Omega-3 fatty acids — particularly EPA and DHA from marine sources — are among the most extensively studied nutritional compounds in the world, with evidence spanning cardiovascular disease, inflammation, brain health, eye health, and pregnancy outcomes. They are the supplement category with arguably the strongest overall clinical evidence base. This guide explains what they do, how much you need, and how to supplement intelligently.
What EPA and DHA Do
Cardiovascular: EPA and DHA reduce triglycerides by 20–30% (dose-dependent; highly effective for hypertriglyceridaemia). They reduce platelet aggregation, lower resting heart rate, have anti-inflammatory effects on blood vessel walls, and modestly lower blood pressure. At high doses (4g EPA, prescription-only icosapentaenoic acid, as in the REDUCE-IT trial), EPA reduced major adverse cardiovascular events by 25% in high-risk adults. Inflammation: omega-3 fatty acids are precursors to resolvins and protectins — anti-inflammatory signalling molecules that actively resolve inflammation. This explains benefits across inflammatory conditions: RA (reduces joint tenderness and NSAID requirement), inflammatory bowel disease, and psoriasis. Brain health: DHA is a major structural component of neuronal cell membranes and photoreceptors. Adequate DHA is critical for fetal brain development (hence recommendations during pregnancy) and supports cognitive function across the lifespan. Mental health: EPA specifically has antidepressant properties demonstrated in multiple RCTs, with an EPA:DHA ratio of at least 2:1 appearing most effective for depression.
Food Sources
The richest sources of EPA and DHA are oily fish: mackerel (~2.6g per 100g), herring (~1.9g), salmon (~1.8g farmed, ~1.2g wild), sardines (~1.4g), trout (~1.2g), tuna (fresh ~0.3g — canning reduces omega-3 content significantly). The NHS recommends at least 2 portions of fish per week, including one oily. Algae-based omega-3 (the original marine source of EPA/DHA) provides a vegan/vegetarian alternative with equivalent bioavailability. ALA from plant sources (flaxseed, walnuts, chia seeds) converts only inefficiently to EPA and DHA (approximately 5–10% conversion) and cannot be relied upon as the primary omega-3 source.
When to Supplement and How Much
Supplementation is worthwhile when dietary intake of oily fish is below 2 portions per week. Maintenance/general health: 250–500mg combined EPA+DHA daily — broadly achievable from 1 portion of oily fish or a standard fish oil capsule. Cardiovascular risk management: 1–2g EPA+DHA daily; prescription-strength 4g EPA (Vascepa/Vazkepa) for hypertriglyceridaemia is GP-prescribable. Depression (adjunct): 1–2g EPA daily, EPA:DHA ratio >2:1. Joint inflammation: 2–3g EPA+DHA daily. Pregnancy: 200mg DHA daily minimum (use algae-based to avoid heavy metal exposure from fish). Always check the EPA+DHA content on the label, not just total fish oil.
Frequently Asked Questions About Omega-3
Are all fish oil supplements the same?
No — quality and EPA/DHA content vary significantly. Check the label for actual EPA+DHA content per capsule rather than total fish oil weight. A 1000mg fish oil capsule may contain as little as 300mg EPA+DHA or as much as 750mg. Triglyceride-form omega-3 is slightly better absorbed than ethyl ester form. Enteric-coated capsules reduce fish burp.
Is omega-3 from algae as good as from fish?
Yes — algae-derived omega-3 provides EPA and DHA with bioavailability equivalent to fish oil. Fish are rich in EPA/DHA because they eat microalgae (directly or indirectly through the food chain). Algae-based omega-3 is the sustainable, vegan-compatible, heavy-metal-free original source.
Can omega-3 cause bleeding?
At standard supplement doses (1–3g EPA+DHA daily), clinically significant bleeding risk is minimal. At doses of 4g+ daily, omega-3 modestly increases bleeding time — relevant consideration if you take anticoagulants or antiplatelet drugs (discuss with GP/pharmacist). Routine surgery precautions apply at high doses.
Browse omega-3 supplements including fish oil and algae-based options at Huncoat Pharmacy. Related: Heart-Healthy Diet, Cholesterol, Brain Health.
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