Omega-3 fatty acids are essential polyunsaturated fats that support numerous vital functions throughout the body, from maintaining heart health to supporting brain development and regulating inflammation. The three main types—alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)—are obtained through diet, primarily from oily fish and plant sources such as flaxseeds and walnuts. Understanding what omega-3s do can help you make informed decisions about dietary intake and whether supplementation may be appropriate for your individual health needs. This article explores the evidence-based roles of omega-3s in cardiovascular function, cognitive health, inflammation, and practical guidance on meeting recommended intakes through food and, where necessary, supplements.

What Are Omega-3 Fatty Acids?

Omega-3 fatty acids are a family of polyunsaturated fats that play important roles in human health. They are characterised by the position of their first double bond, located three carbon atoms from the methyl end of the molecular chain, hence the term 'omega-3'.

The three main types of omega-3 fatty acids relevant to human nutrition are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is considered essential because the human body cannot synthesise it, making dietary intake necessary. EPA and DHA can be produced from ALA in the body, but this conversion is relatively inefficient, with typical rates of about 5-10% for EPA and often less than 5% for DHA (conversion is generally higher in women).

ALA is found primarily in plant sources such as flaxseeds, chia seeds, and walnuts, whilst EPA and DHA are predominantly obtained from marine sources including oily fish and algae.

Omega-3 fatty acids serve as vital structural components of cell membranes throughout the body, particularly in the brain and retina. They also act as precursors to bioactive compounds that play crucial roles in regulating inflammation, blood clotting, and vascular function. These include specialised pro-resolving mediators (SPMs) such as resolvins, protectins and maresins, which influence numerous physiological processes including immune response and cardiovascular function.

The importance of omega-3s in human nutrition stems from decades of research, beginning with observations of low cardiovascular disease rates in populations consuming fish-rich diets. The European Food Safety Authority (EFSA) has authorised health claims for EPA and DHA related to the maintenance of normal heart function, and for DHA in contributing to normal brain and visual development and function.

How Omega-3s Support Heart and Brain Health

Omega-3 fatty acids exert multiple cardioprotective effects through several distinct mechanisms. EPA and DHA help reduce serum triglyceride concentrations by decreasing hepatic synthesis of very-low-density lipoproteins (VLDL) and enhancing triglyceride clearance. Clinical trials have demonstrated that high-dose omega-3 supplementation (2–4 grams daily) can lower triglycerides by 25–30% in individuals with hypertriglyceridaemia. These effects are primarily seen with prescription-strength omega-3 medicines such as Omacor (omega-3-acid ethyl esters) rather than standard over-the-counter supplements. Additionally, omega-3s may modestly reduce blood pressure, improve endothelial function, and decrease platelet aggregation, collectively contributing to reduced cardiovascular risk.

The evidence for omega-3s in secondary prevention of cardiovascular disease has evolved considerably. Whilst earlier studies suggested significant benefits, more recent large-scale trials have shown mixed results. NICE guidance (NG238) states that omega-3 supplements should not be routinely offered for the prevention of cardiovascular disease. However, NICE has approved icosapent ethyl (TA805) for reducing cardiovascular risk in specific high-risk patients with raised triglycerides who are already on statins.

The NHS recommends eating at least 2 portions of fish per week, including 1 portion of oily fish, as part of a heart-healthy eating pattern. A portion is about 140g (cooked weight).

For brain health, DHA is particularly crucial, comprising approximately 40% of polyunsaturated fatty acids in neuronal membranes. During foetal development and early childhood, adequate DHA intake supports normal brain development, visual acuity, and cognitive function. In adults, observational studies have linked higher omega-3 intake with reduced risk of cognitive decline, though intervention trials have produced inconsistent results and there is insufficient evidence to recommend omega-3 supplements specifically for preventing dementia.

Emerging research suggests omega-3s may influence mental health, with some evidence indicating potential benefits in depression, particularly when EPA-rich formulations are used adjunctively with standard treatments. However, omega-3s should not replace conventional psychiatric care, and patients experiencing mental health difficulties should consult their GP for appropriate assessment and evidence-based treatment.

Benefits of Omega-3s for Inflammation and Joint Function

Omega-3 fatty acids possess anti-inflammatory properties that distinguish them from omega-6 fatty acids, which tend to promote inflammatory processes when consumed in excess. EPA and DHA are metabolised into specialised pro-resolving mediators (SPMs), including resolvins, protectins, and maresins. Laboratory and animal studies suggest these compounds may help facilitate the resolution of inflammation rather than simply suppressing it, potentially helping to restore tissue homeostasis following immune activation.

The anti-inflammatory effects of omega-3s occur through multiple pathways. They compete with arachidonic acid (an omega-6 fatty acid) for incorporation into cell membranes and for metabolism by cyclooxygenase and lipoxygenase enzymes. This competition results in the production of less inflammatory eicosanoids compared to those derived from arachidonic acid. Additionally, omega-3s can modulate gene expression by influencing transcription factors such as nuclear factor-kappa B (NF-κB), thereby reducing the production of pro-inflammatory cytokines including interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α).

In rheumatoid arthritis, systematic reviews and meta-analyses have demonstrated that omega-3 supplementation may provide modest symptomatic benefits. Patients taking omega-3 supplements (typically 2.6–3 grams of EPA and DHA daily) have reported reduced joint pain, decreased morning stiffness, and diminished use of non-steroidal anti-inflammatory drugs (NSAIDs). These benefits may take 12 weeks or longer to become apparent. However, omega-3s do not modify disease progression or replace disease-modifying antirheumatic drugs (DMARDs), which remain the cornerstone of rheumatoid arthritis management according to NICE guideline NG100.

