High triglycerides fish oil supplements have gained attention as a potential treatment for elevated blood fats, but understanding their role requires careful consideration of evidence, dosage, and safety. Triglycerides are a type of fat in your blood that, when elevated above 1.7 mmol/L, increase your risk of heart disease, stroke, and pancreatitis. Fish oil supplements contain omega-3 fatty acids (EPA and DHA) that can lower triglycerides by 20–50% at therapeutic doses. However, not all fish oil products are equivalent—prescription-strength preparations differ significantly from over-the-counter supplements in concentration and clinical evidence. This article examines how fish oil works, the evidence supporting its use, and when to seek medical advice for managing high triglycerides.

What Are Triglycerides and Why Do They Matter?

Triglycerides are a type of fat (lipid) found in your blood, formed when your body converts calories it doesn't need immediately into stored energy. After eating, your digestive system breaks down fats from food, and triglycerides are transported through your bloodstream to cells throughout your body. Between meals, hormones trigger the release of triglycerides from fat tissue to provide energy.

Whilst triglycerides are essential for normal bodily function, elevated levels can pose significant health risks. High triglycerides (hypertriglyceridaemia) are generally defined as levels above 1.7 mmol/L, with levels exceeding 10 mmol/L considered very high and associated with risk of pancreatitis. Raised triglycerides contribute to atherosclerosis—the build-up of fatty deposits in artery walls—which increases your risk of heart attack, stroke, and peripheral arterial disease.

Key factors that raise triglyceride levels include:

• Excess body weight and obesity

• Physical inactivity

• Excessive alcohol consumption

• High-carbohydrate diets, particularly refined sugars

• Certain medications (corticosteroids, beta-blockers, thiazide diuretics, oestrogens, retinoids)

• Medical conditions such as type 2 diabetes, hypothyroidism, and kidney disease

High triglycerides often occur alongside other cardiovascular risk factors, including low HDL cholesterol and high LDL cholesterol, forming part of metabolic syndrome. Many people with elevated triglycerides have no symptoms, which is why routine lipid profile testing is important, particularly for those with diabetes, obesity, or a family history of cardiovascular disease.

In the UK, NICE recommends non-fasting lipid testing for initial assessment. If your non-fasting triglycerides are above 10 mmol/L, your GP will arrange a fasting test to confirm the result and assess your risk of pancreatitis. Understanding your triglyceride levels enables you and your GP to assess cardiovascular risk and implement appropriate management strategies, which may include lifestyle modifications, medications, or supplements.

How Fish Oil Supplements Work to Lower Triglycerides

Fish oil supplements contain omega-3 polyunsaturated fatty acids, primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These long-chain fatty acids exert multiple beneficial effects on lipid metabolism, with particularly robust evidence for triglyceride reduction. The mechanism of action involves several interconnected pathways at the cellular and molecular level.

Primary mechanisms include:

• Reduced hepatic triglyceride synthesis: Omega-3 fatty acids decrease the liver's production of very-low-density lipoprotein (VLDL) particles, which are the primary carriers of triglycerides in the bloodstream

• Enhanced triglyceride clearance: EPA and DHA increase the activity of lipoprotein lipase, an enzyme that breaks down triglyceride-rich lipoproteins

• Decreased fatty acid availability: Omega-3s reduce the synthesis of fatty acids in the liver whilst promoting their oxidation (breakdown) for energy

At therapeutic doses (typically 2–4 grams daily of combined EPA and DHA), fish oil can reduce triglyceride levels by approximately 20–50%, with greater reductions observed in individuals with very high baseline levels. The effect is dose-dependent, meaning higher doses generally produce greater triglyceride lowering, though this must be balanced against potential side effects and cost.

It's important to note that whilst fish oil effectively lowers triglycerides, its effects on other lipid parameters are more variable. Some studies show modest increases in LDL cholesterol, particularly with high-dose supplementation. Fish oil may also modestly increase HDL cholesterol (the 'good' cholesterol) and has anti-inflammatory properties that may contribute to cardiovascular protection.

