The authors of a study published in Brain Sciences have investigated the relationship between omega-3 fatty acid levels, brain volume, and cognitive function .
Aging and changes in the brain
With aging comes progressive changes in brain structure and ra eduction in cognitive abilities. The first changes appear in early adulthood when cognitive abilities such as processing speed and efficiency, encoding new memories, working memory, and reasoning skills start to decline. On the other hand, crystallized knowledge, such as vocabulary or general information, was observed to remain stable until after 60 years old on average [2, 3].
The good news is that the decline in cognitive functions is greatly impacted by lifestyle choices, such as physical activity, social contacts, and nutrition , which can all be influenced at the individual level. For example, prior research has revealed a positive relationship between increased consumption of omega-3 fatty acids and improved cognition, decreased neuronal loss, and other brain measurements [5, 6, 7, 8].
However, some studies have not found any association between omega-3 supplementation and cognition, and others have only reported small effects on cognitive and executive functions or memory [9, 10]. The discrepancies between these results indicate that there might be differences in the kinds of impact diet has on specific cognitive abilities and brain regions, and more research is necessary to untangle those relationships.
Therefore, in this study, the researchers explored a healthy, cognitively normal, aging population. They focused on measuring the levels of omega-3 fatty acids and their correlation to cognitive function and brain volume. 40 people completed all steps of the study. Participants were between 63 to 90 years old, with a mean age of 76 years.
The studied population was composed of Seventh-Day Adventist church members. Members of that church are known for being relatively healthy. They have an active lifestyle and a healthy diet. They also don’t smoke or drink alcohol.
Researchers measured the levels of red blood cell omega-3 fatty acids and investigated their relation to brain volume and cognition by performing MRI scans and cognitive tests. Specifically, they measured eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and calculated the participants’ omega-3 index, a combination of EPA and DHA that is weighted to predict omega-3 in red blood cells.
Omega-3 fatty acids, cognition, and brain structures
These researchers noticed variability in the associations of omega-3 fatty acids, cognition, and brain region volume and thickness. EPA and omega-3 fatty acid index were associated with better results on delayed memory and processing speed tests. However, it didn’t correlate with working memory or executive function.
Based on previous studies, these researchers expected to see a more pronounced association between omega-3 fatty acids and the hippocampus, a brain structure important for learning and memory. However, they did not find that any of the omega-3 fatty acids they tested had any correlation with hippocampal volume. Instead, they observed that EPA and omega-3 were correlated with entorhinal cortical volume, a brain region involved in learning and memory that has input and output relationships to the hippocampus.
EPA, DHA, and omega-3 index were also correlated with the total white matter volume. Previous research found a relationship between white matter microstructure, diets high in omega-3, and cognitive functions . These researchers speculated about several ways in which omega-3 fatty acids might have an influence the white matter. Some include decreasing inflammation or oxidative stress, involvement in axonal loss or demyelination pathways, or preservation of fibers vulnerable to aging. However, they didn’t directly test any of those possibilities.
The authors point out that, despite some differences, their findings generally show consistency with previous studies.
Strengths and limitations
This study has certain features that differentiate it from previous studies. For example, it measures fatty acid levels in a way that reflects consumption in the last 120 days. This gives researchers a long-term view compared to other methods that reflect fatty acid levels based on the last few days’ consumption.
Additionally, a previous study of this cohort  showed that its participants have stable and consistent diets throughout their lives, again suggesting that the observed effect is the result of long-term diet and lifestyle choices and not only short-term treatment or supplementation. Two-thirds of the study participants followed a vegetarian or vegan diet. This dietary pattern is not representative of the general population, so this study’s results may not apply to other groups.
The authors also point to a few other limitations of their research, including the small sample of the study population. This sample size limited the ability of researchers to adjust the statistical analysis for several genetic or lifestyle factors. However, since the studied population, Seven-Day Adventists, usually follow similar lifestyles, those factors are unlikely to greatly impact the analysis.
As is usual with association studies, the researchers point out that they cannot determine a causal relationship between the observed associations. They recommend more in-depth studies regarding the link between omega-3 fatty acids and cognitive ability, utilizing different neuroimaging techniques and studying more people for a longer time.
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