June 23, 2005
High Fish Consumption Raises Baby Intelligence But Mercury Lowers IQ

A study of 135 Boston area babies has found that mercury from fish lowers baby IQ but low mercury fish consumption raises baby IQ dramatically. (same article here and here and here)

The women in the study ate fish on average once a week during the second trimester of their pregnancy. The highest intelligence scores were among the babies whose mothers had consumed more than two helpings of fish per week but whose mercury levels remained under 1.2 parts per million, according to the report published online last month in the journal Environmental Health Perspectives.

For each additional weekly serving of fish, the babies' intelligence scores increased by 4 points, or an average of almost 7%. But for every increase of 1 part per million of mercury, the babies' intelligence scores dropped by 7.5 points, or 12.5%. A woman could raise her mercury level by 1 ppm if she ate an average-sized serving of swordfish once a week, said Dr. Emily Oken of Harvard Medical School, the study's lead researcher.

"The range of fish intake in our study was from zero to 5.5 servings per week, so these were not women who were eating fish daily or multiple times a day," said Oken, who specializes in pregnancy and nutrition.

The beneficial effects of the fish consumption is almost certainly coming from the omega 3 fatty acids in the fish. A reduction in mercury exposure combined with an increased consumption of omega 3 fatty acids could produce a large increase in average intelligence in future generations. The resulting increase in the smart fraction of the population would lead to a large increase in economic output and living standards.

The full paper is not on the web at the time I'm typing this but the paper "Maternal Fish Consumption, Hair Mercury, and Infant Cognition in a US Cohort" will be free to view at this link when it gets put on the web.

While poking around trying to find the previous paper I came across another recent research paper on the Environmental Health Perspectives web site about the economic costs of mercury due to lowered IQs.

Methyl mercury is a developmental neurotoxicant. Exposure results principally from consumption by pregnant women of seafood contaminated by mercury from anthropogenic (70%) and natural (30%) sources. Throughout the 1990s, the U.S. Environmental Protection Agency (EPA) made steady progress in reducing mercury emissions from anthropogenic sources, especially from power plants, which account for 41% of anthropogenic emissions. However, the U.S. EPA recently proposed to slow this progress, citing high costs of pollution abatement. To put into perspective the costs of controlling emissions from American power plants, we have estimated the economic costs of methyl mercury toxicity attributable to mercury from these plants. We used an environmentally attributable fraction model and limited our analysis to the neurodevelopmental impacts--specifically loss of intelligence. Using national blood mercury prevalence data from the Centers for Disease Control and Prevention, we found that between 316,588 and 637,233 children each year have cord blood mercury levels > 5.8 µg/L, a level associated with loss of IQ. The resulting loss of intelligence causes diminished economic productivity that persists over the entire lifetime of these children. This lost productivity is the major cost of methyl mercury toxicity, and it amounts to $8.7 billion annually (range, $2.2-43.8 billion; all costs are in 2000 US$). Of this total, $1.3 billion (range, $0.1-6.5 billion) each year is attributable to mercury emissions from American power plants. This significant toll threatens the economic health and security of the United States and should be considered in the debate on mercury pollution controls.

If the new Boston babies study is correct then the economic costs of mercury pollution might be even higher than this latter paper assumes. Therefore the lax and slow approach of the Bush Administration (and, to be fair, the Clinton Administration and other Administrations before it) toward reduction of mercury emissions is even more short-sighted and stupid than I already thought it was. FuturePundit gets angry thinking about the coal burning electric plants emitting mercury and the less noticed (and possibly worse - see below) chlorine plants that do the same.

Marla Cone of the LA Times who wrote the first article I linked to above also wrote a previous article on mercury emissions from coal burning electric plants and chlorine plants and how chlorine plants might be worse than coal plants for mercury emissions.. (same article here and here)

In 2000, 11 chlorine plants reported releasing 14 tons of mercury into the air through smokestacks and unmonitored leaks called "fugitive" emissions. But according to the EPA, another 65 tons of mercury were used there and unaccounted for.

EPA officials, in a 2003 report, said "that the fate of all the mercury consumed" at the chlorine plants "remains somewhat of an enigma."

If even half of that "lost" mercury were released into the air, the plants would have polluted the air with nearly the same volume as the 49 tons released by the nation's 497 mercury-releasing power plants that year, said Oceana's pollution campaign director, Jackie Savitz.

By 2002, two of the 11 plants had closed, and the reported mercury emissions dropped almost in half, to a total of 7.6 tons. The plants, however, had 28 tons of mercury that were unaccounted for, which amounted to about 1% of their total mercury used and stored, according to a 20

An enigma? Are they serious?

Where is all the chlorine plant mercury going? Probably into the atmosphere.

In a lawsuit filed today by NRDC (Natural Resources Defense Council) and Sierra Club, represented by Earthjustice, the groups charge that the rule, issued in December, does not address "lost" mercury pollution from the plants and eliminates prior pollution control requirements. In a parallel legal document, the NRDC today petitioned EPA to reconsider its December rule, and set standards that will guarantee reductions in toxic mercury emissions.

Just nine mercury cell chlorine plants are still in operation in the United States. This handful of plants purchases dozens of tons of mercury each year, to replace mercury that evaporates from the giant vats they use to make chlorine. Each plant has more than 50 of these mercury vats (called "cells" in the industry) measuring approximately 50 feet long by more than five feet wide, and each cell holds some 8,000 pounds of mercury each. In 2000 these plants purchased 65 tons of replacement mercury; in 2002, 130 tons.

