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DFA: EPA/DHA and Cognitive Health (2011)

Citation:

van Gelder BM, Tijhuis M, Kalmijn S, Kromhout D. Fish consumption, n-3 fatty acids, and subsequent five-year cognitive decline in elderly men: The Zutphen Elderly Study. Am J Clin Nutr. 2007 Apr; 85(4): 1,142-1,147.

PubMed ID: 17413117
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the association between fish consumption, the intake of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish and other foods and subsequent five-year cognitive decline.

Inclusion Criteria:

Participant in the Zutphen Elderly Study, a prospective cohort study of men born between 1900 and 1920 who lived in Zutphen, Netherlands.

Exclusion Criteria:

Because poor health status at baseline may influence both cognitive function and food consumption, the investigators selected men without myocardial infarction, stroke, diabetes or cancer at baseline.

Description of Study Protocol:

Recruitment

  • Participant in the Zutphen Elderly Study
  • No information was given on recruitment for the overall study.

Design

  • Original and overall study: Prospective cohort
  • Cross-sectional analysis of data from the cohort. 

Intervention

Comparison groups were based on fish consumption (zero, more than zero to 20 or more than 20g per day) or EPA plus DHA intake (zero to 56, more than 56 to 148 and more than 148mg per day).

Statistical Analysis

  • Differences in baseline variables among different categories of fish consumers were evaluated by using the Kruskal-Wallis test for skewed variables, and analysis of variance was used for normally distributed continuous variables
  • Categorical data were tested for differences with the chi-square test
  • EPA plus DHA intake is highly correlated (Spearman correlation coefficient: 0.88); therefore, the investigators used the sum of EPA and DHA in the analyses
  • To investigate fish consumption as well as the intake of EPA plus DHA in 1990 in relation to cognitive functioning and cognitive decline, different multivariate linear regression models were used
  • Fish consumption (yes or no and classes of zero, more than zero to 20 and more than 20g per day) and the intake of EPA plus DHA (in tertiles of zero to 56, more than 56 to 148 and more than 148mg per day) in 1990 were entered as class variables into the model, and the outcome variables baseline cognitive functioning and five-year cognitive decline (MMSE 1995 to MMSE 1990), which were used singly in the different analyses, were treated as continuous variables
  • Dose-response relations were tested for trend by using a linear regression model
  • Adjustments were made for confounding factors
  • In longitudinal analyses, the investigators adjusted for baseline cognitive functioning because the level of baseline cognitive functioning may influence cognitive decline
  • Additional adjustments were made for dietary antioxidants on the assumption that fish consumers are more likely than fish non-consumers to follow a healthy diet rich in fruit and vegetables
  • Adjustments were also made for depressive symptoms
  • To reduce reporting bias due to impaired cognitive functioning, participants with an MMSE score less than 24 (impaired cognition) in 1990 were excluded
  • A two-sided P-value≤0.05 was considered significant. 
Data Collection Summary:

Timing of Measurements

1990 and 1995.

Dependent Variables

  • MMSE score: Mini-Mental State Examination used to assess global cognitive functioning; includes questions on orientation to time and place, registration, attention and calculation, recall, language and visual construction. The maximum score is 30 points, with a higher score indicating better cognitive functioning.
  • Five-year cognitive decline: MMSE 1995 to MMSE 1990.

Independent Variables

  • Fish consumption: Cross-check dietary history method; dietitians interviewed the participants in their homes with respect to usual food-consumption patterns. A checklist providing information on the frequencies and quantities of foods consumed during the previous two to four weeks was used to verify the participants' food-consumption patterns. Total fish consumption per day was calculated by adding the amount of different types of fish, with zero, more than zero to 20 and more than 20g per day
  • EPA plus DHA intake: Recently available data on the content of these fatty acids in fish and seafood, but also in other animal foods (eggs and meat) and in plant foods were used to calculate this, with zero to 56, more than 56 to 148 and more than 148mg per day.

Control Variables

  • Age
  • Education
  • Energy intake
  • Alcohol consumption
  • Smoking status
  • Physical activity
  • Dietary antioxidants
  • Trans fatty acid intake
  • Depressive symptoms. 
Description of Actual Data Sample:

Initial N

  • All-male study
  • In 1985, 939 men were recruited for original study.

Attrition (final N)

  • In 1990, 556 men were followed up (response rate: 77%)
  • In 1995, 307 men were followed up
  • After exclusion criteria, 228 men were included
  • Information on possible confounding factors was available for 210 men.

