Dioxins in U.S. Farm-Raised Catfish

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Dioxins are highly toxic pollutants that accumulate in tissue fat. Almost all dioxins found in people who don't work in toxic waste dumps or something similarly hazardous are believed to come from food, especially meat, milk, and fish, which account for about 95% of human exposure. We tend to only hear about it in the news, though, when there's some mass poisoning.

In 1957, for example, millions of chickens began dying, blamed on toxic components in certain feed fats. Factory farming was taking off, and the industry needed cheap feed to fatten up the birds. They ended up using a toxic fleshing grease from hide stripping operations in the leather industry that were using dioxin-containing preservatives. A subsequent outbreak in 1969 resulted from a pipe mix-up at a refinery that was producing both pesticides and animal feed.

In the 1990's, a supermarket survey found the highest concentrations of dioxins in farm-raised catfish. The source of dioxins was determined to be the feed, but that's surprising, since catfish aren't fed a lot of animal fat. Turns out it was dioxin-contaminated clay added to the feed as an anti-caking agent, which may have originally come from sewage sludge. The same contaminated feed was fed to chickens, so what may have started out in sewage sludge ended up on the plates of consumers in the form of farm-raised catfish and chicken.

How widespread of a problem did it become? This affected five percent of U.S. poultry production, that's people eating hundreds of millions of contaminated chickens. And if it's in the chickens, it's in the eggs. Elevated dioxin levels were found in chicken eggs too. When the source of the feed contamination was identified, the USDA estimated that less than 1% of animal feed was contaminated, but 1% of egg production means over a million eggs a day. But the catfish were the worst. More than a third of all U.S. farm-raised catfish were found contaminated with dioxins thanks to that ball clay. So the FDA requested that ball clay not be used in animal feeds. They even asked nicely, writing "Dear producer or user of clay products in animal feeds, continued exposure to elevated dioxin levels in animal feed increases the risk of adverse health effects in those consuming animal-derived food products... we are recommending that the use of ball clay in animal feeds be discontinued...We look forward to the industry's cooperation." (You can see the original letter in my video, Dioxins in U.S. Farm-Raised Catfish).

So how cooperative did the industry end up being? Half a billion pounds of catfish continued to be churned out of U.S. fish farms every year but only recently did the government go back and check. Published in 2013, samples of catfish were collected from all over the country. Dioxins were found in 96% of samples tested. Yeah, but just because catfish are bought in the U.S. doesn't mean they came from the U.S. And indeed some of the catfish were imported from China or Taiwan, but they were found to be ten times less contaminated. And indeed, when they checked the feed fed to U.S. catfish, more than half were contaminated, and so it seems likely that mined clay products are still being used in U.S. catfish feeds. Even "just small amounts of mineral clays added to fish feeds, together with the fact that catfish can be bottom-feeders may lead to higher than acceptable dioxin residues in the final catfish products."

The Institute of Medicine suggests strategies to reduce dioxin intake exposure, such as trimming the fat from meat, poultry, and fish, and avoiding the recycling of animal fat into gravy, but if almost all dioxin intake comes from animal fat, then eating a more plant-based diet could wipe out about 98% of exposure. Thus "a vegetarian diet or even just eating more plants might have previously unsuspected health advantages along with the more commonly recognized cardiovascular benefits and decreased cancer risk."

This is a good illustration of how we can't necessarily rely on regulators to protect our families' health. More on dietary dioxins and what we can do about it in Dioxins in the Food Supply and Counteracting the Effects of Dioxins Through Diet.

Even wild fish are exposed to industrial pollutants spewed into our waterways. See, for example:

Farmed fish is the worst, though: Farmed Fish vs. Wild-Caught.

Other pollutants in our food supply and how to avoid them:

Though the best way to detox is not to tox in the first place, our bodies can eventually get rid of much of the toxin load:

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.

Image Credit: Brent Moore / Flickr

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Salmon May Be the Greatest Source of Dietary Pollutants

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In my video Diabetes and Dioxins, I explored a nationwide study that found a strong dose-response relationship between industrial toxins and diabetes. Since then, Harvard researchers have reported a link between persistent pollutants like hexachlorobenzene and diabetes in their Nurse's Health Study (See Food Sources of Perfluerochemicals). This is supported by an analysis they did of six other studies published since 2006 that showed the same thing. The Harvard researchers conclude that "past accumulation and continued exposure to these persistent pollutants may be a potent risk factor for developing diabetes."

