This is going to be a long article and I know not everyone will have time to read it. So I’m going to summarize the key points right up front because I think this information is so important:
Overview
- Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish
- If a fish contains higher levels of selenium than mercury, it is safe to eat
- Most species of commonly eaten fish in the U.S. have more selenium than mercury
- Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
- The benefits of eating fish regularly far outweigh the potential risks, which are negligible
- Pregnant mothers and young children should eat 2-3 servings of oily ocean fish each week
These days a lot of people are scared to eat fish. They’ve been told that fish are full of contaminants like mercury, PCBs and dioxins that cause neurological problems and may increase the risk of cancer. Pregnant women have been especially warned due to the supposed risk of these toxins to the developing fetus.
In the last few articles I’ve established the importance of the long-chain omega-3 fatty acids EPA and DHA in human health. I’ve argued that the conversion of plant-based omega-3 fats like ALA into the longer chain EPA and DHA is extremely poor in most people.
The conclusion is obvious: fish should be a part of our diet. But is it safe to eat fish?
You might be surprised to learn that the answer is a resounding yes. In this article I’ll demonstrate that concerns about toxins in fish have been overblown, and that there is almost no risk associated with eating fish when a few simple precautions are taken.
The selenium story
Although people are increasingly concerned about the effects of mercury levels in fish, recent evidence suggests that the trace amounts of mercury in the fish Americans eat aren’t high enough to pose a health risk.
But measuring only mercury significantly exaggerates this risk, because it ignores the important role of selenium.
This new substance makes it hard for the body to absorb the mercury separately. Simply put, when selenium binds to mercury, mercury is not longer free to bind to anything else – like brain tissue.
Studies have shown that relevant amounts of selenium (Se) can prevent oxidative brain damage and other adverse effects associated with mercury toxicity. (PDF)
University of North Dakota researcher Nicholas Ralston has published several papers on the protective effects of selenium. He describes the relationship between selenium and mercury as follows:
Think of dietary selenium as if it were your income and dietary mercury as if it were a bill that you need to pay. Just as we all need a certain amount of money to cover living expenses such as food and rent, we all need a certain amount of selenium.
And guess what foods are highest in selenium? You’re right! 16 of the 25 best sources of dietary selenium are ocean fish.
He goes on:
Only one major study has shown negative effects from exposure to mercury from seafood, and that seafood was pilot whale meat. Pilot whale meat is unusual in that it contains more mercury than selenium. When you eat pilot whale meat it’s like getting a bill for $400 and a check for less than $100. If that happens too much, you go bankrupt. On the other hand, if you eat ocean fish, it’s like getting a check in the mail for $500 and getting a bill for $25. The more that happens, the happier you are.
What Ralston is telling us is that as long as the fish we’re eating has more selenium than mercury, there’s nothing to worry about.
Fortunately, studies by several independent organizations have consistently shown that most of the fish we eat contain significantly more selenium than mercury. Fish that contain more mercury than selenium include pilot whale, tarpon, marlin, swordfish and some shark.
The following chart illustrates the relative levels of selenium and mercury in commonly eaten ocean fish:
The selenium health benefit value (SeHBV)
Researchers have proposed a new measure of seafood safety called the Selenium Health Benefit Value (SeHBV) that takes the protective role of selenium into account.
Fish with a positive (above zero) SeHBV ratio would be safe to eat, whereas fish with a negative ratio would be unsafe. Using these criteria, most varieties of ocean fish have positive SeHBV ratios and are thus safe to eat.
A study conducted by the Energy & Environmental Research Center (EERC) and the Environmental Protection Agency (EPA) also found that an estimated 97% of the freshwater fish from lakes and rivers in the western U.S. are safe to eat. It is the only study I’m aware of that has measured both mercury and selenium levels in the tissues of freshwater fish. 1
So how much fish is safe to eat?
The joint recommendation for fish consumption of the EPA and FDA as of 2004 is as follows:
- Eat up to 12 ounces (2 average meals) a week of a variety of commonly eaten fish and shellfish found consistently low in mercury, including shrimp, canned light tuna, salmon, pollock, and catfish
- Limit albacore tuna to 6 oz. per week
- Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury
Notice that these recommendations are already quite liberal compared to the fish-phobes who suggest we avoid fish entirely.
But even these recommendations are too strict, because they don’t take the protective effects of selenium into account. As long as the fish is higher in selenium than it is in mercury, there’s no reason to limit consumption to 12 ounces per week.
Like what you’re reading? Get my free newsletter, recipes, eBooks, product recommendations, and more!
What about dioxins and PCBs?
