High mercury in canned and packaged fish: how safe is eating tuna?

I read this interesting U.S. consumer report released in January 2011: “Younger women and children should limit the amount of tuna they eat and pregnant women should not eat tuna at all, because of mercury levels found in the canned and packaged fish”. The consumer report is a non-profit publication of the Consumers Union of the U.S.A.
The report observed that white tuna (albacore) contains far more mercury than light tuna and canned tuna is the most common source of mercury in our diet. It cautiously advised women of childbearing age, pregnant mothers and children to avoid canned and package tuna or go for sea food that contains low mercury but also rich in healthful omega-3 fatty acids e.g. shrimp, crab and cod.
The Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) guidelines currently in operation in the United States advises young children and women of childbearing age to eat up to 12 ounces a week of light tuna or other lower-mercury containing seafood of up to 6 ounces per week of white tuna. This recently released consumer report, which is in conflict with the FDA and EPA, believes that the guidelines presently in operation means too much mercury for pregnant mothers thus predisposing their fetuses and youngsters (who are still developing their nervous systems) to the risks of methyl mercury’s neurotoxicity which includes birth defects of the nervous system.
In response to this report, the National Fisheries Institute (NFI) criticized the consumer report which further limited pregnant mothers as well as growing children from eating tuna. The NFI mentioned a peer-reviewed science which shows that pregnant mothers who limit or avoid seafood may actually be introducing risks from omega-3 deficiency which has adverse consequences on their growing fetuses as well.
In situations like this, where there are uncertainties, public health physicians always suggests the need to apply precautionary principle to be able to play it safe.
In comparison to Nigeria and other low-income economies, reports like this always makes me feel sad. There is no doubt that most of these low-income countries equally have similar agencies entrusted with the task of guiding their governments as well as educating their consumers on environmental and health issues. It is unfortunate to say that these agencies are either ignorant of their responsibilities or there is lack of government commitment towards financing them to effectively discharge their duties for the good of its citizens. Furthermore, because of the level of poverty and poor literacy level in these low income countries where people live in less than a dollar a day, people hardly afford three square meals in a day not talk of selecting which meal is polluted or contaminated with carcinogens and which one is not; a pathetic situation.
I hope those at the helm of affairs of these low-income countries would learn from the high-income ones where the health of its populace takes precedence and not their pockets.
Further readings: Town sees mercury spikes

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18 thoughts on “High mercury in canned and packaged fish: how safe is eating tuna?

  1. Interesting piece, indeed! I don’t know why the concern on women of childbearing age; doesn’t it accumulate in the system to affect their fetuses when they start bearing children or what. I would rather advice pregnant, breast feeding and growing children. Fortunately, there are other sources of Omega-3 fatty acids and not just tuna (whether light or white): cod, shrimps, crabs, nuts, almonds etc. That’s the beauty of nature.

    1. Hadiza, the reason why women of childbearing age were equally cautioned is because of the bioaccumulative nature of mercury in the human system. It is a safe passage to include them and not just narrow the restrictions to pregnant/breast feeding mothers and growing children. I would add that it is important for all classes of people to avoid exposure to mercury (especially the organic type) due to the enormous adverse effects of methylmercury which is not only confined to its neurotoxic effects on the foetus but also in an adult it can as well lead to unexplained miscarriages, arthritis, respiratory failure, permanent brain and kidney damages, and even death. Thanks to you all for your wonderful remarks.

  2. Thanks Hadi for adding breast feeding mothers; since it enters into the blood stream I would expect their word of caution to have added breast feeding mothers rather than those of child-bearing age. It’s a beautiful piece Dr Jalal. We enjoy all your releases; keep it up!

  3. I think the reason why they added women of child bearing age is due to its cumulative effect in the system which by the time she conceives, her foetus would be at risk of damage of its neurological system. Furthermore, it could be that the consumer report people are practicing Dr Jalal’s precautionary principle. Whichever way it swings it’s a safe way to landing. I like the argument between FDA, EPA and the fisheries institute; that’s how science works. Cheers Jalal!

  4. In view of the standard way the FDA and EPA do their things and considering that they are national bodies created by government laws; I would rather say the ‘consumer reports’ is over blowing their research……just heating up the system. Let’s wait for further responses from these two nationally acclaimed bodies who are entrusted with the responsibilities of creating safety guidelines. Well done for the concise post.

