (�0.25–0.20.00 (�0.02–0.01) 0.721 �0.08 (�0.21–0.0

al., 2010).

4. Discussion

This meta-analysis did not find a significant treatmenteffect of n-3 FAs when memory outcomes were combined.Likewise, n-3 FA treatment did not benefit measures ofglobal cognitive performance (as measured by MMSE andADAS–cog) in AD patients. When cognitive subdomainswere assessed, the use of n-3 FAs did not influence recog-nition memory, working memory and executive function,immediate recall, delayed recall, or attention and processingspeed, although the studies included in these analyses variedwith respect to the level of impairment of the includedsubjects. Further subdivision of these studies indicated thatthe effects of n-3 FAs were isolated to CIND populationsfor the immediate recall and attention and processing speedsubdomains.

The effect of n-3 FA treatment was very consistentacross studies in each domain, as none of the studies dem-onstrated significant heterogeneity.

The high degree of safety and tolerability observed inthese RCTs suggests that n-3 FAs, if proven effective,would be a potentially advantageous therapy option forCIND and AD patients. Rates of study dropout, AE, anddropout due to AE did not differ between treatment andplacebo groups. Reported AEs were mild, and only onestudy (Quinn et al., 2010) reported potential treatment-related SAEs. Furthermore, treatment compliance wasexcellent in both groups across the included studies.Although these observations appear similar to the safetyand tolerability profile of memantine when used in mod-erate to severe AD, they contrast with the considerableAE burden of cholinesterase inhibitors in milder ADpatients (Jones, 2010).

Although there was no effect of treatment on immediateverbal recall in our analysis of high-functioning subjects, asignificant benefit to delayed verbal recall was observed.However this effect could not be clearly demonstrated after

Impairment

p � (95% CI) p

0.987 0.09 (�0.12–0.33) 0.3980.301 0.19 (�0.03–0.42) 0.0910.881 �0.02 (�0.24–0.21) 0.8760.821 �0.21 (�0.81–0.40) 0.4230.712 0.09 (�0.17–0.36) 0.4130.483 0.33 (�0.04–0.70) 0.0740.491 n/p n/p0.491 n/p n/p0.964 0.24 (�0.10–0.58) 0.1280.173 0.13 (�0.14–0.41) 0.266

4)2)3).58)0)8)6)6)4)5)

adjusting for publication bias. Interestingly, this effect also

this ar


appeared to be selective to impaired patients (CIND andAD), as healthy subjects did not improve.

Although the present meta-analysis was limited to asmall pool of studies, the results suggest that n-3 FAs mayselectively benefit specific neuropsychological domains insubjects with CIND and in high-functioning patients withAD. There have been consistent reports implicating epi-sodic memory as an early deficit in predementia syndromes

.

.

Immediate Verbal Recall

Dangour

Freund-Levi

Johnson

Vakhapova

Yurko-Mauro

van de Rest

Subtotal (I-squared = 53.9%, p = 0.054)

Delayed Verbal Recall

Dangour

Freund-Levi

Johnson

Vakhapova

Yurko-Mauro

van de Rest

Subtotal (I-squared = 8.2%, p = 0.364)

Study

2010

2006

2008

2010

2010

2008

2010

2006

2008

2010

2010

2008

Year

375

16

14

40

241

196

375

16

14

40

241

196

Treatment

369

16

10

38

242

106

369

16

10

38

242

106

Placebo

Placebo be

-2 -1

Fig. 2. The treatment effect of n-3 FAs on immediate verbal recall and dfunction was classified as subgroups scoring � 26 on MMSE regardlesmeta-analysis, and positive values (x-axis) denote treatment benefit. Summaverbal recall (z � 2.26, p � 0.024, N � 883/781). CI, confidence intervastudy). Note: the size of each group in Freund-Levi et al., 2006 was estimateto color in this figure legend, the reader is referred to the Web version of

Table 4Comparative safety and tolerability outcomes between treatment and plac

Outcome Studies N (T/P) Compar

RR

Adverse events 6 1248/1167 1.01Dropout 7 1351/1268 1.00Dropout due to adverse events 6 1248/1167 1.00