PCBs are synthetic organochlorine compounds previously used in industrial and commercial processes. Dioxins are organochlorine by-products of waste incineration, paper bleaching, pesticide production, and production of certain plastics. Yummy!
While it makes perfect sense to try to avoid these toxins to the greatest extent possible, abstaining from fish isn’t a particularly good strategy.
The highest dietary sources of PCBs and dioxins are not fish, but beef, chicken and pork (34%), dairy products (30%) and vegetables (22%). Fish constitute only 9% of our dietary intake of these chemicals.
However, an analysis has shown that, per 100,000 individuals, consumption of farmed vs. wild salmon would result in 24 vs. 8 excess cancer deaths, respectively, while consumption of either farmed or wild salmon would result in 7,125 fewer coronary heart disease (CHD) deaths.
Another analysis of the same data suggested that, for all ages evaluated (25-35 to 85 years), CHD benefits outweighed cancer risks by 100- to 370-fold for farmed salmon and by 300- to more than 1000-fold for wild salmon.
It’s important to note that the benefits of fish consumption are based on prospective studies and randomized trials in humans, whereas estimated cancer risks include a 10-fold safety factor and are based on experimental data in animals and limited studies in humans at extremely high doses.
Cancer estimates also assumed lifetime salmon consumption of 1,000 mg/d of EPA & DHA (four 6-oz servings of wild salmon every week for 70 years). Of course virtually nobody in the U.S. currently eats this much salmon.
On the other hand, CHD mortality reduction may be achieved with lower intake (i.e. 250 mg/d – one 6-oz. wild salmon serving per week). At this intake, CHD benefits would be the same (7,125 fewer deaths) while lifetime cancer risk would decrease by 75% (6 and 2 estimated deaths per 100,000 for farmed and wild salmon respectively). The CHD benefits would outweigh cancer risks by more than 3500-fold in the case of wild salmon.
Once again, with few exceptions (the species of fish with more mercury than selenium), it’s not only safe but incredibly beneficial to eat fish regularly.
How beneficial? Let’s find out.
Fish consumption, cardiovascular disease and total mortality
In 2006 Mozaffarian & Rimm published a paper in JAMA called “Fish Intake, Contaminants and Human Health: Evaluating the Risks and Benefits“. They analyzed several studies that examined the impact of fish consumption on both coronary and total mortality. They found that modest fish consumption (e.g. 1-2 servings/wk) – especially of oily fish higher in EPA and DHA – reduced the risk of coronary death by 36% and total mortality by 17%, and may favorably affect other clinical outcomes.
The authors summarized their findings this way:
For major health outcomes among adults, based on the strength of the evidence and the potential magnitudes of effect, the benefits of fish exceed the potential risks.
And:
For women of childbearing age, benefits of modest fish intake, excepting a few selected species, also outweigh risks.
They also pointed out that the Japanese eat 900 mg/d of EPA & DHA on average, and have death rates from coronary heart disease 87% lower than those in Western populations (like the U.S.).
If you’re interested in learning more about this study, I recommend listening to the JAMA Audio in the Room interview with its lead author, Mozaffarian.
Fish consumption, pregnant mothers, and children
DHA is essential for proper development of the brain. It is preferentially incorporated into the rapidly developing brain during gestation and the first two years of infancy, concentrating in the gray matter and retinal membranes.
In a meta-analysis of 14 trials, DHA supplementation improved visual acuity in a dose dependent manner. In another trial of 341 pregnant women, treatment with cod liver oil from week 18 until 3 months postpartum raised mental processing scores at age 4 years.
This is consistent with observational studies showing positive associations between maternal DHA levels or fish intake during pregnancy and behavioral attention scores, visual recognition, memory, and language comprehension in infancy.
An FDA report issued in 2008 noted that the nutrients in fish – especially n-3 LCFAs, selenium, and vitamin D – could boost a child’s IQ by an estimated ten points. 2
The FDA report summarizes evidence suggesting that the greatest benefits to children would result if pregnant women of childbearing age, nursing mothers and young children ate more than the 12 ounces of fish per week currently recommended by the EPA.
According to the National Fisheries Institute, Americans currently consume only five ounces a week of fish high in n-3 LCFA, which is less than half the recommended amount. The NFI also estimates that up to 14 percent of women of childbearing age eat no fish at all, despite the fact that n-3 LCFA are essential to proper fetal brain and eye development.
Based on the new understanding of selenium’s protective role, and the importance of DHA for fetal and early childhood development, pregnant mothers should be advised to eat oily ocean fish regularly.
