Abstract
Objectives: Neurocognitive function may be influenced by polyunsaturated fat intake. Many older adults consume omega-3 supplements hoping to prevent cognitive decline. We assessed effects of increasing omega-3, omega-6, or total polyunsaturated fats on new neurocognitive illness and cognition. Design and inclusion criteria: We carried out a systematic review and meta-analysis of randomized controlled trials (RCTs) in adults, with duration _24 weeks, assessing effects of higher vs lower omega-3, omega-6, or total polyunsaturated fats and outcomes: new neurocognitive illness, newly impaired cognition, and/or continuous measures of cognition. Methods: We searched MEDLINE, Embase, Cochrane CENTRAL, and trials registers (final update of ongoing trials December 2018). We duplicated screening, data extraction, and risk of bias assessment. Neurocognitive measures were grouped to enable random effects meta-analysis. GRADE assessment, sensitivity analyses, and subgrouping by dose, duration, type of intervention, and replacement were used to interrogate our findings. Results: Searches generated 37,810 hits, from which we included 38 RCTs (41 comparisons, 49,757 participants).
Meta-analysis suggested no or very little effect of long-chain omega-3 on new neurocognitive illness [risk ratio (RR) 0.98, 95% confidence interval (CI) 0.87-1.10, 6 RCTs, 33,496 participants, I2 36%), new cognitive impairment (RR 0.99, 95% CI 0.92-1.06, 5 RCTs, 33,296 participants, I2 0%) or global cognition assessed using the Mini-Mental State Examination (MD 0.10, 95% CI 0.03-0.16, 13 RCTs, 14,851 participants, I2 0%), all moderate-quality evidence. Effects did not differ with sensitivity analyses, and we found no differential effects by dose, duration, intervention type, or replacement. Effects of increasing a-linolenic acid, omega-6, or total PUFA were unclear. Conclusions: This extensive trial data set enabled assessment of effects on neurocognitive illness and cognitive decline not previously adequately assessed. Long-chain omega-3 probably has little or no effect on new neurocognitive outcomes or cognitive impairment. Implications: Long-chain omega-3 supplements do not help older adults protect against cognitive decline.
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Key Points
A 2012 Cochrane review assessed effects of long-chain omega-3 fats on neurocognition and found no trials of incident dementia and included 3 RCTs assessing effects on cognition. This review aimed to systematically review effects of higher vs lower intakes of LCn3, ALA, omega-6, and total polyunsaturated fatty acids (PUFAs) on new neurocognitive outcomes, new impaired cognition, and cognitive function in randomized controlled trials (RCTs) of at least 6 months’ duration.
The results showed that increasing LCn3 probably has little or no effect on new neurocognitive outcomes, new impaired cognition, global cognition, executive function, processing speed, or memory. Increasing ALA may have little or no effect on global cognition, but no RCTs of ALA reporting other neurocognitive outcomes were found. The effects of increasing omega-6 or total PUFA on new neurocognitive outcomes, cognitive decline and global cognition, executive function, processing speed, or memory are unclear. The review found moderate-quality evidence of little or no effect of LCn3 on neurocognitive outcomes or cognitive ability. We found neither benefits nor harms, and low-quality evidence of little or no effect of ALA on global cognition. Methodologically strong and long-duration trials of increased oily fish intake, nuts and foods high in ALA, and increased omega-6 and total PUFA intake are needed to further inform dietary advice for cognition.