Many people wonder how much tinned tuna they can safely eat each week, particularly given concerns about mercury content. The NHS and UK Food Standards Agency provide clear guidance on tuna consumption, which varies depending on whether you're eating tinned or fresh tuna, and your life stage. For most healthy adults, there is no specific limit on tinned tuna consumption, as it is not classified as an oily fish. However, pregnant women, those trying to conceive, and breastfeeding mothers should limit intake to no more than four medium-sized cans per week. Understanding these recommendations helps you enjoy tuna's nutritional benefits whilst minimising potential mercury exposure risks.

Recommended Weekly Tuna Intake in the UK

The UK Food Standards Agency (FSA) and NHS provide guidance on safe tuna consumption, primarily based on mercury content considerations. For most healthy adults, there is no specific limit on tinned tuna consumption, as it is not classified as an oily fish. However, the NHS recommends that everyone should eat at least two portions of fish per week, including one portion of oily fish, as part of a balanced diet.

Fresh tuna steaks are classified as oily fish, and consumption guidance varies by population group. Girls and women who may become pregnant or are of childbearing age should limit oily fish (including fresh tuna) to no more than two portions per week. Boys, men, and women who are beyond childbearing age can consume up to four portions of oily fish per week.

Specific restrictions apply to certain groups. The NHS advises that pregnant women, those trying to conceive, and breastfeeding mothers should limit their tuna intake to no more than four medium-sized cans (about 140g drained weight per can) or two fresh tuna steaks (about 140g cooked weight each) per week.

These recommendations balance the nutritional benefits of tuna—including high-quality protein, omega-3 fatty acids, and essential vitamins—against potential mercury exposure risks. Mercury is a naturally occurring element that accumulates in fish tissue, particularly in larger, longer-lived predatory species. Whilst tuna provides valuable nutrients, excessive consumption may lead to mercury levels that could affect neurological function over time.

It is important to note that these are guidelines based on average body weights and consumption patterns. Individual dietary patterns, overall fish consumption, and other sources of mercury exposure should also be considered when determining appropriate intake levels.

Mercury Levels in Tinned Tuna: What You Need to Know

Mercury contamination in fish occurs through industrial pollution and natural geological processes. When mercury enters aquatic environments, bacteria convert it to methylmercury, a highly toxic organic form that accumulates in fish tissue through a process called bioaccumulation. Larger predatory fish, including tuna, accumulate higher concentrations because they consume smaller fish throughout their lifespan.

Tinned tuna typically contains lower mercury levels than fresh tuna steaks because manufacturers predominantly use younger, smaller tuna species. According to FSA surveillance data, skipjack tuna, commonly used in standard tinned tuna, generally contains approximately 0.1–0.2 parts per million (ppm) of mercury. In contrast, albacore tuna contains higher levels, typically 0.3–0.4 ppm, whilst fresh tuna steaks from larger species like yellowfin or bigeye may contain 0.3–0.6 ppm or higher.

The UK and European Union set a maximum permitted level of 1.0 mg/kg (1.0 ppm) for mercury in tuna under Regulation (EU) 2023/915, as retained in UK law. Regular monitoring by the FSA ensures commercial products remain below these thresholds. The European Food Safety Authority (EFSA) has established a tolerable weekly intake for methylmercury of 1.3 μg/kg of body weight to guide safe consumption levels.

Mercury's primary concern relates to its neurotoxic effects. Chronic exposure can affect cognitive function, coordination, and sensory perception. The developing nervous systems of foetuses, infants, and young children are particularly susceptible. In adults, excessive mercury exposure may cause paraesthesia (tingling sensations), vision changes, and cognitive difficulties, though such effects typically require consumption well exceeding recommended limits over extended periods. Most individuals consuming tuna within NHS guidelines face minimal risk of mercury-related health effects.

NHS Guidelines for Pregnant Women and Children

Pregnant women, those planning pregnancy, breastfeeding mothers, and young children require more restrictive tuna consumption limits due to mercury's potential impact on foetal and infant neurological development. The NHS advises pregnant women, those trying to conceive, and breastfeeding women to limit tuna intake to no more than four medium-sized cans of tinned tuna (about 140g drained weight each) or two tuna steaks per week (about 140g cooked weight each).

Regarding oily fish consumption, the NHS guidance varies by group. Girls (including those under 16) and women who may become pregnant should consume no more than two portions of oily fish per week. Boys, men, and women beyond childbearing age can have up to four portions of oily fish per week. Fresh tuna counts as oily fish, but tinned tuna does not due to processing methods that reduce fat content.

