Omega-3, EPA and mental wellbeing: the evidence

The interplay between omega-3 fatty acids and mental wellbeing has been the subject of scientific investigation for years. Epidemiological observations raised early on the question of a possible connection between fish consumption in different populations and aspects of mental health. This article summarises the evidence and places it in a neutral context — it describes research findings and expressly does not constitute any health or efficacy claim.

A recurring focus in this research is the question of which omega-3 fatty acid has been at the forefront of studies on mood and wellbeing: in many investigations it was primarily EPA that was examined, less so DHA. One important point up front: there is no EFSA-approved health claim for omega-3 and mood, mental wellbeing or mental health conditions.

EPA and DHA: Two Fatty Acids with Different Emphasis

Omega-3 fatty acids from fish oil or algae oil consist mainly of two long-chain fatty acids: EPA (eicosapentaenoic acid, 20:5n-3) and DHA (docosahexaenoic acid, 22:6n-3). Both are important for health, but differ in their emphasis:

• DHA is the structural building block of nerve cell membranes in the brain and, according to EFSA, contributes to normal brain function (from 250 mg/day). More in the article Omega-3 for the Brain.
• EPA is described in studies primarily in connection with inflammation-modulating metabolic pathways: in the scientific literature it is regarded as a precursor of certain signalling molecules (3-series eicosanoids, E-series resolvins). In research on mental wellbeing, EPA has so far been more of a focus.

This difference is often discussed in the research: the preparations examined differed in their EPA:DHA ratio. This is a characteristic of the study designs and does not allow any statement about what effect can be expected in an individual case.

Biochemical background information on EPA can be found in the foundational article on EPA (Eicosapentaenoic Acid).

A Widely Cited Meta-Analysis: Liao et al., Translational Psychiatry 2019

A frequently cited review on the topic of omega-3 and mental wellbeing appeared in 2019 in the journal Translational Psychiatry. Liao and colleagues summarised several double-blind, placebo-controlled, randomised trials. The following figures reproduce solely the study results reported by the authors and do not constitute any statement about an effect of omega-3 in an individual case.

Figures reported by the authors (standardised mean difference, SMD — a purely statistical measure):

• Overall analysis: across the included studies, the authors reported an SMD of −0.28 (P = 0.004).
• EPA-emphasised formulations: in the subgroup analysis, the reported figures for EPA-emphasised preparations differed from those for DHA-emphasised ones.
• DHA-emphasised formulations: for this subgroup the authors reported no statistically significant difference from the placebo group.

From this the authors concluded that, in this body of data, it was above all the EPA content of the preparations used that was associated with the results. This is an interpretation by the study authors of their data and not a universally valid statement or one that can be transferred to individual people.

EPA and DHA Compared: A Recurring Pattern in Studies

The subgroup analysis of the Liao review does not stand alone. Earlier reviews in this field of research also discussed the EPA content of the preparations used as a possible influencing factor for the reported study results. These observations describe study designs and data patterns, not an established effect.

Why EPA in particular is often to the fore in studies is discussed in the scientific literature with various biological hypotheses.

Mechanisms of EPA discussed in studies

The precise mechanisms are the subject of ongoing research. In the scientific literature, the following hypotheses, among others, are described:

• Inflammation modulation: studies describe EPA as intervening in inflammation-related metabolic pathways, for example via eicosanoids and resolvins.
• Serotonin system: the literature discusses a possible influence of EPA on the signalling of the neurotransmitter serotonin.
• HPA axis: a possible modulation of the stress hormone axis (hypothalamic-pituitary-adrenal axis) is described as a further hypothesis.
• Neuronal plasticity: a possible connection with neurotrophic factors such as BDNF (brain-derived neurotrophic factor) is also discussed.

These points are mechanistic hypotheses from basic research. They do not prove any benefit of omega-3 and are not a health promise.

