Omega 3, EPA and DHA: Evidence and the Omega-3 Index

TL;DR: The Omega-3 Index measures the share of EPA and DHA in red blood cells and is a direct marker of supply. The evidence on omega 3 is limited or mixed depending on the question, and observational studies do not prove a causal benefit. Whether intake makes sense is for a doctor to clarify, not this article.

Why omega 3 is not one thing

“Omega 3” is an umbrella term for several fatty acids with very different roles in the body. The three relevant forms are EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid) and ALA (alpha-linolenic acid). Studies mainly examine EPA and DHA, among other things in relation to inflammatory processes, the cardiovascular system and nervous system function. ALA from flaxseed or walnuts must first be converted to EPA and DHA, and the human body does this only to a very limited extent.

EPA is the precursor of inflammation-resolving mediators such as resolvins and is linked to the modulation of pro-inflammatory signaling. DHA is the dominant fatty acid in brain and retina and plays a role in the membrane structure of nerve cells and in fetal brain development. Depending on the question, studies focus more on EPA or on a balanced EPA/DHA ratio.

Conversion rates from ALA to EPA sit between 5 and 8 percent, and to DHA usually below 1 percent. Plant-based ALA sources are part of a balanced diet but do not replace the direct supply of EPA and DHA from fish or algae. Fatty cold-water fish is among the foods that provide EPA and DHA.

The three omega-3 forms compared

Not every fish oil product is equal. The chemical form influences how much EPA and DHA actually reaches the blood. The three common forms differ in bioavailability, stability and price.

Ethyl ester (EE) is the cheapest and most widely sold form. Fish oil is concentrated by chemically esterifying the fatty acids with ethanol. Bioavailability is lower than the natural form because the body has to cleave the ethyl bond first. In older adults and with weak fat digestion, absorption is significantly lower.

Triglyceride form (rTG) matches the natural form in fish. Re-esterified triglycerides are EE oils enzymatically returned to the triglyceride backbone and combine high concentration with good absorption. Studies report about 70 percent better bioavailability versus EE. It is usually more expensive than EE.

Phospholipid form from krill oil is bound to phospholipids and, according to studies, is absorbed particularly fast. Krill oil contains only 15 to 25 percent EPA and DHA, however, and the price per gram of active ingredient is three to five times higher than for rTG fish oil.

Omega-3 fatty acids are fat-soluble. In bioavailability studies, absorption depended markedly on the fat consumed at the same time. How and when a product is taken is a matter for a doctor.

Telling total oil apart from EPA+DHA content

A common label confusion is the difference between the amount of fish oil and the content of EPA and DHA. Of the total oil in a capsule, often only part is actually EPA and DHA, and the rest is carrier oil. The statement of EPA and DHA content is therefore what carries information, not the total amount of fish oil.

What studies examine

Studies on EPA and DHA exist in several areas. Results differ by question, study population and product; the evidence is mixed overall and limited for individual questions.

General supply. Cohort studies describe associations between low omega-3 supply and cardiovascular events. Observational studies can show associations but cannot prove a causal benefit of taking supplements.

Inflammation markers. Studies examine effects on markers such as hsCRP, for example with elevated values above 1.5 mg/L, chronic joint issues or an autoimmune context. Meta-analyses report small changes in hsCRP; results are not consistent.

Triglycerides and depressive episodes. For elevated triglycerides (above 200 mg/dl) and for depressive episodes, effects have been examined in studies that mostly took place under medical supervision. In depression the focus was mainly on EPA-dominant products with an EPA share above 60 percent. Use in these areas belongs with a doctor, especially when blood thinners are involved.

How to capture starting values such as hsCRP, triglycerides and the Omega-3 Index cleanly is shown in the Biomarker Baseline Checklist.

The Omega-3 Index: what it measures

The Omega-3 Index is the direct measure of omega-3 status. It captures the percentage of EPA and DHA among all fatty acids in the membranes of red blood cells. The advantage over plasma measurements: erythrocyte membranes reflect supply over the last 3 to 4 months, not the last meal. Where the Omega-3 Index typically lies in Germany and Europe is shown in our omega-3 index statistics for Europe.

The ranges are described in several cohort studies. Values below 4 percent count as a high-risk range; Framingham Offspring and PREDIMED data show a clearly elevated cardiovascular risk there. Values between 4 and 8 percent are the middle range and most common in the Western population, with the German average around 5.5 percent. Values above 8 percent are classed as the favorable range and, in observational studies, are associated with lower rates of sudden cardiac death, dementia and all-cause mortality. An association is not proof that a value should be reached through supplements.

