DHA and Adult Memory: Insights from a Systematic Review and Meta-Analysis

Docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid, is a fundamental component of neural membranes and plays a significant role in brain function. While its contribution to early cognitive development is well established, this systematic review and meta-analysis investigates DHA’s impact on memory in healthy adults aged 18 and older, with or without mild memory complaints (MMC).

Objectives

The study aimed to evaluate the effects of DHA, alone or in combination with eicosapentaenoic acid (EPA), on three specific types of memory:

• Episodic memory
• Working memory
• Semantic memory

A secondary objective included reviewing observational studies linking DHA/EPA status to memory performance.

Key Findings

Improvements in Episodic Memory

• DHA/EPA supplementation significantly improved episodic memory in adults with mild memory complaints.
• A daily dose above 1 gram of combined DHA/EPA improved episodic memory across populations, regardless of baseline cognitive status.
• Immediate recall—a component of episodic memory—showed notable gains with supplementation in individuals with mild cognitive symptoms.

Semantic and Working Memory

• No significant differences were found in semantic or working memory between groups receiving DHA/EPA and those on placebo.
• However, within-group analyses (pre- vs post-supplementation) revealed improvements in both memory domains, particularly among adults over 45 and those consuming over 1 gram per day of DHA/EPA.

Observational Evidence

• Observational studies supported the link between higher DHA/EPA blood levels or dietary intake and improved memory in older adults.
• These benefits extended to various memory types and were observed across different study populations, including APOE ε4 carriers.

Dose-Response Insights

• The most reliable improvements in memory occurred in studies where DHA intake ranged between 501–999 mg per day.
• While doses above 1 gram per day also showed benefits, data was more limited in this range.

Methodological Strengths

• This meta-analysis uniquely categorized memory outcomes into distinct domains rather than aggregating them into general cognitive scores.
• It included both randomized controlled trials and a systematic review of observational studies.
• Data were drawn from 15 intervention studies and 13 observational cohorts, mostly involving adults over 45 years old.

Limitations

• A few studies included were rated as having a high risk of bias.
• Definitions and tests for memory categories varied slightly across studies.
• Some participants may have had undiagnosed cognitive decline, despite being classified as healthy.

Conclusion

DHA supplementation, particularly in combination with EPA, is associated with improved episodic memory in adults experiencing mild memory complaints. While findings for semantic and working memory were less consistent in controlled trials, within-group improvements suggest potential long-term cognitive benefits.

These results reinforce the value of DHA and EPA in supporting cognitive health, especially in aging populations. Further long-term research is recommended to explore effects on broader memory domains and across more diverse age groups.

Reference:
Yurko-Mauro K, Alexander DD, Van Elswyk ME (2015). Docosahexaenoic Acid and Adult Memory: A Systematic Review and Meta-Analysis. PLoS ONE 10(3): e0120391 (https://doi.org/10.1371/journal.pone.0120391).