EPA Formulations Compared: What the EPA:DHA Ratio Describes

The preparations used in studies differed in their EPA:DHA ratio. Many standard fish oil products have a ratio of around 3:2 (EPA:DHA) or 1:2, while parts of the research used high-concentration EPA formulations (pure EPA or a high EPA content). The following table summarises which subgroups were considered in the Liao review. It describes study data and is not a product recommendation.

Formulation type	EPA content	Subgroup reported in the study (Liao 2019)	Reported figure (SMD)
Pure EPA	100% EPA, no DHA	Examined	Reported by the authors
EPA-dominant	high EPA content	Examined	Reported by the authors
Mixed (standard)	approx. 40–60% EPA	Heterogeneous data	Variable
DHA-dominant	low EPA content	No significant difference reported	Not significant

The figures in the table reproduce the subgroup results reported by the study authors. They say nothing about the effect a preparation has on an individual person.

What Research on Omega-3 and Concurrent Intake Has Examined

Part of the research has looked at how additional intake of omega-3 presented in studies when participants were already receiving medical treatment. Such studies describe observations under controlled conditions.

The results of individual reviews in this field are inconsistent and are assessed differently in the scientific literature. Important: these figures are purely study reporting and not a recommendation. Anyone under medical or therapeutic care or taking medication should clarify supplementation exclusively with the treating doctor. Making unilateral changes, additions or reductions to an ongoing treatment is not advisable.

Omega-3 Status: Observed Associations in Studies

Individual observational studies have reported that lower EPA and DHA blood levels were measured in certain groups. Whether such differences are a cause, consequence or accompanying circumstance cannot in principle be clarified from observational studies — they show associations, but no cause-and-effect relationship.

The omega-3 index describes the proportion of EPA and DHA in the red blood cells. Which general physical signs may indicate an undersupply of omega-3 is described in the article Omega-3 Deficiency Symptoms.

Changes in maternal DHA levels around pregnancy and birth are also discussed in the research, as DHA requirements increase during pregnancy. These associations are the subject of ongoing research and do not allow any specific benefit to be inferred.

General Wellbeing: An Inconsistent Body of Evidence

Alongside studies in people with a medical diagnosis, there are studies that have looked at omega-3 in connection with general wellbeing and everyday mood fluctuations. The findings are overall inconsistent — partly because such states are difficult to measure and the studies are methodologically very different in design.

Individual studies in healthy adults have examined several weeks of omega-3 intake and also looked at inflammatory markers. Results of such individual investigations cannot be generalised and do not establish any assured benefit.

Overall, the current body of evidence is not sufficient to make robust statements about a benefit of omega-3 for mental wellbeing. Research on this is ongoing.

Dosage: What Studies Have Used

In the studies included, different amounts were used depending on the preparation, often between 1 g and 2 g EPA daily. The pure EPA formulations considered in the Liao review were in some cases at ≤ 1 g EPA/day. These figures describe which doses were used in studies — they are not a recommendation for intake.

For EPA-emphasised formulations, studies typically used daily doses in the range of 1–3 g omega-3. Anyone considering supplementation should discuss the appropriate amount with a doctor or pharmacist — particularly in the case of pre-existing conditions or concurrent use of medication.

A detailed dosage overview can be found in the article on Omega-3 Dosage per Day.

What to Look for When Choosing a Product

Regardless of the reason for use, it is generally worth looking at quality and composition when buying an omega-3 product. The following characteristics are common:

• EPA:DHA ratio: at least 2:1 EPA:DHA, preferably ≥ 3:1 or pure EPA
• Absolute EPA amount: at least 500–1,000 mg EPA per daily dose
• Form: triglyceride form (TG) or re-esterified triglyceride (rTG) has better bioavailability than ethyl ester (EE)
• Oxidation protection: TOTOX value as low as possible (below 10) — fresh oil with antioxidants (e.g. vitamin E)
• Quality certificates: IFOS, Friend of the Sea or comparable testing

Frequently Asked Questions

This article is part of our health overview, which presents all scientifically supported areas of omega-3 benefit — from heart and brain to inflammation and eyes.