Where is hexachlorobenzene found? In a U.S. supermarket survey, salmon and sardines were most heavily tainted with hexachlorobenzene, with salmon "the most contaminated food of all." Farmed salmon specifically is perhaps the greatest source of dietary pollutants, averaging nearly ten times the PCB load of wild-caught salmon.

Wait, isn't there a flaw in this argument? Since many of these chemicals were banned in the 70's, the levels inside people have been going down, whereas the rates of diabetes have been shooting straight up. Therefore, how could pollutant exposure be causing diabetes? This puzzle may be explained by our epidemic of obesity. The nationwide study found that the association between these toxins and diabetes was much stronger among obese subjects than among lean subjects. As people get fatter, the retention and toxicity of pollutants related to the risk of diabetes may increase.

So we're not just exposed by eating the fat of other animals; our own fat can be a continuous source of internal exposure because these persistent pollutants are slowly but continuously released from our fat stores into our circulation.

They don't call them "persistent pollutants" for nothing. These chemicals have such a long half-life that people consuming regular (even just monthly) meals of farmed salmon might end up retaining these chemicals in their bodies for 50 to 75 years.

Hexachlorobenzene in fish has been tied to diabetes; what about the mercury? A 1995 study highlighted in my video, Pollutants in Salmon and Our Own Fat, out of Japan found that diabetics do seem to have higher mercury levels in their body. Mercury alone does not seem to increase diabetes risk, though. It may be the simultaneous exposure to both dioxins and mercury that increases risk, so the safety limits for dioxins and mercury individually may underestimate the risk when they're consumed together in seafood.

So while the pharmaceutical industry works on coming up with drugs to help mediate the impact of these pollutants, a better strategy might be to not get so polluted in the first place.

Unfortunately, because we've so contaminated our world, we can't escape exposure completely. You have to eat something. Some foods are more contaminated than others, though. Exposure to these pollutants comes primarily from the consumption of animal fat, with the highest levels found in fatty fish like salmon. Farmed Atlantic salmon may be the single largest source of these pollutants, and that's the kind of salmon we most commonly find in supermarkets and restaurants.

We hear about advisories warning pregnant women to avoid the consumption of food containing elevated levels of pollutants and mercury, but as a public health journal article points out, since these toxins bio-accumulate in the body for many years "restricting the exposure to these pollutants only during pregnancy would not protect the fetus or future generations against the harmful effects of these hazardous chemicals."

For the existing links between seafood and diabetes risk, see Fish and Diabetes and I explored this concept of our own body fat as a reservoir for disease-causing pollutants in Diabetes and Dioxins.

More on hexachlorobenzene in my video Food Sources of Perfluorochemicals.

Our body has a tougher time getting rid of some toxins than others:

The best way to detox is to stop toxing in the first place.

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: Sharon Mollerus / Flickr

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Dioxins Stored in Our Own Fat May Increase Diabetes Risk

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Finding higher diabetes rates among those heavily exposed to toxic pollutants--such as those exposed to Agent Orange, chemical plant explosions, toxic waste dumps, or heavy metals in fish from the Great Lakes--is one thing. Would the same link be found in a random sampling of the general population? Yes. A strong dose-dependent relationship was found between the levels of these pollutants circulating in people's blood and diabetes. Those with the highest levels of pollutants in their blood stream had 38 times the odds of diabetes.

Interestingly, there was "no association between obesity and diabetes among subjects with non-detectable levels of pollutants." In other words, "obesity was a risk factor for diabetes only if people had blood concentrations of these pollutants above a certain level." We know obesity predisposes us to diabetes, but according to this study, highlighted in my video, Diabetes and Dioxins, this is perhaps true only if our bodies are contaminated with industrial pollutants. This finding implies that virtually all the risk of diabetes conferred by obesity is attributable to these pollutants, and that obesity might only be a vehicle for such chemicals. Could we be carrying around our own little toxic waste dump on our hips?

Now it's entirely possible that the six pollutants they looked at were not themselves causally related to diabetes. Rather, they could just be surrogates of exposure to a mixture of chemicals. After all, 90% of these pollutants in our diet come from animal foods. Except for individuals living or working around industrial sites where these chemicals were used or dumped, the most common source of exposure to PCBs is from diet, from foods of animal origin, especially seafood. The strong relationship the researchers found between certain pollutants and diabetes may just be pointing to other contaminants in animal products.

