DHA (docosahexaenoic acid) is a long-chain omega-3 fatty acid found primarily in fatty fish, shellfish, and algae. It is one of the most important structural fats in your body, making up a significant portion of the fat in your brain and eyes. Your body can produce only tiny amounts of DHA on its own, which means you need to get it from food or supplements.
What DHA Actually Does in Your Body
DHA is a 22-carbon fatty acid with six double bonds in its chain, which gives it an unusually flexible shape. That flexibility matters because DHA embeds itself in cell membranes, particularly in the brain and retina, where it influences how fluid and responsive those membranes are. In the brain, this affects how well signals pass between neurons. DHA helps regulate neurotransmitter release, the activity of receptors and ion channels, and the signaling pathways that keep neurons functioning and surviving.
In the retina, DHA accounts for roughly 50% of the fatty acids in the membranes surrounding the light-sensing cells (photoreceptors). It plays a direct role in how those cells convert light into electrical signals. Animal studies show that when retinal DHA drops significantly, electrical activity in the eye becomes abnormal, pointing to a unique and irreplaceable role in vision.
Foods Highest in DHA
Fatty cold-water fish are by far the richest dietary sources. A standard 3-ounce (85g) cooked serving delivers the following amounts of DHA:
- Canned pink salmon: 630 mg
- Farmed Atlantic salmon: 590 mg
- Sardines (canned): 450 mg
- Atlantic mackerel: 430 mg
- Wild Atlantic salmon: 350 mg
Two servings of fatty fish per week is generally enough to meet most adults’ omega-3 needs. Shellfish like oysters, mussels, and crab also contain DHA, though in smaller amounts. Eggs labeled “omega-3 enriched” contain modest DHA from hens fed algae or flaxseed, but the amounts are far lower than fish, typically 50 to 100 mg per egg.
Why Plant Sources Fall Short
Plants like flaxseed, chia seeds, and walnuts contain a related omega-3 called ALA (alpha-linolenic acid), but your body converts very little ALA into DHA. In men, only 0% to 4% of dietary ALA becomes DHA. Women do slightly better, converting roughly 9%, likely due to the influence of estrogen. This means relying on flax or chia alone is unlikely to provide adequate DHA levels.
The most effective plant-based alternative is algal oil, derived from microalgae. Fish themselves get their DHA by eating algae, so going straight to the source skips the middleman. Algal oil supplements, typically made from a species called Schizochytrium, can deliver over 400 mg of DHA per capsule. Research comparing microalgal oil to fish oil finds similar bioavailability, making it a viable option for vegetarians and vegans.
DHA During Pregnancy
DHA accumulation in the fetal brain accelerates dramatically during the third trimester, roughly from week 29 through birth. The growing fetus depends entirely on the mother’s supply during this window. The Food and Agriculture Organization recommends a minimum of 200 mg of DHA per day for pregnant women, though many studies have used higher doses.
Supplementing with 600 mg of DHA daily during pregnancy has been linked to improved visual acuity in newborns, particularly boys. In another study, mothers who took 500 mg daily during pregnancy had children with better cognitive development scores at age five and a half. MRI imaging of infants whose mothers took 300 mg daily during the third trimester showed a correlation between DHA intake and greater brain volume at birth. Even 200 mg per day during the third trimester was enough to prevent the natural decline in maternal DHA levels that typically occurs late in pregnancy.
Heart Health: DHA vs. EPA
DHA and EPA are often grouped together in supplements and on nutrition labels, but they have distinct effects on the cardiovascular system. DHA consistently lowers both resting blood pressure and heart rate in controlled trials. EPA, on the other hand, does not appear to significantly lower blood pressure, and its effects on heart rate remain unclear.
In one trial of 224 healthy men taking 4 grams per day of either DHA or EPA, both groups saw heart rate drop by about 2 beats per minute. But when researchers looked at actual blood levels, only increases in circulating DHA correlated with the heart rate reduction. A separate trial measuring 24-hour ambulatory readings found that DHA reduced both blood pressure and heart rate throughout the day, while EPA had no significant effect on either.
What Happens When DHA Is Too Low
Chronic low DHA intake doesn’t produce obvious, immediate symptoms the way a vitamin C deficiency might. Instead, the consequences tend to be subtle and cumulative. Low red blood cell levels of DHA have been consistently observed in people with major depression, bipolar disorder, schizophrenia, and ADHD, though these associations don’t prove DHA deficiency caused the conditions.
Population-level patterns are striking. Communities that shifted away from fish-heavy traditional diets to Western diets saw increased rates of depression, seasonal affective disorder, and suicide. Cross-sectional studies have found that adolescents with diets low in long-chain omega-3s report more depressive symptoms. In animal studies, deficiency during development leads to behaviors consistent with depression that emerge after puberty, along with deficits in visual attention and visual acuity.
For developing infants and children, the stakes are higher. Early deficits in DHA accumulation during brain development are associated with suboptimal brain growth and may increase the risk of behavioral and psychological problems emerging later in childhood and adolescence.
How Much DHA You Need
There is no universally established recommended daily allowance specifically for DHA. Most health organizations set combined EPA and DHA targets rather than separating them. A common benchmark is 250 to 500 mg of combined EPA and DHA per day for general health in adults. Pregnant women should aim for at least 200 mg of DHA specifically, with many researchers suggesting 300 to 600 mg is a more effective range.
A single 3-ounce serving of salmon covers a full day’s worth of DHA, and then some. If you eat fatty fish twice a week, you’re likely getting enough without supplements. If you don’t eat fish, an algal oil supplement providing 400 to 500 mg of DHA daily is a reasonable alternative based on the doses used in clinical studies.