"The amount of mercury that these plants are losing' dwarfs the estimated 43 tons of mercury emitted by coal-fired power plants, and it's all disappearing from nine outdated factories," said Earthjustice attorney Jim Pew, who is representing the groups in their lawsuit.

The EPA publicly acknowledges that it has not accounted for the tons of mercury that each plant must replace every year. The agency concluded in its December rule that "the fate of all the mercury consumed at mercury cell chlor-alkali plants remains somewhat of an enigma."

"It's outrageous that the EPA has no apparent interest in discovering what happens to 65 tons of mercury, which these plants likely emit into the air, and plans to do nothing about it," said Jon Devine, an NRDC attorney. "The agency apparently has forgotten what its name stands for."

The EPA and FDA advise pregnant women against consumption of high mercury fish.

Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.

The US Environmental Protection Agency (EPA) and US Food and Drug Administration (FDA) have a table of mercury levels in fish in parts per million (PPM) which you all ought to go take a look at. Look for the ones which are really low in mercury and eat them. Parenthetically, another study provides evidence that mercury might be even higher in some fish than the previous table shows. This study sampled fish purchased in New Jersey (which was not all from New Jersey) and found higher mercury levels than the older FDA/EPA table shows.

To compare actual mercury measures against data reported by the FDA, the team purchased and assayed samples of six additional types of fish (Chilean sea bass, porgy, red snapper, croaker, cod, and whiting) and two types of shellfish (shrimp and scallops) from central New Jersey markets. These species were chosen because of their wide availability in the state.

Mean levels of mercury were higher in the sea bass, croaker, whiting, and shrimp available in New Jersey--as well as the tuna sampled in the first tier of the study--than predicted by the FDA's data; the actual mean for one fish, croaker, was nearly three times the FDA estimate. The authors say these discrepancies show that the FDA should update its database (the data provided were collected mainly from 1990 to 1992). They also suggest that the agency consider providing regional breakdowns of aggregate mercury levels so state agencies can evaluate possible risks for their citizens.

What I'd like to see: A table that takes the amount of omega 3 fatty acids in fish and the amount of mercury and then ranks fish according to the ratio of omega 3 fatty acids to mercury. In other words, how to get the most amount of omega 3 fatty acids to mercury? Not all fish have as much omega 3 fatty acids. Salmon is one of the better fish for omega 3's. It also happens to be very low in mercury. So salmon is my preferred fish.

Higher consumption of low mercury fish will also lead to fewer heart attacks and less heart failure.

(BETHESDA, MD)—Older people who ate fish once or twice a week had a 20 percent lower risk of developing congestive heart failure during 12 years of follow-up, according to a new study in the June 21, 2005, issue of the Journal of the American College of Cardiology.

This is the first study to look at fish intake and the development of heart failure.

“Prior studies have shown fish intake to be associated with lower risk of fatal heart attacks. The results of the present study suggest that intake of fatty fish — high in omega-3 fatty acids — may reduce the risk of developing heart failure as well,” Dr. Mozaffarian added.

From 1989 to 1990, the researchers gave diet questionnaires to 4,738 adults in four cities who were 65 or older and free of congestive heart failure. During 12 years of follow-up, 955 participants developed congestive heart failure. After adjusting the results for other risk factors, those who had reported that they ate tuna or other fish once or twice a week were 20 percent less likely to develop congestive heart failure than those who said they ate such fish less than once a month. Eating fish three or four times a week was linked to a 31 percent lower risk of developing congestive heart failure over the next 12 years. However, fried fish consumption was linked to a higher risk of congestive heart failure.

Update: Since the world's fisheries are becoming depleted and many fish have problems with either mercury or organic toxins or both what we really need is genetic engineering of food crops such as soy, corn, and wheat to make them synthesize large amounts of the omega 3 fatty acids docosahexaenoic acid (DHA) and Eicosapentaenoic Acid (EPA). We need large cheap terrestrial sources of the omega 3 fatty acids. The alpha linolenic fatty acid (ALA) in flax seed is less than ideal and we'd be better off with a food crop that directly produced DHA and EPA.

Share |      Randall Parker, 2005 June 23 12:37 PM  Brain Development

back40 said at June 23, 2005 1:24 PM:

Eat grass fed ruminant meats and you'll get high omega-3. Same for dairy products from grass dairies. It isn't something special about fish, they don't make omega-3, they get it in their diets. This is only true for wild fishes or farmed fishes fed wild prey fish or meal. Grain fed fish like grain fed ruminants are lower in omega-3.

Somebody in the food chain has to eat their greens to get omega-3. For fish it's the little fish that the big oily fish eat, concentrating the oils. Ruminants eat massive quantities of greens, given the opportunity, and so have more omega-3.

A problem of sorts is that grass fed animals aren't very fat. They have higher percentages of omega-3s but less total fat. It also has a good HDL/LDL balance. Less total fat but better quality fat doesn't seem to be a bad deal. Eat more of it and skip some carbs.

Randall Parker said at June 23, 2005 1:47 PM:


If you have references on omega 3 to omega 6 ratios in grass fed beef then I'd like to see them. My impression from reading I did a few years ago is that, yes, grass feeding helps but not much. The difference between grass fed beef and salmon in terms of omega 3-6 ratios is still like orders of magnitude.

I'd love to be proven wrong on this point.

Jim said at June 23, 2005 2:44 PM:

what about those green, wheat-grass smothies that people drink? do they contain o-3 fatty acids, or not nearly concentrated enough?

back40 said at June 23, 2005 3:29 PM:

This story from May of this year from the University of Georgia Ag science dept. talks about a recent 3 year joint study conducted by some Appalachian universities on local grass feeding.