Fish consumption and autoimmune and inflammatory disease
The first evidence of the significant role of dietary intake of n-3 LCFA in reducing inflammation came from epidemiological observations of the low incidence of autoimmune and inflammatory disorders in a population of Greenland Eskimos compared with gender- and age-matched groups living in Denmark. The Eskimos in this study had dramatically lower rates of psoriasis, asthma and type 1 diabetes, as well as a complete absence of multiple sclerosis.
Animal and human studies suggest that n-3 LCFA suppresses cell mediated immune responses. Increasing the amount of n-3 LCFA while decreasing omega-6 fatty acids leads to improvements and a decrease of steroid use in patients with rheumatoid arthritis and asthma.
This is because omega-3s have been shown to suppress the capacity of monocytes to synthesize interleukin-1 (IL-1) and tumor necrosis factor (TNF). IL-1 and TNF are the principal mediators of mediation in several different inflammatory and autoimmune conditions.
Summary
This is simply a re-cap of the overview presented at the beginning of the article. But it’s worth repeating.
- Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish
- If a fish contains higher levels of selenium than mercury, it is safe to eat
- Most species of commonly eaten fish in the U.S. have more selenium than mercury
- Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
- The benefits of eating fish regularly far outweigh the potential risks, which are neglible
- Pregnant mothers and young children should eat 2-3 servings of oily ocean fish each week
Better supplementation. Fewer supplements.
Close the nutrient gap to feel and perform your best.
A daily stack of supplements designed to meet your most critical needs.
- Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343 ↩
- Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343 ↩
I really appreciate this article… I just started eating fish again recently after a few years of abstinence, and its been doing MuchGoodness for me. The facts presented here certainly open my mind to how much options there are available… I was being rather restrictive about it, which in a way is a good thing. Now I can expand my palette in confidence!
Great article. I would like people to keep overfishing in mind, and please look up the fish you buy through Seafood Watch before purchasing. I think as proponents of paleo, we should also be proponents of environmental safety through our actions. Saying that, I’m about to go eat some oyster and sardines.
However Selenium has no protection against radiation. With an estimated 462 trillion bequerels of radiation dumped into the ocean from Fukishima. Will there be any large non-radioactive fish in the Pacific? These internal emitters, migrate to organs such as the thyroid, liver, bone, and brain, often causing cancer.
http://www.washingtonsblog.com/2011/06/coming-to-a-store-near-you-radioactive-fish.html
http://criminalisewar.org/?p=437
Iodine protects from Radiation to some extent…whether its enough to protect from that much…I’m not sure. It might be good to avoid fish from that immediate area or to have plenty of non radiated fish from other areas.
You might do some searches on it as there might be more on Iodine and its protective capacity in regards to radiation. I read something about it on Jack Kruse’s website but don’t remember which blog post.
BRING ON THE SALMON AND HAMACHI!!!! I am going to town on them tonight! Thanks for making me feel as though I can without worrying! LOL
Hi! I enjoyed this posting and also shared it with my fans on facebook! I have been following the paleo diet (low carb, no grains) since Februar 2010 and lost ~50 pounds (no chronic-cardio, just weekly strenth and daily walks)! Back to my weight 12 (!!!) years ago! I want to promote the paleo diet and HIT (training) as best as I can. Thank you!
Hi Chris,
great article. I am recently a converted pescetarian (with ample amount of raw eggs, fruits, veggies, and unpasteurised cheese thrown in for good measure). I eat a lot (as in every day) of Chilean farmed mussels, shrimp, and Alaskan pollock, and one of the criteria for me choosing these foods was, apart from them being among the cheap seafood in the UK (my budget is very tight), the low environmental impact, low level of mercury, PCB’s and dioxins.
However, i was reading Denise Minger’s comments about The China Study, and when she reviewed the parts concerning seafood intake and disease, she said that regular seafood consumers need to be wary of CADMIUM intake. Looking into it, cadmium seems to cause even worse problems than mercury. But surprisingly, everyone seems to focus on mercury when they are concerned about metals from fish.
Thanks to Darrin, one of the commenter’s on the PHD blog, I managed to find some limited info on cadmium intake in the type of seafood i eat mostly – i.e crustaceans and molluscs http://www.foodstandards.gov.au/consumerinformation/nuttab2010/nuttab2010onlinesearchabledatabase/onlineversion.cfm?&action=nutrientFoods&category=Minerals&nutrientID=CD .
Many studies examining cadmium concerns on seafood conclude withthe comment along the lines of “because high cadmium seafood is not a major part of the diet, you should be ok” or “as long as you dont eat it (e.g. mussels) every day, you should be ok”. The problem is, it is a major part of my diet and i DO eat it every day!
