Docosahexaenoic acid (DHA) is a vital omega-3 fatty acid essential for brain, eye, and heart health throughout life. Whilst the body can produce small amounts from plant-based omega-3s, this conversion is highly inefficient. Food that has DHA—primarily oily fish such as salmon, mackerel, and sardines—provides the most effective dietary source. The NHS recommends at least two portions of fish weekly, including one oily variety, to support cardiovascular function and neurological development. For those following plant-based diets or unable to consume fish, algae-based alternatives and fortified foods offer viable options. Understanding which foods contain DHA helps ensure adequate intake for optimal health across all life stages.

What Is DHA and Why Is It Important for Health?

Docosahexaenoic acid (DHA) is a long-chain omega-3 polyunsaturated fatty acid that plays a crucial structural and functional role in human health. As an essential component of cell membranes throughout the body, DHA is particularly concentrated in the brain, retina, and heart tissue. The human body can synthesise small amounts of DHA from alpha-linolenic acid (ALA), another omega-3 fatty acid found in plant sources, but this conversion process is very inefficient—typically less than 1% in adults, with some variation between individuals. Consequently, obtaining DHA directly from dietary sources is considered the most effective way to maintain adequate levels.

DHA is vital for neurological development and function throughout the lifespan. During pregnancy and early childhood, DHA accumulates rapidly in the developing brain and eyes, supporting cognitive development, visual acuity, and neural connectivity. In adults, adequate DHA intake contributes to normal heart function and helps maintain normal blood triglyceride levels. While some research suggests associations between DHA and maintained cognitive function in adults, the evidence is mixed.

Research suggests that DHA possesses anti-inflammatory properties and may play a role in modulating immune responses. The fatty acid is incorporated into cell membrane phospholipids, where it influences membrane fluidity, cell signalling pathways, and the production of bioactive lipid mediators called resolvins and protectins. These compounds help resolve inflammation and support tissue repair.

UK Government dietary advice and the Scientific Advisory Committee on Nutrition (SACN) recognise the importance of omega-3 fatty acids, including DHA, as part of a balanced diet. The NHS recommends consuming at least two portions of fish per week, including one portion of oily fish, to ensure adequate intake of these beneficial fatty acids.

Foods Naturally High in DHA

Oily fish represent the richest and most bioavailable dietary sources of DHA. These marine species accumulate DHA through their consumption of algae and smaller fish within the aquatic food chain. The following fish are particularly high in DHA content (values may vary by season, species, and whether wild or farmed):

• Salmon (farmed and wild): Contains approximately 0.9–1.4g of DHA per 140g NHS portion, with wild-caught varieties typically providing higher concentrations

• Mackerel: Provides around 1.0–1.4g of DHA per 140g portion

• Herring: Offers approximately 0.9–1.2g of DHA per 140g portion

• Sardines: Contain roughly 0.7–1.0g of DHA per 140g portion, and are often consumed whole with bones, providing additional calcium

• Anchovies: Deliver about 0.8g of DHA per 140g serving

• Trout (particularly rainbow trout): Provides approximately 0.5–0.8g of DHA per 140g portion

It's worth noting that canned tuna, while a good source of protein, is not classified as an oily fish in the UK as the canning process reduces the omega-3 content.

Other seafood sources include:

• Mussels, oysters, and other shellfish: Contain moderate amounts of DHA (typically 0.2–0.4g per 140g serving)

• Crab and prawns: Provide smaller but meaningful amounts of DHA

For individuals following plant-based or vegetarian diets, direct DHA sources are limited, as terrestrial plants do not synthesise this fatty acid. However, microalgae—the original source of DHA in the marine food chain—can be consumed directly through algae-based supplements or fortified foods. Some food manufacturers now fortify products such as eggs, milk, yoghurt, and spreads with DHA derived from microalgae, providing options for those who do not consume fish. Standard eggs also contain small amounts of DHA naturally, with omega-3 enriched eggs providing higher levels.

Grass-fed meat and dairy products contain trace amounts of DHA, though concentrations are significantly lower than in marine sources. The body can also convert very small amounts of ALA from plant sources (flaxseeds, chia seeds, walnuts) into DHA, though this process is inefficient and should not be relied upon as the sole source.

How Much DHA Do You Need Daily?