"Health professionals recommend a balance of 2-to-1 or less of omega-6-to-omega-3 fatty acids," she said. "Grain-finished beef typically has a 5-to-1 ratio or higher," she said.

The forage-finished beef had a ratio of less than 2-to-1.

There's some study often referenced as "Iowa State University 2001" but I haven't found it. It claims that some grass fed beef has a ration of less than 1:1. Claims for omega-3 mg/gram place grass fed beef above some oily fish such as snapper but below halibut, trout and salmon.

I wonder sometimes why hard data seems to be so hard to get and can't help but think that ag departments are in a touchy spot given that so much effort has previously gone into advancing the grain fed industry. There's also a historic bias against red meat that affects what researchers choose to study.

This seems to be changing as farmed fishes that have less healthful diets come to dominate the market, and worries about toxins such as mercury in wild fishes get more attention. There's also a resurgence of interest in pastured products as both a useful niche for suffering ranchers and an environmental boon. Perhaps better formal studies will become available?

There is also controversy about dosage. Even if the ratio of omega-6 to omega-3 is good for grass fed animals, and comparable to many fatty fishes, it isn't enough for a therapeutic dosage according to some. For that you need concentrated oils extracted from fishes rather than dietary quantities. I see no reason why such supplements couldn't just as easily be concentrated from grass fed animals though, and as with so many things it isn't certain what proper dosage should be. I find it hard to credit claims that a natural human diet would not be adequate, but it may be that for attempts to reverse past damage or to achieve benefits beyond what can be achieved with diet that supplements and concentrates might have uses. Still, there's no reason to prefer fish as a source, especially when there are concerns about toxins such as mercury.

Eric said at June 23, 2005 3:35 PM:

Not all omega 3 PUFAs are equal. Fish contain 20 carbon and longer omega 3 fats, like EPA and DHA. Those appear to be the most important. Plant sources do not (I think). Fish oil pills, which have been filtered, are probably the best source right now.

Randall Parker said at June 23, 2005 5:26 PM:


Thanks for that. When I went googling on this a few years ago I couldn't much and what I found was worse in terms of omega 3's than what you found.

Keep in mind also that 3-6 ratios vary considerably between fish. Salmon are the best of those I've compared.

Farmed fish: According to a study by the Environmenal Working Group of a couple of years ago two farmed salmon operations do an excellent job of feeding their salmon low toxin food. The Environmental Working Group says the two safe farmed brands of salmon are Black Pearl from the Shetlands and Clare Island Sea Farm from Ireland. Their salmon has even lower toxin levels than wild salmon. I didn't find them as brands for sale anywhere back when I first read the EWG report. But maybe if you googled around you might find them.

From the EWG study on salmon and PCBs:

These first-ever tests of farmed salmon from U.S. grocery stores show that farmed salmon are likely the most PCB-contaminated protein source in the U.S. food supply. On average farmed salmon have 16 times the dioxin-like PCBs found in wild salmon, 4 times the levels in beef, and 3.4 times the dioxin-like PCBs found in other seafood. The levels found in these tests track previous studies of farmed salmon contamination by scientists from Canada, Ireland, and the U.K. In total, these studies support the conclusion that American consumers nationwide are exposed to elevated PCB levels by eating farmed salmon.


A number of studies show that farmed salmon accumulate PCBs from the fishmeal they are fed. The feed is often designed to have high amounts of fish oil and is made largely from ground-up small fish. PCBs concentrate in oils and fat, and previous tests of salmon feed have consistently found PCB contamination.

If farmed salmon with the average PCB level found in this study were caught in the wild, EPA advice would restrict consumption to no more than one meal a month. But because farmed salmon are bought, not caught, their consumption is not restricted in any way.


The fat in farmed salmon contains less healthy omega-3 fatty acids than the fat in wild salmon. Salmon fat is rich in omega-3 fatty acids, essential nutrients important to fetal brain development and linked to reductions in the occurrence or symptoms of autoimmune disease, headaches, cramps, arthritis, other inflammatory diseases, hardening of the arteries, Alzheimer's disease, and heart attacks. But USDA testing data show that the fat of farmed salmon contains an average of 35 percent less omega-3 fatty acids (USDA 2002).


Six of the farmed salmon we tested came from factory-scale farms in Canada, the U.S. (Maine), and Iceland. For one other salmon sample we tested, the supplier was unable to ascertain the country of origin. All told, six of these seven were polluted with PCBs at levels that would be safe to eat no more than once a month, according to EPA health standards. About 23 million Americans eat salmon more than once a month, the majority of it farmed salmon. One salmon imported from Scotland contained PCBs at levels so high that EPA would restrict consumption to no more than 6 meals a year, if the salmon were caught, not bought.

From the EWG recommendations on salmon eating:

