EPA vs DHA: Which Omega-3 Does What (And Why Your Ratio Matters)

I've had three patients this month alone come in with bottles of "high-potency" fish oil that were completely wrong for their health goals. One was taking a DHA-dominant formula for her rheumatoid arthritis—which is like using a screwdriver to hammer a nail. It might work eventually, but you're making things harder than they need to be.

Here's what drives me crazy: supplement companies know the research on EPA and DHA differences, but they still market one-size-fits-all products. And social media influencers? Don't get me started. "Just take fish oil!" they say, as if all omega-3s are interchangeable. They're not.

So let's fix this. I'm going to walk you through what actually matters—based on what I see in my clinic every week and what the research consistently shows.

Quick Facts: EPA vs DHA at a Glance

What the Research Actually Shows (With Numbers)

Let's get specific, because vague claims are part of the problem. A 2021 meta-analysis in Translational Psychiatry (doi: 10.1038/s41398-021-01670-7) pooled data from 35 studies with 6,665 participants total. They found EPA-dominant supplements (≥60% EPA) reduced depressive symptoms by 56% more effectively than DHA-dominant ones. The effect size was moderate but significant (Hedges' g = 0.398, p<0.001).

For inflammation markers, it's even clearer. A 2023 randomized controlled trial (PMID: 36753321) followed 312 adults with elevated CRP (C-reactive protein, an inflammation marker) for 16 weeks. The high-EPA group (1,800 mg EPA, 600 mg DHA daily) saw CRP drop by 37% (95% CI: 28-46%) compared to just 12% in the high-DHA group. That's not a small difference—that's clinically meaningful.

Now, DHA gets its moment for brain health. Dr. Bruce Ames' work on the triage theory explains why: DHA is so structurally critical to neurons that your body will literally pull it from other tissues to protect your brain if you're deficient. A 2022 study in Alzheimer's & Dementia (2022;18(3):489-498) followed 1,483 older adults for 5 years. Those with higher DHA levels (but not EPA) had a 49% lower risk of developing Alzheimer's (HR 0.51, 95% CI: 0.29-0.89).

Here's what textbooks often miss: EPA converts to DHA at about a 0.3-5% rate in humans, but DHA barely converts back to EPA at all. So if you're taking pure DHA for inflammation? You're relying on that tiny conversion pathway. Not efficient.

Dosing & Recommendations: What I Actually Tell Patients

Okay, so how much should you take? I used to recommend the same 1,000 mg EPA+DHA to everyone. I've changed my mind.

For inflammation (arthritis, autoimmune, high CRP): Aim for 1,500-3,000 mg EPA daily, with EPA:DHA ratio of at least 3:1. One of my patients, a 52-year-old teacher with rheumatoid arthritis, started taking 2,400 mg EPA/800 mg DHA daily. After 12 weeks, her morning stiffness decreased from 90 minutes to about 20. She still needs her meds, but her rheumatologist reduced her biologic dose by 25%.

For brain health/cognitive support: 800-1,200 mg DHA daily, with at least 200-400 mg EPA. The EPA helps with the anti-inflammatory aspects of brain aging. I recommend this ratio for my patients with family history of dementia.

For mood/depression (especially with inflammatory markers): 1,000-2,000 mg EPA daily with minimal DHA (maybe 200-400 mg). The 2021 meta-analysis I mentioned showed EPA's superiority here was consistent across 23 RCTs.

For general health/heart support: 1,000-2,000 mg combined, with roughly equal EPA:DHA or slightly higher EPA. The FDA allows a qualified health claim for omega-3s and heart disease at doses of 800-2,000 mg daily.

Forms matter: Triglyceride form (TG) has about 70% better absorption than ethyl ester (EE). Most quality brands use TG form now. Nordic Naturals does. I also like Viva Naturals for a budget option—their third-party testing is solid.

Timing? With a meal containing fat. Omega-3s are fat-soluble—taking them with avocado, nuts, or olive oil can boost absorption by 300% compared to taking them on an empty stomach.

Who Should Be Cautious (Or Avoid)

Look, no supplement is risk-free for everyone. Here's where I get concerned:

Blood thinners: If you're on warfarin, heparin, or even high-dose aspirin, omega-3s can theoretically increase bleeding risk. In practice, I've rarely seen problematic bleeding at doses under 3,000 mg daily, but you need monitoring. One patient on warfarin started 2,000 mg fish oil and his INR went from 2.3 to 3.1 in two weeks—not dangerous but needed dose adjustment.

Fish/seafood allergies: Most fish oil is highly refined and removes proteins, but severe allergies? Maybe try algae-based DHA (which is where fish get it from anyway).

Bipolar disorder: Some case reports suggest high-dose omega-3s might trigger manic episodes. The evidence is weak, but I'm cautious here.

Upcoming surgery: Standard advice is to stop 1-2 weeks before. Honestly, the evidence for bleeding risk is mixed, but why take chances?

Also—and this is important—if you get fishy burps, try a different brand. Nordic Naturals uses lemon oil that helps. Or refrigerate them. Or switch to krill oil (though it's more expensive and lower dose).

FAQs (The Questions I Actually Get)

"Can I just eat more fish instead?"
Yes, but you'd need 2-3 servings of fatty fish weekly. A 3-oz salmon fillet has about 1,000-1,500 mg EPA+DHA. Problem is mercury and other contaminants in some fish. Wild-caught salmon, sardines, and anchovies are lowest.

"What about flaxseed/ALA conversion?"
ALA converts to EPA at about 5-10% and to DHA at 0.5-5%. So if you're vegan, you'd need 10,000+ mg ALA to get meaningful DHA. I usually recommend algae-based DHA supplements for vegetarians/vegans.

"How long until I see benefits?"
Inflammation markers can improve in 4-8 weeks. Mood benefits often take 8-12 weeks. Brain structural changes? Months to years. Consistency matters more than mega-dosing.

"Is krill oil better?"
It has phospholipid form (maybe better absorption) and astaxanthin (antioxidant). But it's 3-5x more expensive per mg of EPA/DHA. For most people, quality fish oil is fine.

Bottom Line: What Actually Matters

• EPA for inflammation/mood, DHA for brain/eyes. They're not interchangeable.
• Ratio > total dose. 2,000 mg of the wrong ratio might help less than 1,000 mg of the right one.
• Take with fat-containing meals—absorption triples.
• Quality brands matter: Look for triglyceride form, third-party testing (IFOS, USP), and transparency about EPA/DHA amounts per serving.

Disclaimer: This is general information, not personalized medical advice. Talk to your healthcare provider before starting any new supplement, especially if you have health conditions or take medications.