Tuna: nearly everything studied about it is contamination

Of the seven syntheses about tuna in our corpus, three are about metals or histamine. That is the shape of this literature, and it is worth saying out loud. The risk assessment that matters puts methylmercury above the safety threshold for children in twelve countries and for adults in one, while cadmium, lead and nickel exceeded their limits without crossing the hazard line. Pooled measurements from 1295 samples put mean mercury at 0.11 micrograms per gram, which is low. The two findings fit together: mercury in tuna is not high, and children are small.

The numbers, per 100 g

How much is actually in it

• Across 1295 samples of canned tuna, mercury averaged a tenth of a microgram per gram and only cadmium and selenium exceeded their limits. — 23 articles covering 1295 samples of canned tuna in Iran (n = 1295 samples) Evidence C source
  Mean concentrations in micrograms per gram wet weight ranked iron 13.17, zinc 9.31, selenium 2.23, aluminium 1.8, chromium 1.63, copper 1.52, arsenic 0.38, nickel 0.33, lead 0.24, cadmium 0.14, mercury 0.11 and tin 0.1; all except cadmium and selenium were below the limits set by EPA, WHO, FAO and the Iranian standards body

What your body absorbs

• Encapsulating tuna oil in powder got more of its omega-3 into toddlers' blood than the plain oil did. — 60 healthy toddlers (n = 60) Evidence B source
  Blood DHA concentrations were significantly higher with the microencapsulated powders than with the plain high-DHA oil; no effect of treatment on sleep or cry patterns

What cooking and storage change

• Scombroid poisoning comes from tuna more than any other fish, and the histamine that causes it survives cooking. — 55 reports describing 103 incidents (n = 103 incidents) Evidence C source
  Mean histamine concentration in poisoning samples was 1107.21 mg/kg (95% CI for the meta-mean 422.62 to 2900.78), with heterogeneity of 100% and a prediction interval of 24.12 to 50822.78; the fish involved was mainly tuna or Istiophoridae; no association was found with sex, alcohol, prior medication or other histamine-releasing foods

What it does to your health

• Tuna oil is one of the newer high-DHA oils, and DHA turns out to act differently from the EPA it was studied alongside for forty years. — published human studies of high-DHA oils including fractionated and concentrated fish oil, tuna oil, calamari oil and microalgae oil Evidence A source
  Current data support DHA as beneficial for heart, cardiovascular and brain function, with effects that differ from and at times complement those of EPA, and DHA has been reported to slow the rate of cognitive decline; inconclusive results were reported in several instances and inconsistent outcomes in others

Who this works differently for

• For children in a dozen countries the methylmercury in canned tuna crossed the safety threshold, while the other metals did not. — published measurements of canned tuna across many countries Evidence C source
  Cadmium, lead and nickel exceeded standard limits but gave hazard quotients below 1 in both adults and children; inorganic arsenic gave a quotient above 1 for children in Egypt; methylmercury gave a quotient above 1 for adults in Tunisia and for children in twelve countries including Portugal, South Korea, Romania and Hong Kong; carcinogenic risk from inorganic arsenic stayed within the threshold range
• Out of 330 thousand papers screened, eight tested whether fish-based food helps malnourished children. — 8 articles out of 330859 screened, covering interventions such as wafer bars, tuna cookies, dried fish powder and fortified porridge (n = 8 studies) Evidence A source
  The included interventions measured zinc levels, height growth, erythrocyte omega-3 content, safety and acceptability, intestinal integrity and cognitive development

The bottom line

The other risk is nothing to do with metals. Scombroid poisoning comes from histamine that forms when fish is kept warm after catching, and tuna is the species most often involved. Histamine is not destroyed by cooking or canning, so the cold chain is the whole defence. On the benefit side, tuna is mostly studied as an oil: encapsulating it changed how much omega-3 reached toddlers' blood, and the review of high-DHA oils reports inconclusive and inconsistent results in its own summary. The question people actually ask, how to weigh omega-3 against mercury for a given species, has no answer in anything we hold. Neither does the idea that tuna's selenium offsets its mercury.

Sources

1. tun-dr-02 · systematic review and meta-analysis of contamination measurements
   Except for Cd and Se, concentrations of other metals in the canned tuna fish were lower than the limits recommended by the United States Environmental Protection Agency (USEPA), World Health Organization (WHO), Food and Agriculture Organization (FAO) and Iran National Standards Organization
   Food Chem Toxicol, 2018 · checked 2026-09-22
2. tun-dr-04 · randomised controlled trial
   The results showed an enhanced bioavailability with significantly greater concentrations of blood DHA levels in formulas with microencapsulated powders. There were no significant effects of treatment on sleep and cry patterns.
   Nutrients, 2020 · checked 2026-09-22
3. tun-dr-03 · systematic review and meta-analysis of outbreak reports
   Fish involved in histamine poisoning was mainly tuna or Istiophoridae species.
   Crit Rev Food Sci Nutr, 2018 · checked 2026-09-22
4. tun-dr-05 · systematic review
   Although inconclusive results were reported in several instances, and inconsistent outcomes observed in others, current data provides substantiated evidence in support of DHA being a beneficial bioactive compound for heart, cardiovascular and brain function, with different, and at times complementary, effects compared with EPA.
   Crit Rev Food Sci Nutr, 2019 · checked 2026-09-22
5. tun-dr-01 · systematic review with risk assessment
   the THQ value due to Me Hg for adult in Tunisia and for children in Tunisia, Malta, Portugal, Latvia, Cambogia, Peru, South Korea, Romania, Hong Kong, United Arab Emirates, Morocco, and Egypt was higher than 1 value.
   Int J Environ Health Res, 2024 · checked 2026-09-22
6. tun-dr-06 · systematic review
   A total of 330,859 articles were screened, out of which eight articles were included in the systematic review.
   Iran J Med Sci, 2024 · checked 2026-09-22