Is there too much mercury in canned tuna?

Tuna fish sandwiches play such a big part in childhood and are part of the canon of kids’ food. But recently, we wondered if canned tuna was safe for our kids to consume? Is there too much mercury in canned tuna for it to be safe for our kids? Or, do the benefits of eating canned tuna outweigh the potential risks?

What is mercury, and where does it come from?

Mercury comes from natural sources like volcanoes and also from pollutants that reach the ocean. It is then converted into methyl mercury (the most toxic form of mercury) by microorganisms in the water and soil. It goes into the food chain and accumulates in larger fish. Large fish, like tuna or swordfish, live longer so they accumulate mercury over a lengthier period. They “can have mercury concentrations in their bodies that are 10,000 times higher than those of their surrounding habitat” (5).

Mercury is a heavy metal, like zinc, iron and lead. However, the body doesn’t use mercury or lead. Both elements are harmful to the brain, heart, kidneys, liver and lungs.

A 25-year study in the Faroe Islands of Denmark started in 1977 showed numerous risks from mercury exposure after exposure of over 3 parts per million (ppm). When pregnant women were exposed to these dangerous levels of mercury, there were damaging effects on developing fetal nervous systems. Some babies were afflicted with blindness, deafness and cerebral palsy. Children’s blood pressure was adversely affected. Also, immunizations were not as effective on children with high mercury exposure. And there were harmful effects on children’s IQ, attention, language, verbal memory, motor speed and hand-eye coordination. Mercury can cause severe neurological damage in both children and adults. In adults, there was a higher risk of hypertension and arteriosclerosis of the carotid arteries.

How much tuna is safe and beneficial?

This Faroe Island study is the basis for the U.S. Food and Drug Administration (FDA) and U.S. Environmental Protection Agency (EPA) fish consumption guidelines. According to the 2015-2020 Dietary Guidelines for Americans, the FDA recommends two to three servings a week as a guideline. Parents are discouraged from serving albacore (or “white” tuna) to children. However, “light tuna” (derived from skipjack, a smaller tuna species) is recommended.

The FDA also expressed guidelines for various ages:

A serving is one ounce for very young children ages two to three.
Two ounces for children ages four to seven.
Three ounces for kids ages eight to 10.
Increasing to four ounces by age 11.
An adult serving is four ounces (about the size of the palm of your hand).
The FDA recommends nursing mothers or women planning to become pregnant to abstain from eating tuna, but allow 12 ounces of canned tuna a week.

Because the distinction between tuna and canned tuna kept coming up, we did some more research. Why is tuna consistently on the list of fish to avoid because of mercury content, but canned tuna deemed safe? Canned tuna comes from a smaller species of tuna than those used for tuna steaks. The FDA averaged that a can of light tuna had about 0.12 ppm of mercury and that albacore had 0.32 ppm. These are averages so variances can occur between cans and even within the meat in one can.

The benefits of eating fish for mothers and fetal health

For pregnant mothers, fish is an optimal source of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) omega-3 fatty acids. Children benefit the most cognitively when the mothers eat two servings a week of fish. It is also known to benefit the development of their visual system. A Canadian study points out that taking DHA and EPA in supplement form does not provide the same benefits as getting it from a food source (1). And, canned tuna is an economical and convenient choice.

When the FDA reissued their seafood guidelines in 2017, a group of scientists and former FDA officials requested the reissued guidelines be revised. They wanted it reworded to “emphasize the net neurodevelopmental benefits to offspring of women who consume fish… and the neurodevelopmental risks to offspring of women who do not consume fish” (2). “When DHA was given to pregnant and lactating women, an increase in maternal intake of 1 g per day of DHA increased the child’s IQ by 0.8 to 1.8 points” (6).

In an attempt to keep pregnant women from avoiding seafood, the new guidelines stated pregnant women should consume 8 to 12 ounces of seafood a week. This revised their previous statement that said not to consume more than 12 ounces a week. The semantic difference was extremely subtle.

Is 12 ounces of tuna the final word?

Philip Spiller, the former director of the FDA’s Office of Seafood, still didn’t like the revised guidelines’ sinister tone. He knew it would cause women to continue to consume fish conservatively or not at all. He issued this statement in response, “It’s important for pregnant women to understand that 12 ounces is not the edge of danger, i.e. that 12 ounces is not a dividing line between safe and unsafe or anywhere close to it” (2). This means that even women who exceed the recommended amount were still far within the range of fetal safety.

Michael Bolger, the then director of chemical assessment at the FDA, also comments that the 12 ounce guideline was not based on any analysis or have any supporting information for this decision. It was just “precautionary” (2).

Net Effects

A number of international studies were published on the benefits of increased fish consumption on fetal development. After these studies caught their attention, Spiller and Bolger co-authored a document called Net Effects. This report weighs the increase in IQ points against the amount of each type of seafood needed to be consumed to accumulate dangerous levels of mercury. For canned light tuna, 196 ounces (about 12.25 pounds) would have to be consumed a week before it became harmful. For albacore, that translated to 67 ounces, which is a little more than four pounds (or about 5.5 times the suggested serving per week).

