Flaxseed oil omega-3 supplementation has gained attention as a plant-based source of alpha-linolenic acid (ALA), an essential fatty acid that the body cannot produce independently. Derived from flax seeds through cold-pressing, this oil provides a vegetarian alternative to marine omega-3 supplements, though it differs significantly in composition and conversion efficiency. Whilst flaxseed oil contributes to overall omega-3 intake, understanding its specific properties, benefits, limitations, and appropriate use is essential for both healthcare professionals and patients. This article examines the evidence base, clinical applications, dosing considerations, and safety profile of flaxseed oil as an omega-3 source within UK clinical practice.

What Is Flaxseed Oil and How Does It Provide Omega-3?

Flaxseed oil, also known as linseed oil, is derived from the seeds of the flax plant (Linum usitatissimum). It has been used for centuries both as a nutritional supplement and in traditional medicine. The oil is extracted through cold-pressing methods to preserve its nutritional content, particularly its omega-3 fatty acid profile.

The primary omega-3 fatty acid in flaxseed oil is alpha-linolenic acid (ALA) , which typically comprises 50–60% of the oil's total fatty acid content. ALA is classified as an essential fatty acid, meaning the human body cannot synthesise it and must obtain it through dietary sources. Unlike marine-based omega-3 supplements that contain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), flaxseed oil provides exclusively plant-based omega-3.

Once consumed, ALA undergoes enzymatic conversion in the body to EPA and subsequently to DHA, though this conversion process is relatively inefficient in humans. Research suggests that only approximately 5–10% of dietary ALA is converted to EPA, and less than 0.5% to DHA. The conversion rate can be influenced by various factors including age, sex, genetic variations, and the presence of other dietary fats. Women generally demonstrate higher conversion rates than men, possibly due to the influence of oestrogen on the enzymes involved.

Flaxseed oil is particularly valued by individuals following vegetarian or vegan diets as a plant-based alternative to fish oil supplements. Each tablespoon (approximately 15ml) of flaxseed oil typically provides around 7–8 grams of ALA. The European Food Safety Authority (EFSA) has established an adequate intake of 0.5% of total energy from ALA, which equates to approximately 1–2 grams daily for most adults. The UK does not have specific dietary reference values for ALA.

Health Benefits of Omega-3 from Flaxseed Oil

Omega-3 fatty acids, including ALA from flaxseed oil, play important roles in human physiology, particularly in cardiovascular health, inflammatory processes, and cellular membrane function. However, it is essential to distinguish between the evidence for ALA and that for marine-based omega-3s (EPA and DHA), as they are not interchangeable.

Cardiovascular health represents one of the most studied areas. Some observational studies suggest that higher dietary ALA intake may be associated with modest reductions in cardiovascular disease risk. A meta-analysis published in the British Journal of Nutrition indicated that increased ALA consumption may be associated with a small reduction in coronary heart disease events. However, randomised controlled trials have shown less consistent results. Current NICE guidance (NG238) does not recommend omega-3 supplements for primary or secondary prevention of cardiovascular disease, with the exception of icosapent ethyl (a prescription-only, highly purified EPA) for specific high-risk patients as outlined in NICE TA805.

Regarding anti-inflammatory effects, ALA may help modulate inflammatory pathways, though the evidence is less robust than for EPA and DHA. Some research suggests potential benefits for inflammatory conditions such as rheumatoid arthritis, but clinical trials have produced mixed results. The limited conversion of ALA to EPA and DHA may explain why flaxseed oil demonstrates less pronounced anti-inflammatory effects compared to fish oil.

Lipid profile improvements have been observed in some studies, with flaxseed oil supplementation potentially having modest effects on total cholesterol and low-density lipoprotein (LDL) cholesterol levels. However, effects on triglycerides appear minimal compared to marine omega-3s.

There is ongoing research into potential benefits for cognitive function, skin health, and menopausal symptoms, but current evidence remains insufficient to support definitive clinical recommendations. Patients should be advised that whilst flaxseed oil contributes to overall omega-3 intake, it should not be considered equivalent to marine sources for conditions where EPA and DHA have established roles, and it is not a substitute for prescribed lipid-lowering or anti-inflammatory therapy.

