Relationship Between Omega-3 Fatty Acids and DHA
DHA (docosahexaenoic acid) is one of the two primary long-chain omega-3 polyunsaturated fatty acids, alongside EPA (eicosapentaenoic acid), that together comprise the marine-derived omega-3 fatty acids responsible for cardiovascular and neurological health benefits. 1
Structural and Metabolic Relationship
DHA is a specific type of omega-3 fatty acid, not a separate entity. The omega-3 family includes several fatty acids, but the clinically relevant marine-derived forms are EPA (20:5n-3) and DHA (22:6n-3). 2, 3
- DHA can be synthesized endogenously from the plant-based omega-3 fatty acid alpha-linolenic acid (ALA), but this conversion pathway is highly inefficient in most individuals. 3
- Young women convert ALA to DHA more efficiently than young men, and young infants may convert better than adults, though variability is substantial. 3
- Because of poor conversion rates, preformed DHA from dietary sources (fatty fish, supplements) is necessary for most people to achieve adequate levels. 3
Tissue Distribution and Functional Differences
DHA has distinct physiological roles that differ from EPA, particularly in neural tissue. 1
- DHA comprises approximately 25% of total fatty acids in the human cerebral cortex and 50% of all polyunsaturated fatty acids in the central nervous system. 1
- DHA is transported into the brain as lysophosphatidylcholine by the Mfsd2a transporter; knockout mice with 50% lower brain DHA levels exhibited cognitive deficits and neuronal cell loss in the hippocampus and cerebellum. 1
- For cognitive function, DHA appears more important than EPA, with DHA levels above the median associated with improvements in verbal fluency, language, memory, and visual-motor coordination. 4
Cardiovascular Mechanisms: Complementary but Distinct
Both EPA and DHA reduce cardiovascular risk through overlapping but non-identical mechanisms. 1
- DHA lowers plasma and liver triglyceride levels through biliary C22:6 omega-3 fatty acid-derived N-acyl taurines that prevent intestinal triglyceride absorption—a mechanism unique to DHA. 1
- Both EPA and DHA serve as precursors to specialized proresolving lipid mediators (SPMs): EPA produces resolvins E-series, while DHA produces resolvins D-series and maresins, which actively resolve chronic inflammation. 1
- In the HEARTS trial, higher plasma EPA+DHA levels were associated with increased resolvin E1 and maresin 1, and the balance between proresolving and proinflammatory lipid mediators predicted plaque regression better than omega-3 fatty acid levels alone. 1
Clinical Dosing Context
When guidelines recommend "omega-3 fatty acids," they typically refer to combined EPA+DHA, not DHA alone. 5
- The American Heart Association recommends 2-4 grams per day of EPA+DHA combined for triglyceride lowering in patients with hypertriglyceridemia. 5
- For secondary prevention of cardiovascular disease, 1 gram per day of combined EPA+DHA is recommended. 5, 4
- For pregnant and nursing women, at least 300 mg of DHA daily is recommended to meet fetal and infant neurodevelopmental needs. 1
Common Pitfall to Avoid
Do not assume that all omega-3 fatty acids are equivalent. Plant-based ALA from flaxseed, walnuts, and canola oil does not provide EPA or DHA directly and relies on inefficient conversion. 6 Marine sources (fatty fish, fish oil, algal oil) provide preformed EPA and DHA, which are the forms with established cardiovascular and cognitive benefits. 1, 7
Human evolution occurred on a diet with an omega-6 to omega-3 ratio of approximately 1:1, whereas modern Western diets have ratios of 10:1 to 25:1, indicating widespread omega-3 deficiency. 8