Omega-3 index: what the test shows and what supplement trials have revealed

The omega-3 index is the proportion of two fatty acids, EPA and DHA, in red blood cell membranes. It is a convenient metric: it reflects fat intake over previous months, not just yesterday's dinner. The downside is different—it is easier to shift the index with capsules than to demonstrate that this shift changes clinical outcomes.

what this indicator is

The idea was proposed in 2004: to measure EPA and DHA not in plasma, where the value fluctuates after the last meal, but in erythrocyte membranes, which live for about four months. The authors correlated this indicator with the risk of death from coronary heart disease and proposed considering it a risk factor — publication in Preventive Medicine.

Subsequently, the indicator developed as a marker: it was linked to cardiovascular events in observational cohorts. Observation shows correlation, not causation — the same limitation discussed in the article about biohacking in general.

randomization check

Causation can only be verified by randomization. A 2019 meta-analysis combined 13 trials of marine omega-3s with 127,477 participants and an average treatment duration of about five years. The risk reduction was small: a frequency ratio of 0.92 for myocardial infarction, 0.92 for death from coronary heart disease, 0.93 for cardiovascular death, and 0.97 for cardiovascular events in general. Stroke was not among the outcomes with a significant reduction. Work in the Journal of the American Heart Association.

That is, we are talking about a reduction of a few percent relative to the baseline risk, not about the difference between “will get sick” and “will not get sick.”

A larger meta-analysis with meta-regression — 40 studies, 135,267 participants — showed the same picture with a beneficial supplement: the number of patients who need to be treated for one prevented case. For myocardial infarction, the risk ratio was 0.87 with this number 272; for coronary heart disease events, it was 0.90 with 192. For cardiovascular events in general, there was no significant effect (0.95 with an upper interval boundary of 1.00). The effect was dose-dependent. Work in Mayo Clinic Proceedings.

The number 272 should be read literally: to prevent one infarction, 272 people must take the supplement for the duration of the trial. The remaining 271 incur only costs and risk.

the downside of the dose

The same dose-dependence was also found on the undesirable side. A meta-analysis of seven large cardiovascular trials with 81,210 participants showed an increased risk of atrial fibrillation with marine omega-3 intake: a risk ratio of 1.25. At doses above a gram per day — 1.49, at doses up to a gram — 1.12. In meta-regression, the risk increased by approximately 11% for each additional gram per day. Publication in Circulation.

This is an important detail, because “biohacker” dosages are usually higher than those studied as dietary.

why the index and the outcome are not the same

The omega-3 index is a surrogate endpoint. Capsules will almost certainly raise it: this is a matter of biochemistry, not efficacy. The question that trials address is different — whether the frequency of heart attacks, strokes, and deaths changes following the index. The answer to this turned out to be far less certain than the shift in the indicator itself.

The gap between a surrogate marker and a clinical outcome is the most common trap in this field. Discussions about cortisol in the article about adaptogens and about aging markers in the material about anti-aging supplements are structured according to the same scheme.

what about fish

The trials tested capsules, not diet. Fish brings not only EPA and DHA: it is also protein, and what it displaces from the plate. It is impossible to separate the contribution of these factors in observational data, and randomizing people to “eat fish for five years” is practically impossible.

A separate topic is the quality of the supplements themselves. Fish oil oxidizes, and the content of active substances in the capsule is checked by the manufacturer, not the buyer. In Russia, such products are circulated as biologically active additives — what this means is discussed in the article about dietary supplements, vitamins, and medicines.

what question the analysis answers

The omega-3 index answers one question: how much EPA and DHA has entered the membranes in recent months. It does not answer what will happen to the vessels, and it does not replace the usual assessment of cardiovascular risk. Decisions about supplements for established diseases are made with a doctor — especially considering the data on atrial fibrillation.

Count it from a photo

Frequently asked questions

What does the omega-3 index measure?

The proportion of two fatty acids, EPA and DHA, out of the total amount of fatty acids in red blood cell membranes. Red blood cells live for about four months, so the indicator reflects intake over previous months, not from the last meal.

Do omega-3 supplements reduce the risk of heart attack?

A meta-analysis of 13 trials with 127,477 participants yielded a rate ratio of 0.92 for myocardial infarction and death from coronary heart disease, and 0.97 for cardiovascular events overall. Stroke was not among the outcomes with a significant reduction.

Do high doses have a downside?

A meta-analysis of seven large trials with 81,210 participants showed an increased risk of atrial fibrillation: a risk ratio of 1.25 overall, 1.49 for doses above one gram per day, and 1.12 for doses up to one gram.

Why is the index easy to raise, but the result not obvious?

Because the index is a surrogate endpoint. Taking EPA and DHA almost inevitably raises their content in cell membranes, but the question in trials is different: whether the frequency of heart attacks, strokes, and deaths changes as a result.

Are fish and capsules the same thing?

The trials tested capsules. Fish also provides protein and displaces other foods from the diet, and it is impossible to separate the contribution of these factors in observational data.

Read next

• Which fats are healthy and which are not — Dividing fats into "healthy" and "unhealthy" is convenient for a headline but almost useless at the grocery shelf: a single product usually contains all types at once, and the difference between them is not about general health benefits, but about specific effects.
• How dietary supplements differ from vitamins and medications — In a pharmacy, two packages of vitamin D sit on the same shelf.
• Longevity supplements: NMN, resveratrol and what human trials measured — This shelf has the best story of any: a molecule, ageing cells, mice that lived longer.

This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.

Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.