Therapeutic doses for significant triglyceride lowering are typically achieved with prescription-only omega-3 products rather than standard over-the-counter supplements.

Evidence for Fish Oil in Managing High Triglycerides

The evidence base for omega-3 fatty acids in managing hypertriglyceridaemia is substantial, with numerous randomised controlled trials and meta-analyses demonstrating consistent triglyceride-lowering effects. This has led to regulatory approval of specific prescription omega-3 preparations for different indications in the UK.

Meta-analyses have found that omega-3 supplementation can reduce triglycerides by approximately 0.3-0.4 mmol/L, with greater reductions in those with higher baseline levels. However, the evidence for cardiovascular benefit varies by formulation:

• Icosapent ethyl (EPA-only): The REDUCE-IT trial demonstrated that high-dose purified EPA (4 grams daily) significantly reduced cardiovascular events in patients with elevated triglycerides despite statin therapy. Based on this evidence, NICE Technology Appraisal 805 recommends icosapent ethyl (Vazkepa) for reducing cardiovascular risk in adults with elevated triglycerides who meet specific criteria.

• Mixed EPA/DHA preparations: By contrast, the STRENGTH trial using a combined EPA/DHA formulation showed neutral results for cardiovascular outcomes despite similar triglyceride lowering. Omega-3-acid ethyl esters (Omacor) are licensed in the UK for hypertriglyceridaemia but not specifically for cardiovascular risk reduction.

Key evidence points include:

• Dose-response relationship: Studies consistently show that doses of 2–4 grams of EPA and DHA daily are required for clinically meaningful triglyceride reduction

• Prescription vs over-the-counter products: Prescription omega-3 preparations contain higher concentrations of EPA and DHA (typically 80–90%) compared to standard supplements (often 30–50%)

• Cardiovascular outcomes: Evidence varies by formulation, with strongest support for pure EPA (icosapent ethyl)

It's important to recognise that over-the-counter fish oil supplements should not be considered equivalent to prescription products for therapeutic effects or cardiovascular outcomes. Prescription omega-3 products are generally considered an adjunct to, rather than a replacement for, lifestyle changes and other lipid-lowering medications when indicated.

Choosing the Right Fish Oil Supplement: Dosage and Types

Selecting an appropriate omega-3 product requires understanding the different formulations available, their omega-3 content, and the dosage needed for triglyceride lowering. Not all fish oil products are equivalent, and the concentration of active ingredients varies considerably between preparations.

Types of omega-3 products:

• Standard fish oil supplements: Contains approximately 30% omega-3 fatty acids (EPA and DHA combined), available over-the-counter

• Concentrated fish oil supplements: Contains 50–70% omega-3s, also available over-the-counter

• Prescription-only omega-3 medicines: Highly purified products containing 80–90% omega-3s, available on NHS prescription for specific indications:

• Omega-3-acid ethyl esters (Omacor): Licensed for hypertriglyceridaemia
• Icosapent ethyl (Vazkepa): Pure EPA formulation approved for cardiovascular risk reduction in specific patient groups

For clinically significant triglyceride lowering, the evidence supports a combined EPA and DHA dose of 2–4 grams daily. This is substantially higher than the general health recommendation of 250–500 mg daily for cardiovascular disease prevention. Achieving therapeutic doses typically requires prescription products rather than over-the-counter supplements.

When selecting a supplement, consider:

• Omega-3 content per capsule: Check the label for actual EPA and DHA amounts, not just total fish oil

• Quality assurance: Look for products tested for contaminants (mercury, PCBs, dioxins) by independent third parties

• Freshness: Choose products with added antioxidants (vitamin E) to prevent oxidation, and check expiry dates

Before starting high-dose omega-3 supplementation, discuss with your GP or pharmacist, particularly if you're taking other medications. If you have significantly elevated triglycerides, your GP can advise whether you meet the criteria for NHS prescription of omega-3 medicines, which are more appropriate for achieving therapeutic doses than over-the-counter supplements.

