Abstract: Long-chain (LC) omega-3 PUFA derived from marine sources may play an important role in cognitive performance throughout all life stages. Docosahexaenoic acid (DHA), the dominant omega-3 in the brain, is a major component of neuronal cell membranes and affects various neurological pathways and processess. Despite its critical role in brain function, human’s capacity to synthesize DHA de novo is limited and its consumption through the diet is important. However, many individuals do not or rarely consume seafood. The aim of this review is to critically evaluate the current evidence from randomised controlled trials (RCT) in healthy school-aged children, younger and older adults to determine whether consumption of LC omega-3 PUFA improves cognitive performance and to make recommendations for future research. Current evidence suggests that consumption of LC omega-3 PUFA, particularly DHA, may enhance cognitive performance relating to learning, cognitive development, memory and speed of performing cognitive tasks. Those who habitually consume diets low in DHA, children with low literacy ability and malnourished and older adults with age-related cognitive decline and mild cognitive impairment seem to benefit most. However, study design limitations in many RCTs hamper firm conclusions. The measurement of a uniform biomarker, e.g., % DHA in red blood cells, is essential to establish baseline DHA-status, to determine targets for cognitive performance and to facilitate dosage recommendations. It is recommended that future studies be at least 16 weeks in duration, account for potential interaction effects of gender, age and apolipoprotein E genotype, include vegan/vegetarian populations, include measures of speed of cognitive performance and include brain imaging technologies as supportive information on working mechanisms of LC omega-3 PUFA.
Alex’s Notes: Docosaehexaenoic acid, or DHA (now you know why it’s always abbreviated), is the dominant fatty acid of the brain, where it regulates numerous processes such as neurogenesis, neuroplasticity, synaptogenesis, membrane fluidity, and neurotransmission. EPA and ALA, on the other hand, play a minor role with more than 99% simply being used to supply cellular energy. DHA also has a significant half-life of 2.5 years, indicating the brain has a relatively slow turnover of this critical fatty acid. Despite its importance, we have a very limited ability to synthesize it de novo from other fatty acids. It reasons that dietary intake is thus essential.
DHA is found in fatty fish and seafood. Any population, including vegans, some vegetarians, and most people following a typical Western diet, have chronically low intakes of DHA. Although intake is low, most don’t show cognitive dysfunction. So the question becomes, will consumption of DHA enhance cognitive performance in healthy children and adults? This review will aim to answer this question by critically examining the evidence from all the clinical trials that have been conducted on healthy school-aged children, younger adults and older adults investigating the effects of long-chained omega-3 PUFA on cognitive performance.
I will let you read the full-text for the in-depth analysis of the many studies reviewed, and instead I will focus on the key take-aways. Much of the research did not measure baseline DHA levels and thus baseline DHA status may be an important confounding variable in many studies. It is likely that those who are more deficient will benefit more from supplementation. Moreover, there is no uniform biomarker, although red blood cell DHA levels are preferred because of their established history with the omega-3 index. As it turns out, every 1g/day of DHA intake increases DHA levels by 1%, with the plateau at 2g/day. As for results,
“The outcomes that were improved with LC omega-3 PUFA supplementation in children included verbal learning and memory , reading [27,29], spelling , non-verbal cognitive development  and processing speed, visual-perceptive capacity, attention and executive function ; in younger adults memory and reaction time of memory were improved ; and in older adults several studies showed improvements in memory [27–29,41,58–60,65,68], while executive function  and visuospatial learning  were also improved.”
So… eat your salmon.