If these pollutants are particularly found in seafood, are people who eat fish at higher risk for diabetes? See my videos Fish and Diabetes, and Pollutants in Salmon and Our Own Fat.

For more on dioxins, see:

For more on PCBs, see:

These pollutants may also play a role in our rising epidemic of allergic diseases. See Alkylphenol Endocrine Disruptors and Allergies and Dietary Sources of Alkylphenol Endocrine Disruptors.

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: Agustin Ruiz / Flickr

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Why Would Eating Fish Increase Diabetes Risk?

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In the past two years, six separate meta-analyses have been published on the relationship between fish consumption and type 2 diabetes. The whole point of a meta-analysis is to compile the best studies done to date and see what the overall balance of evidence shows. The fact that there are six different ones published recently highlights how open the question remains. One thread of consistency, though, was that fish consumers in the United States tended to be at greater risk for diabetes.

If we include Europe, then fish eaters appeared to have a 38% increased risk of diabetes. On a per serving basis, that comes out to be about a 5% increase in risk for every serving of fish one has per week. To put that into perspective, a serving of red meat per day is associated with 19% increase in risk. Just one serving per day of fish would be equivalent to a 35% increase in risk. But why might fish be worse than red meat?

Fish intake may increase type 2 diabetes risk by increasing blood sugar levels, as a review of the evidence commissioned by the U.S. government found. The review found that blood sugars increase in diabetics given fish oil. Another possible cause is that omega 3's appear to cause oxidative stress. A recent study, highlighted in my video, Fish and Diabetes, found that the insulin producing cells in the pancreas don't appear to work as well in people who eat two or more servings of fish a week. Or it may not be related to omega 3's at all but rather the environmental contaminants that build up in fish.

It all started with Agent Orange. We sprayed 20 million gallons of the stuff on Vietnam, and some of it was contaminated with trace amounts of dioxins. Though the Red Cross estimates that a million Vietnamese were adversely affected, what about all the servicemen who were exposed spraying it across the countryside? Reports started showing up that veterans exposed to Agent Orange appeared to have higher diabetes rates than unexposed veterans, a link that's now officially recognized.

These so-called "persistent organic pollutants" are mainly man-made industrial chemicals and are among the most hazardous compounds ever synthesized. They include dioxins, PCBs, and certain chlorine-containing pesticides, all of which are highly resistant to breakdown in the environment.

Initially condemned for their deleterious effect on reproductive function and their ability to cause cancer, there is now a growing body of evidence showing that exposure to these pollutants leads to metabolic diseases such as diabetes. This is a breakthrough that "should require our greatest attention."

For more on the role industrial pollutants may play in our diabetes epidemic, see Diabetes and Dioxins and Pollutants in Salmon and Our Own Fat.

More on the changing views surrounding fish oil supplements in Is Fish Oil Just Snake Oil?

Other foods associated with diabetes risk include processed meat and eggs. See Bacon, Eggs, and Gestational Diabetes During Pregnancy and Eggs and Diabetes, while Indian gooseberries and flaxseeds may help (Amla Versus Diabetes and Flaxseed vs. Diabetes).

Other videos on how polluted our oceans now are include:

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: Gideon / Flickr

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How Contaminated Are Our Children?

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In a study highlighted in my video, California Childen Are Contaminated, researchers analyzed the diets of California children ages two through seven to determine the cancer and non-cancer health effects from food contaminant exposures. It turns out food may be the primary route of exposure to toxic heavy metals, persistent pollutants, and pesticides. "Though food-borne toxic contaminants are a concern for all ages, they are of greatest concern for children, who are disproportionately impacted because they're still developing and have greater intake of food and fluids relative to their weight. Pediatric problems that have been linked to preventable environmental toxin exposures include cancer, asthma, lead poisoning, neurobehavioral disorders, learning and developmental disabilities, and birth defects."

The good news is that changing one's diet can change one's exposure. Quoting from the study, "A diet high in fish and animal products, for example, results in greater exposure to persistent pollutants like DDT and dioxins and heavy metals than does a plant-based diet because these compounds bioaccumulate up the food chain." Plants are at the bottom of the food chain. The sample of California kids, however, was not eating a plant-based diet. Cancer benchmark levels were exceeded by all 364 children for arsenic, the banned pesticide dieldrin, a metabolite of DDT called DDE, and dioxins.

