Omega-3 Blood Test UK: What Your Omega-3 Index, EPA & DHA Levels Actually Mean

1. Why omega-3 matters: EPA, DHA, and cell membrane biology

Omega-3 fatty acids are a family of polyunsaturated fats that your body cannot synthesise in meaningful quantities on its own. The three physiologically important forms are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Each has a distinct biological role, and understanding the difference between them is essential to understanding what an omega-3 blood test is actually measuring.

ALA is the plant-derived form, found in flaxseed, chia seeds, and walnuts. It is classified as an essential fatty acid because the body cannot make it. However, ALA's primary value is as a precursor — in theory, your body can convert it to EPA and then DHA via a series of elongation and desaturation steps. In practice, conversion is remarkably inefficient: research published in the American Journal of Clinical Nutrition (2002) found that conversion of ALA to EPA is roughly 5–10%, and conversion to DHA is less than 1% in most adults. This is the central reason why vegetarian and vegan diets are associated with low omega-3 index values despite often generous ALA intake.

EPA (eicosapentaenoic acid) is the anti-inflammatory workhorse of the omega-3 family. It is the precursor to a series of signalling molecules called eicosanoids — specifically the Series 3 prostaglandins and thromboxanes, which reduce platelet aggregation, dilate blood vessels, and dampen inflammatory signalling. EPA also gives rise to specialised pro-resolving mediators (SPMs) called resolvins of the E series, which actively resolve inflammation rather than merely suppressing it.

DHA (docosahexaenoic acid) is the structural fatty acid. Around 60% of the dry weight of your brain is fat, and DHA constitutes approximately 30–35% of the fatty acids in brain grey matter. It is also the dominant fatty acid in the outer segments of photoreceptors in the retina, and is present in high concentrations in cardiac muscle tissue. DHA's role is architectural: it gives cell membranes fluidity and flexibility, allowing ion channels to open and close efficiently, facilitating neurotransmitter release, and enabling rapid signal transmission between neurons.

Cell membrane fluidity is worth dwelling on. Every cell in your body is surrounded by a phospholipid bilayer. The fatty acid composition of that bilayer directly determines how well it functions. When EPA and DHA are incorporated into membrane phospholipids at adequate levels, membranes are fluid, flexible, and responsive. When the omega-6 fatty acid arachidonic acid (AA) dominates instead — as it does in most Western diets — membranes become more rigid and pro-inflammatory eicosanoid production increases.

The eicosanoid balance between omega-3 and omega-6 derived signalling molecules has consequences that extend far beyond the cardiovascular system. Inflammation is the shared mechanism underlying conditions from systemic inflammation to joint pain, dry eye disease, age-related cognitive decline, and mood disorders. Measuring your omega-3 index gives you a window into the fatty acid composition of every cell membrane in your body.

2. The omega-3 index: what it is and why it matters

The omega-3 index is defined as the percentage of EPA plus DHA relative to the total fatty acids in red blood cell (erythrocyte) membranes. It was developed by cardiologists William S. Harris and Clemens von Schacky and introduced in a landmark paper in Preventive Medicine (2004).

The choice of red blood cell membranes, rather than plasma, is deliberate. Plasma fatty acid levels fluctuate within hours of a meal — eat a tin of sardines for lunch and your plasma EPA will spike by early evening, then fall again by morning. Red blood cells, by contrast, turn over roughly every 120 days. Their fatty acid composition therefore reflects your average omega-3 intake and status over approximately four months, making the omega-3 index a stable, reproducible biomarker rather than a snapshot of what you ate last weekend.

Harris and von Schacky proposed three risk zones based on their analysis of population data and cardiovascular outcomes:

• Below 4%: High-risk zone, associated with the highest rates of fatal coronary artery disease.
• 4% to 8%: Intermediate zone. Still below optimal, with residual cardiovascular and inflammatory risk.
• 8% to 12%: Target zone. Associated with significantly lower cardiovascular mortality and optimal cell membrane function.

