*Geek Box: Arachidonic Acid
Poor arachidonic acid. This 20-carbon length long-chain fatty acid has the dubious distinction of having a final double-carbon bond 6th bonds from the end of the fatty acid, resulting in the ignominious “omega-6” moniker. Run for the hills!
Omega-6 hysteria and poor chemistry sarcasm aside, AA is a critically important fatty acid for the human brain, particularly during developmental periods. Up to 60% of the brain’s dry weight is fats, and of that up to 30% is comprised of polyunsaturated essential fatty acids [EFAs]. The omega-3 docosahexaenoic acid [DHA] comprises over 90% of omega-3 fatty acids in the brain, and AA is present in similar quantities. This ratio of nearly 1:1 in terms of brain fatty acid content may be important for the associated cognitive effects of these fatty acids.
AA is crucial during the brain growth spurt period due to the rapid incorporation of AA [and DHA] into the brain. AA has a number of critical roles in the brain, including brain cell firing, signalling, and long-term potentiation, which is the strengthening of connections between brain cells associated with learning and memory. Levels of AA in the body are maintained at relatively constant levels. Mechanistically, the dietary essential omega-6 fat, linoleic acid [LA], may convert to AA, however we know that there is little conversion of LA to AA, even with massive levels of LA intake. Thus, most of the AA in the body is derived from maternal fat stores, and from triglyceride breakdown in the body.
This means that the AA level of breastmilk may be maintained at constant levels without emphasising specific dietary intakes, while conversely DHA levels are much more variable and require dietary input to maintain sufficient levels. Interestingly, AA appears to be particularly critical for pre-term infants, and AA levels are a determinant of growth attainment in the first year of life in infants born pre-term with low birthweight. The balance of fatty acids for pre-term infants also appears to be important, with cognitive benefits of DHA observed when the percentage of fatty acids as DHA is half or equal to the value AA in infant formula, and attenuated where DHA exceeds AA. While DHA tends to receive the lions share of attention when it comes to fatty acids and brain health, the crucial role of AA in the early life stage should not be overlooked.