Children exceeded safety levels by a greater margin than adults. This is especially of concern for children because all of these compounds are suspected endocrine disruptors and thus may impact normal development. Cancer risk ratios were exceeded by over a factor of 100 for both arsenic and dioxins.

Which foods were the worse? For preschoolers, the number one food source of arsenic was poultry, though for their parents, it was tuna. The number one source of lead was dairy, and for mercury it was seafood. And the number one source of the banned pesticides and dioxins was dairy. (See Preventing Parkinson's Disease With Diet.)

The researchers also recommended children should eat lower quantities of chips, cereal, crackers, and other crispy carbs to reduce acrylamide intake.

The California study didn't split up the groups by gender, but a similar study in Europe found that men had higher levels of some of these pollutants than women. For example, levels of the banned pesticide chlordane were higher in men, but women who never breastfed were right up there alongside men, with the lowest levels found in women who breastfed over 12 months. Therefore, it is likely that the lactation-related reduction in blood pollutant levels partly explains the lower body burdens among women compared with men. So cows can lower their levels by giving some to us, then we can pass it along to our children.

What non-cancer effects might some of these pollutants have? They can affect our immune system. Studies clearly demonstrate the "ability of dioxins and related compounds to have a long-lasting and deleterious impact on immune function." This manifests as increased incidences of respiratory infections, ear infections, cough, and sore throat. At first, most of the data was for during infancy, but now we have follow-up studies showing that the immunosuppressive effects of these toxins may persist into early childhood, so we should try to reduce our exposure as much as possible. Because these pollutants accumulate in animal fat, consuming a plant-based diet-decreasing meat, dairy, and fish consumption-may reduce exposure for children and adults alike.

These findings should come as no surprise to those who saw my video Pollutants in California Breast Tissue. For an overview see CDC Report on Environmental Chemical Exposure and President's Cancer Panel Report on Environmental Risk.

Pollutant exposure may affect the ability to have children in the first place (Male Fertility and Diet and Meat Hormones & Female Infertility). Such a delay, though, may allow one an opportunity to reduce one's toxic burden through dietary change (Hair Testing for Mercury Before Considering Pregnancy and How Long to Detox From Fish Before Pregnancy?).

During pregnancy, pollutants can be transferred directly (DDT in Umbilical Cord Blood), and after pregnancy through breastfeeding (The Wrong Way to Detox). Once our kids are contaminated, How Fast Can Children Detoxify from PCBs? The chemicals have implications for older children too: Protein, Puberty, and Pollutants.

Seafood is not the only source of toxic heavy metals. See:

Videos on primary food sources of other industrial pollutants include:

There are some things we can eat, though, to counteract some of the toxins:

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death,More Than an Apple a Day, and From Table to Able.

Image Credit: Kevin Krejci / Flickr

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How Long to Avoid Fish Before Conception?

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Mothers' increased consumption of fish before and during pregnancy leads to increased exposure to both mercury and the long-chain omega 3 DHA. Mercury may negatively affect brain development in one's unborn baby, whereas DHA may stimulate brain development. However, the negative effect of mercury appears to outweigh the beneficial effect of DHA for most species of fish (see Mercury vs. Omega-3s for Brain Development).

Unfortunately, women of childbearing age appear less aware and knowledgeable about this problem than other women, despite FDA and EPA campaigns to inform every OB/GYN and pediatrician in the country about the potential risks of mercury in fish.

Since mercury sticks around in the body, women may want to avoid fish with high levels of mercury for a year before they get pregnant, not just during pregnancy. The rationale for avoiding fish for a year before pregnancy is because the half-life of mercury in the body is estimated to be about two months. In a study I profile in my video How Long to Detox from Fish Before Pregnancy a group of researchers fed subjects two servings a week of tuna and other high mercury fish to push their mercury levels up, and then stopped the fish. Slowly but surely their levels came back down (see the video for the graph). I know a lot of moms are concerned about exposing their children to mercury containing vaccines, but if they eat even just a serving a week of fish during pregnancy, the latest data shows that their infants end up with substantially more mercury in their bodies than if they were injected with up to six mercury-containing vaccines.

Given the two-month half-life of mercury, within a year of stopping fish consumption our bodies can detox nearly 99% of the mercury. Unfortunately the other industrial pollutants in fish can take longer for our body to get rid of. Certain dioxins, PCBs, and DDT metabolites found in fish have a half-life as long as ten years. So getting that same 99% drop could take 120 years, which is a long time to delay one's first child.