Key: N (T/P), number of subjects in treatment and placebo groups; RR, relative

(Forlenza et al., 2010) with verbal recall noted as a partic-ularly malleable cognitive subdomain in mildly impairedelderly adults. A recent Cochrane review (Martin et al.,2011) reported that both immediate and delayed verbalrecall were successfully improved by memory training inboth healthy participants and those with CIND, and it hasbeen reported that verbal recall and attention deficits stoodout as the most significant difference between CIND pa-

-0.11 (-0.29, 0.07)

0.03 (-0.66, 0.72)

-0.36 (-1.17, 0.46)

0.64 (0.18, 1.09)

0.12 (-0.06, 0.29)

0.04 (-0.20, 0.28)

0.07 (-0.11, 0.26)

0.05 (-0.13, 0.23)

0.52 (0.03, 1.01)

0.16 (-0.65, 0.97)

0.46 (0.01, 0.91)

0.12 (-0.06, 0.29)

0.09 (-0.15, 0.33)

0.13 (0.02, 0.24)

Hedge's g (95% CI)

27.49

5.98

4.49

11.42

27.49

23.12

100.00

33.10

5.18

1.91

6.14

33.10

20.57

100.00

Weight

%

-0.11 (-0.29, 0.07)

0.03 (-0.66, 0.72)

-0.36 (-1.17, 0.46)

0.64 (0.18, 1.09)

0.12 (-0.06, 0.29)

0.04 (-0.20, 0.28)

0.07 (-0.11, 0.26)

0.05 (-0.13, 0.23)

0.52 (0.03, 1.01)

0.16 (-0.65, 0.97)

0.46 (0.01, 0.91)

0.12 (-0.06, 0.29)

0.09 (-0.15, 0.33)

0.13 (0.02, 0.24)

Hedge's g (95% CI)

27.49

5.98

4.49

11.42

27.49

23.12

100.00

33.10

5.18

1.91

6.14

33.10

20.57

100.00

Weight

%

Treatment benefit

00 1 2

verbal recall in high-functioning healthy, CIND, and AD patients. Highgnosis. Effect sizes are calculated using Hedge’s g and random effectsstics: immediate verbal recall (z � 0.75, p � 0.456, N � 883/781), delayedment, N (treatment arm of each study); Placebo, N (placebo arm of each

16 (reported as n � 32 for both arms). For interpretation of the referencesticle.

ups within the included studies

utcome Heterogeneity

CI Z p Q d.f. p I2

–1.05 0.43 0.664 13.11 8 0.108 39.0%–1.02 0.66 0.510 2.40 9 0.984 0.0%–1.01 0.27 0.789 2.19 8 0.975 0.0%

nefit

elayeds of diary statil; Treatd to n �

ebo gro

ative o

95%

0.9660.990.99

risk.


tients and healthy, age-matched controls when tested acrossseveral domains (Jacova et al., 2008). Although these find-ings may result from possible ceiling effects in the neuro-psychological assessment of healthy subjects, they may alsobe the result of possible neurobiological changes in CINDpatients.

The potential cognitive benefit of n-3 FAs in people withCIND may result from targeted modulation of neurogenesisand synaptic plasticity in brain regions that are particularlysusceptible to oxidative stress and amyloid burden. As such,the hippocampus, a region thought to govern verbal recall(Chen et al., 2010; Strange et al., 2002), is sensitive toage-associated brain atrophy in both healthy and impairedindividuals (Hackert et al., 2002; Whitwell et al., 2007).DHA, the most abundant n-3 FA in neuronal membranes(Lauritzen et al., 2001), has been shown to play an impor-tant role in this region by mediating synaptic fluidity andenhancing neurogenesis (He et al., 2009) in the subgranularzone. DHA has also been implicated in reducing inflamma-tion through fatty acid derivatives such as neuroprotectinD1 (Cole et al., 2010) and resolvin species (Kohli and Levy,2009). Despite strong preclinical evidence, the particularmechanism relevant to the clinical cognitive benefits ofDHA remains uncertain, and future work to elucidate itstherapeutic action would be informative.

