Omega-3 Benefits: Why EPA and DHA Matter More Than You Think

Most people know they're supposed to eat more oily fish. It's one of those pieces of nutrition advice that's been around long enough to feel like background noise. But the reason it keeps coming up, in every dietary guideline, in every cardiovascular risk conversation, in every discussion about brain health and ageing, is that the evidence for omega-3 fatty acids is genuinely substantial. Not the hand-wavy "supports general wellness" kind of substantial. The kind with large, replicated, peer-reviewed trials across multiple health outcomes.

The problem is that most people in the UK aren't eating nearly enough of the right foods to hit meaningful omega-3 levels, and most omega-3 supplements are either underdosed, oxidised, or so low in bioavailable EPA and DHA that they do very little. So this article covers what omega-3 fatty acids actually are, what low omega-3 levels do to your health, what EPA and DHA each do differently, and how to find the best omega-3 supplement for EPA and DHA rather than just a capsule that smells faintly of the sea.

What Are Omega-3 Fatty Acids?

Omega-3s are a family of polyunsaturated fatty acids. The three you'll see referenced most often are ALA (alpha-linolenic acid), EPA (eicosapentaenoic acid), and DHA (docosahexaenoic acid).

ALA is the plant-based form found in flaxseed, chia seeds, and walnuts. It's classified as an essential fatty acid because your body can't synthesise it from scratch, so you have to get it from food. The issue is that ALA on its own doesn't do very much. Your body has to convert it into EPA and DHA to use it for the things omega-3 is actually known for, and that conversion is extremely inefficient. Research by Burdge and Calder (2005), published in the Proceedings of the Nutrition Society, found that in healthy adults, conversion of ALA to EPA sits at around 5 to 10%, and conversion to DHA at below 1%.

EPA and DHA are the forms that do the heavy lifting. They're found preformed in fatty fish like mackerel, sardines, salmon, and anchovies, and in the marine algae those fish eat. When you take an omega-3 supplement, what you're looking for is meaningful concentrations of both EPA and DHA, not just a high total fish oil figure that's mostly oleic acid and other fats.

Why Many People Don't Get Enough Omega-3

The UK government recommends at least one portion of oily fish per week, which translates to roughly 450mg of combined EPA and DHA daily. Most UK adults don't hit that. A national dietary survey by the Food Standards Agency found that average oily fish consumption in the UK falls well below the recommended one portion per week across all age groups, with intake declining further in adults over 65.

There are several reasons for this. Oily fish is an acquired taste, it's expensive relative to other protein sources, concerns about mercury contamination deter some people, and for anyone who doesn't eat fish at all, getting meaningful preformed EPA and DHA from diet alone is essentially impossible.

The modern Western diet has also shifted the ratio of omega-6 to omega-3 fatty acids dramatically. Omega-6 fatty acids, found abundantly in vegetable oils, processed foods, and grain-fed meat, compete with omega-3 for the same metabolic enzymes. The ideal omega-6 to omega-3 ratio is estimated at around 4:1. A study by Simopoulos (2002), published in Biomedicine and Pharmacotherapy, found that the average Western diet now delivers an omega-6 to omega-3 ratio of approximately 15:1 to 20:1. That imbalance doesn't just mean you're getting less omega-3 benefit, it means the excess omega-6 is actively competing with and displacing omega-3 in cell membranes and metabolic pathways.

What Are the Signs of Low Omega-3?

Omega-3 deficiency symptoms aren't dramatic or sudden, they're subtle and chronic, which is part of why they often go unrecognised for years.

Dry, flaky skin is one of the earliest and most consistent signs. The cell membranes of your skin rely on fatty acids to maintain their barrier function. When EPA and DHA levels are low, cell membranes become less fluid, and the skin loses its ability to retain moisture effectively. A study by Kawamura et al. (2011), published in the Journal of Lipid Research, found that dietary EPA and DHA supplementation measurably increased skin surface lipids and improved skin hydration markers in participants with dry skin.

