New benefits of oily fish consumption in people at risk of developing Alzheimer's disease discovered

Researchers at the Pasqual Maragall Foundation's research centre, the Barcelonaβeta Brain Research Center (BBRC), with the support of the "la Caixa" Foundation, have led one of the largest studies carried out to date on the possible benefits of omega-3 fatty acid intake in people carrying the genotype that confers a higher risk of developing Alzheimer's disease: APOE ε4 / 4. The research concludes that people in this at-risk group who consume more docosahexaenoic acid (DHA), a nutrient provided by oily fish, have greater cortical preservation in areas of the brain specifically affected in Alzheimer's disease and fewer microbleeds.

"To the benefits that we already knew that consumption of oily fish has on cardiovascular health, we can now add that it provides greater brain resilience in Alzheimer's disease in those people with a higher genetic risk of developing it," explains Dr. Aleix Sala, first author of the research, a specialist in nutrition and researcher at the BBRC. This study, adds Sala, "opens up the possibility of improving the design of dietary interventions with DHA supplementation, focusing especially on people at higher risk of developing Alzheimer's disease".

The study has been published in The American Journal of Clinical Nutrition, and has also involved researchers from the Hospital del Mar Medical Research Institute; the CIBER on Fragility and Healthy Ageing (CIBER-FES); the CIBER on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN); the VU University Medical Center in Amsterdam; and the Aiginition Hospital in Athens.

Omega-3s are a family of fatty acids that have a distinctive chemical structural feature and are naturally present in certain foods of animal and plant origin. The type of fatty acid analysed in this study is DHA, which is mainly found in oily fish: tuna, sardines, salmon, anchovies, etc. This fatty acid is very abundant in the brain, is key to cognitive function, begins to accumulate from the third trimester of gestation, and has been shown to be less present in the brains of people with Alzheimer's disease.

Humans are able to "manufacture" this acid in our bodies, but we do so very inefficiently. The best way to ensure adequate levels of DHA is through the intake of oily fish, as the omega-3 acids we get from vegetables such as walnuts and soya are of a different type.

The research involved a sample of 340 participants aged between 45 and 75, with no cognitive alterations, from the Alfa Study of the BBRC, promoted by the "la Caixa" Foundation. These people came to the Pasqual Maragall Foundation's facilities to undergo clinical, cognition and neuroimaging tests, and to answer questionnaires on lifestyle habits, among others.

One of these questionnaires asked about the consumption of 166 foods, which are the ones that have made it possible to quantify the regular intake of DHA. From the participants' responses, the researchers looked for associations between reported DHA intake, cognition, the presence of brain microbleeds and cortical thickness in brain regions that atrophy in Alzheimer's disease, also taking into account the APOE genotype of each participant.
The APOE gene is present in all people and can occur as a result of a combination of the Ɛ2, Ɛ3 and Ɛ4 alleles. In the case of Alzheimer's disease, individuals with two Ɛ4 alleles have the highest risk of developing the disease.

Once the analyses were done, the researchers did not observe any relationship between DHA intake and cognition, but detected the findings described in the brain structure. As Dr Juan Domingo Gispert, head of the Neuroimaging group at the BBRC, points out, "the results of this study are in line with others that show that people with a higher genetic risk of developing Alzheimer's are precisely those who benefit most from a healthy lifestyle, in this case, with regard to diet".

Currently, there are no routine tests to determine a person's genetic predisposition to develop Alzheimer's disease, as there is no clinical benefit in revealing this information. There is still no treatment available to stop or prevent Alzheimer's, there are multiple risk factors that contribute to its development and, in no case, being a carrier of this genotype determines that one will have the disease in the future.

Therefore, apart from the personal genetic load, Dr Sala stresses that "although our findings between oily fish and Alzheimer's disease affect only part of the population, we must continue to recommend regular consumption (two portions per week) of salmon, sardines or anchovies, among others, as they provide cardiovascular benefits to everyone".

The next step for the BBRC researchers will be to analyse biomarkers of consumption of up to 20 types of fatty acids in a larger population of Alpha Study participants, and to study their possible relationship with other biomarkers of Alzheimer's disease detected in blood, cerebrospinal fluid and through various tracers in Positron Emission Tomography (PET) scans.