In this new paper, the second Framingham study generation (average age 67) was observed for a relationship between red blood cell omega 3 (specifically DHA) levels, scores on cognitive testing, and MRIs. It's a snapshot, just some interesting info, but let's see what we find.
Many studies measure levels of omega 3 in the body. Plasma levels (from the blood) reflect dietary intake over a few days. Red blood cells live about 120 days, so RBC membranes have omega 3 levels that correlate to dietary intake over the same amount of time. These levels also correlate with fatty acid concentrations in other tissues, like the heart.
First off, the MRIs. The images were studied to look for measures of brain aging, such as lower brain volume, hippocampal volume, and white matter hyperintensity volume. Gray matter is the cell bodies, white matter is the wiring (more or less), and "white matter hyperintensity" can indicate scarring or other damage. The Framingham participants in the lowest quartile of RBC DHA amount had the oldest-looking brains, with lower total volumes and more white matter hyperintensity. Once you got past the lowest quartile, however, there was no further relationship between the DHA levels and these brain findings. So it appears there is a threshold where you need enough omega 3, and beyond that more omega 3 is not helpful (if we assume causation, that lower dietary omega 3 will cause problems and higher is protective).
The cognitive testing was fairly basic, but given over 1500 participants in the study, that is not surprising. Delayed verbal memory, visuospatial memory, similarities testing, and a trails test were done. In general these tests can give a rough picture of how good your memory, reasoning, attention, and executive functioning are. RBC DHA levels were continuously and positively associated with 3 of the 4 tests (only verbal memory had no association).
We know from other observational studies that regular fish consumption is (for the most part) associated with a lower risk of cardiovascular disease and dementia. It seems that the ability to make DHA and EPA from the shorter ALA decreases as we age, so the older we are, the more important it is to get long chain omega 3s in the diet. As I have reviewed in past blog posts, controlled trials supplementing with DHA, EPA, or both seem to have no effect in advanced dementia, but do seem to have a positive effect in mild cognitive impairment (a very early form of dementia that can progress further) and very mild Alzheimer's dementia.
Alzheimer's dementia and vascular dementia (dementia caused by the cumulative damage of strokes) are the most common forms of dementia, and having sufficient long chain omega 3s could protect us from both. DHA and EPA seem to lower blood pressure, vascular inflammation, and reduce blood clotting. These long chain omega 3s are also vital constituents of the "lipid rafts" and therefore cell membrane function. As I've reviewed in the past, good levels of DHA in the brain seem to reduce neuroinflammation and the creation of amyloid beta plaques (associated with Alzheimer's).
Since long chain omega 3 fatty acids duke it out with the omega 6s for a spot on the plasma membrane of cells, it seems plausible that you don't need to eat fish three times a week if you keep your omega 6 intake low. If you listen to this guy, your omega 6 intake will be high. If you avoid processed foods, peanut and seed oils, and large quantities of most nuts and poultry and conventional eggs and lard… well, omega 6 will be less. Your brain can tell the difference!