Tuna is a nutritious and convenient protein source widely enjoyed across the UK, offering valuable omega-3 fatty acids, vitamins, and minerals. However, as a large predatory fish, tuna accumulates methylmercury, raising important questions about safe consumption frequency. Understanding how often you can eat tuna depends on several factors, including pregnancy status, age, and the type of tuna consumed. The NHS and Food Standards Agency provide evidence-based guidance to help balance tuna's nutritional benefits against potential mercury exposure risks. This article explores safe consumption frequencies for different population groups, mercury levels in various tuna species, and practical strategies for incorporating tuna into a healthy, balanced diet whilst minimising health risks.

Understanding Mercury Levels in Tuna

Tuna is a popular fish consumed widely across the UK, valued for its protein content, omega-3 fatty acids, and convenience. However, tuna accumulates methylmercury—a toxic form of mercury—through bioaccumulation in the marine food chain. As a large, predatory fish with a longer lifespan, tuna feeds on smaller fish that have already absorbed mercury from contaminated waters, leading to higher concentrations in its tissues.

Methylmercury poses particular concern because it crosses the blood-brain barrier and can affect neurological development, especially in foetuses and young children. The compound binds to proteins in the body, potentially disrupting cellular function. In adults, chronic high-level exposure may lead to sensory disturbances, coordination problems, and cognitive impairment, though such cases are rare with typical dietary consumption.

Different tuna species contain varying mercury levels. Larger species such as bluefin, bigeye, and albacore typically contain higher concentrations due to their size and position in the food chain. Skipjack and yellowfin tuna, commonly used in canned products, generally have lower mercury levels. While UK guidance on tuna consumption applies to tuna generally rather than by specific species, understanding these variations provides helpful context for making informed choices.

Tuna remains a nutritious food, and awareness of consumption frequency helps minimise potential health risks whilst maintaining the benefits of regular fish intake as part of a balanced diet. The Food Standards Agency (FSA) and NHS provide guidance that balances nutritional benefits against potential mercury exposure.

NHS Guidelines on Safe Tuna Consumption Frequency

The NHS provides clear guidance on tuna consumption to help the UK population balance nutritional benefits with mercury exposure risks.

For most adults who are not pregnant or trying for a baby, there is no specific limit on tuna consumption. However, the NHS recommends eating at least two portions of fish per week, including one portion of oily fish. This is part of a balanced diet that supports heart health and overall wellbeing.

It's important to note that fresh tuna counts as an oily fish, while canned tuna does not count towards your oily fish intake because the canning process reduces the omega-3 content. The NHS advises that adults should eat no more than four portions of oily fish per week, with women who might have a baby in the future advised to have no more than two portions of oily fish weekly.

For those who are pregnant or trying for a baby, the NHS specifically recommends:

• Consuming no more than four medium-sized cans of tuna per week (with a drained weight of approximately 140g per can)

• Alternatively, no more than two fresh tuna steaks per week (approximately 140g cooked weight each)

Tuna provides valuable nutrition including high-quality protein, vitamin D, selenium, and B vitamins, all contributing to cardiovascular health, immune function, and overall wellbeing. Fresh tuna also provides omega-3 fatty acids (EPA and DHA), which support heart health.

These evidence-based recommendations reflect ongoing monitoring of mercury levels in UK fish supplies and international safety data, ensuring public health protection whilst promoting the established benefits of regular fish consumption. Adults with specific health conditions or concerns about mercury exposure should discuss their individual circumstances with their GP or a registered dietitian.

Recommended Tuna Intake for Pregnant Women and Children

Pregnant women and those trying for a baby require specific guidance due to the heightened vulnerability of the developing nervous system to methylmercury exposure.

For women who are pregnant or trying to conceive, the NHS recommends:

• Limiting tuna consumption to no more than four cans per week (approximately 140g drained weight per can)

• Or two fresh tuna steaks per week (approximately 140g cooked weight)

• These limits help protect foetal neurological development whilst maintaining nutritional benefits

Methylmercury readily crosses the placental barrier and can accumulate in foetal brain tissue during critical developmental periods. The omega-3 fatty acids in fish support foetal brain and eye development, so complete avoidance is not recommended—rather, pregnant women should choose lower-mercury fish options such as salmon, mackerel, sardines, and trout for additional servings.

For breastfeeding women, there is no specific tuna limit. However, the NHS advises limiting oily fish to 2 portions per week and avoiding shark, swordfish and marlin due to their high mercury content. Fresh tuna counts as an oily fish; canned tuna does not.

