DFA: EPA/DHA and Cognitive Health (2011)
The purpose of the review is to report findings from recent epidemiologic and experimental studies regarding the potential role of omega-3 fatty acids (n-3) in the prevention and treatment of cognitive decline and Alzheimer's disease.
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Article search procedures
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Assessment of study quality
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Types of interventions and outcomes investigated
- Observational studies measured:
- Relationship between n-3 FA plasma concentrations and incident dementia or cognitive status, relationship between erythrocyte membrane EPA/DHA levels and incident dementia or Alzheimers disease
- Relationships between fish or seafood intake and incidence of Alzheimers disease, risk of incident dementia, risk of dementia, verbal learning or cognition
- Intervention studies investigated:
- Effects of EPA/DHA supplement vs. placebo over 26 weeks on cognition and attention
- Effect on Neuropsychiatric Inventory, Montgomery-Asbergs Depression Scale, Care Givers Burden or activities of daily living
- Effects of n-3 treatment on neuroinflammation in Alzheimer's disease patients
- Effects of n-3 FA supplementation on clinicians' interview-based impression of change scale in Alzheimer's disease patients
- Experimental studies included discussion of docosahexaenoic acid metabolites, amyloid peptide generation, and signal transduction mechanisms.
Populations included
Studies reviewed focused on older adults, including those that were demented, non-demented, and had Alzheimer's disease (including mildest form).
The results of each reviewed study was described. Articles were grouped into one of three categories for description, epidemiological observational studies, intervention studies or experimental studies. Analytical methods were not used in this review.
Observational studies
13 were included in the review (six with dietary recall and seven with biochemical indicators for assessment of n-3 FA levels)
- Studies with biochemical indicators included older persons; non-demented, demented and those with Alzheimers disease; sample sizes of 1,214, 663, 2,251, 120, 935 and one "smaller group" plasma n-3 concentrations or erythrocyte membrane n-3 FA concentrations were measured
- Dietary recall studies: Included older persons (>65, >55, and "older individuals," 70-79 years and 70-74 years; sample sizes of 8,000, 5,000, 210, 1,500, 867 and 2,031; fish or seafood intake or EPA/DHA intake were measured.
Intervention studies
Five were included in the review. Studies included the following characteristics:
- Sample sizes: 302, 46, samples sizes for other studies were not reported
- >65 years old (MMSE more than 21); ages for other studies were not reported
- Healthy adults, mildest form or Alzheimer's disease, APOEepsion4 carriers vs. non-carriers, or Alzheimer's disease patients.
Experimental studies
The discussion of these studies included findings related to docosahexaenoic acid metabolites, amyloid peptide generation and signal transduction mechanism.
The number of of articles identified for possible inclusion in the review was not described.
Key Findings
Observational studies
Results are conflicting among these studies, but most show beneficial effects of n-3 FA on cognition.
Experimental studies
EPA and DHA may potentially have ameliorating effects on amyloid fragment formation, signal transduction and angiogenesis. Metabolites of EPA and DHA may have a role in Alzheimer's disease pathology. This is under investigation.
Intervention studies
One reported positive effects of supplementation, while two did not. However, post hoc analysis indicated that selected individuals with mild forms of Alzheimer's disease or cognitive decline may respond to treatment.
Other Findings
The evidence for use of n-3 FAs in the prevention and treatment of dementia, cognitive decline and Alzheimer's disease is still unclear. The author lists several factors that suggest that DHA, especially, may impact cognitive performance and indicates that DHA or fish intake may be a beneficial preventive option at the population level. Also, it may emerge as a adjuvant therapy option in selected cases of early Alzheimer's disease.
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Quality Criteria Checklist: Review Articles
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| Relevance Questions | |||
| 1. | Will the answer if true, have a direct bearing on the health of patients? | Yes | |
| 2. | Is the outcome or topic something that patients/clients/population groups would care about? | Yes | |
| 3. | Is the problem addressed in the review one that is relevant to dietetics practice? | Yes | |
| 4. | Will the information, if true, require a change in practice? | Yes | |
| Validity Questions | |||
| 1. | Was the question for the review clearly focused and appropriate? | Yes | |
| 2. | Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? | No | |
| 3. | Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? | No | |
| 4. | Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? | No | |
| 5. | Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? | Yes | |
| 6. | Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? | No | |
| 7. | Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? | No | |
| 8. | Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? | Yes | |
| 9. | Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? | No | |
| 10. | Was bias due to the review's funding or sponsorship unlikely? | ??? | |