Tuna is a popular fish consumed widely across the UK, valued for its versatility, taste, and nutritional profile. As a rich source of high-quality protein and omega-3 fatty acids, tuna offers substantial health benefits when incorporated into a balanced diet. However, concerns about mercury contamination and appropriate consumption levels—particularly for pregnant women and children—require careful consideration. This article examines the nutritional advantages of tuna, potential health risks, safe consumption guidelines from UK health authorities, and practical advice for selecting and incorporating tuna into your diet responsibly.

Nutritional Benefits of Tuna for Your Health

Tuna is widely recognised as a nutritious food choice, offering substantial health benefits when consumed as part of a balanced diet. This popular fish is an excellent source of high-quality protein, providing all essential amino acids necessary for tissue repair, immune function, and muscle maintenance. A typical 100g serving of tuna delivers approximately 25-30g of protein whilst remaining relatively low in calories, making it particularly valuable for those managing their weight.

Beyond protein, tuna contains omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These polyunsaturated fats play crucial roles in cardiovascular health by helping to reduce triglyceride levels, lower blood pressure, and decrease inflammation throughout the body. It's worth noting that fresh tuna is considered an oily fish by the NHS, while canned tuna is not classified as oily fish. Fresh tuna generally contains less omega-3 than some other oily fish such as salmon, mackerel and sardines.

Tuna also provides a range of essential micronutrients. It contains vitamin D, which supports bone health and immune function—a useful dietary source in the UK where sunlight exposure is limited during winter months, though levels vary by species and processing method. Additionally, tuna contains substantial amounts of vitamin B12 (essential for neurological function and red blood cell formation), niacin (vitamin B3), and selenium, a powerful antioxidant that protects cells from oxidative damage.

The mineral profile of tuna includes phosphorus for bone health, potassium for blood pressure regulation, and magnesium for muscle and nerve function. Fresh tuna varieties, particularly darker-fleshed species, also contain iron, though in smaller quantities than red meat. These combined nutritional attributes make tuna a valuable component of dietary patterns recommended by the NHS and other UK health authorities for maintaining overall health and preventing chronic disease.

Potential Health Risks and Mercury Concerns

Whilst tuna offers considerable nutritional benefits, it is important to acknowledge potential health risks, primarily related to mercury contamination. Mercury occurs naturally in the environment but industrial pollution has increased levels in aquatic ecosystems. Fish absorb methylmercury—the organic form of mercury—from water and their diet, with concentrations accumulating in tissues over time through a process called bioaccumulation.

Larger, longer-lived predatory fish species accumulate higher mercury levels because they consume smaller contaminated fish throughout their lifespan. Fresh tuna steaks (particularly bluefin, bigeye, and albacore species) typically contain higher mercury concentrations than smaller fish or canned tuna varieties. The Food Standards Agency (FSA) monitors mercury levels in fish consumed in the UK and provides guidance to minimise exposure whilst maintaining the health benefits of fish consumption.

Mercury exposure poses particular concern because methylmercury can cross the blood-brain barrier and affect neurological development and function. High-level exposure may cause symptoms including sensory disturbances, coordination problems, and cognitive impairment. However, it is important to note that the levels found in commercially available tuna, when consumed according to recommended guidelines, are generally considered safe for most adults.

Other potential considerations include histamine formation in improperly stored tuna, which can cause scombroid poisoning—characterised by flushing, headache, and gastrointestinal symptoms. To reduce this risk, ensure tuna is properly refrigerated and consumed promptly. Discard any fish with an unusually peppery or metallic taste. If you experience flushing, headache, dizziness or swelling shortly after eating tuna, seek urgent medical attention.

Some individuals may experience allergic reactions to fish proteins. If you develop hives, swelling, wheezing, difficulty breathing, or feeling faint after consuming tuna, call 999 immediately as these could indicate a severe allergic reaction (anaphylaxis).

Canned tuna often contains added salt, which may be a consideration for those managing hypertension or following sodium-restricted diets. The NHS advises checking labels and choosing products canned in water rather than brine when monitoring salt intake.

For most healthy adults following FSA guidelines, the benefits of moderate tuna consumption outweigh the risks. However, certain populations require additional precautions, as discussed in subsequent sections.

How Much Tuna Is Safe to Eat Weekly

The Food Standards Agency and NHS provide clear guidance on safe tuna consumption levels, balancing nutritional benefits against mercury exposure risks. For most adults, the NHS recommends eating at least two portions of fish per week, including one portion of oily fish. It's important to note that fresh tuna counts as an oily fish, while canned tuna does not. The NHS advises that men, boys, and women who are not planning pregnancy can eat up to four portions of oily fish weekly, with each portion weighing approximately 140g when cooked.

When it comes to tuna specifically, there are no official upper limits for adults who are not pregnant or breastfeeding. However, as part of a varied diet, it's sensible to include different fish species rather than consuming tuna exclusively. Canned tuna, which typically comes from smaller species with lower mercury levels, can generally be consumed more frequently as part of a varied diet since it doesn't count toward oily fish limits.

For women who are pregnant, planning pregnancy, or breastfeeding, more specific restrictions apply due to the developing nervous system's vulnerability to mercury. The FSA recommends these groups:

• Limit oily fish consumption to no more than two portions per week (fresh tuna counts toward this limit)

• Limit tuna specifically to no more than two tuna steaks per week (approximately 140g cooked weight each)

• Or four medium-sized cans of tuna per week (approximately 140g drained weight per can)

These recommendations aim to minimise mercury exposure whilst allowing pregnant women to benefit from tuna's nutritional value, including omega-3 fatty acids important for foetal brain development.

