Omega-3 acids, more accurately termed omega-3 fatty acids or omega-3 polyunsaturated fatty acids (PUFAs), are essential fats that play vital roles in human health. The body cannot produce alpha-linolenic acid (ALA), making dietary intake crucial. These fatty acids form integral components of cell membranes, particularly in the brain, retina, and cardiovascular system, whilst also serving as precursors to compounds that regulate inflammation and immune responses. The NHS recommends consuming at least two portions of fish weekly, including one portion of oily fish, to ensure adequate omega-3 intake. Understanding omega-3 acids and their dietary sources is fundamental to maintaining nutritional wellbeing and supporting various aspects of health throughout life.

What Is Omega-3 Acid and Why Is It Important?

Omega-3 acids, more accurately termed omega-3 fatty acids or omega-3 polyunsaturated fatty acids (PUFAs), are a family of fats that play crucial roles in human health. Alpha-linolenic acid (ALA) is considered essential, meaning the body cannot synthesise it and must obtain it through diet. Other omega-3 fatty acids like EPA and DHA can be produced from ALA, though this conversion is limited. The '3' in omega-3 refers to the position of the first double bond in the carbon chain, three carbons from the methyl (omega) end of the molecule.

These fatty acids are integral structural components of cell membranes throughout the body, particularly in the brain, retina, and cardiovascular system. They influence membrane fluidity, which affects how cells communicate and function. Beyond their structural role, omega-3 fatty acids serve as precursors to bioactive compounds including specialised pro-resolving mediators (SPMs) such as resolvins and protectins, which help regulate inflammation, blood clotting, and immune responses.

The NHS recommends that adults consume at least two portions of fish per week (about 140g each), including one portion of oily fish, to ensure sufficient omega-3 intake. This recommendation is based on the Scientific Advisory Committee on Nutrition (SACN) and Committee on Toxicity (COT) advice on fish consumption.

Whilst uncommon in the UK, inadequate omega-3 intake may contribute to various health concerns. Some research suggests that modern diets may contain a higher ratio of omega-6 to omega-3 fatty acids compared to traditional diets, though the health implications of this ratio remain an area of ongoing research. Understanding omega-3 acids and ensuring adequate dietary intake forms an important component of nutritional wellbeing.

Types of Omega-3 Fatty Acids: EPA, DHA and ALA

The omega-3 family comprises several distinct fatty acids, but three are particularly relevant to human nutrition: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Each has unique characteristics and biological functions.

Alpha-linolenic acid (ALA) is an 18-carbon fatty acid found primarily in plant sources. It is the only omega-3 fatty acid considered strictly essential, as the body cannot produce it at all. However, ALA must be converted to the longer-chain EPA and DHA to exert many of the health benefits associated with omega-3 intake. This conversion process occurs in the liver but is inefficient in humans—with studies suggesting that typically less than 10% of ALA is converted to EPA, and less than 1% to DHA, though rates vary considerably between individuals. Factors including age, sex, genetic variation, and overall diet influence conversion efficiency, with women generally showing higher conversion rates than men.

Eicosapentaenoic acid (EPA) is a 20-carbon fatty acid found predominantly in marine sources. EPA serves as a precursor to series-3 prostaglandins and series-5 leukotrienes, which possess anti-inflammatory properties. It plays important roles in cardiovascular health, immune function, and may contribute to mood regulation, though NICE does not recommend omega-3 supplements to treat depression. EPA can be further elongated to form DHA, though this conversion is also limited.

Docosahexaenoic acid (DHA) is a 22-carbon fatty acid that represents the longest-chain omega-3 commonly found in the diet. DHA is highly concentrated in the brain and retina, where it is a significant component of neuronal membranes and photoreceptor cells. It is particularly important during pregnancy and infancy for proper neurodevelopment. DHA also supports cardiovascular health and may help maintain cognitive function in older adults.

Because of the inefficient conversion of ALA to EPA and DHA, direct dietary intake of these long-chain omega-3 fatty acids from marine sources is generally recommended for optimal health benefits.

Health Benefits of Omega-3 Acids

Omega-3 fatty acids have been extensively studied for their effects on various aspects of human health, with evidence supporting several key benefits.

Cardiovascular health represents one of the most well-established areas of omega-3 research. EPA and DHA contribute to the maintenance of normal heart function, with the GB Nutrition and Health Claims Register approving a health claim for a daily intake of 250 mg combined. However, it's important to note that NICE guideline NG238 advises against offering omega-3 supplements for routine cardiovascular disease prevention. An exception is icosapent ethyl (Vazkepa), a prescription-only medicine recommended by NICE (TA805) for specific high-risk adults with raised triglycerides alongside statin therapy. Omega-3 fatty acids may help support healthy triglyceride levels and blood pressure, though they should not replace prescribed cardiovascular medications.