  5. Thanks Jalal for this educating post; I am now an addict to your blog because I always check my mail box to see if you have any new post. I would like to add a point or two to what is in your post. Tuna consumption is not the main source of getting mercury into the human system but rather people are commonly exposed to mercury through the inhalation of vapors produced through the burning of mercury directly or indirectly. This is the commonest pathway that exposes people to the acute and chronic effects of mercury which can in addition to the adverse effects which you mentioned earlier can also cause severe developmental problems in children and fetuses, memory loss and psychotic reactions. Kudos!

    1. Thanks Howard for the additional points; that’s how it should be (winks). I guess there is one important point which almost skipped my mind; mercury exposure negatively impacts on the human immune system thus triggering all sorts of non-specific immune-related disorders.
      An interesting point to add here is the way microorganisms, in water contaminated with mercury, processes mercury; that’s how it initiates contamination of the ecosystems and food chains by converting elemental mercury into methylmercury and its subsequent accumulation in the fatty tissues of fish, mollusks, and other food sources. Also, an important but often overlooked source of mercury entering our food chain is through livestock feeding on mercury contaminated fields.
      On the issue of main source of mercury reaching the human system, I believe this depends on the common source of mercury pollution e.g. industrial mining, chemical manufacturing, solid waste disposal, metals smelting or big smokestack across the street. In some communities, the main source could be through consumption of tuna, others through vapours in the air or livestock.

  6. Thanks a lot for selecting this topic on mercury poisoning; its an issue that keeps bothering me a lot especially considering the fact that I had amalgam fillings recently. I would be glad if anyone of you guys out there could answer me on why is it that the medical circle sometimes keeps conflicting themselves. Last week or two I read a write-up on the safety of amalgam fillings to humans considering its mercuric content; the report said it’s safe: EU-Commission report “….no risks of adverse systemic effects exist and the current use of dental amalgam does not pose a risk of systemic disease…” (http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_016.pdf). I, however, subscribed to updates on that subject. This morning I got a mail from the site that it is not safe again; the statement reads: “Dental amalgam is by far the main source of human total mercury body burden. This is proven by autopsy studies which found 2-12 times more mercury in body tissues of individuals with dental amalgam. Autopsy studies are the most valuable and most important studies for examining the amalgam-caused mercury body burden” (http://www.ncbi.nlm.nih.gov/pubmed/21232090). It further said the earlier study conducted by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) which concluded that amalgam fillings are safe have severe methodical flaws.

    1. Catherine, research in science and medicine is an on-going affair. Take for example the issue of adding fluoride supplements in drinking water which the CDC considered it to be among the top 10 public health achievements of the 20th century. In the past week or two, the FDA and EPA suggested that fluoride content in water should be reduced to avoid fluorosis. It said the amount recommended in the past was far too much for human consumption.
      In response to your question, the reason why the first report released by the SCENIHR mentioned amalgam filling as safe is because in their studies, they only relied on mercuric level in urine and blood (which has no direct correlation to its levels in the body tissues or the severity of clinical symptoms. The recent study which says dental amalgam is by far the main source of human total mercury body burden, considered autopsy as well. It was autopsy reports that found 2-12 times more mercury in body tissues of individuals with dental amalgam. It is considered that autopsy studies are the most valuable and most important studies for examining the amalgam-caused mercury body burden. The autopsy reports they reviewed consistently showed that many individuals with amalgam have toxic levels of mercury in their brains or kidneys.
      I hope am able to answer your question.

  7. I’ve been so much interested in reading and making some researches on the main causes of several cancer related diseases. I read an article in a Health magazine that says: the easiest way to get predisposed to cancer (and especially breast cancer) is through soft drinks and canned foods because of their preservatives and also the pollution of car smoke. I also want some explanations on dioxins that often enters our food chains. It is disturbing to me considering the fact that these are things we normally use in our daily lives and thus difficult to adjust or change. My questions here are basically four: 1. What are the likely precautionary measures that one should observe to avoid getting sick from the smoke we discharge from our vehicles 2. What is dioxin and how can we avoid it reaching our food chains? 3. Can these dioxins be reduced or totally eliminated? 4. Is it true that taking much vegetables reduces the rate of having breast cancers with about 76%? I would be very glad and grateful if my questions are answered. Thanks in advance and well done for such a wonderful blog post.