The fact that we can still find DDT in umbilical cord blood decades after the pesticide was banned speaks to the persistence of some pollutants. There's a shortcut for moms, but it's The Wrong Way to Detox.

What effects do these other pollutants have? Well, high concentrations of industrial contaminants are associated with 38 times the odds of diabetes--that's as strong as the relationship between smoking and lung cancer! Isn't diabetes mostly associated with obesity though? Well, these pollutants are fat-soluble, so "as people get fatter the retention and toxicity of persistent organic pollutants related to the risk of diabetes may increase." This suggests the shocking possibility that obesity "may only be a vehicle" for such chemicals.

Now the pollutants could just be a marker for animal product consumption, which may be why there's such higher diabetes risk, since more than 90% of the persistent organic pollutants comes from animal foods. And indeed, in the U.S. every additional serving of fish a week is associated with a 5% increased risk of diabetes, which makes fish consumption about 80% worse than red meat. PCBs are found most concentrated in fish and eggs (Food Sources of PCB Chemical Pollutants), which may be why there are lower levels of Industrial Pollutants in Vegans. This may also help explain the remarkable findings in Eggs and Diabetes.

More on the risks of mercury can be found in these videos:

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: Tatiana Vdb / Flickr

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What to Eat to Reduce Our Toxic Exposure

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It is not very common that a single molecule attracts enough interest to merit international scientific conferences of its own. "Ah receptor," however, "belongs to the rare elite of such molecules." Ah receptors are an important factor in how our immune system works. For background, see my video, The Broccoli Receptor: Our First Line of Defense. The latest conference offered "new reports about the way plant-derived compounds in our diet are necessary for a fully functioning immune system of the gut." One study in particular out of the journal Nature, "expanded our understanding of how diet impacts immunity and health by showing that a plant-derived nutrient profoundly shapes the capacity for intestinal immune defense." And intestinal defense not only protects us against the pathogens we may ingest, but also against toxic chemicals.

We're constantly exposed to a wide range of toxins, from such sources as cigarette smoke, exhaust fumes, furnace gases, cooked meat and fish, cow's milk, and even mother's milk (because of what mothers themselves are exposed to) as seen in my video Counteracting the Effects of Dioxins Through Diet. Many of these pollutants exert their toxic effects through the Ah receptor system. For example, dioxins invade the body mainly through the diet (where we get more than 90% of our exposure) as it concentrates through the food chain, presenting a serious health concern. But there are phytonutrients in fruits, vegetables, tea, red wine, and beans that block the effects of dioxins at levels close to what we find in people's bloodstream. Just three apples or about a tablespoon of red onion a day may cut dioxin toxicity in half. And the half-life of these phytonutrients in the body is only about 25 hours, so we have to keep eating these health-promoting foods day after day.

At first we just thought that it was only cruciferous vegetables that could dock in these receptors and fend off toxins, but does that make evolutionary sense? As Lora V. Hooper from the Howard Hughes Medical Institute notes, "Given the variety and flexibility of most mammalian diets, a specific dependence on cruciferous vegetables for optimal intestinal immune function would seem overly restrictive. Rather, it seems likely that many other foods contain compounds with similar immune-stimulatory properties."

Indeed, "the search for foods containing similar immunomodulatory compounds has begun." We now know that a wide variety of natural plant compounds can counteract the chemical pollution to which we're all exposed. There is actually one animal product that has also been shown to potentially block the cancer-causing effects of dioxins: camel urine. Camel urine--but not cow urine--was found to inhibit the effects of a known carcinogenic chemical. Importantly, the researchers emphasize that virgin camel urine showed the highest degree of inhibition, performing better than pregnant camel urine, for example. So the next time our kids don't want to eat their fruits and veggies, we can just say, "It's either that, or camel pee."

I report different mechanisms but similar outcomes in Plants vs. Pesticides and Eating Green to Prevent Cancer. So this all suggests a double benefit of eating lower on the food chain, since it would also entail lower exposure to toxic contaminants in the first place (Industrial Pollutants in Vegans).

How Chemically Contaminated Are We? Check out the CDC Report on Environmental Chemical Exposure. Where are dioxins found so we can avoid them in the first place? See Dioxins in the Food Supply.

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Images thanks to Feliciano Guimaraes / Flickr

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