The NHS and FSA specifically advise that pregnant women, those trying to conceive, breastfeeding mothers, and children should avoid eating shark, swordfish, and marlin entirely due to their very high mercury content.

It is worth noting that whilst these restrictions apply to tuna and certain other fish, pregnant women and children are encouraged to consume other fish varieties with lower mercury content. The NHS recommends two portions of fish weekly, including one portion of oily fish such as salmon, mackerel, or sardines, which provide essential omega-3 fatty acids (particularly DHA) crucial for foetal brain and eye development. These species typically contain significantly lower mercury levels than tuna.

Parents and expectant mothers should maintain perspective: tuna remains a nutritious food choice when consumed within recommended limits. The restrictions are precautionary measures based on potential cumulative effects rather than evidence of harm from moderate consumption. If you have concerns about mercury exposure during pregnancy or childhood, discuss your dietary patterns with your GP or midwife, who can provide personalised guidance based on your overall fish consumption and nutritional needs.

Health Benefits and Risks of Regular Tuna Consumption

Tuna offers substantial nutritional benefits that support cardiovascular health, cognitive function, and overall wellbeing. According to the British Nutrition Foundation, a typical 100g serving of tinned tuna provides approximately 25–30g of high-quality protein, making it an excellent choice for muscle maintenance and repair. Tuna is also rich in vitamin D, vitamin B12, niacin, and selenium—nutrients essential for bone health, red blood cell formation, energy metabolism, and antioxidant defence.

Fresh tuna contains significant amounts of omega-3 polyunsaturated fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The NHS notes these fatty acids demonstrate anti-inflammatory properties and are associated with reduced cardiovascular disease risk. Evidence from observational studies suggests regular fish consumption correlates with lower rates of coronary heart disease and stroke. However, tinned tuna contains considerably less omega-3 than fresh tuna or other oily fish due to processing methods, so it should not be relied upon as a primary omega-3 source.

The primary risk associated with regular tuna consumption relates to mercury exposure, as discussed previously. Additionally, some tinned tuna products contain high sodium levels, which may be problematic for individuals managing hypertension or cardiovascular conditions. Checking labels and choosing products tinned in spring water rather than brine can help reduce sodium intake.

Another consideration involves histamine formation in improperly stored tuna. Scombroid poisoning, though rare in commercially processed products, can occur if tuna is stored at inappropriate temperatures before canning. Symptoms include flushing, headache, and gastrointestinal upset, typically resolving within hours. If you experience severe allergic-type symptoms (wheezing, swelling, chest tightness) or if symptoms are severe or prolonged, seek urgent medical help. For milder symptoms, contact NHS 111 or your GP. Purchasing from reputable suppliers and following storage instructions minimises this risk.

Balancing these factors, tuna remains a valuable component of a healthy, varied diet when consumed within recommended limits. The key is moderation and diversity—incorporating various fish species and protein sources rather than relying exclusively on tuna ensures optimal nutrition whilst minimising potential risks.

Safe Tuna Portions: Albacore vs Skipjack

Understanding the differences between tuna varieties helps consumers make informed choices about consumption. Skipjack tuna (Katsuwonus pelamis) is the most common species used in standard tinned tuna products in the UK, often labelled simply as "tuna chunks" or with the species name. Skipjack are smaller fish, typically weighing 2–3kg when caught, with shorter lifespans of approximately 8–12 years. Their size and lifespan result in lower mercury accumulation, generally 0.1–0.2 ppm according to FSA surveillance data.

Albacore tuna (Thunnus alalunga), sometimes labelled as such on packaging, are larger fish weighing 10–25kg with lifespans up to 12 years. This extended lifespan and larger size allow greater mercury bioaccumulation, typically resulting in levels of 0.3–0.4 ppm—approximately two to three times higher than skipjack. While albacore is less common in UK supermarkets than in some other countries, it is available in some speciality products.

It's important to note that current NHS and FSA guidance does not set different consumption limits for different tuna species in the UK. The standard advice for pregnant women, those trying to conceive, and breastfeeding mothers remains no more than four medium-sized cans of tinned tuna or two fresh tuna steaks per week, regardless of species.

Product labelling in the UK typically indicates tuna species, though not always prominently. When labels are unclear, consumers can contact manufacturers for clarification or choose products with clearer species identification.

From a sustainability perspective, skipjack populations are generally better managed than some other tuna species. Choosing products certified by the Marine Stewardship Council (MSC) or similar organisations supports sustainable fishing practices. Balancing nutritional needs, mercury considerations, and environmental responsibility allows consumers to enjoy tuna as part of a health-conscious, sustainable diet whilst minimising potential risks associated with excessive consumption.

Frequently Asked Questions