  • For consumers, choose wild and canned salmon instead of farmed, and eat an eight-ounce serving of farmed salmon no more than once a month. Trim fat from fish before cooking, and choose broiling, baking, or grilling over frying, as these cooking methods allow the PCB-laden fat to cook off the fish.
  • Congress should pass a funding increase for FDA to support testing of farmed salmon and other protein sources for PCBs, and to review the PCB standard for salmon and other commercial seafood, with a view toward achieving convergence on the more protective and contemporary EPA standard.
  • The Food and Drug Administration must move quickly to conduct a definitive study of PCB contamination in farmed salmon, and make all results public. This testing is critical, since FDA will be unable to regulate PCBs in farmed salmon until they conduct these studies. FDA is charged with ensuring that commercially-sold seafood is safe to eat, but currently has little data on the distribution of PCB concentrations in the farmed salmon supply. The FDA’s existing testing program targets a handful of fish a year and does not provide the FDA with the data needed to assess potential public health impacts for the estimated 52 million Americans eating salmon. Testing carries heightened importance because of the rapid growth of farmed salmon consumption, increasing population-wide at an average yearly rate of 0.16 pounds per person (NFI 2001).
  • The FDA must issue a PCB health advisory for seafood consumption in line with current PCB health guidance issued by the EPA.
  • The farmed salmon industry should shift aquaculture practices to produce fish lower in PCBs. Farmed salmon carry higher PCB loads not only because the fish fat itself contains more PCBs, but because the salmon farming industry intentionally fattens the fish to maximize market weight (Jacobs 2002). Data from the U.S. Department of Agriculture shows that farmed salmon contain 52 percent more fat than wild (USDA 2002). Salmon fat itself can be a rich source of omega-3 fatty acids, essential nutrients important to fetal brain development and linked to reductions in the occurrence or symptoms of headaches, cramps, arthritis, autoimmune disease, other inflammatory diseases, hardening of the arteries, and heart attacks. However, by consuming too much farmed salmon, some people in the U.S. may be exceeding government guidelines to protect against immune system damage, fetal brain damage, and cancer associated with the PCBs that lace salmon fat.
  • The federal government should regulate salmon farming practices to protect wild salmon populations. Currently, standard salmon farming practices can endanger wild salmon populations through environmental pollution (feces, pesticides, and antibiotics), through the spread of pathogens and parasites from tightly-packed fishpens to surrounding waters, and through the accidental but common release of non-native species that could interbreed with and overrun native salmon populations. Wild Pacific salmon are a unique, healthy resource that cannot be duplicated in a fish farm, and that stand to be harmed by current farming practices.
Randall Parker said at June 23, 2005 5:29 PM:


You bring up an important question: What kinds of omega 3 fatty acids are found in grass fed beef and in what ratios? Yes, from my own reading I'm included toward the view that EPA and DHA should be what we should go for.

Fish oil pills: I'd prefer wild salmon. Who knows how well the various kinds of fish oil are filtered? In most cases they don't tell you what kind of fish they took the fish oil out of. Plus, you have to take a lot of pills to get as much omega 3s as you can get from eating salmon.

Randall Parker said at June 23, 2005 5:34 PM:

One other point: The EWG recommendation to trim and cook the fat off of fish pretty much defeats the purpose of eating the fish in the first place. Don't eat fish which has high PCBs in their fat. The whole point of eating the fish (aside from taste) is to get the healthy omega 3 fats.

Randall Parker said at June 23, 2005 5:38 PM:

Also, even wild chinook salmon from British Columbia have high levels of chemical contaminants:

Farm-raised salmon contain much higher levels of flame retardants than most wild salmon, and some wild Chinook have the highest levels of all, according to new research. Building on an earlier study of chemicals in the two types of fish, the findings suggest that consumers should choose their salmon carefully.

The report appeared online Aug. 10 in Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world’s largest scientific society.

Polybrominated diphenyl ethers (PBDEs), which are used widely as flame-retardant additives in electronics and furniture, are released into the environment both at their manufacturing sources and through everyday product wear and tear, according to the researchers.

They measured PBDEs in 700 samples of farmed and wild salmon from around the world, including most major salmon-producing regions. The study, which is by far the largest of its kind, used the same samples from an earlier study that revealed significantly higher levels of organochlorine chemicals like PCBs and dioxins in farmed salmon than in wild.

With one exception, they report, all farm-raised samples had much higher levels of flame retardants than wild salmon. They also found that farmed salmon from Europe had higher levels than those from North America, and that both European and North American farm-raised salmon had higher levels than those raised in the southern hemisphere.

One surprising outcome of the study was that wild Chinook salmon from British Columbia had the highest average PBDE levels of all the samples. "There’s something about Chinook that’s different, particularly with PBDEs," says the study’s lead author, Ronald Hites, Ph.D., an environmental chemist at Indiana University. The elevated levels could be related to the Chinook’s feeding behaviors, according to the researchers. Among all the wild species in the study, Chinook tend to feed higher in the food web and grow to be larger fish.

While it’s difficult to make direct comparisons, the concentrations found in farmed salmon are similar to levels that have been measured in people in recent years, Hites says.

The findings suggest that, in spite of the heart-healthy omega-3 fatty acids found in all salmon, consumers should limit their intake of farmed salmon and wild Chinook. They should also insist that all salmon be clearly labeled to indicate its source, the researchers say.

Randall Parker said at June 23, 2005 6:08 PM:

I just went checking again and now I'm not clear about how Black Pearl and Clare Island compare with wild salmon.

"The corporations that are running the fish farms have the responsibility to make sure that the food they sell is safe and not contaminated with toxic chemicals,'' said Michael Green, executive director of the Center for Environmental Health.

Some farmed salmon companies -- Black Pearl and Clare Island Sea Farm - - are producing salmon that have very low PCB levels similar to those of wild salmon, Green said. These producers use herring and sardine fish meal, canola oil, soya and other uncontaminated ingredients.

But did Black Pearl exaggerate their claim?

Jane Houlihan, the research director for the Environmental Working Group, which published one of the early reports on PCB's in farmed salmon, said Black Pearl made its claims based on 12 PCB chemicals rather than the 100 cited in the Science article. Black Pearl subsequently acknowledged that and has removed the PCB claim from its Web site.

Ms. Houlihan added that Black Pearl ''is trying to do a lot of good things,'' raising the salmon without chemicals and without antibiotics. ''They just need to do total PCB testing,'' she said. Whole Foods markets, a large retailer of natural and organic foods, sell Black Pearl fish alongside wild salmon.

