EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are long-chain omega-3 polyunsaturated fatty acids essential for cardiovascular, neurological, and inflammatory health. Whilst the body can convert plant-based omega-3s into EPA and DHA, this process is inefficient, making dietary intake from oily fish or supplements the primary source. EPA supports anti-inflammatory signalling, whilst DHA is crucial for brain and retinal function. Understanding what EPA and DHA are, their health benefits, and appropriate intake levels helps inform dietary choices and supplementation decisions. This article explores their roles, sources, and clinical applications within UK guidance.

What Are EPA and DHA? Understanding Omega-3 Fatty Acids

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are long-chain omega-3 polyunsaturated fatty acids that play important roles in human health. The body can produce small amounts of these fatty acids from alpha-linolenic acid (ALA), which is the essential omega-3 fatty acid, but dietary intake is the main source for optimal physiological function.

Both EPA and DHA are primarily found in marine sources, particularly oily fish and certain algae. Structurally, EPA contains 20 carbon atoms with five double bonds, whilst DHA contains 22 carbon atoms with six double bonds. This structural difference influences their distinct biological activities within the body. EPA is found in cell membranes and contributes to the production of signalling molecules called eicosanoids, which help modulate inflammatory responses. These EPA-derived compounds are generally less pro-inflammatory than those derived from omega-6 fatty acids.

DHA is highly abundant in the brain and retina, where it is a major component of the polyunsaturated fatty acids in these tissues. It is important for maintaining cell membrane fluidity, supporting neuronal function, and facilitating cellular communication. During foetal development and early childhood, DHA accumulation in neural tissues is particularly rapid, highlighting its importance for cognitive and visual development.

The body can convert alpha-linolenic acid (ALA), a plant-based omega-3 fatty acid found in foods such as flaxseeds and walnuts, into EPA and subsequently into DHA. However, this conversion process is inefficient in humans, with conversion rates typically ranging from less than 1% to 10%, varying by individual factors including sex and overall diet. Consequently, direct dietary sources of EPA and DHA are considered more reliable for meeting physiological requirements, particularly during certain life stages such as pregnancy.

Health Benefits of EPA and DHA

Cardiovascular health represents one of the most extensively researched areas regarding EPA and DHA benefits. These omega-3 fatty acids may exert cardioprotective effects through multiple mechanisms, including reducing triglyceride concentrations, modestly lowering blood pressure, decreasing platelet aggregation, and improving endothelial function. However, NICE does not recommend routine omega-3 supplements for primary or secondary prevention of cardiovascular disease, instead emphasising obtaining these nutrients through dietary sources.

Clinical evidence demonstrates that EPA and DHA can reduce serum triglycerides by 20–30% in individuals with hypertriglyceridaemia. Prescription omega-3 acid ethyl esters are licensed in the UK as an adjunct to dietary measures for treatment of hypertriglyceridaemia. These fatty acids work by reducing hepatic synthesis of very-low-density lipoproteins (VLDL) and enhancing triglyceride clearance from the bloodstream. Additionally, NICE has approved icosapent ethyl (a purified EPA product) for reducing cardiovascular risk in specific high-risk patients with elevated triglycerides who are already taking statins.

Neurological and mental health benefits are increasingly studied, with DHA's structural role in brain tissue supporting cognitive function throughout the lifespan. Observational studies suggest associations between higher omega-3 intake and reduced risk of cognitive decline, though evidence from randomised controlled trials remains mixed. Some research indicates potential benefits for mild cognitive impairment, but there is no established link for preventing or treating dementia.

For mental health conditions, EPA appears potentially relevant for mood regulation. Some studies suggest modest benefits in major depressive disorder when omega-3 supplements are used adjunctively with standard antidepressant therapy, though results are inconsistent and NICE does not recommend omega-3 supplements as a treatment for depression. During pregnancy, DHA supports foetal brain and retinal development, though UK guidance does not recommend routine DHA supplementation. The NHS recommends pregnant women consume oily fish whilst observing safety limits regarding mercury exposure.

Anti-inflammatory properties of EPA and DHA may provide symptomatic benefits for individuals with inflammatory conditions such as rheumatoid arthritis, with some evidence suggesting reduced joint pain and stiffness. However, omega-3s should complement rather than replace conventional disease-modifying treatments.