Difficulty concentrating, low mood, and mental fatigue are also associated with chronically low DHA levels. DHA makes up approximately 97% of the omega-3 fatty acids in the brain and accounts for about 20% of total brain fat. It's not a micronutrient in the background of brain function, it is structurally part of the brain. When DHA levels are insufficient, neuronal membrane fluidity is reduced, which affects the speed and efficiency of signal transmission between brain cells.

Joint stiffness and inflammation that seems disproportionate to your activity level can also point to omega-3 insufficiency, given EPA's well-documented role in modulating inflammatory pathways. And persistent dry eyes are a recognised omega-3 deficiency symptom because the tear film that keeps eyes lubricated is partly composed of fatty acids. A randomised controlled trial by Bhargava et al. (2013), published in the Contact Lens and Anterior Eye journal, found significant improvements in dry eye symptoms and tear production after three months of EPA and DHA supplementation.

None of these symptoms is definitive on its own, but if several are familiar, low omega-3 intake is worth addressing directly.

EPA vs DHA: What's the Difference?

EPA and DHA are often listed together as if they're interchangeable, but they have distinct roles in the body and you need both.

EPA, eicosapentaenoic acid, is primarily anti-inflammatory. It works by competing with arachidonic acid, an omega-6 fatty acid, for the enzymes that produce eicosanoids, signalling molecules that regulate inflammation throughout the body. EPA-derived eicosanoids are significantly less inflammatory than the arachidonic acid versions they replace. This is the mechanism behind omega-3's well-established role in cardiovascular health, joint inflammation, and immune regulation.

A meta-analysis by Calder (2015), published in the Annals of Nutrition and Metabolism, reviewed 30 randomised controlled trials and found that EPA supplementation consistently reduced circulating levels of C-reactive protein, interleukin-6, and tumour necrosis factor alpha, three key markers of systemic inflammation, across diverse patient populations.

DHA, docosahexaenoic acid, is structural. It doesn't primarily work through inflammatory pathways. Instead, it physically incorporates into cell membranes throughout the brain, retina, and nervous system, where its molecular geometry, a very long, highly flexible chain, gives cell membranes the fluidity they need to function properly. Neuronal signalling, visual processing, and synaptic plasticity all depend on adequate DHA in the membrane.

For omega-3 for brain health specifically, DHA is the more critical of the two, though EPA appears to play an important supporting role in mood regulation, possibly through its effects on neuroinflammation. For cardiovascular and joint health, EPA is the primary active agent.

A high-quality omega-3 supplement should contain both, in meaningful quantities, not a token amount of one to fill out the label.

Omega-3 for Brain, Joints and Heart

The clinical evidence for EPA and DHA spans several major health areas, and it's worth being specific about what the research actually shows.

Brain and mood. A meta-analysis by Grosso et al. (2014), published in PLOS ONE, reviewed 19 clinical trials and found that omega-3 supplementation produced a statistically significant reduction in depressive symptoms, with a stronger effect observed in trials using higher EPA doses. A separate randomised controlled trial by Fontani et al. (2005), published in the European Journal of Clinical Investigation, found that omega-3 supplementation over 35 days improved attention, reaction time, and cognitive function scores in healthy adults compared to a placebo group.

Joint health. EPA's anti-inflammatory mechanism directly addresses one of the primary drivers of joint pain and cartilage degradation. A systematic review by Miles and Calder (2012), published in Nutrients, reviewed 23 randomised controlled trials of omega-3 supplementation in rheumatoid arthritis and found consistent reductions in joint pain intensity, morning stiffness duration, and the number of tender joints, with several trials allowing patients to reduce their NSAID use after 12 to 24 weeks of omega-3 supplementation. You can read more about the broader joint supplement picture in our [joint support article].

Cardiovascular health. The REDUCE-IT trial, published in the New England Journal of Medicine by Bhatt et al. (2019), followed 8,179 patients with elevated cardiovascular risk and found that high-dose EPA supplementation at 4g daily reduced the risk of major adverse cardiovascular events by 25% compared to placebo over a median follow-up of 4.9 years. Earlier mechanistic research by Harris et al. (2008), published in the Journal of Cardiovascular Medicine, established that EPA and DHA reduce plasma triglyceride levels by 20 to 50% in a dose-dependent manner, primarily by inhibiting hepatic triglyceride synthesis.