The index has since been validated in multiple large cohort studies. An analysis using data from the Framingham Heart Study found that each 1% increase in the omega-3 index was associated with a measurable reduction in all-cause mortality. Subsequent research has linked a higher omega-3 index to slower cellular ageing (measured by telomere length), lower plasma triglycerides, and reduced risk of sudden cardiac death.

Population data consistently shows that average omega-3 index values vary dramatically by geography and diet. Japanese fishing communities regularly achieve indices above 12%, with some individuals exceeding 15%. The average in North America and much of northern Europe sits between 4% and 6%. The UK's low oily fish consumption — only one in four adults meets the NHS recommendation of at least two portions of fish per week including one oily — means most people are operating well below the optimal zone without knowing it.

3. Other omega-3 blood markers: plasma EPA+DHA, omega-6:omega-3 ratio, and AA:EPA ratio

The omega-3 index is the most clinically validated long-term marker, but it is not the only omega-3 metric you may encounter on a comprehensive fatty acid panel. Understanding each one helps you interpret a full report.

Plasma EPA and DHA

Plasma (or serum) EPA and DHA levels measure the fatty acids circulating in your blood at the time of the test, typically expressed as a percentage of total plasma fatty acids or in micromoles per litre (µmol/L). Because plasma fatty acids fluctuate rapidly with recent dietary intake, this marker is more useful as a short-term indicator of recent consumption than as a long-term status measure. A single high-EPA meal two days before your test will elevate plasma EPA without changing your omega-3 index by more than a fraction of a percent.

Plasma EPA and DHA are still clinically meaningful, particularly when comparing a patient's response to supplementation over several weeks, or when a quick snapshot of recent intake is needed. For the purposes of cardiovascular risk stratification, however, the omega-3 index is the preferred marker.

Omega-6:omega-3 ratio

The omega-6:omega-3 ratio reflects the overall balance between pro-inflammatory and anti-inflammatory fatty acids in your diet. The two families compete for the same desaturase and elongase enzymes, meaning a high omega-6 intake suppresses the conversion of ALA to EPA and DHA, and competes with EPA for incorporation into cell membranes.

The ideal ratio is considered to be below 4:1. In pre-agricultural populations, the ratio is estimated to have been approximately 1:1–2:1. In the modern Western diet — dominated by vegetable oils rich in linoleic acid (sunflower, corn, soybean oil) and minimal oily fish — the ratio has ballooned to roughly 15:1 to 20:1 in many Western populations. Research by Simopoulos, published in Biomedicine & Pharmacotherapy (2002), established that this imbalance promotes the pathogenesis of cardiovascular disease, cancer, and inflammatory and autoimmune diseases.

AA:EPA ratio

The arachidonic acid to eicosapentaenoic acid (AA:EPA) ratio is a more granular measure of the pro-inflammatory:anti-inflammatory balance at the eicosanoid level. AA is the omega-6 fatty acid from which Series 2 prostaglandins and thromboxanes — broadly pro-inflammatory and pro-thrombotic signalling molecules — are derived. EPA counters this by competing for the same cyclooxygenase enzymes and producing the less inflammatory Series 3 equivalents.

A lower AA:EPA ratio indicates a less inflammatory eicosanoid environment. Optimal is generally considered below 5:1–6:1, though some functional medicine practitioners target below 3:1. Japanese populations eating traditional diets achieve ratios around 1.5:1–3:1. The typical Western diet produces ratios of 10:1–20:1.

4. What a low omega-3 index means for your health

A low omega-3 index is not an abstract statistical risk. It has measurable, documented effects on cardiovascular function, cognitive health, visual function, joint health, and mood regulation.

Cardiovascular risk

The cardiovascular evidence is the most robust. The original Harris-von Schacky paper found that individuals with an omega-3 index below 4% had 10 times the risk of sudden cardiac death compared with those above 8%. Subsequent analyses using Framingham cohort data confirmed that a higher omega-3 index was independently associated with lower rates of cardiovascular events, even after adjusting for traditional risk factors such as blood pressure, smoking, and cholesterol.

