Introduction: Alzheimer's disease (AD) is a neurodegeneration disorder characterized by progressive impairments of memory, language, reasoning, and other cognitive functions. Evidence suggests that omega-3 fatty acids may act as a possible protection factor in AD.

Objective: To evaluate the results available in the literature involving omega-3 fatty acids supplementation and its effect on cognitive function in AD patients.

Methods: A systematic review of MEDLINE (from PubMed), Excerpta Medica Database, and Cochrane Library databases was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Inclusion criteria consisted in original intervention studies, controlled by placebo, that assessed the impact of supplementation or dietary intake of omega-3 fatty acids on cognitive function, in humans with AD, without limitation for prime date of publication.

Results: Initial search resulted in 361 articles. Seven studies fully met the inclusion criteria. Most studies did not find statistically significant results for the omega-3 fatty acids supplementation compared to placebo, and those who show some benefit do it only in a few cognitive assessment scales. However, the effects of omega-3 fatty acids appear to be most effectively demonstrated in patients with very mild AD.

Conclusion: The effects of omega-3 fatty acids supplementation in mild AD corroborate epidemiological observational studies showing that omega-3 fatty acids may be beneficial in disease onset, when there is slight impairment of brain function. Although some studies have shown changes in scales of cognitive function in more severe cases, they are not enough to support omega-3 fatty acids supplementation in the treatment of AD.