How to Take Flaxseed Oil: Dosage and Forms

Flaxseed oil is available in several formulations, each with distinct advantages for different patient preferences and needs. The most common forms include liquid oil, soft gel capsules, and as a component of ground flaxseeds.

Liquid flaxseed oil is the most concentrated form and is typically taken by the tablespoon. A standard serving is often 1 tablespoon (15ml), providing approximately 7-8 grams of ALA, which exceeds the EFSA adequate intake of 1-2 grams daily. Many people may need less than a full tablespoon to meet their needs. The liquid form can be consumed directly or added to foods such as smoothies, salad dressings, or yoghurt. It is important to note that flaxseed oil should not be used for cooking or frying, as heating destroys the beneficial omega-3 fatty acids and may produce harmful compounds. The oil should be stored in a dark, airtight container in the refrigerator to prevent oxidation and rancidity.

Soft gel capsules offer a convenient alternative for those who find the taste of liquid oil unpalatable. Typical capsule strengths range from 500mg to 1,000mg, with dosages varying by product. Patients should follow manufacturer instructions to achieve their desired ALA intake. Capsules are often taken with meals to enhance absorption and reduce the likelihood of gastrointestinal discomfort.

Ground flaxseeds (also called milled flaxseeds or linseed) provide not only omega-3 but also dietary fibre and lignans. Approximately 1–2 tablespoons of ground flaxseed daily can contribute to omega-3 intake, though the oil content is lower than in extracted oil. Whole flaxseeds pass through the digestive system largely undigested and should be ground before consumption. The UK Food Standards Agency advises sensible intake limits for raw milled linseed due to naturally occurring compounds called cyanogenic glycosides.

Patients should be advised to start with lower doses and gradually increase to assess tolerance, noting that flaxseed oil is calorie-dense (approximately 120 kcal per tablespoon). Those taking anticoagulant medications or with bleeding disorders should consult their GP before commencing supplementation, as omega-3 fatty acids may have mild antiplatelet effects.

Side Effects and Safety Considerations

Flaxseed oil is generally well tolerated when used at recommended doses, but patients should be informed of potential adverse effects and important safety considerations. The most common side effects are gastrointestinal and include:

• Loose stools or diarrhoea, particularly when starting supplementation or with higher doses

• Bloating and flatulence

• Nausea, especially when taken on an empty stomach

• Abdominal discomfort

These effects are typically mild and often resolve with continued use or dose reduction. Taking flaxseed oil with food can minimise gastrointestinal symptoms.

Drug interactions warrant careful consideration. Flaxseed oil may have additive effects with anticoagulant and antiplatelet medications, including warfarin, aspirin, clopidogrel, and direct oral anticoagulants (DOACs). Whilst the risk of clinically significant bleeding is considered low, patients on these medications should inform their GP before starting supplementation. There is no official contraindication, but monitoring may be appropriate in some cases. Patients should consider stopping high-dose omega-3 supplements 1-2 weeks before elective surgery after discussing with their surgical team.

Allergic reactions to flaxseed are uncommon but possible. Patients with known flax or linseed allergy should avoid flaxseed oil. Signs of allergic reaction include rash, itching, swelling, or difficulty breathing. If symptoms of anaphylaxis occur (such as swelling of the face/throat or breathing difficulties), patients should seek emergency medical attention by calling 999 or 112.

Quality and storage are critical safety considerations. Flaxseed oil is highly susceptible to oxidation, which produces harmful free radicals and an unpleasant, bitter taste. Patients should purchase products in dark bottles, check expiration dates, and store opened bottles in the refrigerator for no longer than 6–8 weeks. Rancid oil should be discarded.

Special populations require additional consideration. Pregnant and breastfeeding women should consult their healthcare provider before using flaxseed oil supplements, though dietary sources are generally considered safe. There is insufficient evidence regarding safety in children, and supplementation should only be undertaken under medical supervision. Patients with hormone-sensitive conditions should be aware that flaxseeds (though not necessarily the oil) contain phytoestrogens, though there is no official link to adverse effects in these populations.

Patients are advised to report any suspected side effects to the Medicines and Healthcare products Regulatory Agency (MHRA) through the Yellow Card Scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).

Frequently Asked Questions