For osteoarthritis, the evidence is less robust, with studies showing variable results. Some research suggests omega-3s may help reduce joint pain and improve function, though effects are generally modest. Patients with inflammatory joint conditions should discuss omega-3 supplementation with their rheumatologist or GP as part of a comprehensive management plan, rather than relying on supplements alone for symptom control.

Dietary Sources and Recommended Intake of Omega-3s

The richest dietary sources of EPA and DHA are oily fish, including salmon, mackerel, sardines, herring, trout, and fresh tuna (note that tinned tuna does not count as oily fish as the omega-3 content is reduced during processing). A typical 140g portion of cooked salmon provides approximately 2.5–3 grams of combined EPA and DHA. White fish and shellfish contain lower amounts, whilst fish oil supplements offer concentrated doses ranging from 250mg to over 1000mg per capsule, depending on formulation.

Plant-based sources provide ALA rather than EPA and DHA. Foods rich in ALA include:

• Flaxseeds and flaxseed oil – approximately 1.3–1.8g ALA per tablespoon of ground flaxseed

• Chia seeds – about 2.5g ALA per tablespoon

• Walnuts – roughly 2.5g ALA per 30g serving

• Rapeseed oil – contains modest amounts of ALA

• Soya beans and tofu – provide smaller quantities

For vegetarians and vegans, algal oil supplements derived from microalgae offer a direct source of DHA and sometimes EPA, bypassing the inefficient conversion from ALA.

The NHS recommends that adults consume at least 2 portions of fish per week, including 1 portion of oily fish. A portion is about 140g (cooked weight). For pregnant women, the advice is modified: oily fish consumption is encouraged for foetal brain development, but should be limited to 2 portions weekly due to potential pollutant exposure. Pregnant women should also limit tuna to no more than 2 fresh tuna steaks or 4 medium-sized cans per week due to mercury content. Certain fish (shark, swordfish, marlin) should be avoided completely during pregnancy, as should fish liver oils (which contain high levels of vitamin A).

There is no single official recommended daily intake for omega-3s in the UK, though EFSA suggests 250mg of combined EPA and DHA daily for cardiovascular health maintenance in adults. The Scientific Advisory Committee on Nutrition (SACN) recommends a population average intake of approximately 450mg daily, though this is not an individual requirement.

Practical tips for increasing omega-3 intake include incorporating tinned sardines or mackerel into salads, choosing salmon for main meals, adding ground flaxseeds to porridge or smoothies, and using rapeseed oil for cooking. Individuals with fish allergies or dietary restrictions should discuss alternative sources with a registered dietitian.

Who May Benefit from Omega-3 Supplements?

Whilst dietary sources of omega-3s are preferable for most people, certain groups may benefit from supplementation. Individuals with hypertriglyceridaemia (elevated blood triglycerides) may be prescribed high-dose omega-3 preparations (typically 2–4 grams daily of EPA and DHA) by their GP or lipid specialist. These prescription-strength formulations (such as Omacor) are licensed medicines regulated by the MHRA and differ from over-the-counter supplements in their concentration, quality assurance, and proven efficacy.

NICE has also approved icosapent ethyl (Vazkepa) for reducing cardiovascular risk in adults with established cardiovascular disease, raised triglycerides, and who are taking statins.

Pregnant and breastfeeding women require adequate DHA for foetal and infant neurodevelopment. Whilst dietary intake through oily fish is ideal, women who do not consume fish may consider supplementation, particularly if dietary intake is insufficient. Supplements should be specifically formulated for pregnancy, free from vitamin A (which can be teratogenic in high doses), and sourced from fish low in environmental contaminants. Algal DHA supplements are suitable for vegetarians and vegans. Women should consult their midwife or GP before starting any supplements during pregnancy.

Vegetarians and vegans who do not consume fish may have lower EPA and DHA status, as conversion from plant-based ALA is limited. Algal oil supplements provide a suitable alternative, offering direct sources of DHA and EPA without animal products. These individuals should ensure adequate ALA intake from plant sources whilst considering supplementation to achieve optimal omega-3 status.

People with certain inflammatory conditions, such as rheumatoid arthritis, may experience modest symptomatic benefits from omega-3 supplementation as an adjunct to conventional treatment. However, supplements should not replace prescribed medications, and patients should discuss their use with their rheumatologist or GP.

Important safety considerations include potential interactions with anticoagulant medications (such as warfarin), as high-dose omega-3s may increase bleeding time. Patients taking warfarin should inform their anticoagulation service before starting omega-3 supplements and have their INR monitored more frequently initially. Common adverse effects of supplements include fishy aftertaste, gastrointestinal discomfort, and nausea, which can often be minimised by taking capsules with meals or choosing enteric-coated formulations.

Individuals should be aware that most over-the-counter omega-3 products are regulated as food supplements rather than medicines. When purchasing these products, look for reputable brands that provide third-party testing for purity and potency and clearly state the EPA and DHA content. If you are considering omega-3 supplementation for a specific health condition, discuss this with your GP or a registered dietitian to ensure it is appropriate for your individual circumstances and will not interact with existing treatments.

If you experience any suspected side effects from omega-3 products, report them through the MHRA Yellow Card scheme.

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