Dioxin in Salmon Presents Serious Health Concerns

salmonAs previously documented, a diet that balances omega-3 and omega-6 consumption seems to be optimal for human health. Today, omega-6 fats are prevalent in our diets because they are in many foods containing seed oils, such as corn and canola oil. To balance the ratio of omega-3 to omega-6, many researchers have encouraged reducing seed oil consumption and increasing fish consumption. Wild salmon is a great source of omega-3 fatty acids and farmed salmon usually has an even higher omega-3 fatty acid content. However, salmon is also has high levels of dioxin, a carcinogen and endocrine disrupter. So, should salmon be included as a part of a healthy diet or avoided because of toxicity concerns? 

I began researching salmon because I was curious about whether farmed salmon had as favorable a lipid content as wild salmon. I found two papers (1,2) that compared the fatty acid content of wild versus farmed salmon. The farmed salmon measured up well. It had a higher level of omega-3 fatty acids than wild salmon. Farmed salmon also had a higher level of omega-6 fatty acids. The ratio of omega-3 to omega-6 was slightly lower in the farmed salmon. However, I concluded that farmed salmon provided a very healthy fat profile and was roughly equivalent to wild salmon.

But in the studies, I found concerns about the dioxin content of fatty fish. Dioxins are a group of chemicals released as industrial pollution. In addition to being a potent carcinogen, dioxin also acts as an endocrine disrupter, meaning that consumption of dioxin may cause feminizing effects, especially in children. There have been a multitude of studies in animals and humans showing negative effects of dioxin.

Dioxins collect in fat and levels vary between foods. Dioxin levels are measured in units termed “total dioxin-like toxic equivalency” (TEQ). Figure 1 shows a comparison of dioxin concentrations of wild and farmed salmon from several regions and other foods. In general, European farmed salmon has higher levels of dioxins than American farmed salmon.

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Figure 1. Dioxin Concentration of Salmon and Other Foods. WS= Wild Salmon; FS=Farmed Salmon. Levels of dioxin were much higher in farmed than wild salmon. Wild salmon dioxin concentrations varied depending on type of salmon. The wild salmon from SE Alaska (Chinook) had the highest levels of dioxin, while others (Coho, Pink, Chum) from the same area had similar levels as Kodiak and BC wild salmon. Butter has a high level of dioxin per gram but dioxin intake from butter would be lower when accounting for serving size. Sources: (1,2).

At present there are no federal guidelines for salmon consumption with respect to dioxin. A 2005 report in Environmental Health Prospectives found that to meet the U.S. EPA’s recommendation for dioxin consumption, farmed salmon would need to be eliminated entirely from the diet and wild salmon would need to be limited to once per month to minimize cancer risks. This may be overly cautious. The European equivalent would allow for one farmed salmon meal per month or 16 wild salmon meals per month. It is important to note that these estimates do not account for dioxin intake from non-salmon sources.

Unfortunately, industrial pollution has turned salmon, a once very healthy food source, into a potential health hazard. It is difficult to weigh the benefits of the omega-3 content of salmon against the negative of toxicity issues. One thing to keep in mind is that dioxins stay in the body for a very long time. They have a half-life of 7 to 11 years. So even if a small amount of dioxin is ingested at a meal, the cumulative effect over the course of a lifetime can be great. For that reason, I suggest that people limit salmon consumption and definitely choose wild rather than farmed salmon. Please note that nearly all Atlantic salmon is farmed. Pacific salmon is generally wild caught but can also be farmed. To my knowledge, there are no labeling requirements to distinguish wild versus farmed salmon. If the package does not clearly indicate the salmon is wild-caught, it is most likely farmed.

Fortunately, fish oil supplements are usually free of dioxins because they are produced from fish that are lower on the food chain and any contaminants are removed. The one dietary supplement I recommend is fish oil because of its wide ranging health benefits and the limited availability of safe food sources of omega-3 fatty acids. Be sure to buy fish oil from a reputable company that tests the levels of dioxins.

15 thoughts on “Dioxin in Salmon Presents Serious Health Concerns

  1. This article has many errors and false claims about dioxin levels in farmed and wild salmon. The levels in both types of salmon are well within daily consumption limits. There is no reason to avoid any food in the North American food supply because of dioxins, according to the FDA: “Consumers should eat a balanced diet and follow the Dietary Guidelines for Americans, 2010, and should not avoid any particular foods because of dioxin.” http://www.fda.gov/food/foodborneillnesscontaminants/chemicalcontaminants/ucm077524.htm

    • As you state, the FDA recommends eating a balanced diet and they do not recommend avoiding any specific foods due to dioxin content. The problem is those recommendations are based on the 2003 NAS report “Dioxins and Dioxin-like Compounds in the Food Supply: Strategies to Decrease Exposure.” That report published several months before the data on dioxin levels in farmed salmon was published in Science. Surprisingly, the FDA has not specifically addressed the problems around farmed salmon.

