Omega-3, Omega-6, and Polyunsaturated Fat for Cognition: Systematic Review and Meta-analysis of Randomized Trials.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 32305302 · doi:10.1016/j.jamda.2020.02.022
What was done
The authors conducted a systematic review and random-effects meta-analysis of randomized controlled trials (RCTs) in adults with an intervention duration of 24 weeks or longer. They searched MEDLINE, Embase, Cochrane CENTRAL, and trial registries through December 2018. The review evaluated the effects of higher versus lower intake of omega-3, omega-6, or total polyunsaturated fats on new neurocognitive illness, new cognitive impairment, and continuous measures of cognition (including the Mini-Mental State Examination, MMSE). Risk of bias was assessed, and GRADE certainty assessments, sensitivity analyses, and subgroup analyses (dose, duration, intervention type, replacement) were performed.
What was found
Across 38 included RCTs (41 comparisons, 49,757 participants), long-chain omega-3 showed: - No or very little effect on new neurocognitive illness: RR 0.98 (95% CI 0.87 to 1.10; 6 RCTs, 33,496 participants, I² = 36%; moderate-quality evidence). - No effect on new cognitive impairment: RR 0.99 (95% CI 0.92 to 1.06; 5 RCTs, 33,296 participants, I² = 0%; moderate-quality evidence). - Negligible difference in global cognition via MMSE: MD 0.10 points (95% CI 0.03 to 0.16; 13 RCTs, 14,851 participants, I² = 0%; moderate-quality evidence). Results did not differ in sensitivity analyses or across subgroups by dose, duration, intervention type, or replacement. Effects of increasing alpha-linolenic acid, omega-6, or total PUFA remained unclear.
Why it matters
Despite widespread use of omega-3 supplements by older adults to protect brain health, this comprehensive meta-analysis of randomized trials shows they provide no meaningful protection against cognitive decline or neurocognitive disorders.
Limits
The effects of alpha-linolenic acid, omega-6, and total PUFA intake could not be clearly resolved from the available evidence. Trials shorter than 24 weeks were excluded, and continuous cognitive outcomes were largely assessed via MMSE rather than detailed neuropsychological test batteries.
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