Am i right to be concerned over cadmium levels if i eat a daily diet containing molluscs and shrimp daily?
Its post like this that make people very ill…mercury at ANY level is horribly toxic to the body. I’ve never had filling in my mouth but became very mercury toxic just from eating tuna. I would highly recommend anyone who reads this to do your own research on the subject. No matter how protective selenium is mercury does not leave the body…it stays in your body (and more specifically your brain) for a very very long time, in which it causes a host of different problems. Pretty much any mainstream “disease” in my opinion is caused from some level of heavy metal poisoning (usually mercury poisoning).
Always do your own research folks.
There are a few problems with your observations: 1) life evolved in the sea amid ever-present methyl mercury, so how toxic can trace levels really be? 2.) Our bodies excrete mercury, which is why it can be measured in hair and finger nails. 3.) Some of the healthiest, longest-lived people on the planet eat fish every day, all of which has trace levels of mercury (see point one). 4.) You completely ignore the real science, which has never found a link between the very small trace levels of mercury in common seafood and toxicity. 5.) You ignore the fundamental truth that “the dose makes the poison.” Even water can kill you if you drink too much of it. Chris’s point is that this has to be considered from a risk – benefit perspective.
“We only see and hear what we are programmed to see and hear.” –Dan Sullivan
Randy, in response to your points
1.Mercury levels have been increasing since industrialization. Mercury contamination of the coral sands in the Yongle archipelago in the South China Sea showed a deposition level at the end of the 20th century that was 9 times the pre-industrial level. Coal powered power plants release about 1,000 tons of mercury into the atmosphere each year. Levels of mercury are biomagnified by a factor of up to 10 million compared to the concentration in seawater. Add to that medical and dental exposure to mercury and some individuals will be overwhelmed.
2. Yes our bodies excrete mercury, but some less well than others. Zinc is necessary for metallothionein synthesis (a detoxifier of heavy metals) and selenium for glutathione peroxidase ( an important antioxidant). Mercury depletes both of these elements. A study of 40 women with fibromyalgia and 40 controls found that even though both groups had the same blood levels on average, the fibromyalgia group had only one-third the level of mercury in their urine – so they were excreting less mercury and it was gradually accumulating in their bodies.
Other points – low doses of mercury can cause neurological damage decades later. In one study monkeys were given 50 micrograms of methylmercury (the amount that would be found in 150 g of albacore tuna) for 7 years. Six years after dosing had ceased, some of the exposed animals exhibited clumsiness during routine activities. Human beings, with a much longer life span, have decades for these neurological deficits to manifest.
Liu, X., Xu, L., Chen, Q., Sun, L., Wang, Y., Yan, H., … & Huang, J. (2012). Historical change of mercury pollution in remote Yongle archipelago, South China Sea. Chemosphere, 87(5), 549-556.
Rosborg, I., Hyllén, E., Lidbeck, J., Nihlgård, B., & Gerhardsson, L. (2007). Trace element pattern in patients with fibromyalgia. Science of the Total Environment, 385(1), 20-27.
Rice, D. C. (1988). Delayed neurotoxicity in monkeys exposed developmentally to methylmercury. Neurotoxicology, 10(4), 645-650.
I’m struggling to find a site detailing the selenium v mercury content in fish. Do you have any suggestions or links to this information?
Chris,
I’m from Minnesota and there is plenty of freshwater fish to be caught and consumed. I’ve been searching the internet for more info on the selenium levels of the fish in the Twin Cities metro area (mainly northern pike, largemouth bass, crappies, sunfish and walleye), but the info available is vague at best. Dr. Rolston’s research seems to indicate that most minnesota fish should be high in selenium, but I would imagine it would be different in the Metro than in the rest of Minnesota, due to more industry, greater population density, less open land and little to no farming. What are some markers I can look for, such as selenium levels in soil, other animals, etc that would indicate whether the fish from metro lakes have high selenium levels. Thanks for any response.
Ben
This is a very informative article, thank you! I would like to ask one question concerning PCBs in other foods (esepcially meat). I only buy organic meat which is not possible for fish (organic fish often is farmed fish, I think “oragnic wild-caught” is just nor possible). Does organic meat contain significant levels of PCBs as well, esepcially when compared to wild caught fish? I have found the information that PCBs gather in the fatty tissue, are there significant amounts in lean seafood?
Thank you!
Thank you for this analysis, glad to see some sanity backed with data to counter the fearmongering.
Now, if I could only source BPA-free canned tuna in Europe…
What is king mackerel?
Is ordinary mackerel ok? What about herring & sardines/pilchards?
