Omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been investigated for their potential role in supporting brain health and treating dementia, including Alzheimer's disease. The scientific rationale is based on the fact that DHA is a major component of neuronal cell membranes and is important for cognitive function. Epidemiological studies have suggested that populations with higher dietary intake of omega-3 fatty acids, particularly from fish, tend to have lower rates of cognitive decline and dementia.

However, randomized controlled trials (RCTs) and meta-analyses on omega-3 supplementation in individuals with dementia or mild cognitive impairment have yielded mixed results. Some studies have shown modest benefits in slowing cognitive decline, particularly in people with mild symptoms or those not yet diagnosed with dementia, while others have shown no significant effect. For example, a 2020 Cochrane review concluded that omega-3 supplementation does not consistently improve cognitive function in people with dementia. The evidence is somewhat stronger for prevention or very early intervention, but not for established disease.

Overall, while there is a scientific basis for investigating omega-3s in dementia and some supportive epidemiological data, high-quality clinical evidence for their effectiveness as a treatment for established dementia is limited. Thus, the use is justified based on scientific inquiry, but the strength of the evidence is moderate to low.