EPA and DHA, the long-chain omega-3 fatty acids found primarily in oily fish, are structural components of neuronal cell membranes. They influence membrane fluidity, neurotransmitter receptor function, and the resolution of neuroinflammation. The brain preferentially accumulates DHA over other fatty acids, and DHA deficiency correlates with measurable changes in cognitive function, mood regulation, and neuroinflammatory status.
What the Research Shows for Cognitive Decline
A landmark study of 2,157 older adults published in JAMA Internal Medicine found that those with the highest red blood cell DHA concentrations had a 47 percent lower risk of developing dementia over 7 years compared to those with the lowest levels. The association was not explained by confounding from general healthy behaviour. DHA status in blood is a reliable indicator of long-term dietary omega-3 intake from food rather than supplementation.
EPA, Depression, and Inflammatory Signalling
EPA rather than DHA appears to be the primary omega-3 fatty acid involved in mood regulation. EPA is the substrate for anti-inflammatory eicosanoids that resolve neuroinflammation. Multiple meta-analyses of randomised controlled trials have found that EPA-dominant omega-3 interventions significantly reduce depressive symptoms, with effect sizes comparable to antidepressant medication in populations with elevated inflammatory markers.
Best Dietary Sources
- Mackerel: one of the richest sources, providing 4 to 5 grams of combined EPA and DHA per 100 grams
- Sardines: affordable, sustainable, and providing approximately 2 grams per 100 grams
- Salmon: wild salmon provides more EPA and DHA than farmed, typically 1.5 to 2.5 grams per 100 grams
- Herring: historically the most consumed oily fish in northern Europe, excellent EPA and DHA source
- Anchovies: concentrated omega-3 source used in small amounts in cooking
- Aim for at least two portions of oily fish per week, ideally three