To confirm the therapeutic potential of n-3 FAs in treat-ing cognitive impairment, 2 limitations within the currentliterature must be addressed. First, there is consistent epi-demiological evidence to suggest that a high level of plasmaand membrane DHA reduces the risk of cognitive decline,and as little as 180 mg/day of dietary DHA has been foundto be protective (Schaefer et al., 2006). Although all of thestudies included in this meta-analysis used doses of DHAthat exceeded this value, the results indicate that dose wasnot related to treatment effect. It is possible that the benefitfrom n-3 FA therapy is not contingent on large changes inplasma DHA but on surpassing and sustaining a thresholdDHA level. However, the lack of quantifiable baselineplasma or membrane DHA reported by these studies pre-cluded examination of this relationship in this meta-analy-sis. Perhaps more importantly, ApoE genotype was infre-quently reported in studies using healthy and CINDpatients. The ApoE-�4 is a genetic risk factor for AD and isassociated with memory impairment and a heightened riskof decline in patients without dementia (Green et al., 2009).ApoE-�4 status also appears to be a predictor of response ton-3 FA treatment. Several reports have indicated that theprotective effect of n-3 FAs intake is lost in ApoE-�4carriers (Huang, 2010) and that plasma DHA levels showlittle change in these carriers despite treatment (Plourde etal., 2009). As only 3 included studies reported ApoE geno-type, this meta-analysis was unable to explore the effect ofApoE-�4 status on n-3 FA treatment, therefore limiting the
interpretation of our findings.
This study was restricted to literature reporting neuro-psychological effects of n-3 FAs in patients without psychi-atric comorbidities and to participants aged 50 and older.Thus, inferences cannot be made about this treatment onyounger populations or those with cognitive impairment asa result of comorbid mental illness. This report was alsolimited by substantial between-studies variation with re-spect to patient groups, assessment procedures, and treat-ment formulations, necessitating the use of random effectsmodels that produced wider confidence intervals. The meth-ods used to estimate change score standard deviations mayhave resulted in underestimating the true effect size; how-ever, the present findings are supported by consistencybetween the calculated effects for each outcome and thefindings of each included study. The MMSE cutoff score of26 used to identify impairment was not adjusted for age andlevel of education in our subanalysis of high-functioningsubjects, potentially limiting these results. Most impor-tantly, this meta-analysis was limited by a lack of studiesinvestigating the effect of n-3 FA treatment on performancein specific neuropsychological domains. In fact, the poten-tial protective effect of n-3 FAs in healthy elderly adultswithout dementia was recently reviewed (Lim et al., 2006),and a lack of available relevant studies was noted. Thestudies included in this meta-analysis demonstrated a highquality of reporting and no significant risk of publicationbias. However, the lack of well-powered randomized-con-trolled trials testing n-3 FAs in CIND populations limitedour subgroup analyses to only a few RCTs.

5. Conclusions

Omega-3 fatty acid treatment was associated with asmall, but significant, benefit for immediate recall and at-tention and processing speed in subjects with CIND but notin healthy subjects or those with AD. Potential moderatorsof treatment response such as ApoE genotype and baselineplasma DHA levels could not be investigated from thecurrent literature. Nevertheless, the present findings suggestthat the effects of n-3 FAs on cognitive decline are notuniform, and that there is a need to identify potentiallyresponsive populations.

Disclosure statement

The authors declare no actual or potential conflicts ofinterest including any financial, personal, or other relation-ships with other people or organizations within three yearsof beginning the work submitted that could inappropriatelyinfluence (bias) their work.

The authors declare no conflicts of interest regardinginstitution contracts relating to this research through whichthese institutions or any other organization may stand to
gain financially now or in the future.


Acknowledgements

We acknowledge the Institute of Aging and the CIHRTraining Program in Neurodegenerative Lipidomics, theOntario Graduate Scholarship Program, and the AlzheimerSociety Research Program for their support.

The following authors contributed substantially to con-ception and design (G.M., W.S., K.L.L., N.H.), data collec-tion (G.M., S.A.C.) and analyses, and presentation of data(G.M., W.S., S.A.C., K.L.L., N.H.). All authors revised thepaper critically for important intellectual content and gavefinal approval of the version to be published.

We thank Dr. Shinto and Dr. Sinn for their correspon-dence.

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Effects of omega-3 fatty acids on cognitive performance: a meta … · Effects of omega-3 fatty acids on cognitive performance: a meta-analysis Graham Mazereeuw a,b, Krista L. Lanctôta,b,c,