In Net Effects, they summarized that the choice amount of fish for pregnant woman to consume was 8 to 10 ounces a week. Spiller emphasized that this guideline should be considered “an optimum range for enhancing neurodevelopment, not a maximum past which fetal harm is guaranteed.” Instead, the guideline’s message was misconstrued. It became less about an opportunity to take advantage of fish’s developmental benefits, but more about avoiding developmental harm from mercury. And then, unfortunately, when Spiller and his boss left the FDA, this informative document went largely overlooked.

Is it safe for children to have tuna?

Philip Landrigan is a pediatrician and the Dean of Global Health at Mount Sinai School of Medicine in New York and the Director of the Children’s Environmental Health Center. In an interview, he said, “Children are more resistant to mercury than the fetus, and so I don’t take quite such a hard line thinking about children as I do thinking about fetuses.”

Recently, the American Academy of Pediatrics also issued a statement that U.S. children are not consuming enough seafood. Some studies show that early consumption of fish can also reduce allergic diseases, such as eczema and asthma in children.

Some considerations

The original Faroe Island study involved mothers’ consumption of pilot whale, which could have 100 times the concentration of methyl mercury of regular fish. Is it really an appropriate reference for authoring seafood consumption guidelines for American women? More importantly, should it be the one and only reference? Pal Weihe, one of the authors of this study, recommends “people to eat fish species low in mercury without any limitation. If you are eating low-mercury fish, I can’t imagine that you could eat so much that you would have any problem.”

Also, note that when the National Academy of Sciences (NAS) developed the guidelines for an “acceptable” amount of mercury intake based on the Faroe Island study, they went a step further and divided that number by ten. The U.S. guideline is considered the most conservative in the world. For example, Canada divided the acceptable dosage by just five.

Spiller also added, “We didn’t know if people were actually being harmed above the reference dose, or what the nature of the harm was. Anything and everything we would do at that point would have to be done as a matter of precaution. We had no analytical basis for it” (2). In fact, the international studies that initially caught Spiller and Bolger’s attention imply women who consume more than 12 ounces of seafood a week during pregnancy have children with higher IQs (3, 4).

Lastly, Spiller and Bolger also suspected that the EPA needed to make these cautious estimates in order to maintain their emission limits on coal-burning power plants. If the EPA admitted that there was an acceptable amount of mercury exposure, it would also imply an acceptable amount of mercury emissions as well.

The verdict on tuna’s benefits

Canned tuna is a great option for delivering the benefits of DHA and EPA omega-3 fatty acids to kids. These benefits range from improved cognitive ability to improved vision to reducing the risk of eczema. There is an array of seafood options to choose from, but what is more kid-friendly than a tuna fish sandwich? And, it turns out there isn’t too much mercury in canned tuna for it to be safe to eat.

Oh, one more thing… If tuna is packed in water, you don’t lose the omega-3 oils when draining the can because water and oil do not mix. However, tuna packed in olive oil has more selenium and vitamin D.

This article is for informational purposes only, even if it features the advice of physicians and medical practitioners. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific or personal medical conditions. Your use of the site indicates your agreement to be bound by our Terms of Use and Privacy Policy.

Publications

(1) Abelsohn, Alan, et al. “Healthy Fish Consumption and Reduced Mercury Exposure: Counseling Women in Their Reproductive Years.” Canadian Family Physician Medecin De Famille Canadien, College of Family Physicians of Canada, Jan. 2011, www.ncbi.nlm.nih.gov/pmc/articles/PMC3024155/.

(2) Behr, Annie. “The Scales Have Tipped on Fish and Pregnancy. Why Haven’t the Recommendations Caught Up?” Slate Magazine, Slate, 20 May 2017, slate.com/technology/2017/05/pregnant-women-should-eat-more-fish-not-less.html.

(3) Daniels, Julie L et al. “Fish intake during pregnancy and early cognitive development of offspring.” Epidemiology (Cambridge, Mass.) vol. 15,4 (2004): 394-402. doi:10.1097/01.ede.0000129514.46451.ce

(4) Oken, Emily, et al. “Associations of Maternal Fish Intake during Pregnancy and Breastfeeding Duration with Attainment of Developmental Milestones in Early Childhood: a Study from the Danish National Birth Cohort.” OUP Academic, Oxford University Press, 1 Sept. 2008, academic.oup.com/ajcn/article/88/3/789/4649216.

(5) Ware RDN, Megan. “Tuna: Risks and How Often to Eat It.” Medical News Today, MediLexicon International, 28 June 2018, www.medicalnewstoday.com/articles/306246.php#risks.

(6) Weiser, Michael J, et al. “Docosahexaenoic Acid and Cognition throughout the Lifespan.” Nutrients, MDPI, 17 Feb. 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC4772061/.”