    1. Thanks for your questions. If you read through my earlier blog postings (scarcity of water and sanitation in Nigeria 28th Dec. 2010, EPA warns on PCB risks in schools 14th Jan. 2011, updates on PCBs 10th Jan. 2011), there are discussions on dioxins and PCBs which I believe you would find very useful.
      Coming back to your questions, let me take them one after the other:
      1. Quest: What are the likely precautionary measures that one should observe to avoid getting sick from the smoke we discharge from our vehicles?
      Ans: The easiest way to avoid getting adverse ill-health from the smoke that we discharge from our vehicles is to reduce or stop polluting the environment; this could be achieved by encouraging walking, cycling, using public transport like buses and trains, regular servicing of vehicles and taking those vehicles discharging excessive smoke off our streets, discourage bush burning, avoid using fossil fuels etc. We should encourage use of re-usable energy with a view to achieving sustainable development.
      2. Quest: What is dioxin and how can we avoid it reaching our food chains?
      Ans: Dioxins are man-made persistent environmental pollutants found throughout the world predisposing us to cancers. Dioxins came into being as a result of unregulated industrial processes. They are highly toxic causing reproductive and developmental problems, damages to the immune system, interfering with hormones and also causing cancer. Dioxins accumulate in the food chain, mainly in the fatty tissue of fish, animals and other poultry products thus more than 90% of human exposure is through food.
      3. Quest: Can these dioxins be reduced or totally eliminated?
      Ans: Prevention or reduction of human exposure is best done via source directed measures i.e. strict control of industrial processes to reduce formation of dioxins as much as possible and avoid discharging industrial wastes into our seas and oceans (see my blog post of 14th Jan. 2011 on EPA warns on PCB risks in schools).
      4. Quest: Is it true that taking much vegetables reduces the rate of having breast cancers with about 76%?
      Ans: Fresh fruits and vegetables have antioxidants (eg beta-carotene, lycopene, vitamins C, E, and A). These antioxidants protects our cells from the getting damaged by unstable molecules known as free radicals (which predisposes us to cancer). The antioxidants interacts and stabilizes these free radicals thus preventing our cells from getting damaged. In view of the benefits of these antioxidants, I will encourage you to take fresh fruits and green vegetables much more than soft drinks.

  8. Jalal, I’m impressed with the way you answered my question but my mind is not at rest because of the amalgam filling that is in my mouth. I need to discuss further with my dentist on the best way out. Thanks once more and keep the good work!

  9. Well done Doc; it keeps getting more interesting. I like the way you answered Cath and also the example you gave on fluoride supplements. Cheers!

  10. Good questions from Shukra Michika with outstanding answers from the blogger. Couldn’t be more better. Glad for coming across your wonderful blog.

  11. @Shukra: thanks for asking those chained questions; you have indirectly educated us on so many issues and grateful to Jalal for the good answers provided which people with poor medical background would equally understand.

  12. I’ve being much disturbed about the causes of cancer especially with the dioxin and canned food but thanks to the amazing blogger here for further explanations on how we should go about with it. I am much grateful; this is indeed a wonderful post. I would also like to ask another question: Are there other causes of cancer that you think we should know? Thanks a lot once more; this blog is quite productive and educating.

  13. Jalal,thanks once more for this beautiful blog post. I gained lots of knowledge out of it and especially the discussions which followed. Like Shukra, I would equally like to ask if you could tell us those chemicals that have the potentials of causing cancer to us. Thanks a lot and have a great day wherever you are.

    1. Thanks to Khalil and Shukra for asking somehow similar questions. I would like you to note that exposure to any toxic agent after a period of as much as thirty years (as observed in asbestos as a cause of lung cancer) often results in chemically induced cancer. It has been observed that since after industrial revolution, there are hundreds of chemicals that are capable of inducing cancer in humans and or animals especially after prolonged or excessive exposure; these chemicals are referred to as Carcinogens. We have several examples of them and some well known ones, which I believe you would like to know, include the following:
      • Fumes of the metals cadmium, nickel, and chromium are implicated in the causation of lung cancer
      • Vinyl chloride causes liver sarcomas
      • Exposure to arsenic compounds increases the risk of skin and lung cancer
      • Exposure to compounds like benzene and cyclophosphamide can result in chemically induced changes in the bone marrow resulting in leukaemia. There are several more but is beyond the scope of this discussions.
      Equally important are some suspected carcinogens which include the following: UV radiation, verapamil, visibility reducing particulates, volatile organic compounds, venyl acetate, welding fumes, wood dust (certain hard wood as beech and oak), wood preservatives (containing arsenic & chromate) etc.
      I hope I’m able to answer your questions.
      Sent from my BlackBerry® Smartphone, from Etisalat. Enjoy high speed internet service with Etisalat easy net, available at all our experience centres

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