Brain and cognitive function benefit from adequate omega-3 intake, particularly DHA. During pregnancy and early childhood, DHA is important for normal brain and eye development. The NHS advises that pregnant women consume fish within recommended limits to support foetal development. In adults, observational studies suggest associations between omega-3 intake and cognitive performance, though evidence from intervention trials remains mixed.

Anti-inflammatory effects of omega-3 fatty acids, particularly EPA, may benefit individuals with inflammatory conditions. These fatty acids compete with omega-6 fatty acids for the same metabolic enzymes, potentially resulting in the production of less inflammatory compounds. Some evidence suggests modest benefits in rheumatoid arthritis symptoms, though omega-3 supplementation should complement, not replace, standard treatment as recommended by NICE.

Mental health research indicates potential roles for omega-3 fatty acids in mood regulation. However, findings are not conclusive, and NICE guideline NG222 does not recommend omega-3 supplements as a treatment for depression. The Royal College of Psychiatrists notes that whilst omega-3 supplementation shows promise in some studies, it should not replace evidence-based treatments for mental health conditions.

Eye health is supported by DHA, which is a structural component of the retina. The GB Nutrition and Health Claims Register recognises that DHA contributes to the maintenance of normal vision (with a daily intake of 250 mg).

It is important to note that whilst omega-3 fatty acids offer health benefits, they are not a panacea. Individuals should maintain realistic expectations and consult healthcare professionals before using supplements to address specific health concerns.

Food Sources and Dietary Recommendations for Omega-3

Obtaining adequate omega-3 fatty acids through diet is achievable with informed food choices. The richest sources differ depending on the type of omega-3 fatty acid.

Marine sources provide the most bioavailable forms of omega-3s—EPA and DHA. Oily fish represents the primary dietary source and includes:

• Salmon (wild and farmed): approximately 1.5–2.5 g omega-3 per 100 g

• Mackerel: approximately 2.5–3.0 g per 100 g

• Sardines: approximately 1.5–2.0 g per 100 g

• Herring: approximately 1.5–2.0 g per 100 g

• Trout: approximately 1.0–1.5 g per 100 g

• Fresh tuna (not tinned): approximately 0.5–1.5 g per 100 g

The NHS recommends consuming at least two portions of fish per week (approximately 140 g each), including one portion of oily fish. This provides roughly 450 mg of EPA and DHA daily. However, certain groups should limit oily fish intake: pregnant women, those planning pregnancy, and breastfeeding mothers should consume no more than two portions weekly; girls and women of childbearing age should limit intake to two portions weekly. Pregnant women should avoid shark, swordfish and marlin completely due to mercury content, and limit tuna to no more than two tuna steaks or four medium-sized cans per week.

Plant sources provide ALA, though remember the conversion to EPA and DHA is limited. Good sources include:

• Flaxseeds (linseeds) and flaxseed oil: approximately 2.5 g ALA per tablespoon of seeds

• Chia seeds: approximately 2.5 g ALA per tablespoon

• Walnuts: approximately 2.5 g ALA per 30 g serving

• Rapeseed oil: approximately 1.0 g ALA per tablespoon

• Soya beans and soya products: moderate amounts

Fortified foods increasingly include added omega-3s, such as certain eggs, milk, yoghurts, and spreads. Check labels for specific content.

Supplementation may be appropriate for individuals who do not consume fish, including vegetarians and vegans. Algal oil supplements provide EPA and DHA from microalgae and represent a suitable plant-based alternative. General omega-3 supplements are regulated as food supplements under UK food law, while specific omega-3 medicines (such as omega-3-acid ethyl esters and icosapent ethyl) are regulated by the MHRA. When considering supplementation:

• Typical doses range from 250–1000 mg combined EPA/DHA daily

• Higher doses (2–4 g daily) may be used therapeutically but should only be taken under medical supervision

• Omega-3 supplements may interact with anticoagulant medications, increasing bleeding risk; if taking warfarin, your doctor may need to monitor your INR more closely when starting or stopping omega-3 supplements

• Common side effects include fishy aftertaste, gastrointestinal discomfort, and nausea

Special populations have specific considerations. Pregnant women should follow NHS guidance on fish consumption and avoid fish liver oil supplements due to their high vitamin A content, which may harm the unborn baby. Infants receive DHA through breast milk or fortified formula. Older adults may benefit from maintained omega-3 intake for cognitive and cardiovascular health.

Individuals taking anticoagulants, those with bleeding disorders, or anyone considering high-dose supplementation should consult their GP or pharmacist before starting omega-3 supplements. If you experience unusual bleeding, bruising, or gastrointestinal symptoms after starting supplementation, contact your healthcare provider promptly and consider reporting suspected side effects via the MHRA Yellow Card scheme.

Frequently Asked Questions