DHA and EPA are two types of omega-3 fatty acids found primarily in fish and marine algae. They serve different but complementary roles in the body: DHA is a major structural component of your brain, eyes, and cell membranes, while EPA is best known for producing signaling molecules that help control inflammation. Your body needs both, and most people don’t get enough from diet alone.
How DHA and EPA Differ
Both DHA and EPA are long-chain polyunsaturated fatty acids, but they have distinct chemical structures that shape what they do. EPA has 20 carbon atoms and 5 double bonds. DHA has a longer chain with 22 carbon atoms and 6 double bonds. That extra length and flexibility is part of why DHA integrates so well into the membranes of cells in the brain and retina, where it accumulates in far higher concentrations than anywhere else in the body.
EPA’s primary job is different. It serves as a raw material for producing signaling molecules called eicosanoids, which regulate your cardiovascular, immune, and endocrine systems. When EPA levels are high relative to competing omega-6 fatty acids, the balance of these signaling molecules shifts toward less inflammation. Both EPA and DHA also generate compounds called resolvins that actively help resolve inflammation once it has done its job.
What DHA Does for the Brain and Eyes
DHA is the dominant omega-3 in your central nervous system. It accumulates rapidly in the developing brain during the last trimester of pregnancy and continues building through the first two years of life, though the brain maintains high DHA levels throughout your entire lifespan. During the third trimester alone, a fetus accumulates roughly 50 to 60 milligrams of DHA per day, concentrating it in the gray matter and retinal membranes.
This early accumulation matters. Autopsy studies of human infants have found about 25% more DHA in the brain cortex of breastfed babies compared to formula-fed infants. The most well-established developmental benefit is improved visual acuity. A meta-regression analysis found that the dose of DHA in infant supplements explained the variation in visual development outcomes between studies, and the effect appears to be driven by DHA specifically, not EPA.
In adults, DHA continues to support brain health. Analysis of human cadaver brains has shown that people with Alzheimer’s disease have lower DHA levels in the frontal lobe and hippocampus compared to unaffected individuals. Whether supplementing with DHA prevents cognitive decline is still an open question, but its structural role in the brain is well established.
How Both Support Heart Health
EPA and DHA together have well-documented effects on several cardiovascular risk factors. Their most consistent benefit is lowering triglycerides, which are blood fats linked to heart disease. They do this by helping the liver burn fatty acids more efficiently, reducing the production of fat-carrying particles, and clearing those particles from the bloodstream faster. DHA appears to be slightly more effective than EPA at lowering triglycerides specifically.
Both fatty acids also support heart rhythm and blood vessel health. They’re abundant in the membranes of heart muscle cells and neurons, where they help regulate your autonomic nervous system. This shows up as a lower resting heart rate, increased heart rate variability (a marker of cardiovascular fitness), and faster heart rate recovery after exercise. In one study, children receiving 400 milligrams of EPA plus 200 milligrams of DHA daily for three months showed significant improvements in heart rate variability, along with lower triglycerides and higher HDL (“good”) cholesterol.
The American Heart Association recommends about 1 gram of combined EPA and DHA per day for people with documented heart disease. For people with high triglycerides, doses of 2 to 4 grams per day can reduce triglyceride levels by 20% to 40%. For general prevention, eating at least two servings of fatty fish per week covers most people’s needs.
Best Food Sources
Fatty fish are by far the richest dietary sources of preformed EPA and DHA. Per 100 grams of edible fish (roughly a 3.5-ounce serving):
- Atlantic mackerel: 0.9 g EPA, 1.6 g DHA (2.5 g combined)
- Lake trout (siscowet): 1.2 g EPA, 1.8 g DHA (3.0 g combined)
- Farmed Atlantic salmon: 0.6 g EPA, 1.2 g DHA (1.8 g combined)
- Canned sardines: 0.4 g EPA, 0.6 g DHA (1.0 g combined)
A single serving of salmon or mackerel easily provides more than 1 gram of combined EPA and DHA, which is enough to meet most daily recommendations.
Plant-Based Options and ALA Conversion
Plant foods like flaxseed, chia seeds, and walnuts contain a different omega-3 called ALA (alpha-linolenic acid). Your body can convert ALA into EPA and DHA, but the process is inefficient. On a typical diet, only about 6% of ALA converts to EPA and about 3.8% converts to DHA. If your background diet is high in omega-6 fats (common in processed foods and vegetable oils), those conversion rates drop by another 40 to 50%. This means relying on flaxseed alone won’t meaningfully raise your DHA or EPA levels.
For people who don’t eat fish, algal oil is the most practical alternative. Algae are actually where fish get their omega-3s in the first place, so going straight to the source works. A recent bioavailability study found that DHA and EPA from microalgal oil supplements are absorbed just as well as from fish oil. The main difference is that most algal oil products have a higher ratio of DHA to EPA (roughly 3:1) compared to fish oil (roughly 3:2), so if you specifically need more EPA, you may need to check labels or choose a product formulated with more EPA.
Side Effects at High Doses
At typical supplemental doses, side effects are mild and mostly digestive: heartburn, nausea, fishy aftertaste, or bad breath. Some people notice bad-smelling sweat or occasional headaches. These issues are more common with fish oil than with algal oil, and taking supplements with meals usually helps. Prospective studies suggest that intakes of 0.5 to 1.8 grams per day are both effective and well tolerated for most adults.