The mechanisms are well-characterised. Low omega-3 status is associated with higher resting heart rate, reduced heart rate variability, elevated plasma triglycerides, greater platelet aggregation, and impaired endothelial function — a cluster of risk factors that collectively increase the probability of both coronary artery disease and arrhythmia. The VITAL study (2019), published in the New England Journal of Medicine, found that omega-3 supplementation at 1g/day reduced the rate of major cardiovascular events by 28% in participants who consumed less than 1.5 portions of fish per week at baseline.

Cognitive decline

Analysis of Framingham Heart Study data by Tan and colleagues, published in Neurology (2012), found that participants with the lowest plasma DHA levels had significantly smaller brain volumes — including in the hippocampus, the brain region central to memory consolidation — compared with those in the highest DHA quartile. Lower DHA was also associated with poorer performance on tests of visual memory, executive function, and abstract thinking.

Dry eyes and visual function

DHA accounts for approximately 30–60% of fatty acids in the retina's rod outer segments. Insufficient DHA impairs the regeneration of the visual pigment rhodopsin, slows dark adaptation, and has been associated with increased risk of age-related macular degeneration. Low omega-3 status is also linked to reduced tear film stability and dry eye symptoms, as EPA and DHA contribute to the lipid layer of the tear film that prevents evaporation.

Joint inflammation and mood

Low EPA:AA ratios are associated with higher levels of inflammatory cytokines, including IL-6 and TNF-α, which underpin the joint pain and stiffness characteristic of inflammatory arthritis. In mental health, meta-analyses published in Translational Psychiatry (2016) found that omega-3 supplementation — particularly EPA-dominant preparations — produced clinically significant reductions in depressive symptoms, with an effect size comparable to that of some antidepressant medications in mild-to-moderate depression.

5. NHS vs private omega-3 testing

Omega-3 status is not measured by any standard NHS blood test. The routine NHS cardiovascular risk screen includes total cholesterol, LDL, HDL, triglycerides, and blood glucose — but not the omega-3 index, plasma EPA+DHA, or the omega-6:omega-3 ratio. This is not an oversight; it reflects the fact that omega-3 testing requires specialist fatty acid analysis equipment (gas chromatography) that is not part of standard NHS laboratory workflows.

The NHS does not have a clinical pathway that triggers omega-3 testing. Even if you present to your GP with symptoms of deficiency — dry eyes, joint stiffness, poor sleep, or mood difficulties — you are unlikely to be offered a fatty acid panel through NHS routes. The National Institute for Health and Care Excellence (NICE) does not currently recommend routine population-level omega-3 screening.

In the private sector, omega-3 testing is available via several routes. Companies such as OmegaQuant offer standalone omega-3 index testing using a finger-prick dried blood spot (DBS) card, which you complete at home and post to a laboratory. The DBS format is well-validated: studies comparing DBS cards with venous blood samples show excellent correlation with coefficients above 0.97 for EPA and DHA measurement.

Helvy's Nutrition panel includes the omega-3 index alongside vitamin D, B12, folate, iron, ferritin, magnesium, and zinc — allowing you to see how your omega-3 status fits within the broader nutritional picture. Given that omega-3 deficiency frequently co-occurs with vitamin D insufficiency in populations with low sunlight and oily fish intake, measuring both simultaneously provides more actionable insight than a single biomarker.

6. Omega-3 index ranges: from high risk to optimal

The table below summarises the established omega-3 index risk categories based on the Harris-von Schacky framework and subsequent validation studies:

It is worth noting that most UK adults who do not eat oily fish regularly will fall between 4% and 6% — technically within the “intermediate” band, but far from optimal. A daily fish oil supplement providing 1–2g of combined EPA and DHA can typically raise the omega-3 index by 2–3 percentage points over 16 weeks, which is sufficient to move many people from the intermediate into the lower end of the optimal range.