Age

  • 1990: 70 to 89 years
  • 1995: 75 to 94 years.

Other relevant demographics

By fish consumption:

  • Education (years) (P=0.04):
    • 0g per day: 9.6±3.3
    • More than zero to 20g per day: 11.1±4.2
    • More than 20g per day: 11.5±4.7
  • Physical activity (minutes per week):
    • 0g per day: 570.8±358.2
    • More than zero to 20 g per day: 696.4±668.1
    • More than 20g per day: 541.4±337.2
  • Alcohol consumers (percentage):
    • 0g per day: 71
    • More than zero to 20g per day: 78
    • More than 20g per day: 85
  • Current smokers (%):
    • 0g per day: Nine
    • More than zero to 20g per day: 24
    • More than 20g per day: 18
  • Depressive symptoms (percentage):
    • 0g per day: Six
    • More than zero to 20g per day: One
    • More than 20g per day: One
  • PUFA intake (g):
    • 0g per day: 15.7±8.5
    • More than zero to 20g per day: 16.4±9.5
    • More than 20g per day: 18.2±9.0
  • EPA and DHA (mg) (P<0.001):
    • 0g per day: 14.7±11.1
    • More than zero to 20g per day: 126.1±103.0
    • More than 20g per day: 346.8±291.0
  • No differences in intake of vitamins C and E and beta-carotene.

Location

Zutphen, Netherlands.

Summary of Results:

 Key Findings

  • In 1990, 24% of the participants did not consume fish, 41% consumed between more than zero and 20g fish per day and 35% consumed more than 20g fish per day
  • Fish consumption consisted of lean fish (67%; raw lean fish contains less than 12g fat), fatty fish (32%; raw fatty fish contains 12g or more of fat) and crustacean and shellfish (1%)
  • Men who did not consume fish had an average EPA plus DHA intake of 15mg per day because of the small amounts of these fatty acids in animal foods other than fish and in plant foods
  • Cognitive functioning in 1990 did not differ between those who consumed or did not consume fish in 1990, after adjustment for age, education, alcohol consumption, smoking status, physical activity and energy intake, nor did it differ among the categories of fish consumers
  • Men who did not consume fish had a subsequent cognitive decline of 1.2 points, which was four times the decline in men who consumed fish (P=0.01)
  • The decline in cognitive functioning was 1.0 point stronger in men who did not consume fish than in those who did consume fish. (Reviewer note: These two sentences seem the same and it is somewhat difficult to match them to the data in Table 2.)
  • No differences in cognitive functioning were found in 1990 among the tertiles of EPA plus DHA intake. However, a dose-response relation was noted between tertiles of EPA plus DHA intake and five-year cognitive decline (P=0.01). The difference in cognitive decline between the highest and lowest tertiles of EPA plus DHA intake was 1.1 points (-0.9, -0.7, 0.2, lowest to highest tertile).
  • Adjustments for trans fatty acid and antioxidant intakes did not attenuate results. 

Other Findings

Decrease in participants in 1995 was due to death before 1995, did not respond in 1995, poor health status or missing values in 1990. These men overall were older, had fewer years of education, had lower baseline cognitive test scores, were less physically active and had a lower percentage of alcohol users than did the men who participated. They also had lower fish consumption and EPA plus DHA intake in 1990 than did men who participated in the study (data was not shown in article).

Author Conclusion:

Limitations as cited by authors:

  • Selection bias due to death and non-response could have influenced the results. However, that bias would probably have led only to an under-estimation of the strength of the associations, because the men who dropped out of the current study consumed less fish and had a lower intake of EPA plus DHA and lower cognitive test scores
  • Bias due to cognitive impairment in 1990 could have influenced our results, because men with an impaired cognition could have changed their dietary habits or they may have given imprecise information about their actual food consumption. By excluding those with MMSE score less than 24, differential mis-classification was not a major problem in the study
  • Cannot exclude residual confounding by risk factors that were not measured
  • A moderate intake of EPA plus DHA may postpone cognitive decline in elderly men
  • Results from other studies are needed before definite conclusions about this association can be drawn.
Funding Source:
Government: Grant from European Union for the Healthy Ageing: Longitudinal Study in Europe
Reviewer Comments:
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? ???
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) N/A
  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.) Yes
  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.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  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%.) Yes
  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? N/A
5. Was blinding used to prevent introduction of bias? No
  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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? N/A
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? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
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? Yes
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? No
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