Canned tuna and mercury: what a nutritionist says about the risks and serving sizes

Tinned tuna is an affordable, protein-rich food that is widely consumed in Romania. Psychonutritionist Gina Tăujan explained to Digi24.ro that it may contain methylmercury, a neurotoxic substance, but stressed that the risks arise mainly from repeated, prolonged exposure rather than occasional consumption.

Why tuna is beneficial in the diet

According to the specialist, tuna provides complete proteins containing all essential amino acids. Depending on the species and method of preservation, it may also contain Omega-3 fatty acids, vitamin B12, vitamin D, selenium, and phosphorus, contributing to the maintenance of muscle mass, the functioning of the nervous system, and heart health. Tăujan notes that tuna in brine generally contains more salt, whilst tuna in oil has a higher caloric value.

Where mercury in tuna comes from

Methylmercury is a compound that accumulates in marine organisms and is passed along the food chain, originating from both natural sources and human activity. Small fish generally accumulate relatively small amounts, but the concentration increases as they are consumed by larger species. As a result, long-lived species at the top of the food chain, including certain types of tuna, can have higher levels of methylmercury.

Not all species contain the same amount: skipjack tuna generally contains less mercury than albacore tuna, whilst bigeye tuna is among the species with higher concentrations.

How much tuna is advisable

There is no universally applicable portion size — this depends on body weight, the species chosen, and the total amount of fish consumed in one's diet. As a European reference point, the tolerable weekly intake of methylmercury is 1.3 micrograms per kilogram of body weight. Rather than performing constant calculations, the specialist recommends choosing species with a low mercury content and maintaining a varied diet.

What can happen with excessive exposure

The risks are associated with repeated exposure and accumulation in the body, not with the occasional consumption of a tin of tuna. Significant exposure to methylmercury can affect both the central and peripheral nervous systems, and symptoms may include tremors, headaches, memory or sleep disturbances, changes in sensitivity, and coordination problems. People who frequently eat large quantities of high-mercury fish and notice such signs should consult a doctor.

Gina Tăujan points out that a single occasion of higher consumption does not automatically mean poisoning, and recommends alternating tuna with other species such as sardines, salmon, trout, or herring.

Who should be more careful

Pregnant women, those who may become pregnant, breastfeeding mothers, and young children should pay particular attention to the species chosen and the quantity consumed, as the developing nervous system is more vulnerable to the effects of methylmercury. This does not mean eliminating fish from the diet during pregnancy, as it provides important nutrients for both mother and child — however, it is recommended to favour species with low mercury content and to vary them. For children, the portion size and type of fish should be adapted to their age, with quantities being smaller than for adults, making the selection of low-mercury species even more important.