For children, the NHS does not set specific tuna limits, but advises:

• Children should eat fish as part of a varied and balanced diet

• Girls can have up to 2 portions of oily fish per week; boys can have up to 4 portions

• Portions should be age-appropriate and smaller than adult servings

• Parents should offer variety, including lower-mercury fish species

Children's developing nervous systems remain vulnerable to neurotoxic effects, and their smaller body weight means mercury concentrations per kilogram are proportionally higher. However, fish consumption in childhood supports cognitive development, so balanced inclusion rather than elimination is appropriate.

Parents and pregnant women should consult their midwife, health visitor, or GP if they have specific concerns about fish consumption or dietary mercury exposure.

Health Benefits and Risks of Regular Tuna Consumption

Regular tuna consumption offers substantial nutritional benefits when incorporated appropriately into a balanced diet, though understanding both advantages and potential risks enables informed dietary choices.

Key health benefits include:

• High-quality protein: Tuna provides all essential amino acids necessary for tissue repair, immune function, and enzyme production

• Omega-3 fatty acids: Fresh tuna contains EPA and DHA, which support cardiovascular health by reducing triglycerides, improving endothelial function, and potentially reducing arrhythmia risk

• Micronutrients: Tuna is rich in selenium (supporting antioxidant defences), vitamin D (essential for bone health and immune function), vitamin B12 (crucial for neurological function and red blood cell formation), and niacin

• Low saturated fat: Tuna provides a lean protein source, supporting weight management and cardiovascular health

Observational studies suggest regular fish consumption is associated with reduced cardiovascular disease risk, improved cognitive function in older adults, and better metabolic health markers. NICE guidelines recognise fish consumption as part of a heart-healthy dietary pattern.

Potential risks to consider:

• Mercury exposure: As discussed, excessive consumption may lead to mercury accumulation, particularly concerning for vulnerable groups

• Histamine reactions: Improperly stored tuna can develop high histamine levels, causing scombroid poisoning with symptoms including flushing, headache, and gastrointestinal upset. Seek urgent medical care for severe symptoms such as breathing difficulties, chest tightness, or significant drop in blood pressure

• Sodium content: Canned tuna, especially varieties in brine, may contain significant sodium, relevant for individuals managing hypertension

• Fish allergy: Though less common than some food allergies, fish allergies can cause serious reactions in susceptible individuals

• Sustainability concerns: Overfishing affects some tuna populations, though this represents an environmental rather than direct health risk

There is no established link between moderate tuna consumption and other commonly cited concerns such as cancer risk when consumed within recommended limits. The balance of evidence supports tuna as a valuable dietary component when frequency guidelines are observed, particularly when varied with other fish species to optimise nutritional intake whilst minimising potential risks.

Choosing Lower-Mercury Tuna Options in the UK

Making informed choices about tuna species and products available in UK supermarkets helps maximise nutritional benefits whilst minimising mercury exposure.

Lower-mercury tuna options include:

• Skipjack tuna: The most common species in UK canned tuna, skipjack typically contains lower mercury levels among commercially available tuna species

• Yellowfin tuna: Moderately sized with lower mercury than larger species, though slightly higher than skipjack

• Canned tuna in spring water: Whilst mercury content relates primarily to species rather than canning medium, spring water varieties avoid added sodium from brine

Higher-mercury options to limit:

• Albacore tuna: Contains higher mercury levels than skipjack; often sold as premium canned tuna or fresh steaks

• Bluefin tuna: The largest tuna species with higher mercury levels; less common in UK supermarkets but found in restaurants, particularly for sushi

• Bigeye tuna: Similar mercury levels to bluefin; sometimes used in fresh tuna steaks

When shopping, check product labels for species information. Many UK retailers now provide clearer labelling about tuna type. Pole-and-line caught skipjack often appears in products emphasising sustainability, which typically also represents the lower-mercury option.

Practical strategies for UK consumers:

• Alternate tuna with other fish such as salmon, mackerel, sardines, and trout to diversify nutrient intake and reduce cumulative mercury exposure

• Choose skipjack-based products for regular consumption, reserving albacore or fresh tuna steaks for occasional meals

• Consider MSC-certified (Marine Stewardship Council) products, which often use more sustainable, typically smaller tuna species

• Choose tuna in spring water or low-salt options if managing blood pressure; rinsing canned tuna may help reduce sodium content

If you experience symptoms potentially related to mercury exposure—such as persistent tingling, coordination difficulties, or unexplained neurological symptoms—contact your GP for assessment. For suspected adverse reactions to medicines, report these through the MHRA Yellow Card scheme. However, such presentations from dietary tuna consumption alone are exceptionally rare when following NHS guidelines. These practical choices enable continued enjoyment of tuna's nutritional benefits whilst maintaining safety for all family members.

Frequently Asked Questions