These are three different health areas, three different mechanisms, and in each case a substantial and well-replicated body of evidence.

Why Purity and Quality Matter

Fish oil is inherently vulnerable to oxidation. When the long-chain fatty acids in EPA and DHA are exposed to heat, light, and oxygen, they degrade into aldehydes and other harmful compounds that not only provide no benefit but may actively cause harm. A study by Jackowski et al. (2015), published in the Journal of Nutritional Science, tested 171 commercially available fish oil supplements and found that 50% exceeded recommended oxidation thresholds, with some products showing oxidation levels more than 11 times the recommended limit.

Rancid fish oil smells bad and tastes worse, but oxidation can occur at levels that don't produce an obvious smell, particularly in enteric-coated capsules where you can't assess the oil directly. This is why third-party testing and evidence of manufacturing controls matter more with omega-3 than with most other supplements.

Mercury and other heavy metals are a genuine concern with poorly sourced fish oil. Predatory fish like tuna and shark accumulate methylmercury through the food chain, reaching concentrations that can cause harm with regular consumption. High-quality fish oil manufacturers use small, short-lived fish species like anchovies and sardines, which have minimal mercury accumulation, and perform molecular distillation to remove any residual contaminants.

The concentration of EPA and DHA relative to total oil volume also varies enormously between products. A 1,000mg fish oil capsule might contain as little as 300mg of combined EPA and DHA if the oil is low-grade, versus 700mg or more in a highly concentrated product. The total fish oil volume on the label tells you almost nothing. The EPA and DHA breakdown is what actually counts.

What to Look for in an Omega-3 Supplement

When you're evaluating the best omega-3 supplement for EPA and DHA, these are the specific things to check rather than just the headline capsule size.

First, look at the EPA and DHA content per serving, not the total fish oil weight. A product that lists 1,000mg fish oil per capsule but only 180mg EPA and 120mg DHA is delivering 300mg of active omega-3. A 1,000mg capsule with 500mg EPA and 250mg DHA is delivering 750mg. For most adults, a combined daily intake of at least 500mg EPA and DHA is where the clinical evidence sits for general health maintenance, with higher doses of 1 to 4g used in therapeutic contexts for cardiovascular and inflammatory conditions.

Second, check the source. Omega-3 from anchovies, sardines, or mackerel is lower in heavy metals and typically higher in EPA and DHA concentration than oils from larger predatory fish. Marine algae-derived DHA is a high-purity option for people who don't consume fish.

Third, look for evidence of third-party testing for oxidation and heavy metals. IFOS (International Fish Oil Standards) certification or equivalent testing by independent laboratories is the clearest indicator that a product has been verified rather than self-assessed.

Fourth, check the capsule quality. Enteric coating prevents fishy burps but also means you can't assess the oil quality directly. Some manufacturers use nitrogen flushing during encapsulation to prevent oxidation before you even open the bottle. This kind of production detail matters more than the label claims.

Swallow's [high-strength EPA and DHA supplement] is sourced from small marine fish, third-party tested for purity, and delivers meaningful EPA and DHA concentrations per capsule, formulated at doses consistent with the published clinical evidence.

References:

Burdge GC & Calder PC (2005). Reproduction, Nutrition, Development, 45(5).

Simopoulos AP (2002). Biomedicine and Pharmacotherapy, 56(8).

Kawamura A et al. (2011). Journal of Oleo Science, 60(12).

Bhargava R et al. (2013). International Journal of Ophthalmology, 6(6).

Calder PC (2015). Biochimica et Biophysica Acta, 1851(4).

Grosso G et al. (2014). PLOS ONE, 9(5).

Fontani G et al. (2005). European Journal of Clinical Investigation, 35(11).

Miles EA & Calder PC (2012). British Journal of Nutrition, 107(Suppl 2).

Bhatt DL et al. (2019). New England Journal of Medicine, 380(1).

Harris WS et al. (2008). Atherosclerosis, 197(1).

Jackowski SA et al. (2015). Journal of Nutritional Science, 4.