What about the fish in general available to those of us in the UK? (North Atlantic and North Sea I suppose).
For ALAs, I notice you recommend flax seed oil. In an interview with Dr Mercola, Dr Rudi Moerck was as skeptical about flax seed oil as you are about fish oil (he is also cautious about fish oil). The reason being that it is oxidised even by the time it gets into the bottles/capsules.
For ALAs, his preference would be chia seeds, which he says are smaller and digestible without being ground (whereas flax seed are indigestible, and once ground, need to be consumed within a few hours, so buying ready ground seeds is not an answer).
For DHA/EPA he strongly recommends krill oil, but then, you could say he is biased in that respect.
I have read that you are as lukewarm towards krill oil as you are towards fish oils, so I assume you will not agree with him on that. However, I would be interested to hear your take on his comments about flax seeds, flax seed oil, and chia seeds.
Flax seed oil, from the information that I’ve seen, does not convert well into our body. As far as sardines go, they have very high selenium, iodine, and omega 3 levels and very low mercury levels. The smaller the fish, in general, the lower the mercury level. According to Seafood Watch, look for Mackeral from the Atlantic and areas other than the Gulf of Mexico, where overfishing is occuring.
When it comes to Dr.Mercola, btw, he seems like a fear mongerer more than a reliable source.
Since you seem to be a critic of Dr. Mercola I’m curious as to your thoughts on one particular product that I’m thinking of buying.
I’ve heard of Full Spectrum lights being good from other sources so I think they make sense, but I’m wondering if his specific bulbs are a good pick? Its 119 dollars for 12 bulbs which is about 9 something a bulb. Do you know of any good sources for a close to natural light full spectrum bulb that’s cheaper?
Your article makes me feel much better about eating fish. My concern which I don’t think has been addressed here (I scanned the comments so I might have missed it) is what’s done to the fish after it’s caught. I keep reading about chemicals grocery store fish departments put on the fish to make it look better on display. I always ask grocery managers about this, but who is going to admit, “yeah, we poison our fish so it looks pretty!” Sometimes I buy fish and I feel really sick after eating it so I’m always leery about what I don’t know and the marketing scams businesses use to make an extra buck. It’s easier to just not eat it rather than worry.
When it comes to grocery stores bleaching and using borax to clean and polish junk fish, the Thailand fish farms seem to be the worst offenders. (Source: BottomFedeer by Grescoe )
Is Borax even an issue though? http://en.wikipedia.org/wiki/Borax Its a good source of Boron which is a trace mineral we need. The other things they used to bleach, clean, and polish the junk fish might be bad, but I’m thinking a little Borax residue isn’t an issue. Your thoughts?
Hello Chris
This is a great and informative article. I’m glad to hear this because whenever I eat fish it has a dramatic effect on my overall health, including a very noticeable, at any weight, leaned out face. I tend to put weight on chin and cheeks, and fish brings this down within 2-3 days of eating it. Any ideas on why this is?
Also, with the recent happenings in Japan, should we be taking any precautions regarding what type of fish to buy or not?
This is very interesting- a few years ago I was tested for mercury and had high levels of mercury- I did chelation to get rid of it – the thing is I didn’t know if the cause was my mercury fillings (which I subsequently had removed) or the fact that during a summer college course for 8 weeks I had a tuna fish sandwich from the college cafeteria literally almost everyday those 8 weeks- which one do you think it could have been? My mercury levels were quite high. It seemed like you were saying to still be cautious with tuna- is that because it’s ratio of selenium to mercury is not as good as some other fish like salmon?
Thanks!
I’d worry more about the BPA from canned tuna, and other canned fish for that manner, than the mercury levels
Thanks for the article. It’s important to note that fish is included in the diets of the world’s healthiest countries.
Thanks, Chris. Very informative. I reposted this on my FB page and a reader asked, “What about the concerns of radiation from Japan on the world’s oceans?” I personally don’t think this is an issue, for non-Japanese fish, but what do you think?
I thought PCBs were mainly a problem in farmed fish, which you did not cover, because of what they are fed. Same with cattle and chicken. They are fed industrial food waste (ground up carcasses, feathers and worse) and other bizarre but cheap ingredients. Isn’t it important, for your recommendations to be valid, to warn consumers to make sure they know the fish they eat is wild caught?
what about the broadway actor who had really bad mercury poisoning from eating lots of sushi? i think his name is jeremy piven……..
Hi Chris,
I have a question after reading this. When the selenium binds with the mercury does this cause the selenium to be unavailable for use by our bodies? Does the protective action of this process cause the selenium to be excreted with the mercury?
Thanks for your work.
Hannah