      Thanks for pointing out the inconsistencies between the FDA’s recommendations and the scientific data in regards to dioxin levels. That’s part of the reason I wrote the article. I hope the FDA will look into this issue. I’m not sure what you’re referring to when you state there are “many errors and false claims” in the article, but if you can give any specifics I’d be happy to discuss those issues.

      Clearly the omega-3 fatty acids in salmon have clear benefits. However, I feel that it’s healthiest to consume dioxin-free sources of omega-3 fats. For now, fish oil capsules are the best recommendation I can make. I am also researching whether certain types of fish have high levels of omega-3’s with low levels of dioxin. I’ll update you all on my findings.

      • My problem is that you are citing studies from 2001 and 2004 in regards to dioxin levels in salmon. Referring to them as definitive 10 years later without any context is misleading, and a false claim in my opinion. Here’s a number of studies done since then that show levels are low in both farmed and wild salmon, and that salmon consumption is beneficial:

        http://www.hsph.harvard.edu/nutritionsource/fish/

        http://onlinelibrary.wiley.com/doi/10.1002/etc.662/abstract;jsessionid=11B5005962B57D09B71809BDBEE44702.f04t02?deniedAccessCustomisedMessage=&userIsAuthenticated=false

        http://pubs.acs.org/doi/pdf/10.1021/es072497j

        http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281301/

        http://ajcn.nutrition.org/content/94/6_Suppl/1986S.full

        Also, the FDA report is not based on 2003 data, it’s based on annual collections:

        ” FDA expanded the program to approximately 1,700 food and feed samples in 2003, 2004 and 2005, and collected and analyzed approximately 1,100 food and feed samples in 2006, 2007, 2008, 2009, 2010 and 2011. FDA plans to collect and analyze approximately 1,100 food and feed samples in 2012 and include additional analytes (nine dioxin-like PCB congeners) in select samples. FDA has posted data for dioxin levels in TDS and non-TDS samples and posted exposure estimates using these results.”

        If you don’t want to believe the FDA, here’s a recent report from the UNFAO which concludes the same thing about most seafoods, including farmed and wild salmon, which is that the benefits of eating oily fish far outweigh the risks from dioxins and mercury, and are wholistically better for you than just taking capsules: http://www.fao.org/docrep/014/ba0136e/ba0136e00.pdf

      • Grant, the reason I am citing studies from 2001 and 2004 is that is when the last large comparison was made between farmed and wild salmon. Please let me know if you know of any updated studies.

        The Harvard blog post downplays the risk of salmon consumption but mistakenly states that the levels of dioxin in salmon are similar to that in meats, dairy products and eggs. Looking at the graph above, you can see that is certainly not the case. They repeatedly mention that dioxin is not a major problem with fish because fish have low levels of dioxin. Data on farmed salmon dioxin levels suggests that this is not the case. I’m not sure when this post was written, but it needs to be updated to factor in the high levels of dioxin in farmed salmon.

        The Kelly paper was not specifically looking at dioxin levels but was looking at other organochlorines. That paper did find 2-11 times higher levels of OCPs in farmed vs wild salmon. For this article, I was specifically researching dioxin and I’m not sure about the health effects of the OCPs but it’s probably worth looking into.

        The Luoma paper discusses the difficulty of interpreting the scientific data and making sweeping recommendations. The TEQ levels of dioxin in the samples they cite from other studies are quite low. Oddly, it seems they did not include studies that found higher levels of dioxin, such as the 2003 Science paper. The conclusion of the paper is that scientists should be careful when interpreting data. I fully agree and I feel I have done so in my post.

        The Middaugh paper argues that factors other than the risk of dioxin and other toxins should be considered when making broad recommendations. It argues that the health benefits of fish, cultural, societal, and economic concerns should be included when making broad recommendations. These are important when making population level recommendations, but individuals care about the health effects of the food they eat, not about economic loss to salmon farmers. Middaugh et al also encourage removing fatty sections of the fish to reduce dioxin intake. Unfortunately, those fatty sections are also responsible for the health benefits.

        The Miles paper supports omega-3 consumption for the health of pregnant women. I fully agree that omega-3 fats should be consumed, but I would recommend getting them via fish oil supplements that have been tested and shown to be free of dioxin. This way a growing fetus can obtain omega-3 fatty acids while minimizing toxins.

        The FDA does test over 1,000 food samples per year for dioxin levels, but only a fraction, if any, of those samples are salmon. There certainly isn’t enough sampling to compare an adequate sample size of wild vs. farmed salmon. The FDA themselves state that they are not able to adequately sample foods for dioxin.

        In the UNFAO report, I cannot find any mention that, “the benefits of eating oily fish far outweigh the risks from dioxins and mercury” in regards to farmed salmon. I do see that they report farmed salmon as having on average more than 6.5 times the dioxin of wild salmon.