I originally saw the claims about Black Pearl and Clare Island in another article for which I've lost the URL.

Anyway, wild salmon is good. But avoid while Chinook from British Columbia.

Randall Parker said at June 23, 2005 6:33 PM:

Here's the claim for low contaminants in Black Pearl Salmon.

Seattle (WA), USA: Seizing the fallout from the farmed salmon contaminant study published last week, one seafood importer says that he can source farmed salmon with more than 300 times less dioxins and 1,000 times lower PCB concentrations than were found in the wild salmon sampled in the Science study.

Richard Martin, founder of Boston-based Martin International Corp., told IntraFish that test results from an independent lab in Durham, North Carolina show that the organic Atlantic salmon he sources from four or five private growers in the Shetland Islands show significantly less amounts of dioxins and dioxin-like PCBs when compared to fish tested in Science study.

Although he only submitted two fish for testing from the Shetland farms, Martin - who provided the test results to IntraFish - said that his product shows that farmed fish that are largely free of chemicals can be produced.

For dioxins, the product tested at .0005 parts per billion. For PCBs, it tested at .0031 ppb. Compared directly with the study samples, the Shetland fish had 340 times lower concentration of dioxin and 1,532 times lower concentration of PCBs than wild salmon. When compared with the farmed salmon samples, the product fared even more favorably, he noted.

Sold under the Black Pearl/Natural Choice brand on the U.S. market, the product is made with U.K. Soil Association-certified organic feed manufactured by Ewos, he said, which uses 100 percent recycled fishery products processed for human consumption. In addition, the Black Pearl farmed salmon is produced without the use pesticides, anti-fouling agents, anti-fungal agents or antibiotics, the importer added.

But if he's using 4 or 5 private growers and yet tested only 2 fish he didn't test fish from all his growers.

David Nishimura said at June 23, 2005 7:26 PM:

Kudos for all the fish-related references you've collected here.

I do wonder about the study that prompted all this, however:
Did the study correct for variations in parental intelligence, or socioeconomic status?
That fish is "brain food" has been a (IMHO correct) folk belief for centuries, but I could also see that fish eating could correlate with greater education, wealth, and intelligence, rather than being the cause of it.

Randall Parker said at June 23, 2005 8:00 PM:


I wondered the same thing about parental IQ and SES and all that. Since the paper is not yet on the web we will have to wait and see what they did to control for parental IQ and other factors.

Randall Parker said at June 23, 2005 8:45 PM:

I found Black Pearl's website and it has some interesting information on their salmon. They have one wild kind and two farmed kinds. The differences in the ratio of omega 3 to total fats is not that much between the kinds. I took their ratios of EPA+DHA to total fat and found they all were between 15% and 18%. The farmed had more total fat as expected. But it didn't suffer a diminution of the healthy fraction of fat as a result.

The Black Pearl Shetland Atlantic Salmon and Black Pearl Icelandic Atlantic Salmon both get a mixture of some fish extracts and grains. This is better than just getting fish to eat. It is not clear to me which might have more PCBs or other chemicals we ought to avoid. But these look like better than the average farm fish.

You can also compare their lab results for the two farmed salmon. Shetland has more data points but slightly higher as compared to Icelandic. Also, they don't provide lab test results of their wild salmon to compare to as a reference unfortunately.

Eric said at June 23, 2005 8:48 PM:

Check out this paper: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12509593&dopt=Abstract
Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children's IQ at 4 years of age.

OBJECTIVES: Docosahexaenoic acid (DHA; 22:6 n-3) and arachidonic acid (AA; 20:4 n-6) are important for development of the central nervous system in mammals. There is a growth spurt in the human brain during the last trimester of pregnancy and the first postnatal months, with a large increase in the cerebral content of AA and DHA. The fetus and the newborn infant depend on maternal supply of DHA and AA. Our hypothesis was that maternal intake of DHA during pregnancy and lactation is marginal and that high intake of this fatty acid would benefit the child. We examined the effect of supplementing pregnant and lactating women with very-long-chain n-3 polyunsaturated fatty acids (PUFAs; cod liver oil) on mental development of the children, compared with maternal supplementation with long-chain n-6 PUFAs (corn oil). METHODS: The study was randomized and double-blinded. Pregnant women were recruited in week 18 of pregnancy to take 10 mL of cod liver oil or corn oil until 3 months after delivery. The cod liver oil contained 1183 mg/10 mL DHA, 803 mg/10 mL eicosapentaenoic acid (20:5 n-3), and a total of 2494 mg/10 mL summation operator n-3 PUFAs. The corn oil contained 4747 mg/10 mL linoleic acid (18:2 n-6) and 92 mg/10 mL alpha-linolenic acid (18:3 n-3). The amount of fat-soluble vitamins was identical in the 2 oils (117 micro g/mL vitamin A, 1 micro g/mL vitamin D, and 1.4 mg/mL dl-alpha-tocopherol). A total of 590 pregnant women were recruited to the study, and 341 mothers took part in the study until giving birth. All infants of these women were scheduled for assessment of cognitive function at 6 and 9 months of age, and 262 complied with the request. As part of the protocol, 135 subjects from this population were invited for intelligence testing with the Kaufman Assessment Battery for Children (K-ABC) at 4 years of age. Of the 135 invited children, 90 came for assessment. Six children did not complete the examination. The K-ABC is a measure of intelligence and achievement designed for children aged 2.5 years through 12.5 years. This multisubtest battery comprises 4 scales: Sequential Processing, Simultaneous Processing, Achievement (not used in the present study), and Nonverbal Abilities. The Sequential Processing and Simultaneous Processing scales are hypothesized to reflect the child's style of problem solving and information processing. Scores from these 2 scales are combined to form a Mental Processing Composite, which serves as the measure of intelligence in the K-ABC. RESULTS: We received dietary information from 76 infants (41 in the cod liver oil group and 35 in the corn oil group), documenting that all of them were breastfed at 3 months of age. Children who were born to mothers who had taken cod liver oil (n = 48) during pregnancy and lactation scored higher on the Mental Processing Composite of the K-ABC at 4 years of age as compared with children whose mothers had taken corn oil (n = 36; 106.4 [7.4] vs 102.3 [11.3]). The Mental Processing Composite score correlated significantly with head circumference at birth (r = 0.23), but no relation was found with birth weight or gestational length. The children's mental processing scores at 4 years of age correlated significantly with maternal intake of DHA and eicosapentaenoic acid during pregnancy. In a multiple regression model, maternal intake of DHA during pregnancy was the only variable of statistical significance for the children's mental processing scores at 4 years of age. CONCLUSION: Maternal intake of very-long-chain n-3 PUFAs during pregnancy and lactation may be favorable for later mental development of children.

