the risk of developing it would be halved 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. They therefore come exclusively from the diet, like certain minerals and vitamins. For decades, they have been the subject of studies revealing their many 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 policies, through early prevention of the risk of Alzheimer’s 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 into EPA and DHA. However, the rate of conversion of ALA into DHA being too low to cover our daily needs, DHA is considered essential, it must be provided by food.

Evidence that dietary factors may influence the risk of Alzheimer’s disease continues to mount. More specifically, DHA is enriched in membrane phospholipids of the central nervous system, and therefore plays a major role in mental and visual functions, especially in babies and the elderly. This is why scientists have long suggested that it has a positive effect on the maintenance of 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 with Alzheimer’s disease. The authors found that supplemental dietary intake of omega-3 DHA could on the one hand slow 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.

Oily fish against Alzheimer’s

In order to test their hypothesis, the researchers conducted a prospective observational study, within the Framingham Offspring Cohort – including 1490 participants without dementia, aged over 65 – for an average duration of 7 years. They looked at the association of red blood cell docosahexaenoic acid (DHA) with onset Alzheimer’s disease, while testing for an interaction with the 4 allele of the APOE gene — coding for 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. Indeed, he and his colleagues found that omega-3 levels in blood erythrocytes (or red blood cells) are very good predictors of mortality risk. Given marginal synthesis de novo of DHA, measurement of circulating or tissue levels of DHA is a valid biomarker of dietary DHA intake, which circumvents the uncertainties of self-reported dietary data.

In addition, Aleix Sala-Vila adds in a press release: “ Having higher levels of these acids in the blood, as a result of regularly including oily fish in the diet, increases life expectancy by nearly five years “.

In the current study, the team found that the risk of developing Alzheimer’s disease with a high blood level of DHA (6.1%) was 49% lower compared to a lower level (3.8%). ). Furthermore, the authors estimated that an increase in erythrocyte DHA from the first to the fifth trimester of the study provided approximately 4.7 additional years of life without Alzheimer’s disease. This last conclusion confirms that of 2021.

Infographic summarizing the main conclusion of the study regarding 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 definite 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, including among the early forms. The genetic part of this determinism is important and is represented by various risk factors. The first and main of these factors is the APOE gene 4 allele (APOE4) encoding apolipoprotein E, helping to transport cholesterol in the blood.

The APOE gene exists in three “forms” called E2, E3 (the most frequent) and E4 alleles. 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 major, both by the strength of the associated risk and by the high frequency. Indeed, nearly 10% of carriers of an APOE4 allele who have reached the age of 75 develop the disease, compared to 33% for homozygous carriers — carrier of the same allele twice — APOE4/E4 of the same age. At the age of 85, these figures rise to nearly 30% and 70%, respectively, for heterozygotes — carriers of two different alleles — APOE3/E4 and for homozygotes APOE4/E4. In the general Caucasian population over 54 years of age, the proportion of carriers of an APOE4 allele is 24%, and homozygous APOE4/E4 is 2%. The importance of this genetic risk factor for the individuals concerned, but also for the general population, justifies research programs in therapeutic prevention.

Graphs showing the influence of blood DHA levels for Alzheimer’s disease (a) and dementia from all causes (b), and according to the absence (c) or presence (d) of APOE4. The higher the DHA value, 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 noted that increased intake of DHA may reduce the risk of developing Alzheimer’s disease, particularly in people who carry the APOE4 allele, suggesting that they may benefit more from higher levels of DHA. DHA higher than non-carriers.

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

Source: Nutrients

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