Can you eat too much tinned tuna?

Lauren Ball, Emily Burch, Southern Cross University, University of Queensland

Tinned tuna is a lunchbox staple for many people. It’s affordable, high in protein and doesn’t need cooking, making it a nutritious and convenient option for busy days.

But if you’re eating tuna most days, you might have wondered whether it’s possible to have too much. Or perhaps you’ve watched your child happily eat a tuna sandwich every day for a week and wondered if that’s too much of a good thing.

The concern usually comes down to mercury. Mercury can be harmful in high amounts, particularly during pregnancy and early childhood. But the amount of mercury in seafood varies considerably between species – and that’s where much of the confusion begins.

For most Australians, the evidence on tinned tuna is reassuring. Let’s unpack this.

Why does tuna contain mercury?

Mercury is a naturally occurring element in the environment. It enters rivers and oceans through natural processes, such as volcanic activity and weathering of rocks, as well as from some industrial activities.

In water, bacteria convert mercury into a form called methylmercury. Fish absorb it from the water and food they eat.

When larger fish eat smaller fish, the mercury builds up inside them over time. Because bigger fish usually live longer, they often contain more mercury than smaller fish.

This isn’t unique to tuna. Large fish such as shark (flake), swordfish and some marlin can also contain higher mercury levels because they are larger predatory fish.

Is all tuna the same?

No. Most tinned tuna sold in Australia comes from smaller tuna species, such as skipjack and yellowfin. Because these are generally younger and smaller than the species commonly sold as fresh tuna steaks, they typically contain much lower levels of mercury.

This is why health advice distinguishes between tinned tuna and larger predatory fish.

How much mercury is safe to eat?

Food Standards Australia New Zealand (FSANZ) uses international safety guidelines to estimate how much mercury people can consume over time without increasing health risks. This limit is called the provisional tolerable weekly intake (PTWI).

For most people, the PTWI is 3.3 micrograms (µg) per kilogram of body weight per week. For pregnant women, the limit is about half that, at 1.6µg per kilogram of body weight per week.

To put this into perspective, a person weighing 70kg would have a PTWI of about 231µg of mercury per week. But if pregnant, that drops to 112µg of mercury a week.

Limited research has specifically examined mercury concentrations in canned tuna products sold in Australia. So evidence from international studies is often used to indicate expected mercury concentrations. But levels may vary between countries, species and products.

A 2025 Spanish study analysed 60 cans of tuna and found an average mercury concentration of 0.138mg/kg.

Based on these findings, a small 95g can of tuna could contain about 13µg of mercury.

For a person of 70kg, this means:

• one can of tuna per week may provide roughly 13µg of mercury, or less than 6% of the recommended weekly limit

• one can of tuna every day for a week may provide about 92µg of mercury per week, or approximately one third (40%) of the recommended weekly limit.

For a typical four-year-old who weighs 20kg, they can eat up to 66µg of mercury per week. One can of tuna may use up about one fifth (20%) of a four-year-old’s weekly mercury allowance.

This means two to three cans of tuna a week, which is what you’d use to make a week’s worth of tuna sandwiches, is unlikely to be a concern.

But overall, children have a much lower mercury limit than adults because they are smaller and weigh less.

What is mercury poisoning?

Mercury poisoning occurs after prolonged exposure to high levels of mercury.

Depending on the amount and duration of exposure, symptoms can include numbness or tingling in the hands and feet, muscle weakness, problems with coordination, changes in vision or hearing, and difficulties with memory or concentration.

These symptoms are extremely unlikely to occur from eating the amounts of tinned tuna typically in an Australian diet.

What about other fish?

Some Australian fish contain much higher levels of mercury than canned tuna, and their intake should be limited. It’s recommended you consume no more than one serving of shark (flake), swordfish, broadbill or marlin per week and avoid other fish during the same week.

Should I eat the same protein every day?

Even though tinned tuna is a healthy choice, eating the same food every day isn’t ideal. Not because of mercury, but because no single food provides every nutrient we need.

Fish provides omega-3 fats and iodine.

But there are health benefits from other sources of protein:

• eggs are rich in choline (a nutrient important for metabolism)
• legumes provide fibre and plant protein
• lean meats contribute iron and vitamin B12
• tofu provides plant protein and can also be a source of calcium
• nuts and seeds provide healthy fats, fibre and a range of vitamins and minerals.

Including a variety of these foods across the week makes it easier to meet your nutritional needs than relying on any single food.

The bottom line

Tinned tuna is a nutritious, affordable and convenient source of protein.

For most Australians, eating tinned tuna regularly, even every day, is unlikely to result in unsafe mercury exposure.

Rather than avoiding it because of concerns about mercury, it’s best enjoyed as one of a variety of protein-rich foods that together make up a healthy, balanced diet.

This article is republished from The Conversation under a Creative Commons license. Read the original article.