Invisible Scientist said at June 23, 2005 10:00 PM:

In addition to fish oil, there are a lot of natural food supplements that actually raise your IQ considerably. These are documented in Dr. Ray Sahelian's book "Mind Boosters". However, the fish oil tablets CAN contain some mercury, even though that fish oil is claimed to be distilled molecularly, and so I strongly recommend using vegetable based alternative oils such as flax seed oil or algie based DHA instead of fish oil tablets.

But choline is known to increase the memory of the babies if the pregnant mothers eat vegetables that contain that substance.

remo williams said at June 24, 2005 12:41 AM:

"A reduction in mercury exposure combined with an increased consumption of omega 3 fatty acids could produce a large increase in average intelligence in future generations."

Future generations is equivalent to 30-100 year out, and even by just 2035, nano-implants will have likely leap-frogged omega 3 fatty acids by several magnitudes. I try to get my omega 3 fatty acids through walnuts and fish because I live in the present, but this is not the stuff of 'future generations.'

back40 said at June 24, 2005 7:19 AM:


"What kinds of omega 3 fatty acids are found in grass fed beef and in what ratios? Yes, from my own reading I'm included toward the view that EPA and DHA should be what we should go for."

This CSU Chico study may be the sort of thing you seek.

There are 3 major types of omega-3 fatty acids that are ingested in foods and used by the body: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Once eaten, the body converts ALA to EPA and DHA, the two types of omega-3 fatty acids more readily used by the body. "Extensive research indicates that omega-3 fatty acids reduce inflammation and help prevent certain chronic disease such as heart disease and arthritis. These essential fatty acids are highly concentrated in the brain and appear to be particularly important for cognitive and behavioral function (University of Maryland, College of Medicine)." . .

Scientists discovered the many benefits of EPA and DHA in the early 1970's when Danish physicians observed that Greenland Eskimos had an exceptionally low incidence of heart disease and arthritis despite the fact that they consumed a high-fat diet. More recent research has established that EPA and DHA play a crucial role in the prevention of atherosclerosis, heart attack, depression and cancer (Simopoulos, 1991; Simopoulos 2002; Connor, 2000). In addition, omega-3 consumption by individuals with rheumatoid arthritis has led to the reduction or discontinuation of their ordinary treatment (Kremer, 1989; DiGiacomo, 1989).

The human brain has a high requirement for DHA. Low DHA levels have been linked to low brain serotonin levels, which are connected to an increased tendency for depression and suicide. Several studies have established a clear association between low levels of omega-3 fatty acids and depression. In fact, countries with a high level of omega-3 consumption have fewer cases of depression, decreased incidence of age-related memory loss as well as a reduction in impaired cognitive function and a lower risk of developing Alzheimer's disease. . .

Many scientists believe that increases in these chronic diseases are no accident, it is directly related to the change in our dietary patterns over the last 200 years. Our ancestors lived on an omega-6:omega-3 ratio of 1:1, while our current dietary habits are closer to 10-20:1 (Simopoulos, 1991; Pepping, 1999). Researchers believe the ideal omega-6 intake should be no more than 4-5 times that of our omega-3 intake. The National Institutes of Health recently published recommended daily intakes of fatty acids, specific recommendations include 650 mg of EPA and DHA, 2.22 g/day of alpha-linolenic acid and 4.44 g/day of linoleic acid.

Diet can significantly alter the fatty acid composition in fed cattle. Cattle fed primarily grass enhanced the omega-3 content of beef by 60% and also produces a more favorable omega-6 to omega-3 ratio. . .

More important is the ratio of omega-3 to omega-6. Both conventional and grass-fed beef provide acceptable 6:3 ratios, however grass-fed beef is closer to the ideal of a 1:1 ratio.

It doesn't compare cattle to fish oils but it provides data about cattle fat with varied feeds. It also doesn't seem to matter much what type of Omega-3 acids are consumed since ALA is converted to EPA/DHA. There must be some cost for conversion, at least in energy, but the end result for brains seems the same unless more EPA is produced than DHA. No data. Yet.

The mental health and functional benefits of DHA for adults seem as important as mental benefits for babies. Lots of other benefits too.

Brock said at June 24, 2005 7:25 AM:

Considering the much higher prevalence of fish in Asian diets over Western ones, I wonder how much of the IQ difference between populations this accounts for.

Mr. Econotarian said at June 24, 2005 7:28 AM:

I wonder if this explains Japanese IQ...

