the risk of developing it would be cut in half with a high level of omega-3 DHA

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Omega-3s have a very good reputation in the medical world. Natural constituents of certain fats, they are said to be polyunsaturated due to their chemical structure, and essential because the human body cannot produce them. Therefore, they come exclusively from the diet, as do certain minerals and vitamins. For decades, they have been the subject of studies revealing their multiple roles in maintaining our health. Recently, American researchers showed that people with high levels of DHA (a type of omega-3) in their blood are 49% less likely to develop Alzheimer’s disease than those with lower levels. This discovery could revolutionize public health policy, through early prevention of Alzheimer’s risk and potentially save billions in health care costs.

Omega-3s are used in the composition of certain vegetable oils and certain so-called “fatty” fish, but these sources are not equivalent. Plant products provide omega-3 alpha-linolenic acid (ALA). For their part, “fatty” fish (sardines, trout, mackerel, salmon, etc.) provide omega-3 EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Theoretically, we could only supply ALA to the body, supposedly converting it to EPA and DHA. However, the conversion rate of ALA to DHA is too low to cover our daily needs, DHA is considered essential, it must be provided by food.

Evidence continues to mount that dietary factors may influence the risk of Alzheimer’s disease. More specifically, DHA is enriched in membrane phospholipids of the central nervous system and therefore plays an important role in mental and visual functions, especially in infants and the elderly. That is why scientists have long suggested that it has a positive effect on maintaining mental health (depression, dementia, including Alzheimer’s disease).

Thus, recently, a team from the Fatty Acid Research Institute (FARI), led by Aleix Sala-Vila, became interested in this omega-3 and its link to Alzheimer’s disease. The authors found that supplemental dietary intake of omega-3 DHA could, on the one hand, delay the development of the disease and, on the other hand, reduce the risk of developing it by almost half. This new study is published in the journal nutrients.

Blue fish against Alzheimer’s

To test their hypothesis, the researchers conducted a prospective observational study, within the Framingham Offspring Cohort, that included 1,490 participants without dementia, older than 65 years, for an average duration of 7 years. They looked at the association of red blood cell docosahexaenoic acid (DHA) with the onset of Alzheimer’s disease, while testing for an interaction with allele 4 of the APOE gene, which encodes a protein that helps transport cholesterol in the blood.

This study is based on the previous work of Aleix Sala-Vila, published in The American Journal of Clinical Nutrition, in 2021. In fact, he and his colleagues found that omega-3 levels in the erythrocytes (or red blood cells) of the blood are very good predictors of mortality risk. Given the marginal synthesis de novo of DHA, measurement of circulating or tissue levels of DHA is a valid biomarker of dietary DHA intake, circumventing the uncertainties of self-reported dietary data.

Furthermore, Aleix Sala-Vila adds in a press release: “ Having higher levels of these acids in the blood, as a result of the regular inclusion of oily fish in the diet, increases life expectancy by almost five years. “.

In the current study, the team found that the risk of developing Alzheimer’s disease with a high level of DHA in the blood (6.1%) was 49% lower compared to a lower level (3.8%). ). In addition, the authors estimated that an increase in red blood cell DHA from the first to fifth trimesters of the study provided approximately 4.7 additional years of life free of Alzheimer’s disease. This last conclusion confirms that of 2021.

Infographic summarizing the main conclusion of the study on a higher intake of omega-3 DHA and a lower risk of developing Alzheimer’s disease. © A. Sala-Vila et al., 2022

Omega-3 against genetic risk factors

As a result, the authors established a definitive link between a genetic factor, DHA, and the risk of Alzheimer’s disease. It is important to specify first of all that the vast majority of cases of Alzheimer’s disease correspond to patients for whom there is a multifactorial determinism, even among the early forms. The genetic part of this determinism is important and is represented by different risk factors. The first and foremost of these factors is allele 4 of the APOE gene (APOE4), which encodes apolipoprotein E, which helps transport cholesterol in the blood.

The APOE gene exists in three “forms” called alleles E2, E3 (the most common), and E4. While carriers of the E2 allele have a lower risk of developing Alzheimer’s disease, carriers of at least one E4 allele have a higher risk. The importance of this factor is therefore greater, both due to the strength of the associated risk and its high frequency. In fact, nearly 10% of carriers of one APOE4 allele who have reached the age of 75 develop the disease, compared with 33% of homozygous carriers—carrying the same allele twice—APOE4/E4 for the same age. At the age of 85 years, these figures increase to almost 30% and 70%, respectively, for heterozygotes, carriers of two different alleles, APOE3/E4, and for homozygotes APOE4/E4. In the general Caucasian population older than 54 years, the proportion of carriers of an APOE4 allele is 24% and APOE4/E4 homozygotes is 2%. The importance of this genetic risk factor for affected individuals, but also for the general population, justifies research programs in therapeutic prevention.

omega 3 influence dementia
Graphs showing the influence of blood DHA levels for Alzheimer’s disease (a) and all-cause dementia (b), and according to the absence (c) or presence (d) of APOE4. The higher the value of DHA, the lower the incidence of the disease. © A. Sala-Vila et al., 2022 (modified by Laurie Henry for Trust My Science)

As a result, the researchers noticed that a greater DHA intake can reduce the risk of developing Alzheimer’s disease, particularly in people carrying the APOE4 allele, suggesting that they can benefit more than higher levels of DH than non -carriers.

This discovery, which is consistent with a growing experimental research base, changes the perspective of public health and prevention, as well as health care costs. The authors conclude in the study: Since the estimated health spending in 2021 for all patients with Alzheimer’s disease or other forms of dementia is 355 billion dollars in the United States (not including care provided by family members and other unpaid caregivers), any profitable strategy to delay the onset of Alzheimer’s disease is of great interest to public health “. They add: “ Delaying Alzheimer’s disease by 5 years leads to an additional 2.7 years of life and an additional 4.8 years without Alzheimer’s disease, knowing that an individual who would have contracted Alzheimer’s disease costs more than $500,000 in care “.

Source: Nutrients

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