Mercury in canned tuna: use this tip to choose the safer variety.

A recent review of 148 tins of tuna from several European countries found a clear pattern: every single sample contained mercury, and some tins had far more than nutrition specialists would normally expect. A dietitian has since shared a straightforward shopping tactic that can noticeably cut the risk for consumers - without having to give up their favourite fish altogether.

Why canned tuna accumulates so much mercury

Mercury enters rivers and seas through industry, coal-fired power stations and other sources. In water it can be converted into an organic form that builds up in fish. The bigger and older the fish, the more of it tends to collect in its tissues.

Tuna sit high up the food chain. They eat lots of smaller fish that may already be contaminated. That’s where the key issue lies:

• Small, short-lived fish: usually low mercury levels
  
• Large, long-lived predators such as tuna: markedly higher levels
  

On top of that, legal limits are considerably more lenient for tuna than for many other species. For most fish eaten as food, the limit is 0.3 milligrams of mercury per kilogram, but for tuna the permitted maximum is 1 milligram per kilogram - more than three times higher. In the review, more than half of the tins exceeded the stricter 0.3 threshold, and around one in ten was even above 1 mg/kg.

Salt content matters too: at roughly 1.5 grams of salt per 100 grams of tuna, a small tin can quickly provide around a third of the recommended daily intake.

The species matters: which canned tuna tends to come out better

Not all tuna is the same. The wording on the tin can refer to different species, which vary greatly in size and lifespan - and therefore in how much mercury they typically accumulate.

Species / label used in shops	Typical size / age	Likely mercury trend
Skipjack (often labelled simply as “tuna”)	smaller, short-lived	around 0.2 mg/kg, generally lower
Yellowfin (Albacore, often “light tuna” or “tuna chunks”)	larger, older	usually two to three times higher
White tuna (Germon)	large predator	also clearly elevated

Analytical data indicates that tins made from skipjack tend to be noticeably lower on average. Products containing yellowfin or white tuna often reach higher values, largely because these fish have more time at sea to accumulate heavy metals.

“Anyone who regularly eats tuna from a tin should specifically choose varieties from smaller species - over time, that makes a noticeable difference to personal exposure.”

One supermarket trick for canned tuna: look for the right word on the label

The dietitian quoted in the media offers a tip that takes seconds in the aisle. The key is not to focus only on brand and price, but to check the exact species name - usually on the back of the tin or underneath the main product name.

What to check on the tin when buying canned tuna

• Look for the species name: if the tin says “skipjack”, it is usually the better option.
  
• Avoid vague descriptions: terms such as “light tuna”, “tuna chunks” or just “tuna” without a clear species can indicate larger species.
  
• Read the ingredients list: many brands include the scientific species name in small print - if you take a moment to check, you can choose more precisely.
  
• Don’t stick to one brand: trying different brands often helps you find one that consistently uses smaller species.
  

The expert’s central message: prioritise tins where the fish meat comes from smaller tuna species. On average these contain fewer heavy metals and fit better into day-to-day eating for people who reach for tuna once or several times a week.

How much fish is still considered safe?

Health authorities repeatedly stress that fish remains a valuable part of a balanced diet. It provides omega‑3 fatty acids, high-quality protein, vitamin D, iodine and selenium. The cardiovascular system in particular can benefit when some processed meats and red meat are replaced with fish.

Many specialists advise planning about two fish meals per week, ideally:

• one serving of an oily fish such as salmon, sardines, mackerel or herring
  
• one serving of a leaner fish such as cod, pollock, haddock or plaice
  

If you keep to this sort of pattern and rotate species regularly, you reduce the likelihood of building up too much of any one contaminant. The main concern is when someone eats the same highly contaminated species very often over a long period - for instance, large portions of tuna, swordfish or shark several times a week.

Extra caution for pregnant women and young children

Mercury can affect the nervous system. Unborn babies and very young children are far more sensitive than adults, which is why guidance is stricter for certain groups.

Who needs to be especially careful

• pregnant women
  
• breastfeeding women
  
• children under three years old
  

Across many guidelines, the advice for these groups includes:

• Eat large predatory fish such as tuna only rarely, preferably not from wild-caught sources or only in small amounts.
  
• Avoid heavily contaminated species entirely, such as swordfish, certain sharks, marlin or large rays.
  
• Choose smaller oily fish instead, such as sardines, herring or small mackerel.
  

“The smaller the fish on the plate, the lower the heavy-metal burden tends to be - this simple rule of thumb is especially helpful for expectant parents when choosing.”

Practical alternatives to a daily tin of tuna

Many people choose tins because they’re affordable, keep for a long time and are ready to use. Even so, it’s easy to swap out some of that routine without making your diet worse.

• Sandwich fillings: instead of tuna with mayonnaise, try hummus, egg spread, lentil pâté or mackerel in tomato sauce.
  
• Fast pasta: tomato sauce with sardines or smoked salmon, paired with spinach or courgette.
  
• Salads: boiled eggs, chickpeas, beans or feta also add protein without the same heavy-metal concern.
  
• Store-cupboard planning: keep tins of mackerel, herring or sardines instead of stocking multiple tuna tins.
  

If you love tuna, you don’t have to remove it completely. A sensible middle ground is to limit the amount, choose the species deliberately, and avoid building in several tins every week.

What mercury can do in the body

After you eat it, mercury can be absorbed through the gut into the bloodstream and accumulate in tissues - especially the brain. Possible consequences of long-term higher intake include concentration difficulties, problems with fine motor control, or developmental delays in children. For healthy adults who only eat tuna occasionally, the risk is limited. However, people who frequently consume more contaminated fish can raise their personal exposure substantially.

The positive news is that small changes - choosing smaller species more often and not relying on the same options every day - can significantly reduce heavy-metal intake while still keeping the benefits of eating fish.

What consumers can also watch for in future

Manufacturers often list the tuna species only in small print. Buying more deliberately sends a signal to the industry. If more shoppers actively choose tins made from smaller species, pressure increases for clearer labelling and for brands to use fish that tends to carry lower contamination.

For consumers, the best protection remains a mix of common sense and a quick label check: fish is fine, but in moderation, with variety - and, when picking up a tin, with particular attention to which species actually ended up inside.