Potential Side Effects and Safety Considerations

Omega-3 supplements are generally well-tolerated, but side effects can occur, particularly at the higher doses used for triglyceride lowering. Understanding potential adverse effects and safety considerations helps you make informed decisions and recognise when to seek medical advice.

Common side effects include:

• Gastrointestinal symptoms: Fishy aftertaste, belching, nausea, loose stools, and indigestion are the most frequently reported complaints. Taking supplements with meals or using enteric-coated preparations may reduce these effects

• Fishy body odour or breath: Some individuals notice a fishy smell in sweat or breath

• Mild increases in LDL cholesterol: Particularly with very high doses

Important safety considerations:

Bleeding risk: Omega-3 fatty acids have antiplatelet effects that may increase bleeding risk. If you're taking anticoagulants (warfarin, DOACs) or antiplatelet medications (aspirin, clopidogrel), discuss with your GP before starting high-dose omega-3s. For those on warfarin, more frequent INR monitoring may be needed initially.

Atrial fibrillation risk: High-dose omega-3 fatty acids, particularly EPA, have been associated with increased risk of atrial fibrillation in some studies. Seek medical advice if you experience palpitations or irregular heartbeat, especially if you have a history of heart rhythm problems.

Blood pressure effects: Omega-3s may modestly reduce blood pressure. If you have hypertension and take medication, your GP may need to monitor your blood pressure when starting supplementation.

Allergies: Individuals with fish or shellfish allergies should exercise caution, though highly purified fish oil preparations typically contain minimal allergenic proteins. Algae-based omega-3 supplements provide an alternative source of DHA.

Contaminants: Quality concerns include potential contamination with mercury, PCBs, and other environmental pollutants. Reputable manufacturers use molecular distillation and testing to ensure purity.

Pregnant or breastfeeding women should avoid high-dose fish oil supplements and should not take cod liver oil (due to vitamin A content). Standard prenatal omega-3 supplementation at lower doses is generally considered safe.

If you experience any suspected side effects, report them through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

When to See Your GP About High Triglycerides

High triglycerides are typically discovered through routine blood tests, as most people experience no symptoms. However, certain situations warrant prompt medical attention, and regular monitoring is essential for managing cardiovascular risk effectively.

You should arrange to see your GP if:

• You've been told you have high triglycerides but haven't discussed a management plan

• You have multiple cardiovascular risk factors (diabetes, high blood pressure, family history of heart disease, obesity)

• You're experiencing symptoms that might indicate very high triglycerides, such as recurrent abdominal pain (which could suggest pancreatitis)

• You've made lifestyle changes but your triglycerides remain elevated

• You're considering starting fish oil supplements and take other medications

• You're experiencing side effects from fish oil or other lipid-lowering treatments

Seek urgent medical attention if:

• Your non-fasting triglycerides are above 10 mmol/L (requires prompt fasting test and assessment)

• You develop severe, persistent abdominal pain (particularly if radiating to your back)

• You have unexplained nausea and vomiting

• You experience symptoms of acute pancreatitis, which can occur with very high triglycerides

Your GP will typically assess your overall cardiovascular risk using tools such as QRISK3, which incorporates multiple risk factors beyond lipids alone. Based on this assessment, they may recommend:

Initial management approaches:

• Lifestyle modifications (weight loss, reduced alcohol, increased physical activity, dietary changes)

• Treatment of underlying conditions (diabetes, hypothyroidism)

• Consideration of lipid-lowering medications (statins, fibrates, or prescription omega-3 preparations)

• Referral to specialist lipid clinics for severe hypertriglyceridaemia (persistent levels >7.5-10 mmol/L) or suspected genetic causes

NICE recommends regular monitoring of lipid profiles, typically 3 months after starting treatment and then annually once stable. Your GP will work with you to develop a personalised management plan that addresses your individual risk factors and treatment goals.

Frequently Asked Questions