The target of 8% or above is not a theoretical ideal. It is the threshold at which observational studies consistently show reduced cardiovascular event rates, and it is achievable for most people through a combination of dietary change and targeted supplementation. Aiming higher — towards 10–11% — requires consuming multiple portions of oily fish per week or using higher-dose EPA and DHA supplements, which is the pattern seen in Japanese populations where cardiovascular mortality is among the lowest in the world.

7. Who should get an omega-3 blood test?

Because the NHS does not offer omega-3 index testing, and because symptoms of low omega-3 status overlap with numerous other conditions, the question of who should proactively test is worth addressing directly.

Vegetarians and vegans

This is the group with the highest likelihood of a clinically significant omega-3 index deficiency. Plant-based diets provide ALA from walnuts, flaxseed, and chia, but as noted above, conversion to EPA and DHA is negligible. A large cross-sectional study published in the American Journal of Clinical Nutrition (2014) found that vegans had plasma DHA concentrations approximately 59% lower than omnivores. Testing provides a baseline, and algal oil supplementation (the only plant-derived source of preformed DHA) offers an effective correction strategy.

People with cardiovascular risk factors

If you have elevated cholesterol, elevated apolipoprotein B, raised Lp(a), or a family history of cardiovascular disease, understanding your omega-3 index provides an additional modifiable risk factor to work on. Unlike many cardiovascular risk markers, omega-3 status can be substantially improved within months.

People on statins

Statins reduce LDL cholesterol effectively, but they do not raise the omega-3 index. Patients on long-term statin therapy who eat little oily fish may have a well-managed LDL profile alongside a persistently low omega-3 index, leaving residual cardiovascular risk unaddressed. Combining statin therapy with omega-3 optimisation is supported by emerging evidence from the REDUCE-IT trial, which enrolled patients already on statin therapy.

Pregnant women and people planning pregnancy

DHA is critical for foetal brain and retinal development, with accumulation accelerating substantially in the third trimester. NICE guideline NG62 does not currently recommend omega-3 supplements as a routine antenatal intervention, but notes the importance of adequate DHA intake. Women who consume no oily fish during pregnancy are at particular risk of maternal DHA depletion as the foetus draws on maternal stores.

Athletes

High-intensity exercise generates oxidative stress and pro-inflammatory cytokines as part of the normal recovery process. Adequate EPA and DHA accelerate the resolution phase of this inflammatory response, supporting faster recovery, reduced delayed-onset muscle soreness, and potentially improved training adaptation. This is explored in more detail in our athlete blood test guide.

Anyone not meeting the fish recommendation

The NHS recommends two portions of fish per week, including at least one portion of oily fish (salmon, mackerel, sardines, herring, or fresh tuna). If you eat oily fish less than once a week, you are likely to have an omega-3 index below 6% and would benefit from testing to understand your baseline before deciding whether dietary change alone is sufficient.

8. Dietary sources of omega-3

Food remains the most reliable way to maintain a healthy omega-3 index, and understanding the difference between marine and plant sources is essential for making informed choices.

Marine sources: EPA and DHA direct

Oily fish are by far the most efficient dietary route to raising the omega-3 index because they provide preformed EPA and DHA that is directly incorporated into cell membranes without the conversion bottleneck. Typical EPA+DHA content per 100g serving:

• Mackerel: approximately 2,200–2,600mg EPA+DHA
• Salmon (farmed Atlantic): approximately 1,800–2,200mg EPA+DHA
• Sardines (canned in oil): approximately 1,400–1,800mg EPA+DHA
• Herring: approximately 1,600–2,000mg EPA+DHA
• Anchovies: approximately 1,400–1,700mg EPA+DHA
• Trout: approximately 700–1,000mg EPA+DHA

The Scientific Advisory Committee on Nutrition (SACN) reviewed fish consumption guidance in 2004 and concluded that eating two portions of fish per week, including one oily, would provide approximately 450mg of EPA+DHA daily on average. This is consistent with what epidemiological data suggests is the minimum level associated with cardiovascular benefit.