Food Sources and Supplements Containing EPA and DHA

Oily fish represent the richest natural dietary sources of EPA and DHA. Species particularly high in these omega-3 fatty acids include:

• Salmon (farmed and wild): approximately 1.5–2.5g combined EPA and DHA per 100g

• Mackerel: approximately 2.0–3.0g per 100g

• Herring: approximately 1.5–2.0g per 100g

• Sardines: approximately 1.0–1.5g per 100g

• Anchovies: approximately 1.4–2.0g per 100g

• Trout: approximately 1.0–1.5g per 100g

The NHS recommends consuming at least two portions of fish weekly, including one portion of oily fish (approximately 140g cooked weight). However, certain populations should observe precautions: pregnant women, those planning pregnancy, and breastfeeding mothers should limit oily fish consumption to two portions weekly due to potential pollutant accumulation. They should also limit tuna (fresh or canned) consumption and avoid shark, swordfish, and marlin entirely due to mercury content. Note that canned tuna is not classified as oily fish. Women of childbearing age should also avoid these high-mercury fish species.

For individuals who do not consume fish, alternative sources include:

• Omega-3 enriched eggs: Produced by hens fed omega-3-rich diets, providing modest amounts of DHA

• Algal oil supplements: Derived from microalgae, offering a vegetarian and vegan source of DHA and sometimes EPA

• Fortified foods: Some dairy products, spreads, and infant formulas are fortified with omega-3s

Omega-3 supplements are widely available in various formulations, including fish oil capsules, cod liver oil, krill oil, and algal oil. Fish oil supplements typically provide combined EPA and DHA in varying ratios, with standard capsules containing 180mg EPA and 120mg DHA, though concentrated preparations offer higher doses. Cod liver oil also contains vitamins A and D, which may contribute to excessive vitamin A intake if taken alongside other supplements—pregnant women should avoid cod liver oil due to vitamin A teratogenicity risks.

When selecting supplements, consumers should look for products certified by independent testing organisations to ensure purity, potency, and absence of contaminants such as heavy metals, PCBs, and dioxins. The Medicines and Healthcare products Regulatory Agency (MHRA) regulates omega-3 medicinal products, whilst food supplements fall under food safety legislation overseen by the Food Standards Agency (FSA).

Recommended Daily Intake and Dosage Guidelines

The UK does not have a formal Recommended Daily Allowance (RDA) for EPA and DHA specifically, but various health organisations provide guidance on adequate intake levels. The Scientific Advisory Committee on Nutrition (SACN) recommends that adults consume approximately 450mg of combined EPA and DHA daily, achievable through one to two portions of oily fish weekly.

For specific health conditions, higher intakes may be appropriate:

• Hypertriglyceridaemia: Prescription omega-3 preparations typically provide 2–4g of combined EPA and DHA daily, used under medical supervision

• Cardiovascular risk reduction: NICE has approved icosapent ethyl (a purified EPA product) for specific high-risk patients already taking statins

• Pregnancy and lactation: The NHS recommends following dietary guidelines for fish consumption, including safety limits for certain species

• Inflammatory conditions: Doses of 2–3g combined EPA and DHA daily have been studied for symptomatic relief, though evidence quality varies

When considering supplementation, several factors warrant attention. Omega-3 supplements are generally well-tolerated, but common adverse effects include gastrointestinal disturbances (fishy aftertaste, nausea, loose stools) and mild increases in bleeding tendency. Individuals taking anticoagulant or antiplatelet medications (warfarin, aspirin, clopidogrel) should consult their GP before commencing high-dose omega-3 supplements due to potential additive effects on bleeding risk. Those taking warfarin should have their INR monitored when starting or stopping omega-3 supplements. If you experience any suspected side effects from supplements, report them through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Patients with fish or shellfish allergies should exercise caution with fish oil supplements and may prefer algal oil alternatives. Those with diabetes should monitor blood glucose levels when initiating omega-3 supplementation, as very high doses may slightly affect glycaemic control, though this effect is generally minimal.

Quality considerations include choosing supplements with clearly stated EPA and DHA content and those tested for contaminants. Taking supplements with meals containing fat may enhance absorption. If you are considering omega-3 supplementation for a specific health condition, particularly at doses exceeding 1g daily, consult your GP or a registered dietitian to ensure appropriateness, avoid potential drug interactions, and establish whether dietary modification might be preferable to supplementation. Regular monitoring may be necessary for individuals taking prescription omega-3 preparations for hypertriglyceridaemia.

Frequently Asked Questions