Children should also observe moderation. The NHS advises that girls can eat up to two portions of oily fish weekly, while boys can eat up to four portions. Children's portion sizes should be appropriate for their age and size. Parents should ensure tuna forms part of a varied diet including different fish species with lower mercury content, such as salmon, mackerel, and sardines.

It is worth noting that these are general guidelines, and individual circumstances may warrant different approaches. Those with concerns about mercury exposure or fish consumption should consult their GP or a registered dietitian for personalised advice. Maintaining variety in protein sources—including other fish, poultry, legumes, and plant-based options—ensures balanced nutrition whilst minimising potential risks from any single food source.

Choosing the Right Type of Tuna

Understanding the different types of tuna available helps consumers make informed choices based on nutritional content, mercury levels, sustainability, and culinary preferences. Fresh tuna steaks come from various species, each with distinct characteristics. Bluefin tuna, prized for its rich flavour and high fat content, contains elevated mercury levels and faces sustainability concerns due to overfishing. Yellowfin and bigeye tuna offer excellent nutritional profiles but also contain moderate to high mercury concentrations.

Albacore tuna (sometimes labelled as "white" tuna in the UK) has a milder flavour and firmer texture than other varieties. Whilst nutritionally valuable, albacore typically contains higher mercury levels than skipjack tuna. Skipjack tuna, the most commonly used species for standard canned tuna in the UK, comes from smaller, faster-growing fish that accumulate less mercury. From both safety and sustainability perspectives, skipjack represents an excellent choice for regular consumption.

When selecting canned tuna, several factors merit consideration:

• Liquid medium: Tuna canned in spring water contains fewer calories and less fat than varieties in oil. Contrary to common belief, water-packed tuna often retains more omega-3 fatty acids per drained weight than oil-packed versions, as the oil can draw out some of the fish's natural fats. Tuna in brine contains significantly more sodium.

• Salt content: Check nutrition labels, as sodium levels vary considerably between brands. Reduced-salt and no-added-salt varieties are available for those monitoring sodium intake.

• Texture: Chunk versus flaked affects texture rather than nutritional value, though chunk tuna may contain slightly more omega-3s due to including darker meat.

Sustainability considerations are increasingly important given declining fish stocks and environmental concerns. Look for tuna certified by the Marine Stewardship Council (MSC) or check the Marine Conservation Society's Good Fish Guide for up-to-date sustainability ratings. Pole-and-line caught tuna generally has lower environmental impact than fish caught using purse seine nets or longlines.

For those seeking to maximise omega-3 intake whilst minimising mercury exposure, other oily fish like salmon, mackerel or sardines are often better choices than tuna. However, skipjack tuna canned in spring water represents a good lower-mercury option. Fresh tuna steaks from sustainable sources can be enjoyed occasionally as part of a varied diet. The key is balancing nutritional benefits, safety considerations, environmental responsibility, and personal preferences when incorporating tuna into your regular eating pattern.

Tuna During Pregnancy and for Children

Pregnancy represents a critical period when maternal nutrition directly influences foetal development, making careful consideration of tuna consumption particularly important. The developing nervous system is especially vulnerable to methylmercury exposure, which can cross the placental barrier and potentially affect cognitive development, motor skills, and sensory function. However, the omega-3 fatty acids in tuna—particularly DHA—are crucial for foetal brain and eye development, creating a need to balance benefits against risks.

Pregnant women should follow FSA guidance strictly: limit consumption to no more than two fresh tuna steaks (approximately 140g cooked weight each) or four medium cans of tuna weekly. Additionally, as fresh tuna counts as an oily fish, pregnant women should observe the overall limit of no more than two portions of oily fish weekly. This allows expectant mothers to benefit from tuna's high-quality protein, vitamin D, and omega-3 content whilst minimising mercury exposure. Women should prioritise canned tuna over fresh steaks during pregnancy, as it typically contains lower mercury levels and doesn't count toward oily fish limits. Choosing skipjack varieties further reduces exposure.

It is advisable for pregnant women to diversify their fish intake, incorporating lower-mercury options such as salmon, sardines, mackerel, and trout. These alternatives provide comparable or superior omega-3 content with minimal mercury risk. Women should avoid taking fish liver oil supplements during pregnancy due to their high vitamin A content. Regarding raw fish, the NHS advises that sushi is safe during pregnancy if the fish has been previously frozen, though mercury limits still apply. Women with concerns about fish consumption during pregnancy should discuss their diet with their midwife or GP, who can provide personalised guidance.

Breastfeeding mothers should observe the same precautions as pregnant women, limiting tuna to two steaks or four cans weekly and total oily fish to two portions weekly. Methylmercury can transfer through breast milk, but the overall benefits of breastfeeding far outweigh concerns about mercury from moderate tuna consumption within recommended limits.

For infants and young children, tuna can be introduced as part of weaning from around six months of age, following current NHS guidance on introducing allergenic foods. Start with small amounts of well-cooked, flaked tuna (canned varieties are suitable), ensuring no bones remain. Children's portion sizes should be age-appropriate. Girls should consume no more than two portions of oily fish weekly, while boys can have up to four portions. As children's bodies are smaller and their nervous systems still developing, limiting higher-mercury fish is prudent.

If children refuse fish, speak with a GP or registered dietitian about ensuring adequate omega-3 intake through other dietary sources or appropriate supplementation. When concerns arise about mercury exposure or any adverse reactions to tuna, contact your GP for assessment and advice. If you suspect a side effect from any supplement or medicine, report it through the MHRA Yellow Card Scheme.

Frequently Asked Questions