Note that canned tuna (in brine or water) is not a significant source of EPA and DHA — the canning process substantially reduces its omega-3 content. Fresh or frozen tuna does contain meaningful EPA+DHA (approximately 300–500mg per 100g), but it counts as white fish for NHS guidance purposes; only one portion of fresh tuna per week is recommended due to mercury content.

Algae-based DHA for vegans

Marine algae — specifically microalgae such as Schizochytrium and Nannochloropsis species — are the original source of DHA in the marine food chain. Fish accumulate DHA by eating smaller fish and crustaceans that eat phytoplankton. Algal oil bypasses this food chain entirely and provides directly bioavailable DHA and, depending on the species, EPA. It is the only plant-based source of preformed long-chain omega-3s. Algal oil supplements typically provide 200–500mg DHA per capsule and are well-tolerated. Studies confirm they raise the omega-3 index comparably to fish oil at equivalent DHA doses.

Plant sources: ALA only

Walnuts, flaxseed (linseed), chia seeds, hemp seeds, and rapeseed oil provide ALA. These foods are nutritionally valuable and should be included in a balanced diet, but they should not be relied upon as a primary omega-3 strategy for anyone concerned about their omega-3 index. Given the conversion rate of less than 10% to EPA and less than 1% to DHA, even generous daily consumption of flaxseed is unlikely to move the omega-3 index meaningfully. They are a complement to, not a replacement for, preformed EPA and DHA.

9. Omega-3 supplementation: fish oil, algal oil, and krill oil

If dietary sources alone are insufficient to achieve your target omega-3 index, supplementation is a well-validated strategy. The key decisions are form (fish oil, algal oil, or krill oil) and molecular structure (triglyceride versus ethyl ester).

Fish oil

Fish oil is the most studied form. Commercially available fish oils are derived from small pelagic fish (anchovies, sardines, mackerel) and provide EPA and DHA in concentrations that vary considerably between products. Many standard supermarket fish oil capsules (often labelled “omega-3 fish oil 1000mg”) contain only 180mg EPA and 120mg DHA per capsule — just 300mg combined. To achieve the 1–2g of combined EPA+DHA per day associated with cardiovascular benefit, you would need three to seven such capsules daily. High-strength pharmaceutical-grade fish oils provide 500–1000mg EPA+DHA per capsule and are far more practical.

Triglyceride vs ethyl ester form

EPA and DHA in fish oil are present either as natural triglycerides (the form found in fish) or as ethyl esters (a concentrated form produced by transesterification during manufacturing). Triglyceride form is absorbed approximately 70% more efficiently than ethyl ester form, particularly when taken without food. When taken with a fat-containing meal, the absorption gap narrows considerably. Ethyl ester products are not inferior if taken consistently with food, and they allow higher EPA+DHA concentrations per capsule. The key is consistency of use.

Algal oil

As described in the dietary sources section, algal oil is the correct choice for vegans and vegetarians. It is also a sustainable alternative for anyone concerned about the environmental impact of fish oil. Well-formulated algal oil supplements provide comparable omega-3 index elevation to fish oil at equivalent EPA+DHA doses. Look for products providing at least 500mg combined EPA+DHA per daily dose, and check that the product specifies both EPA and DHA content — some algal oils provide DHA only.

Krill oil

Krill oil is derived from Antarctic krill and provides EPA and DHA in phospholipid form, which some researchers argue improves brain uptake because phospholipid-bound DHA may cross the blood-brain barrier more efficiently. Krill oil also contains astaxanthin, a potent antioxidant that may prevent EPA and DHA oxidation. Head-to-head studies comparing krill oil with fish oil at equivalent EPA+DHA doses show broadly comparable omega-3 index elevation, though krill oil is significantly more expensive per gram of EPA+DHA. Unless you have a specific reason to prefer krill oil, fish oil or algal oil are more cost-effective for most people.