        None of the papers you present contradict the fact that farmed salmon has higher levels of dioxin than wild salmon. Most of the arguments are based around whether salmon consumption recommendations should be changed on a broad scale. If you find any updated data about levels of dioxin in farmed vs. wild salmon, I would love to review it.

        The fact is dioxin is a carcinogen and endocrine disrupter. Salmon in general has a considerable amount of dioxin. Farmed salmon has a very high level of dioxin. Salmon has beneficial omega-3 fatty acids, but those same fatty acids can be obtained from fish oil supplements without any toxins (make sure the company is reputable). It seems clear to me that if a person is concerned about getting omega-3 fatty acids while minimizing toxins, fish oil supplements are a much better choice than salmon. If a person wants to consume salmon, wild salmon appears to be much safer than farmed.

      • Well, it looks to me that you’ve found what you wanted to find. You didn’t bother following the link on the Harvard blog to look at Mozzafarian’s data. You didn’t bother reading through the UN FAO report to see how they calculated risks versus benefits, then plug the farmed and wild salmon data into their tables to see how they compare.

        Yes, wild salmon often has higher levels of dioxin than farmed. But the level in farmed is not “very high” as you assert. They are at safe levels, well within daily consumption limits set by Canada, the USA and EU.

        You also misrepresented the Kelly study. POPs are dioxin-like substances and that data should not be dismissed so glibly.

        I strongly disagree that fish oil supplements are a better choice than salmon, because salmon provide omega-3 benefits as well as vitamins, selenium and a lean protein.

        Both farmed and wild salmon are safe choices, and neither should be avoided for any reason. That’s what the body of science shows.

      • Grant, thanks for your input. I always strive to have an open discussion and review all available studies.

        As an scientist, I disagree with your interpretation of the data. I like salmon and have no reason to be biased. All of my investigation came after buying a salmon fillet and wondering about the health benefits. I would like to promote farmed salmon due to the lower cost and beneficial omega-3’s but based on the dioxin concerns I cannot do so, especially when safer alternatives are available.

        Being an employee of a salmon producer, you are in the unique position to help implement practices that reduce dioxin load in your salmon. Has your company done any testing on levels of dioxin in their salmon? If not, I would encourage them to do so. If your company produced salmon with consistently low levels of dioxin you could benefit your current customers and gain new ones.

      • We do regular testing of our salmon, yes, and our levels of dioxins are extremely low. Unfortunately this data is not published, although we are working to make it public.

        I must disagree with how much credence you seem to be giving to suggestions that current dioxin levels should be cause for concern. I can find no evidence to suggest that current levels in any kind of salmon pose any kind of health risk to anyone.

        I would encourage you to take another look at the UN FAO report, specifically the data table on page 47. Farmed Atlantic salmon has a TEQ of 1.65 parts per trillion and EPA+DHA of 21.30 mg/g, compared to wild Pacific salmon which has a TEQ of 0.25 ppt and EPA+DHA of 11.6 mg/g.

        However, when you look at the tables on page 29, it shows that with those numbers, eating farmed Atlantic salmon once per week results in a net 39,200 fewer deaths per million people, and that eating wild Pacific salmon once per week results in a net 25,150 fewer deaths per million people.

        Both are good choices and provide greater health benefits than supplements because they provide a lean source of protein, vitamins and other needed compounds in our diet.

        The benefits of eating oily fish far outweigh the risks.

      • In regards to current dioxin levels, the literature is clear that dioxin exposure is unhealthy. Dioxins are carcinogenic, act as endocrine disrupters, can pass through the placental barrier and cause development abnormalities, and may cause immune function and cardiovascular defects. It’s difficult to determine the level at which these negative effects begin affecting people. Foran et al. (link below) argue that negative effects could be had from eating one farmed salmon meal per month or even less. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257546/

        Part of the problem is that any one meal does not dictate the risk of developing negative effects from dioxin. Dioxins have half-live of 7-11 years (some types have half-lives of over 100 years). So, eating many dioxin-containing meals increases the overall level of dioxin in the body increases the risk of developing negative effects. For optimal health, it makes good sense to limit dioxin intake.

        In regards to the UN FAO report, I agree that that adequate EPA and DHA intake is important for prevention of cardiovascular disease and can save lives. The table indicates 600 people per million would die of dioxin exposure if they were eating farmed salmon once per week (not to mention those who survive but suffer health effects). If people consumed dioxin-free fish oil, they could gain the life preserving effects of omega-3 fats without anyone dying of dioxin exposure.

        Glad to hear that your company is testing for dioxin and I do hope the results are made public. Clearly some people are concerned about this issue and I hope your company takes it seriously. We could certainly use a company that produces farmed salmon with low dioxin levels.

      • I wish there was no such thing as dioxin. I developed severe pain after eating a large amount of wild salmon we caught in bc Canada during that big run years ago. I developed severe hormone problems, serious pain, and was eventually diagnosed with endometriosis. I had surgery. I still have effects. I love fish. I hate dioxin. There is no safe amount.

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