Several studies have shown that dietary factors, including the consumption of products containing docosahexaenoic acid (22:6n-3, DHA), influence the risks associated with Alzheimer’s disease (AD). In addition, DHA has also been shown to reduce the risk of various AD-related events, such as cerebral glucose hypometabolism, beta-amyloid peptide aggregations into fibrils and oligomers, and neuroinflammation.
DHA is an omega-3 fatty acid essential to the structure of the human nervous system, cerebral cortex, retina and skin. DHA can either be synthesized from alpha-linolenic acid or obtained from consuming human breast milk, fatty fish, fish oil, or algal oil.
Study: Red blood cell DHA is inversely associated with risk of incidence of Alzheimer’s disease and all-cause dementia: Framingham Offspring Study. Image Credit: NOOMEANG / Shutterstock.com
Previous studies have shown that increased intake of DHA reduces the likelihood of developing Alzheimer’s disease in carriers of the APOLIPOPROTEIN E (APOE)-ε4 allele. Under natural conditions, the de novo DHA synthesis is marginal, as detection of DHA in tissues or blood is primarily attributed to dietary intake.
The lifespan of red blood cells (RBCs) is about 120 days. As a result, researchers evaluating long-term DHA intake are more effective in red blood cells than in other blood lipid pools such as serum/plasma phospholipids and total serum/plasma.
A previous study conducted in Canada, in which the study cohort included people over the age of 65, reported no association between RBC DHA and the incidence of dementia. This study also reported that higher blood mercury, which is a biomarker of fish consumption, was associated with a reduced risk of dementia.
Although epidemiological data on RBC DHA status and cognition are widely available, evidence on the relationship between RBC DHA status and the incidence of AD is limited. Moreover, the interaction between APOE the genotype and DHA remains unclear.
About the study
Scientists have recently hypothesized that high levels of DHA in red blood cells are strongly associated with a reduced likelihood of Alzheimer’s disease and dementia from all causes. They also hypothesized the existence of an interaction between APOE-ε4 and DHA. Taken together, these hypotheses were tested in a recent study Nutrients study using the Framingham Offspring Cohort.
The Framingham Health Study is an ongoing population-based study that is based in Framingham, Massachusetts. This cohort was created in 1948 to identify factors associated with the development of cardiovascular disease.
The Offspring Cohort was created in 1971 and included the children of participants in the original cohort. To date, the entire cohort has been studied for nine examination cycles at a frequency of approximately once every 4 years.
The current study was conducted during the eighth cycle of reviews and included 3,021 participants. The authors collected participants’ red blood cells and determined the DHA content.
Participants were excluded from the study if they had missing erythrocyte fatty acid measurements, had dementia, were under the age of 65, or had missing information about their APOE genotype. Finally, 1,531 participants were considered for the present study and were followed for a median of 7.2 years for a diagnosis of dementia.
The current study reported that an increase in DHA concentration in red blood cells was associated with a reduced risk of AD and all-cause dementia. Participants who were in the top quintile of RBC DHA had nearly half the risk of developing AD during follow-up compared to those in the bottom quintile.
The researchers also determined the possible interaction between RBC DHA and APOE-ε4 carrier. To this end, an inverse relationship between RBC DHA and AD risk in ε4 carriers was observed, with ε4 carriers associated with a higher genetic risk of late AD compared to non-carriers. Thus, the results of the study strongly indicate that ε4 carriers would greatly benefit from a higher intake of DHA compared to non-carriers.
The current study supports a link between diet and brain health. Specifically, an increase in DHA intake appears to increase DHA levels in red blood cells, which is beneficial for brain health. The authors estimate that by delaying the onset of AD by five years, an individual could have an additional 2.7 years of life to live.
Taken together, the results of the study are consistent with those of a previous study that found cross-sectional associations between RBC DHA and an individual’s cognitive performance.
In the future, researchers should focus on identifying better markers such as eicosapentaenoic acid (EPA, 20:5n-3) and/or DHA that can be used to predict a person’s risk of dementia. individual. In addition, an optimal sampling system must be established to analyze omega-3 content in patients with dementia.
Strengths and limitations
One of the main strengths of the current study is the large cohort of older adults living in a community setting and under continuous monitoring for dementia. Additionally, due to the continued collection of varying health measures from participants over the years, scientists could include these data as potential confounders in statistical models.
Nevertheless, this study had some limitations. For example, due to its observational nature, the authors failed to address causality and establish the directionality of associations. Another shortcoming of this study is its low number of ε4 carriers.
An additional limitation is that scientists have been unable to determine whether single measurement of RBC DHA is appropriate for estimating AD risk over a long period of time compared to more frequent measurements.
- Sala-Vila, A., Satizabal, CL, Tintle, N., et al. (2022) Red blood cell DHA is inversely associated with risk of incidence of Alzheimer’s disease and all-cause dementia: a Framingham offspring study. Nutrients, 14(12), 2408. doi:10.3390/nu14122408.
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