The NICE guidance nuance

A frequently cited but often misunderstood point: NICE guideline CG181 (2014, updated 2023) no longer recommends omega-3 fatty acid supplements for secondary prevention of cardiovascular events after myocardial infarction, having previously done so. This reversal followed the publication of ORIGIN and other large trials that found no significant benefit of 1g/day EPA+DHA for secondary prevention in patients already on modern pharmacotherapy. This does not mean omega-3s are ineffective — the REDUCE-IT trial demonstrated clear benefit at 4g/day of a pure EPA preparation in high-risk patients on statins (see Section 10). The NICE guidance applies specifically to low-dose omega-3 supplements for secondary prevention post-MI, and should not be interpreted as meaning that omega-3 status is irrelevant to cardiovascular health. For primary prevention in people with low omega-3 status, the evidence base for correction remains sound.

10. Omega-3 and cardiovascular health: the trial evidence

The clinical trial landscape for omega-3 and cardiovascular health is nuanced, and understanding the key studies helps contextualise what an omega-3 test result actually means for your cardiac risk.

REDUCE-IT (2018)

The REDUCE-IT trial, published in the New England Journal of Medicine (2018), is the most consequential omega-3 cardiovascular trial to date. It enrolled 8,179 patients with established cardiovascular disease or type 2 diabetes who were on statin therapy and had elevated triglycerides (1.52–5.63 mmol/L). Patients were randomised to icosapent ethyl (a highly purified form of EPA) at 4g/day or a mineral oil placebo. Over a median of 4.9 years, icosapent ethyl produced a 25% relative risk reduction in major adverse cardiovascular events (MACE), including a 20% reduction in cardiovascular death. This is a remarkably large effect size for a single intervention in an already-treated population.

REDUCE-IT has been the subject of active academic debate, primarily because of concerns that the mineral oil placebo may have raised LDL and inflammatory markers in the control group, potentially inflating the apparent benefit of EPA. However, a subsequent analysis of the pharmacological data and supportive evidence from multiple mechanistic studies suggests that the majority of the observed benefit is real, and the ESC 2019 dyslipidaemia guidelines incorporated icosapent ethyl as a Class IIa recommendation for high-risk patients with elevated triglycerides on statin therapy.

VITAL (2019)

The VITAL trial, published in the New England Journal of Medicine (2019), enrolled 25,871 adults without prior cardiovascular disease. Participants were randomised to 1g/day of omega-3 fatty acids (460mg EPA+380mg DHA) or placebo. The primary endpoint of major cardiovascular events was not significantly reduced in the overall population. However, pre-specified subgroup analyses revealed a 28% reduction in myocardial infarction among participants who ate less than 1.5 portions of fish per week at baseline — precisely the group with the lowest omega-3 index. This is a clinically important finding: the benefit of supplementation appears most pronounced in people who are actually deficient.

STRENGTH (2020)

The STRENGTH trial tested omega-3 carboxylic acid (a mixture of EPA and DHA) at 4g/day versus corn oil placebo in high-risk patients on statins. Unlike REDUCE-IT, STRENGTH showed no significant reduction in cardiovascular events. The trial was terminated early at 90% of target enrolment. Crucially, post-hoc analyses suggested that corn oil may be a more neutral placebo than mineral oil, which complicates direct comparison with REDUCE-IT and supports the view that the REDUCE-IT benefit was at least partially attributable to the mineral oil placebo's pro-inflammatory effects. The mixed-EPA+DHA versus pure-EPA distinction is also believed to be clinically relevant.

