Long-chain omega-3 polyunsaturated fatty acids and cognitive decline in non-demented adults: a systematic review and meta-analysis.

CONTEXT: Long-chain omega-3 polyunsaturated fatty acids (LCn-3PUFAs) are widely considered as nootropic agents that may be beneficial in reversing cognitive impairment. OBJECTIVE: The present systematic review of randomized controlled trials was conducted to determine the changes in cognitive function after intervention with LCn-3PUFA supplementation in non-demented adults, including those with mild cognitive impairment. DATA SOURCES: Five databases (MEDLINE, CINAHL, Scopus, EMBASE, and the Cochrane Library) were searched systematically along with reference lists of selected articles. STUDY SELECTION: Studies were eligible for inclusion if they measured the effect of LCn-3PUFA supplementation on cognition in non-demented adults. DATA EXTRACTION: A total of 787 records were screened, of which 25 studies were eligible for inclusion. Treatment effects were summarized as global cognitive function for primary outcome and measured using the Mini-Mental State Examination and individual cognitive domains for secondary outcome. The pooled effect sizes were estimated using Hedge's g and random-effects modeling. DATA ANALYSIS: Results from randomized controlled trials indicate that LCn-3PUFAs have no effect on global cognitive function (Hedge's g = 0.02; 95% confidence interval, -0.12 to 0.154), and among the specific cognitive domains, only memory function showed a mild benefit (Hedge's g = 0.31; P = 0.003; z = 2.945). CONCLUSION: The existing literature suggests that LCn-3PUFA supplementation could provide a mild benefit in improving memory function in non-demented older adults. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration no. CRD42017078664.