Omega-3: what are their real health benefits? What science really says

Summary

Omega-3s are among the most studied nutrients in the world. For several decades, they have been presented as protective for the heart, brain, eyes and even mood. Yet the results of the major scientific studies are sometimes contradictory.

Why do some studies show a spectacular benefit while others find no effect at all?

The answer largely lies in the fact that not all omega-3s are identical. Their origin, composition, dose and the population studied considerably influence their effects.

Today, the scientific literature makes it possible to clearly distinguish firmly demonstrated benefits from those that are still debated.

What are omega-3s?

Omega-3s are polyunsaturated fatty acids essential for the normal functioning of the body. Three main forms are distinguished.

Alpha-linolenic acid (ALA)

ALA is an essential fatty acid. Our body is unable to produce it. It must be supplied by the diet. It is found mainly in:

• rapeseed (canola) oil;
• walnuts;
• flax seeds;
• chia seeds;
• certain vegetable oils.

ALA is the precursor of the other two omega-3s. However, this conversion is very limited.

In adults, less than 10% of ALA is converted into EPA, and often less than 5% into DHA. This conversion varies according to sex, age, hormonal status and omega-6 intake.

EPA (eicosapentaenoic acid)

EPA is essentially found in oily fish:

• sardine;
• mackerel;
• herring;
• anchovy;
• salmon.

It mainly has anti-inflammatory and cardiovascular properties.

DHA (docosahexaenoic acid)

DHA is a major constituent of:

• the brain;
• the retina;
• the nervous system.

It plays a particularly important role during pregnancy and the first years of life.

Why are omega-3s important?

The membranes of all our cells contain fatty acids. Omega-3s influence:

• their fluidity;
• communication between cells;
• inflammatory mechanisms;
• certain immune functions;
• the production of many signalling molecules.

They also take part in the synthesis of specialised mediators called resolvins, protectins and maresins, involved in the resolution of inflammation.

It is important to stress that omega-3s are not anti-inflammatories in the classic sense of the term: they mainly promote the return to a state of balance after an inflammatory response.

Which benefits are well demonstrated today?

1. An effective reduction in triglycerides

This is probably the best-established benefit. At high doses (2 to 4 g/day of EPA ± DHA), omega-3s generally allow a reduction in triglycerides of 20 to 40%, sometimes more in patients with severe hypertriglyceridaemia.

2. Cardiovascular protection… under certain conditions

For a long time, all omega-3 supplementation was considered protective. The major studies have shown that the reality is more complex.

The REDUCE-IT trial demonstrated that a dose of 4 g/day of icosapent ethyl (purified EPA) reduced major cardiovascular events by 25% in high-risk patients already treated with a statin.

Conversely, the STRENGTH trial, using an EPA + DHA combination, found no significant benefit.

These results suggest that not all omega-3 formulations have the same efficacy, even if differences in formulation, placebo and blood concentrations reached could also explain part of the discrepancies.

3. Pregnancy and neurological development

DHA is essential for the brain development of the foetus. A sufficient intake during pregnancy is associated with better visual and neurological development.

Several learned societies recommend a daily intake of about 200 to 300 mg of DHA in pregnant women, particularly when the consumption of oily fish is low.

4. Eye health

DHA represents nearly half of the fatty acids present in the membranes of the retinal photoreceptors.

People who eat fish regularly appear to have a lower risk of age-related macular degeneration (AMD). Conversely, supplementation trials have not convincingly demonstrated that they slow the progression of already established AMD.

Are the benefits demonstrated for the brain?

The brain contains a high concentration of DHA. This long suggested that supplementation could prevent brain ageing. The results are now much more nuanced.

The major studies have not shown a clear improvement in memory in healthy older people.

Regarding Alzheimer's disease, some observational studies suggest that a high omega-3 status is associated with a lower risk, but intervention trials have not confirmed a significant clinical benefit. Omega-3s should therefore not be considered a validated preventive treatment for this disease.

Omega-3s and depression

Several meta-analyses show a modest benefit of certain EPA-rich formulations as a complementary treatment in patients with depression, in combination with standard management.

However, they replace neither antidepressants when they are indicated, nor psychotherapy.

Omega-3s and inflammatory diseases

Omega-3s appear to have a beneficial effect in certain chronic inflammatory diseases, such as rheumatoid arthritis, where they may help reduce pain and the use of anti-inflammatory drugs.

In dermatology, their value has been studied in psoriasis and atopic dermatitis, but the results remain heterogeneous and do not allow their systematic use to be recommended.

Should diet or supplements be preferred?

In most cases, a balanced diet remains the best strategy. The main sources are:

• sardines;
• mackerel;
• herring;
• anchovies;
• salmon;
• trout;
• rapeseed and walnut oils;
• flax or chia seeds.

Supplements can be useful when dietary intake is insufficient or when a precise medical indication exists, particularly for the treatment of certain hypertriglyceridaemias.

Are all supplements equal?

No. The quality of a supplement depends on several criteria:

• actual concentration of EPA and DHA;
• stability of the oil (low oxidation);
• purity (absence of contaminants such as heavy metals or PCBs);
• chemical form (natural triglycerides, re-esterified triglycerides or ethyl esters).

Products that have undergone independent testing generally offer greater quality guarantees.

Are there any risks?

Omega-3s are generally very well tolerated. The most common side effects are:

• fishy-tasting burping;
• mild digestive discomfort.

At high doses (above 4 g/day), some studies have reported a slight increase in the risk of atrial fibrillation in predisposed patients. An increased risk of bleeding has not been clearly demonstrated at usual doses, but caution is recommended in people treated with anticoagulants.

What is the relationship between omega-3 and omega-6?

Omega-3s and omega-6s use certain common enzymes. Western diets often provide much more omega-6 than omega-3.

The aim is not to eliminate omega-6, which is also essential, but to restore a better dietary balance, in particular by increasing natural sources of omega-3.

What the studies do not demonstrate

The scientific data do not make it possible to claim that omega-3s:

• prevent the development of Alzheimer's disease;
• improve memory in all adults;
• prevent all cancers;
• replace a balanced diet;
• systematically reduce cardiovascular risk regardless of the formulation used.

Their efficacy depends on the molecule, the dose, the indication and the patient's profile.

The Valorian analysis

Omega-3s remain among the best-studied nutrients in preventive medicine, but also among the most misunderstood. For a long time, they were presented as a universal solution against cardiovascular disease, brain ageing or inflammatory disorders. The work of the last fifteen years has shown that this view was too simplistic.

Today, the literature allows for greater precision. The benefits are solid for certain indications, such as reducing triglycerides or the use of high-dose purified EPA in highly selected cardiovascular patients. Conversely, the evidence is much less convincing for the prevention of cognitive decline, of many chronic diseases, or in healthy people taking low-dose supplements.

The key message is that not all omega-3s are equivalent. Confusing a diet rich in oily fish, a standard food supplement and a purified-EPA medicine leads to misinterpretations of the studies.

For most people, the most relevant strategy remains a varied diet that regularly includes oily fish and plant sources of ALA. Supplementation should be considered when an indication is clearly identified or when a sufficient dietary intake cannot be achieved.