What this means for you

The trial evidence supports a clear conclusion: people with low omega-3 status who eat little oily fish benefit from correcting that deficiency. Very high-dose pure EPA (4g/day) produces substantial cardiovascular risk reduction in high-risk patients with elevated triglycerides on statins — an approach now endorsed by ESC guidelines. For the general population, the most evidence-based strategy remains achieving an omega-3 index above 8% through dietary sources and, where necessary, supplementation. Knowing your number is the prerequisite for acting on it. See also our guide to heart health blood tests for the full cardiovascular biomarker picture.

11. Omega-3 and brain health: DHA, grey matter, and cognition

DHA is not merely present in the brain in large quantities — it is structurally essential to it. The grey matter of the human cerebral cortex contains approximately 10–15g of DHA. This DHA is concentrated in synaptic membranes, where it maintains the fluidity required for efficient neurotransmitter release and receptor function. The retina is similarly DHA-dependent, with DHA making up approximately 30–60% of fatty acids in photoreceptor outer segments.

The Framingham cohort analysis by Tan and colleagues (Neurology, 2012) found that participants in the lowest quartile of plasma DHA had significantly smaller total brain volumes, smaller hippocampal volumes, and lower scores on cognitive tests assessing visual memory, executive function, and abstract reasoning — compared with those in the highest DHA quartile. These differences persisted after adjustment for age, education, sex, and cardiovascular risk factors.

The MIDAS study (Memory Improvement with Docosahexaenoic Acid Study), a randomised controlled trial published in the Alzheimer's & Dementia journal (2010), found that healthy adults aged 55 and over with self-reported memory complaints who supplemented with 900mg/day of DHA for 24 weeks made significantly fewer errors on a paired associate learning test compared with placebo. Episodic memory improved by the equivalent of approximately three years of memory-related ageing reversal. The participants in MIDAS were not clinically cognitively impaired — this was a study of healthy older adults with subjective memory concerns.

Prenatal DHA is also important. DHA accumulates in the foetal brain and retina primarily during the third trimester and continues accumulating rapidly in the first two years of life. Breast milk DHA content directly reflects maternal DHA status, meaning that a mother with a low omega-3 index provides less DHA to her breastfed infant. While NICE does not currently recommend routine DHA supplementation in pregnancy, the evidence base supports adequate intake through oily fish or algal DHA for pregnant women who do not eat oily fish.

It is important to note that the evidence for omega-3 supplementation in established Alzheimer's disease is much weaker — the omega-3 story in brain health appears most relevant to prevention and to maintaining cognitive function in healthy ageing, rather than to treating established neurodegenerative disease.

12. Omega-3 and inflammation: SPMs, resolvins, and protectins

For decades, the anti-inflammatory role of omega-3s was explained primarily through competition with omega-6 fatty acids for cyclooxygenase and lipoxygenase enzymes, reducing production of pro-inflammatory eicosanoids. This mechanism is real and important, but it represents only part of the picture. Research over the past two decades has revealed a second mechanism that may be even more significant: the generation of specialised pro-resolving mediators (SPMs).

SPMs are a family of bioactive lipid mediators derived from EPA and DHA that actively programme the resolution of inflammation — a process distinct from, and more sophisticated than, simple suppression. Charles Serhan at Harvard Medical School, whose research has been published in the Journal of Clinical Investigation and other leading journals, identified the major SPM classes:

• Resolvins of the E series (RvE1, RvE2): Derived from EPA. They act on specific receptors on neutrophils and macrophages to halt neutrophil infiltration, promote macrophage efferocytosis (clearance of cellular debris), and reduce pro-inflammatory cytokine production.
• Resolvins of the D series (RvD1–RvD6): Derived from DHA. They share many of the neutrophil-dampening and macrophage-promoting actions of E-series resolvins, and are particularly implicated in resolution of acute pulmonary and joint inflammation.
• Protectin D1 (neuroprotectin D1): Derived from DHA. Named for its neuroprotective effects, it inhibits pro-inflammatory gene expression and promotes survival of neural cells under oxidative stress conditions.
• Maresins (MaR1, MaR2): Also DHA-derived. Discovered more recently, maresins stimulate macrophage phagocytic capacity and tissue regeneration.

