Dietary and supplemental long-chain omega-3 fatty acids as moderators of cognitive impairment and Alzheimer's disease

Purpose There is an ever-growing body of literature examining the relationship between dietary omega-3 polyunsaturated fatty acids (omega 3 PUFAs) and cerebral structure and function throughout life. In light of this, the use of omega 3 PUFAs, namely, long-chain (LC) omega 3 PUFAs (i.e., eicosapentaenoic acid and docosahexaenoic acid), as a therapeutic strategy to mitigate cognitive impairment, and progression to Alzheimer's disease is an attractive prospect. This review aims to summarise evidence reported by observational studies and clinical trials that investigated the role of LC omega 3 PUFAs against cognition impairment and future risk of Alzheimer's disease. Methods Studies were identified in PubMed and Scopus using the search terms "omega-3 fatty acids", "Alzheimer's disease" and "cognition", along with common variants. Inclusion criteria included observational or randomised controlled trials (RCTs) with all participants aged >= 50 years that reported on the association between LC omega 3 PUFAs and cognitive function or biological markers indicative of cognitive function linked to Alzheimer's disease. Results Evidence from 33 studies suggests that dietary and supplemental LC omega 3 PUFAs have a protective effect against cognitive impairment. Synaptic plasticity, neuronal membrane fluidity, neuroinflammation, and changes in expression of genes linked to cognitive decline have been identified as potential targets of LC omega 3 PUFAs. The protective effects LC omega 3 PUFAs on cognitive function and reduced risk of Alzheimer's disease were supported by both observational studies and RCTs, with RCTs suggesting a more pronounced effect in individuals with early and mild cognitive impairment. Conclusion The findings of this review suggest that individuals consuming higher amounts of LC omega 3 PUFAs are less likely to develop cognitive impairment and that, as a preventative strategy against Alzheimer's disease, it is most effective when dietary LC omega 3 PUFAs are consumed prior to or in the early stages of cognitive decline.