What is the difference between DHA and EPA?

What each one is

DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) are long-chain omega-3 fats. EPA has 20 carbon atoms and DHA has 22.^[1] Microalgae make both, and fish collect them through the food chain.^[1] DHA is especially high in the retina, the brain and sperm.^[1]

Most fish oil has more EPA than DHA: a typical 1000 mg capsule has 180 mg of EPA and 120 mg of DHA.^[1] Algal oil is high in DHA and low in EPA.^[4]

In the body

Both become part of the membranes of cells, and cells make signal molecules called eicosanoids from both.^[1] EPA and DHA compete with arachidonic acid, an omega-6 fat, and this moves the balance toward less inflammatory activity.^[1] The body can turn ALA, the plant omega-3, into EPA and then into DHA, but reported conversion rates are below 15%.^[1]

Blood fats

A 2011 review pooled placebo-controlled trials of EPA alone (10 trials) and DHA alone (17 trials), and 6 trials that compared the two.^[2]

• Both lowered triglycerides, and DHA lowered them more in the direct comparisons.^[2]
• DHA raised LDL cholesterol by 7.23 mg/dL against placebo. EPA did not raise it. In the direct comparisons, DHA raised LDL cholesterol 4.63 mg/dL more than EPA.^[2]
• DHA raised HDL cholesterol by 4.49 mg/dL. EPA did not.^[2]

In the ComparED trial, 154 adults took 2.7 g of EPA, 2.7 g of DHA and corn oil, each for 10 weeks.^[5] DHA lowered triglycerides by 13.3% and EPA by 11.9%.^[5] DHA raised HDL cholesterol by 7.6% and LDL cholesterol by 6.9%. EPA raised LDL cholesterol by 2.2%.^[5]

Blood pressure and blood vessels

A 2018 review looked at 6 trials that gave more than 2 g a day of EPA or DHA of at least 90% purity.^[6] DHA improved the function of blood vessels and lowered heart rate and blood pressure more than EPA did. Both made platelets less active.^[6] The authors wrote that larger studies must confirm these differences.^[6]

Mood

A 2019 review of 26 trials with 2,160 people found that products with at least 60% EPA, at 1 g of EPA a day or less, eased symptoms of depression.^[3] Products with pure DHA or mostly DHA did not.^[3]

Inflammation

In ComparED, DHA lowered interleukin-18, a signal of inflammation, by 7.0%, and EPA by 0.5%.^[5] A 2026 review of 96 trials found the largest falls in cytokines, the signal proteins of inflammation, with products that had more DHA than EPA.^[7]

What is still unknown

The large heart trials described by the NIH tested fish oil or prescription products with EPA and DHA together, or EPA alone.^[1] The ComparED authors wrote that more studies are needed on how long-term DHA alone changes the risk of heart disease.^[5]