The optimal daily intake of DHA varies according to age, physiological status, and individual health circumstances. In the UK, there is no specific recommended daily allowance (RDA) exclusively for DHA; instead, guidance focuses on portion-based recommendations for fish consumption.

The European Food Safety Authority (EFSA) recommends that adults consume approximately 250mg of long-chain omega-3 fatty acids (EPA and DHA combined) daily for general cardiovascular health. This recommendation can typically be met by consuming one to two portions of oily fish per week, with each portion being approximately 140g according to NHS guidance.

Specific population groups have different requirements:

• Pregnant and breastfeeding women: EFSA recommends an additional 100–200mg of DHA daily beyond the standard adult intake of 250mg EPA+DHA. This supports foetal brain and eye development during pregnancy and continues to benefit the infant through breast milk. The NHS advises that pregnant and breastfeeding women should eat no more than 2 portions of oily fish per week due to potential contaminants, and should avoid shark, marlin and swordfish completely.

• Infants and children: DHA requirements are proportionally higher relative to body weight during periods of rapid growth and development. Breast milk naturally contains DHA when maternal intake is adequate. For formula-fed infants, UK regulations require infant formula to contain minimum levels of DHA.

• Older adults: Some evidence suggests that maintaining adequate DHA intake may support cognitive health in ageing, though there is no official separate recommendation for this age group.

Practical considerations: A 140g NHS portion of oily fish such as salmon provides a substantial contribution to weekly omega-3 requirements. Men, boys, and women who are not pregnant or planning pregnancy can eat up to 4 portions of oily fish weekly. Individuals who do not consume fish regularly may struggle to meet these targets through diet alone and should consider alternative sources or supplementation after consulting with a healthcare professional.

It is worth noting that excessive intake of omega-3 fatty acids may increase bleeding risk in some individuals, particularly those taking anticoagulant medications or antiplatelet agents. EFSA indicates that supplemental intakes of combined EPA and DHA up to about 5g daily do not raise safety concerns for adults, but medical advice should be sought if you are on medication.

Who Should Consider DHA Supplements?

While obtaining DHA from whole food sources is preferable, certain individuals may benefit from supplementation when dietary intake is insufficient or physiological demands are increased.

Individuals who may benefit from DHA supplementation include:

• Pregnant and breastfeeding women who do not regularly consume oily fish: While routine DHA supplementation is not specifically recommended in UK pregnancy guidance, some research suggests associations with improved visual and cognitive development in infants. Women considering supplements should choose products specifically formulated for pregnancy, avoiding those with vitamin A content (such as cod liver oil), which can be harmful during pregnancy.

• Vegetarians and vegans: Since plant-based diets lack direct sources of DHA, individuals following these dietary patterns should consider algae-based DHA supplements. These provide a sustainable, marine-free source of DHA that aligns with plant-based principles whilst ensuring adequate intake.

• Individuals with limited fish consumption: Those who dislike fish, have fish allergies, or have concerns about environmental contaminants (mercury, polychlorinated biphenyls) in fish may struggle to meet DHA requirements through diet alone.

• People with certain health conditions: Individuals with cardiovascular disease, hypertriglyceridaemia, or inflammatory conditions may be advised by their healthcare provider to increase omega-3 intake. However, supplementation should only be undertaken under medical supervision, as high doses may interact with medications such as anticoagulants (warfarin, DOACs) or antiplatelet agents (aspirin, clopidogrel).

Important safety considerations:

DHA supplements are generally well-tolerated, but potential adverse effects include gastrointestinal discomfort, fishy aftertaste, and, at high doses, increased bleeding tendency. In the UK, food supplements are regulated under food law by the Food Standards Agency (FSA) and local authorities. Quality and purity can vary between products. Look for supplements that have been tested for contaminants and provide clear information about DHA content per dose.

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

When to contact your GP:

• Before starting supplementation if you are pregnant, breastfeeding, or have existing health conditions

• If you are taking anticoagulant or antiplatelet medications

• If you experience unusual bleeding, bruising, or other adverse effects after starting supplementation

For most healthy adults consuming a balanced diet that includes regular oily fish, supplementation is unnecessary. A healthcare professional can provide personalised advice based on individual dietary patterns, health status, and nutritional requirements.

Frequently Asked Questions