DFA: EPA/DHA and Cognitive Health (2011)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the associations between blood levels of the essential (n-3) PUFA-ALA, EPA, and DHA and major dimensions of cognitive function in 280 healthy persons in middle adulthood not taking fish oil supplements.

Inclusion Criteria:
  • Participants were required to speak English as their primary language for the past five years
  • The participants were from a subset of the original Adult Health  and Behavior (AHAB) project who enrolled in supplemental data collections that included the serum fatty acid analysis.
Exclusion Criteria:

This study was part of the University of Pittsburgh Adult Health and Behavior (UPAHB) project which excluded:

  • Subjects with reported history of atherosclerotic cardiovascular disease, chronic kidney or liver disease, cancer treatment in the preceding year, major neurological disorders, schizophrenia or other psychotic illness and, in women, current pregnancy or perimenopausal menstrual irregularities
  • Subjects with diabetes; severe hypertension (blood pressure 180/100mm Hg or higher); severe obesity (BMI 40kg/m2 or higher); renal insufficiency (serum creatinine higher than 160µmol per L); excessive alcohol intake (higher than 260g alcohol per week); and use of fish oil supplements or antihypertensive, diabetic, lipid-lowering, antiarrhythmic, glucocorticoid, weight-loss and psychotropic medications.
Description of Study Protocol:


Subjects were recruited via mass e-mail solicitation from communities of southwestern Pennsylvania (primarily Allegheny County).


Subjects completed a series of psychosocial, lifestyle and demographic  questionnaires, and a project nurse conducted a medical history and medication use interview and measured several standard risk factors, including BP and BMI (kg/m2). A morning blood sample was obtained after an overnight fast. All these procedures were completed on the same day.

Statistical Analysis

  • All statistical analyses were performed using SPSS v15. Digit completion time, DHA, and EPA were log-transformed to better approximate a normal distribution. Two-step multiple regression analysis was used to examine the relationships between blood levels of fatty acids and aspects of cognitive functioning. Standard covariates of age, gender and race were entered in step one, and each fatty acid variable of interest was entered in step two. Dependent measures were the performance scores on each of the neuropsychological tests. Composite measures (based on the mean of standardized scores) were generated for general memory and working memory according to the WMS-3 guidelines. Other test scores were not combined, as each test has unique features and scores were not highly correlated with one another (Pearson R2<0.20 for all).
  • Potential interactions between fatty acid variables and both gender and age were tested in these linear regression models. Independent variables were mean-centered and the interaction variables were calculated as the product of two variables of interest and then added to the model for analysis. Potential non-linear associations between the fatty acid levels and cognitive functioning were examined by regressing each cognitive variable on a non-linear function of the fatty acid variables. These functions were generated by transforming the raw fatty acid variables into logarithmic, quadratic, cubic and square root predictor variables. Significance was defined as P≤0.05.
Data Collection Summary:

Timing of Measurements

All data collection including psychosocial, lifestyle and demographic questionnaires; medical history and medication use interview; measured standard risk factors (blood pressure and BMI); morning blood sample; and neuropsychological testing were completed on the same day. 

Dependent Variables

  • Health literacy (vocabulary score)
  • Cognitive functioning (non-verbal reasoning and mental flexibility, attention and concentration, general memory, working memory, verbal knowledge and processing)
  • Blood pressure.

Independent Variables

Fasting serum eicosapentaenoic acid (EPA), docosahexaenonic acid (DHA) and α-linoleic acid (ALA) (percentage total fatty acid pool, mol%).

Control Variables

  • Age
  • Gender
  • Race.
Description of Actual Data Sample:
  • Initial N: 308 were enrolled in supplementary data collection that included serum fatty acid analysis. A total of 283 met the additional exclusion criteria and also had a stored fasting serum sample available for fatty acid analysis.
  • Attrition (final N): Three of the 283 serum samples produced undetectable chromatogram peaks, leaving 280 subjects.
  • Age: 44.6±6.7 years
  • Ethnicity: 89% white
  • Other relevant demographics: 48% male
  • Location: Southwestern Pennsylvania, primarily Allegheny County.
Summary of Results:

Key Findings

  • Higher DHA (mol percentage) was related to better performance on tests of non-verbal reasoning and mental flexibility, working memory and vocabulary (P≤0.05)
  • Neither EPA nor ALA was notably related to any of the five tested dimensions of cognitive performance
  • Among the n-3 PUFA, only DHA was associated with major aspects of cognitive performance in non-patient adults less than 55 years old, suggesting that DHA is related to brain health throughout the lifespan and may have implications for clinical trials of neuropsychiatric disorders
  • Blood pressure may confound or mediate these associations as higher BP is linked to cognitive dysfunction and dietary intake of n-3 fatty acids can lower BP. Diastolic BP correlated inversely with matrix reasoning, digit vigilance, general memory and verbal fluency (R=-0.14 to -0.20, P<0.05)
  • Better educated individuals may, through greater health literacy, choose to  eat fish more frequently than other persons as demonstrated with a positive association between DHA and vocabulary score.

Standardized β from Linear Regression Models of Serum Phospholipid Fatty Acids and Cognitive Function Test Scores in Middle-aged Adults

  DHA    EPA    ALA   
   β1 P β β
Non-verbal reasoning and mental flexibility      
Matrix reasoning  0.202  <0.001  0.072  0.22  -0.085  0.15 
Trail making2 0.116  0.043 0.042 0.47  -0.94  0.10 
Attention and concentration       
Stroop interference  0.039  0.52  0.016  0.80  0.001  0.99 
Digit vigilance2 0.079  0.17  0.089  0.13  0.087  0.13 
General Memory       
Composite 0.080  0.17  0.032  0.58  0.090  0.12 
Logical memory  0.122  0.035  0.035  0.56  0.082  0.16 
Verbal paired associates  0.101  0.091  0.035  0.57  -0.084  0.12 
 Faces 0.041  0.49  0.025  0.68  0.074  0.21 
 Family -0.011  0.85  -0.0028  0.64  0.094  0.11 
Working memory       
Composite 0.163  0.005  0.113  0.054  -0.020  0.73 
Letter-number sequencing  0.137  0.019  0.041 0.48  -0.059  0.32 
Spatial span  0.144  0.010  0.124  0.038  -0.006  0.92 
Forward digit span  0.092  0.12  0.034  0.58  0.008  0.90 
Backward digit span  0.177  0.002  0.146  0.014  -0.006  0.93 
Verbal knowledge and processing       
Vocabulary 0.169  0.002  0.056  0.32  -0.020  0.72 
Verbal fluency  0.073  0.22  0.003  0.97  0.019  0.75 

1 All associations were adjusted for age, gender and race.

2 The signs of the coefficients for trail making and digit vigilance were reversed to be consistent with  other tests such that higher scores always indicate better performance. 

Author Conclusion:

DHA may be the n-3 fatty acid most closely related to cognitive function and this finding is consonant with some prior work on cognitive aging and dementia. The null findings for ALA suggest that intake of this precursor to EPA and DHA may not have important effects on cognitive functioning.

Funding Source:
Government: US NIH Grants PO1 40962 and T32 HL007560
Reviewer Comments:

Cross-sectional design cannot establish any association between the n-3 fatty acids on cognitive performance is causal.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) No
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) No
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? N/A
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes