For most adults, two to three servings of tuna per week is a safe upper range, but the exact limit depends on which type of tuna you’re eating. Canned light tuna contains roughly a third of the mercury found in albacore (white) tuna, so you can eat more of it before reaching concerning levels. A single serving is about 4 ounces, or roughly the size of your palm.
Why Mercury in Tuna Matters
All tuna contains some methylmercury, a form of mercury that accumulates in fish tissue over their lifetimes. Larger, longer-lived tuna species build up more of it. Your body absorbs methylmercury easily when you eat fish, and it crosses into the brain and nervous system. In small amounts, your body clears it gradually. But if you consistently eat more than your body can process, mercury accumulates and can cause real harm.
The EPA sets the safe daily intake at 0.1 micrograms of methylmercury per kilogram of body weight. For a 150-pound adult, that works out to about 6.8 micrograms per day. Eating a single 4-ounce serving of albacore tuna delivers roughly 40 micrograms of mercury in one sitting. Your body doesn’t need to clear it all that day since mercury is eliminated slowly over weeks, but the math shows how quickly regular tuna consumption adds up.
Mercury Levels Vary Dramatically by Type
Not all tuna is equal when it comes to mercury. The FDA’s testing data shows a nearly threefold difference between the lowest and highest mercury tuna varieties commonly sold:
- Canned light tuna (usually skipjack): 0.126 ppm mercury
- Fresh skipjack: 0.144 ppm
- Canned white/albacore: 0.350 ppm
- Fresh yellowfin: 0.354 ppm
Bigeye tuna, often used in sushi and sashimi, runs even higher. The pattern is straightforward: bigger tuna species live longer, eat more prey, and accumulate more mercury. Skipjack are small and short-lived, which is why canned light tuna is the safest everyday option. A study comparing canned varieties found white tuna averaged 0.407 ppm versus 0.118 ppm for light, confirming that simply switching from white to light cans cuts your mercury intake by more than half.
How Many Cans Per Week Is Safe
Using the EPA’s reference dose and the FDA’s mercury data, here’s what the numbers look like for a 150-pound adult eating 4-ounce servings:
With canned light tuna, you can safely eat about three servings per week and stay well within the EPA’s limit. With albacore or yellowfin, two servings per week is a more appropriate ceiling. If you’re eating tuna steaks at restaurants (which are often yellowfin or bigeye and tend to be larger than 4 ounces), one serving per week is a reasonable limit.
These aren’t hard cutoffs where one extra can triggers poisoning. Mercury builds up gradually over weeks and months. The concern isn’t a single heavy-tuna week but a sustained pattern of eating it daily or near-daily. If you eat tuna every day for lunch, even the lower-mercury canned light variety starts pushing you toward the upper boundary of safe intake.
Pregnancy, Breastfeeding, and Children
Mercury is most dangerous to developing brains. A fetus, infant, or young child is far more vulnerable to neurological effects than an adult, which is why the guidelines are stricter for these groups. The FDA recommends pregnant and breastfeeding women eat two to three servings of lower-mercury fish per week (including light tuna) but limit albacore tuna to no more than one serving. Bigeye tuna is on the FDA’s “avoid” list during pregnancy entirely.
Children need smaller portions. A serving is about 1 ounce for ages 1 to 3, 2 ounces for ages 4 to 7, 3 ounces for ages 8 to 10, and 4 ounces by age 11. These smaller portions mean that even a full adult-sized can of tuna, split over a few meals, can represent multiple servings for a toddler.
Signs You’re Getting Too Much Mercury
Chronic low-level mercury exposure doesn’t cause sudden, dramatic symptoms. It develops slowly. The earliest signs are often subtle: tingling or “pins and needles” in the hands, feet, and around the mouth. As exposure continues, you might notice difficulty with coordination, muscle weakness, or changes in vision, particularly a narrowing of peripheral vision. Speech and hearing can also be affected in more severe cases.
These symptoms are reversible if you reduce your exposure, but it takes time. Mercury’s half-life in the body is roughly 70 to 80 days, meaning it takes months for levels to drop significantly after you change your diet. If you eat tuna frequently and notice any of these neurological symptoms, cutting back and mentioning it to a doctor is worth doing. A simple blood test can measure your mercury level.
Tuna’s Nutritional Upside
The reason this is a balancing act rather than a simple “avoid tuna” message is that tuna is genuinely nutritious. It’s high in protein, low in fat, and one of the more affordable sources of omega-3 fatty acids. A 3-ounce serving of canned light tuna provides about 190 milligrams of the omega-3 fats DHA and EPA combined, which support heart and brain health. Fresh yellowfin provides about 100 milligrams per serving.
These numbers are moderate compared to fatty fish like salmon or sardines, which deliver significantly more omega-3s with less mercury. If you’re eating tuna primarily for the omega-3 benefits, those alternatives give you more nutritional value per serving with less risk. But if you enjoy tuna for its taste, convenience, or price, eating it in moderation still delivers meaningful nutrition.
Practical Ways to Reduce Your Risk
The simplest strategy is to choose canned light tuna over white or albacore whenever possible. That single swap cuts your mercury exposure roughly in half per serving. Beyond that, rotating tuna with lower-mercury fish like salmon, sardines, tilapia, shrimp, or pollock lets you eat seafood regularly without concentrating your mercury exposure on one species.
Portion awareness matters too. A restaurant tuna steak is often 6 to 8 ounces, which counts as two servings. A standard 5-ounce can of tuna, once drained, is a little over one serving. Keeping track doesn’t need to be precise. A rough weekly count of how many times you eat tuna is enough to stay in a safe range. If it’s three or fewer servings of light tuna, or two or fewer of albacore, you’re well within the limits that health agencies consider safe for adults.