Randall Parker said at June 24, 2005 9:16 AM:


This part from that CSU Chico web page makes me entirely unexcited by the grass fed beef:

When lipid content is standard, a serving of grass-fed beef would provide 88.5 mg of omega-3, roughly 13% of the RDI for EPA/DHA, while the conventional product would supply an estimated 54.6 mg or 8% of RDI for omega-3.

The issue here is not just ratio of omega 3 to omega 6 PUFAs. Absolute levels matter. Most of the fat in beef appears to be neither (which is to be expected - meat fat is heavily saturated). Unless you wnat to eat 6 or 7 servings of beef a day (which is not a good idea) grass fed beef just isn't going to get you there. This accords with the impression I formed from previous reading. Fish is still the only game in town.

As for ALA as a precursor to DHA and EPA: I came across one web page last night that referred to a study that claimed tohave found little increase in DHA or EPA in breast milk as a result of ALA supplementation of lactating mothers. So that makes flax seed less exciting as well. ALA is not an omega 3 fatty acid. It gets converted into one though.

Also, I've read claims that high ALA consumption might increase the risk of prostate cancer among men. Not sure if it poses any sort of risk to women.

Another option is the Neuromins DHA supplement that is extracted from algae.

Engineer-Poet said at June 24, 2005 9:47 AM:

Yet another reason for people to fish the oceans to emptiness, like the Grand Banks of Newfoundland.

Just wonderful.

Randall Parker said at June 24, 2005 9:57 AM:

Geez EP, I take a more positive view:

Yet another reason to raise standards for fish farm feed so that more fish can come from aquaculture than from wild fish.

Also, yet another reason to do genetic engineering to grains to put genes in them to make large amounts of DHA and EPA.

BTW, In my web searching for this post I came across mention of some sort of limits on salmon catches in Alaska. Does the US government regulate salmon catch sizes?

Lei said at June 24, 2005 10:32 AM:

I read this in the New York Times a couple of months ago:

Tests performed for The New York Times in March on salmon sold as wild by eight New York City stores, going for as much as $29 a pound, showed that the fish at six of the eight were farm raised.

I like your idea of genetically modified food with higher levels of DHA and EPA. Meanwhile, I still eat fish but in moderation.

Brian Stone said at June 24, 2005 11:16 AM:

The paper is out now. They did not control for parental IQ. They actually say that they collected this data, but from context they clearly meant the opposite:

As with all observational studies, it is possible that we did not completely adjust for potentially confounding factors. For example, we did collect information on parental IQ or home environmental stimulation, as Project Viva includes many outcomes of interest in addition to cognition and we wished to reduce participant burden. Both of these factors might be associated with fish intake, and have been associated with child cognition in prior studies, although usually only beginning in the later half of the second year of life. We also did not measure exposure to persistent organic pollutants such as polychlorinated biphenyls ...

How much does fish consumption rise with socioeconomic status, which of course in turn is strongly correlated with (parental) IQ? As an example of this association, in Eur J Clin Nutr. 2005 May 18, "Correlates of regular fish consumption in French elderly community dwellers: data from the Three-City study" Barberger-Gateau P et al., the authors find that fish consumption strongly correlates with higher education (OR from 1.19 to 1.65, P=0.0003). And of course higher education strongly correlates both with socioeconomic status and IQ. Does anyone have any more direct data on the relationship between fish consumption and adult IQ or socioeconomic status?

(To make things more complicated, there may be a causal mechanism in the other direction, with adult fish consumption affecting adult IQ, rather than being due to it; but while some of the variance in adult IQ may be due to fish consumption, clearly a lot isn't.)

I've only glanced at other work in this area, but it seems to concentrate on the effect of mercury, treating parental IQ as a confounder. I suppose we will have to wait for someone to do the study properly. On the other hand, the mercury data is probably good.

All these considerations aside, a key question is that if indeed there is an effect of fish consumption on child IQ, how long does it persist? A longer-term study would obviously be required.

Randall Parker said at June 24, 2005 11:26 AM:

Brian Stone,

Thanks for watching for the paper. Note that Eric Evans gives a link to a paper that did randomized assignment of pregnant women to get omega 3 or omega 6 fatty acids and that paper found a relationship between intelligence and omega 3 supplementation. So there might be something to this result in spite of the lack of some needed controls.

Brian Stone said at June 24, 2005 11:54 AM:


There is now a huge amount of data available about the benefits of consumption of omega-3 -rich fish. I think it is quite likely that there is an effect on child IQ. But it was disappointing to find that this study was not well enough done to be able to support this conclusion. Not to control for parental IQ is surprising, particularly considering that the Seychelles study published in the Lancet, with its controversial result of no correlation of mercury with neurocognitive deficit, did control for this.

By the way, sardines have a pretty good omega-3 to mercury ratio, not much worse than salmon, depending on where the sardines come from.

Eric said at June 24, 2005 11:59 AM:


The genetic model organism C. elegans has the genes needed to make long chain fatty acids. The link above is about a transgenic mouse strain given the C. elegans gene fat-1, which catalyzes the conversion of omega-6 to omega-3 fatty acids. In theory, the same could be done with livestock -- cows, chicken, pigs -- to increase their levels of omega-3 PUFAs.

Randall Parker said at June 24, 2005 12:03 PM:

I keep looking for the best fish to get omega 3 fatty acids from. The ideal fish would have a high ratio of omega 3s to total calories and be low in mercury and other toxins. This table suggests mackerel might be best for omega 3 concentration:

Buy the fattiest fish. Try mackerel, anchovies, herring, sardines, salmon, tuna and turbot. Frozen and canned are OK, the USDA says. Eat enough. Daily, if you eat 2,000 calories, get at least 650 milligrams of omega-3, experts say.