The clinical implication is that omega-3s do not simply reduce inflammation — they accelerate its resolution. Chronic low-grade inflammation, the kind measured by high-sensitivity CRP (hs-CRP) and linked to cardiovascular disease, type 2 diabetes, and depression, reflects a failure of inflammation to fully resolve rather than just an excess of pro-inflammatory signalling. Adequate EPA and DHA status supports the active resolution mechanisms that prevent this chronicity.

Meta-analyses of omega-3 supplementation trials confirm reductions in circulating hs-CRP, IL-6, and TNF-α at doses of 2–4g combined EPA+DHA per day. If your inflammation markers are elevated alongside a low omega-3 index, addressing omega-3 status is one of the most evidence-based nutritional interventions available.

13. How to prepare for an omega-3 blood test

One of the practical advantages of the omega-3 index is that it does not require fasting before the test. Because the index measures the fatty acid composition of red blood cell membranes rather than circulating plasma lipids, a meal eaten earlier in the day will not meaningfully alter your result. This makes the dried blood spot finger-prick format particularly convenient — you can complete the test on a normal morning without any preparation other than ensuring your hands are warm (to facilitate blood flow) and that the collection card is stored away from heat sources before postage.

The four-month RBC turnover window means your omega-3 index reflects habitual intake over the preceding three to four months. This has two practical consequences. First, a single exceptional fortnight of oily fish consumption or a month of supplementation will have a limited effect on your result — sustained dietary change is what moves the index. Second, if you want to assess the impact of an intervention (changing diet or starting supplementation), you need to retest after at least three months, and ideally four, to see the full effect.

If you currently take a fish oil supplement, there is no need to stop before testing. The whole point of the test is to understand your actual status — including the effect of any supplement you are already taking. If you have recently started supplementation and want a true baseline, you could either test before starting or note your supplement start date and retest in four months.

Plasma EPA and DHA measurements, by contrast, are more sensitive to recent intake. If your panel includes plasma fatty acids alongside the omega-3 index, you may wish to avoid an unusually large oily fish meal in the 48 hours before testing, simply to avoid a misleading spike in the short-term markers. For the omega-3 index itself, this precaution is not necessary.

14. Interpreting your results with Helvy

Helvy's Nutrition panel includes the omega-3 index alongside vitamin D, vitamin B12, folate, iron, ferritin, magnesium, and zinc. This combination is not arbitrary. These nutrients frequently co-vary because they share dietary sources and lifestyle determinants.

People who eat little oily fish are often also low in vitamin D (oily fish is one of the few significant dietary sources of vitamin D), and may have lower B12 if they also eat little red meat or dairy. Vegans are particularly likely to present with low omega-3 index, low B12, and potentially low zinc simultaneously — a pattern that would be invisible if only a single marker were tested.

When you receive your Helvy results, each marker is presented with a personalised range context — not just whether you are within the laboratory reference interval, but where you sit within the evidence-based optimal range. For the omega-3 index, the target zone is 8–12%, and results are presented with tailored dietary and supplementation guidance based on how far your number sits from that target.

If your omega-3 index result falls below 6%, your report will include an explanation of the cardiovascular and inflammatory significance of that level, practical dietary guidance calibrated to your eating habits, and evidence-based supplementation recommendations including dosing and form. If you have concurrent low vitamin D, the report will note the likely shared dietary driver and address both in the same action plan.

For the full picture of how omega-3 status interacts with other cardiovascular biomarkers, see our guides on apolipoprotein B, Lp(a), and heart health blood tests. Omega-3 status is one piece of a broader cardiovascular picture, and understanding how it sits alongside your other markers is the most useful way to prioritise action. You may also find our guide to supplements that are actually worth taking useful for evaluating where omega-3s sit in the broader evidence hierarchy.

15. Frequently asked questions