Omega-3 index

What the research found.

• The 8 percent omega-3 index figure comes from a 2004 review, and that review was about dying of heart disease. Its authors describe the figure as an informed estimate drawn from studies already published. No arthritis result went into it, because there wasn't one in the data they worked from.

  Harris and von Schacky, Preventive Medicine, 2004

• Fish oil supplements cut arthritis pain across 30 trials, and the figure came out at minus 0.24. The true value reaches as far as minus 0.004, which is nearly zero. So the effect is real and it's small, and stating it any other way would overstate what these trials found.

  Senftleber and colleagues, Nutrients, 2017

• In rheumatoid arthritis, taking omega-3 raised blood EPA by 0.74 and cut tender joint counts by 0.59. Three other measures moved too little to count, which were the sedimentation rate, C-reactive protein, and the DAS-28, a score built from a 28-joint count, a blood marker, and your own health rating. So the symptom measure moved and the disease-activity measures didn't.

  Wang and colleagues, Clinical Rheumatology, 2024

• The original dose data is thin, and the sample sizes belong right next to the figures they produced. Half a gram a day raised the index from 4.7 percent to 7.9 percent, in 22 people. A gram a day raised it to 9.9 percent, in 9 people.

  Harris and von Schacky, Preventive Medicine, 2004

What the number means.

What the test measures

The omega-3 index measures two fish oils, called EPA and DHA, and reports them as a share of all the fat in your red blood cell walls. Red cells live about four months, which is what makes the measurement useful, because it reflects what you have eaten over months rather than what you ate yesterday. That's a genuine advantage over measuring the same two oils in plasma.

The test does what it says, and it reliably measures your fish oil level. So the question this page answers is a different one, which is what you can do with that information if you have a rheumatic disease. The answer turns out to depend on where the target came from.

Where the 8 percent target came from

The figure comes from a single 2004 paper in Preventive Medicine, and reading that paper changes how the number looks. Its authors proposed the omega-3 index as a new risk factor, and they worked the target out from studies already published, which were observational groups and prevention trials. Their outcome was dying of heart disease, where an index of 8 percent or above was associated with the most heart protection and an index of 4 percent or below with the least.

The authors are frank about how they got there, writing that on the basis of the data they were able to make an informed estimate of the indexes tied to low and high risk. That's an honest description of what they did, and it's also a long way from a trial result. No arthritis result went into the figure, because there wasn't one in the data they worked from.

What happened since is that the number traveled. It now turns up on rheumatology sites, including this one until tonight, as a target for people with autoimmune disease. That makes two leaps at once, because it leaps from dying of heart disease to swollen joints, and it leaps from a link in observational data to a goal worth chasing.

What no trial has ever done

The missing piece here is specific and it's worth naming. No trial in any disease has randomized people to hit an omega-3 index target and compared them against people who didn't. Every trial of fish oil in arthritis gave EPA and DHA in grams, then measured what happened to the patients.

That difference sounds like an academic one, and it isn't. Knowing that a dose of fish oil cuts pain a little is one thing, and knowing that hitting 8 percent cuts pain more than hitting 6 percent is another. The first has been tested, the second hasn't been tested at all, in this disease or in any other, and a target tells you that hitting it is the point when no study has shown that.

What the omega-3 trials did find

The trial evidence for omega-3 in arthritis is real and modest, and it's worth keeping separate from the index question entirely. One review pooled 42 trials, with 30 of them reporting complete pain data, and fish oil cut pain by 0.24, though the true value reaches as far as minus 0.004, which is about as close to zero as a real result gets. The trials varied a lot among themselves, the effect held up in rheumatoid arthritis, and in osteoarthritis it didn't reach the mark.

A 2024 review in rheumatoid arthritis splits the results in a way that teaches you something. Taking omega-3 raised blood EPA by 0.74 and DHA by 0.62, cut the omega-6 to omega-3 ratio by 1.06, cut triglycerides by 0.47, and cut tender joint counts by 0.59. Three measures fell only slightly and not one reached the mark, which were the sedimentation rate, C-reactive protein, and the DAS-28, a score built from a 28-joint count, a blood marker, and your own health rating.

Read those together and they describe something specific. Omega-3 changes your blood fats reliably, it improves tender joints and pain somewhat, and it doesn't measurably quiet the inflammatory disease itself. That's a useful thing rather than a letdown, as long as somebody describes it accurately.

How much moves the number

The original 2004 paper reports dose figures, and the sample sizes belong right next to them. Half a gram of EPA and DHA a day raised the index from 4.7 percent to 7.9 percent, in 22 people, and a gram a day raised it to 9.9 percent, in 9 people. Those are small groups to draw a dose curve from, and the paper presents them as such.

Say you want to raise how much you're getting. Oily fish is the better route where you can manage it, because you get protein and vitamins along with the oils, and a supplement is a fair substitute for people who don't eat fish. The amount of real EPA and DHA per capsule varies hugely between products, so read the label for those two figures rather than for the total fish oil content.

What to do with a result

Say you've had the test and the number is back. The number tells you your fish oil level, and that's a real piece of information, though what it can't tell you is what to change, because no study has ever aimed treatment at it. Picture somebody at 5 percent who eats no fish, who might reasonably decide to eat more, and that decision doesn't need the test at all.

Fish oil affects how your platelets work, and that's the practical point that counts most here. So tell your rheumatologist you take it, above all if you're on a blood thinner, and tell any surgeon before a procedure. That's a real interaction, unlike the target range, and it's the part of this whole subject worth acting on.

Questions patients ask.