Canned tuna has a reputation as a convenient, protein-rich food, but it carries several legitimate health concerns that make it less ideal than it appears. Mercury contamination is the most well-known issue, but it’s not the only one. The canning process itself degrades key nutrients, introduces chemical contaminants from packaging, and can concentrate sodium to levels worth watching. Here’s what’s actually going on inside that can.
Mercury Is the Biggest Concern
All tuna contains methylmercury, a toxic form of mercury that accumulates in fish tissue over time. Because tuna are large predators that eat smaller fish, they concentrate mercury at higher levels than most seafood. The type of canned tuna you buy makes a significant difference: canned light tuna (usually skipjack) averages 0.126 parts per million of mercury, while canned white tuna (albacore) averages 0.350 ppm, nearly three times as much, according to FDA monitoring data.
Methylmercury is particularly damaging to the nervous system. It disrupts the balance of chemical signaling between brain cells, interferes with calcium regulation, triggers oxidative stress, and can cause nerve cell death even at low levels of exposure. These effects are why health agencies are especially cautious about tuna consumption for pregnant women and young children, whose developing brains are most vulnerable. The EPA and FDA recommend eating two to three servings per week of lower-mercury fish, but albacore tuna is categorized as a “good choice” rather than a “best choice,” meaning only one serving per week is advised.
For adults who aren’t pregnant, occasional canned tuna isn’t likely to cause problems. But if you’re eating it multiple times a week as a go-to protein, mercury exposure adds up. The body eliminates methylmercury slowly, with a half-life of roughly 70 to 80 days, so frequent consumption keeps your levels elevated.
The Canning Process Destroys Omega-3s
One of the main reasons people eat tuna is for omega-3 fatty acids, the fats linked to heart and brain health. But canning significantly reduces those benefits. During commercial processing, tuna is cooked twice: once as a pre-cook step and again during sterilization inside the sealed can. This double heat exposure breaks down the omega-3 fatty acids EPA and DHA.
Oil-packed tuna loses even more. The omega-3s migrate out of the fish and into the surrounding oil, so when you drain the can, you’re pouring a portion of those beneficial fats down the sink. Water-packed tuna retains slightly more, but it still delivers less omega-3 content than a fresh or frozen piece of tuna would. If omega-3 intake is your goal, canned tuna is a surprisingly inefficient way to get it compared to salmon, sardines, or fresh tuna steaks.
Microplastics in Every Can
A study published in Food Chemistry found a significant presence of microplastic particles in commercial canned tuna. Researchers detected an average of 692 microplastic particles per 100 grams in water-packed tuna and 442 particles per 100 grams in oil-packed tuna. About 90% of those particles were between 1 and 50 micrometers in size, small enough to potentially cross biological barriers in the body.
Microplastic research in humans is still evolving, but the sheer volume of particles in canned tuna is notable. The contamination likely comes from ocean pollution absorbed by the fish during its lifetime, combined with particles introduced during processing and packaging. This isn’t unique to tuna, but the concentrations are high enough to be worth knowing about if you eat it regularly.
Can Linings and Chemical Leaching
The inner coating of metal cans has historically contained bisphenol A (BPA), an industrial chemical that can mimic estrogen in the body. Small amounts of BPA can leach from the lining into the food inside. The good news is that more than 95% of canned foods in the U.S. are now made without BPA-containing liners. The bad news is that the replacement chemicals are less studied, and some researchers have raised questions about whether BPA substitutes carry similar risks.
If you do eat canned tuna, storing cans at moderate temperatures (not in a hot garage or car), never cooking food directly in the can, and transferring leftovers to a separate container all reduce the amount of chemical transfer from the lining.
Sodium Adds Up Quickly
Canned tuna packed in water contains about 70 milligrams of sodium per ounce. Oil-packed tuna runs higher at roughly 118 milligrams per ounce. A typical can holds around five ounces, which means a single serving of oil-packed tuna could deliver nearly 600 milligrams of sodium before you add anything else to it. That’s about a quarter of the recommended daily limit.
For people managing blood pressure or following a low-sodium diet, this is worth factoring in. Rinsing canned tuna under water before eating can reduce sodium content somewhat, and choosing water-packed varieties helps. But many people don’t realize how much sodium they’re getting from a food they consider “clean” and simple.
Purine Content and Gout Risk
Tuna is a moderate-to-high purine food. Purines are natural compounds that your body breaks down into uric acid. For most people this isn’t an issue, but for anyone with gout or elevated uric acid levels, regular tuna consumption can trigger painful flare-ups. The Mayo Clinic notes that some types of seafood are higher in purines than others and recommends that people with gout limit their fish intake to small portions.
This doesn’t mean tuna causes gout on its own. But if you’re already prone to high uric acid levels, eating canned tuna several times a week could push you over the threshold for a flare. It’s one of those risks that only applies to a subset of people, but it’s a common enough condition (affecting roughly 4% of American adults) to be worth mentioning.
Histamine and Scombroid Poisoning
Tuna is one of the fish species most associated with scombroid poisoning, a type of food poisoning caused by high histamine levels in the fish. When tuna isn’t kept cold enough before or during processing, bacteria convert an amino acid in the flesh into histamine. Once histamine forms, cooking and canning don’t destroy it.
The FDA’s action level for tuna is 50 milligrams of histamine per 100 grams of fish, while actual illness cases typically involve concentrations near or above 100 mg per 100 grams. Symptoms include facial flushing, headache, sweating, abdominal cramps, and diarrhea, usually within minutes to a couple of hours after eating. It often gets mistaken for an allergic reaction. While most commercial canning operations have quality controls in place, scombroid remains one of the most commonly reported types of seafood-related illness.
What This Means in Practice
Canned tuna isn’t toxic, and eating it occasionally won’t harm most people. The concerns become real when it’s a dietary staple. If you’re eating canned tuna three or four times a week, you’re accumulating mercury, consuming meaningful amounts of sodium, getting fewer omega-3s than you think, and ingesting hundreds of microplastic particles per serving. Choosing light tuna over white, opting for water-packed over oil-packed, and limiting intake to two or three cans per week reduces most of these risks substantially. For a low-mercury, high-omega-3 alternative, canned salmon or sardines deliver similar convenience with a better safety profile.