A week's quota might be ONE of these:

6 ounces fresh mackerel*
10 ounces canned sardines
11 ounces pickled herring
12 ounces fresh salmon*
13 ounces canned salmon
14 ounces fresh tuna*
24 ounces canned albacore tuna
* weight before cooking
Eric said at June 24, 2005 12:03 PM:

btw, it's my understanding that fish do not produce omega-3 fats themselves, rather it enters the food chain from algae, and so it concentrates in some fish.

back40 said at June 24, 2005 12:09 PM:

"Unless you wnat to eat 6 or 7 servings of beef a day (which is not a good idea) grass fed beef just isn't going to get you there. This accords with the impression I formed from previous reading. Fish is still the only game in town."

ummm, no.

"One UK study showed a half-pint of milk gives 10% of their recommended daily intake (RDI) of Omega-3, while a "matchbox sized piece of organic cheese will give you up to 88%"."

A varied diet including grass fed (organic or not) beef and dairy products can easily provide a normal RDI of omega-3 it seems.

Zaiden's Anima said at June 24, 2005 12:12 PM:

I personally consume Member's mark fish oil, which came clean for mercury in the consumer labs report(less than 1.5ppb, iirc), and in the consumer reports magazine.(not sure if these two are related or are the same thing.).

It seems that if other toxins are shown to be low in future studies, it may not be a good supplement to take for pregnant women.

Randall Parker said at June 24, 2005 12:31 PM:


Yes, I read the Wikipedia Omega 3 fatty acid entry while I was writing the post originally. But my reaction to the organic cheese report was that either it was not accurate or that one couldn't count on organic cheese to be that way consistently. I mean, what is organic milk? Is it grass fed always? Or it is just not given antibiotics and always given food that was not grown on fertilized or pesticide sprayed fields?

So I'm not convinced as of yet that organic cow cheese is a reliable high dose source of omega 3 fatty acids. Can you find anything on the web that substantiates the claim and indicates that organic milk and cheese in general are high concentration sources of omega 3 fatty acids?

back40 said at June 24, 2005 2:49 PM:

Correct. Organic is irrelevant. It is grass fed that matters. Most organic dairies are grass based, but not all. See http://www.annieappleseedproject.org/ormilgoodsou.html which references the original study which so many repeat without reference. This may seem like heresy to some but for me grass fed is a higher standard than organic, and much of the organic standard is superstitious mumbo-jumbo. Harmless for the most part but dumb.

I don't have access to that study though. I so wish I had access to real papers and didn't have to make do so often with second and third hand stuff. This would all be so much easier and faster with a real literature search and open access.

lindenen said at June 24, 2005 3:04 PM:

A more practical question on this topic: is it possible to develop a home test for mercury so that individuals can test the fish they buy or want to purchase to make sure it's safe? Maybe there should be a law banning the sale of fish with particular levels of mercury? How do they test it? Do they puree the fish or what?

michael vassar said at June 24, 2005 4:53 PM:

Not controlling for parental IQ basically makes this study worthless. At any rate we know the results can't be right because the effect is simply too large for a trait which varies this much between cultures. The results imply that people who eat a great deal of fish would have, on average, an IQ at least 22 pts higher than people who never ate fish. Such a difference would be casually obvious. Every traditional culture would know that fishermen were smart in the same way that they know that blacksmiths were strong.

remo williams said at June 25, 2005 5:02 AM:

The Japanese may have slightly higher IQs due to fish, but by the time they hit 30, much of that differential has evaporated because of sake and beer. You think Im joking......

Engineer-Poet said at June 25, 2005 7:12 AM:

Maybe an oppressive culture is more tolerable after you've killed off some of the neurons in the pain circuits. ;-)

blue said at June 26, 2005 11:58 AM:

Is eating seaweed a good idea? Is seaweed also susceptible to mercury contamination?

michael vassar said at June 26, 2005 12:07 PM:

Ironically, prenatal or perinatal choline supplementation protects mice and rats almost completely from the neurological adverse effects of alcohol. At any rate, the Japanese simply don't have high enough IQs to be consistant with this study. Not even close.

C buening said at August 5, 2008 9:59 AM:

"The results imply that people who eat a great deal of fish would have, on average, an IQ at least 22 pts higher than people who never ate fish. Such a difference would be casually obvious. Every traditional culture would know that fishermen were smart in the same way that they know that blacksmiths were strong."

At a glance, this may seem true, however if you take into account the boston study that this discussion leads with - "for every increase of 1 part per million of mercury, the babies' intelligence scores dropped by 7.5 points, or 12.5%", if these fisherman, or the japanese for that matter, are consuming higher levels of mercury along with their Omega daily intake, maybe the benefit is offset, or worse.

A study that takes multiple factors, including parental IQ, type of fish, levels of mercury and quality of Omega 3, age and length of exposure into consideration is needed before any real conclusions can be made.

Franz said at April 18, 2009 9:48 AM:

Indeed, nutrition is a very important variable in explaining some differences in intelligence and: it's almost free when you think you just need to improve on your eating habits to mobilise those parts of your already inherent intelligence that you own but couldn't fully use due to nutrition-caused underperformance. When mothers were undernourished in omega-3 fatty acids, as a British study also showed, their babies/toddlers also ended to score lower on IQ tests than their peers whose mothers had adequate levels of the essential fatty acids. However, I would follow all this up with methods of intelligence training after these babies are born. Pity most schools do not bother investigating but rather take any student's IQ as a given fact and feed him/her the same information regardless if they understand it or not rather than investigating what keeps them from understanding (mostly an intelligence problem).

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