The test is usually a dry blood spot from a finger prick: a card kit comes to your home, the sample is taken by finger prick and sent to the lab. Costs are 40 to 60 euros depending on the provider. The index only shifts visibly over 12 to 16 weeks; at shorter intervals you mostly see measurement noise. How biomarkers can be interpreted overall is explained in the cornerstone article Understanding Blood Values.

Interpreting quality labels on fish oil

Omega 3 is one of the supplement categories with frequent quality problems: oxidation, heavy metals and inaccurate content statements are widespread. The following six pieces of information help to classify a product.

1. Certificate of Analysis (COA) per batch. The manufacturer publishes values for EPA and DHA content, heavy metals (lead, mercury, cadmium, arsenic), PCBs, dioxins and oxidation.
2. TOTOX value. TOTOX (Total Oxidation Value) measures rancidity. Values below 10 are considered acceptable, below 5 very good. Higher values mean the oil is already partially oxidized.
3. Statement of the chemical form. With ethyl ester products, absorption is lower than with the triglyceride form (rTG).
4. EPA and DHA content on the label. The statement of EPA and DHA is what carries information, not just the term “fish oil”.
5. Dark glass or light-blocking softgels. Light accelerates oxidation.
6. IFOS certification. International Fish Oil Standards (IFOS) test batches for purity and oxidation and rate them on a 5-star scale.

A structured classification with a scoring rubric is offered by the Supplement Quality Audit.

Interactions and side effects

The EFSA has assessed the safety of EPA and DHA and sees no relevant adverse effects in healthy adults within the range it evaluated. Even so, three points are known that should be clarified with a doctor.

Blood thinners. Omega 3 slightly dampens platelet aggregation. With warfarin, aspirin or NOACs like apixaban and rivaroxaban, bleeding tendency may rise, especially at higher intake. In studies the risk was not significantly elevated at low intake. Before planned surgery and with any combination involving blood thinners, intake should be clarified with a doctor.

LDL cholesterol. At very high intake of DHA-rich products, studies describe a slight rise in LDL cholesterol in some people. At the same time, triglycerides and VLDL are measured lower in studies. The overall profile should be assessed by a doctor, including the LDL subfraction.

Fish burps and GI. The most common side effect is a fishy aftertaste or mild burping. It is often linked to product quality, for example a high TOTOX value.

Plant-based source: algae oil

Algae oil is the only serious plant-based source of EPA and DHA. The same algae that fish feed on are cultivated in tanks and the oil is extracted. The final product contains EPA and DHA in bioavailable form, without the detour through the food chain.

Differences from fish oil that are mentioned: no fishy taste, less burping, lower heavy metal load (algae do not bioaccumulate contaminants like large predator fish), vegan, more sustainable. The price per gram of EPA and DHA is higher, and some products are more DHA-heavy. Several head-to-head studies describe similar effects on the Omega-3 Index at equal intake as with fish oil. Whether algae oil is an option is a question of diet and medical advice.

Following lab values over time

Lab values can only be interpreted when a starting value exists. It is common to look at the Omega-3 Index (dry blood spot, 40 to 60 euros), hsCRP (high-sensitivity CRP as an inflammation marker, 10 to 20 euros) and fasting triglycerides (usually part of a lipid panel) together. For the starting value and later comparison measurements, identical conditions matter: the same lab, fasted in the morning. For a broader look at the starting point with reference ranges, see the cornerstone article Understanding Blood Values.

How changes over time can be evaluated in a structured way is described in the article on evaluating trend data. A change in a value says nothing about whether a measure is responsible for it, however, and whether action is needed is for a doctor to judge.

For the long view see Long-Term Biomarker Tracking, because the Omega-3 Index shifts slightly with the seasons and only stabilizes over 2 to 3 yearly measurements. An overview of frequently discussed supplement categories is given in the Supplement Beginners Guide.

Conclusion

Omega 3 is one of the better-studied topics in the supplement field, and the Omega-3 Index is a direct biomarker of supply. The evidence remains limited or mixed depending on the question, though, and associations from observational studies are not proof of benefit. On labels, the content of EPA and DHA counts, not the total amount of fish oil, and quality information such as COA, TOTOX value and chemical form helps with classification.

Whether, in what form and in what amount a product makes sense is decided by a doctor, especially with blood thinners, chronic conditions or abnormal lab values. In Lab2go you can record lab values, notes and the Omega-3 Index in one place so the trend over years becomes visible. Information on the plans is on the pricing and plans page.

This article is for information and is not a substitute for medical advice. It gives no recommendation to take any product. Intake, the dose set by a doctor and therapy must be clarified with a doctor, especially with blood thinners or chronic conditions.