Posted by Larry Hoover on June 29, 2004, at 12:10:37
In reply to Re: Fish Oil, posted by Questionmark on June 28, 2004, at 14:37:19
> i'm almost positive i've read in at least one place before (one place in particular being a health pamphlet called Nutrition Action, with one of its issues having a section on fish farming and contamination) that a number of potentially harmful contaminants are lipid-soluble and therefore found in the oils of fish. i wish i could remember some examples, but i cannot. i thought that even mercury was one, but maybe not. In any case, i'm almost sure that there were some that are. i could be wrong, of course, but i don't think i am. Thoughts/comments on this?
> Thanks.Okay. This issue is right up my alley. It's my core competency, as an environmental toxicologist. I hope I don't talk *too* much about the issues.
First, with respect to the report you recall....there is a political activist group in the United States which is trying to prevent the continued captive-fish farming activities on the west coast of North America. It was quite deceptive for that group to fund a study which assessed the contaminant burden in both farmed and wild-caught salmon without revealing the motive behind their attack. Their real motives involve habitat destruction due to intensive nutrient fallout from the fish pens, risk of fish disease, impact on aboriginal peoples, and the risk of genetic dilution or displacement of native fish stocks (Atlantic salmon are being raised on the Pacific coast). They'll do anything to create doubt about the safety of farmed fish, so they raise the POP flag.
POPs are persistent organic pollutants. (These things are 'persistent' because bacteria don't know what to do with them (they haven't evolved to eat them, i.e. they don't have enzymes that fit), and because UV light from the sun doesn't blow them apart.) As a class, POPs are generally fat soluble (e.g. PCBs, dioxins, pesticides). As a result, they are not easily excreted (in urine or feces), and instead accumulate in fat-storage tissue. That also leads to increased concentrations in predators eating contaminated prey, via a mechanism called biomagnification. The higher up the food chain you eat, the more likely you are to face increased POP burdens.
In the study released this spring (I'm sure that's the one that caught your eye), farmed salmon was associated with a PCB burden of 36 parts per billion. The FDA upper limit is 2,000 ppb. One reviewer of the study data applied the carcinogenesis risk estimate (using accepted mathematical models of actual risk from PCB exposure) to the salmon in question, and derived an increase in cancer incidence of 1 case per 100,000 consumers eating the fish for 70 years (one entire lifetime). It strains credulity to perceive that increase as a palpable risk. I'm also sure that the headline "Farmed fish are a cancer risk" gets a lot more publicity than one that says "Farmed salmon increase cancer risk by 1 case in 100,000 lifetimes of exposure". For perspective, there is a far far higher cancer risk from drinking chlorinated drinking water. (But again, for perpective, there is a far far greater risk, yet again, from drinking untreated water.)
Back to POPs. One of the most important aspects to interpreting data as reported in that fish study is to consider the context in which they are collected. For example, dietary exposure to PCBs and dioxins is continuously falling (in general terms), and has been falling for at least two decades. It is revealing to find that eggs and grain in 1982 (Britain) had similar levels of PCBs and dioxins as do fish today, and that historically, daily intake via different foods was quite similar between e.g. meat, fish, milk, eggs, and grain. See: http://www.foodstandards.gov.uk/multimedia/pdfs/fsis38_2003.pdf, and refer to the tables at the end of the article. (The British government seems to be a tad more diligent in analyzing and publishing data than are North American administrations. For more, see: http://www.foodstandards.gov.uk/science/surveillance/) The take-home points are: a) *all* food is contaminated by POPs ; and, b) contamination levels are falling over time.
The first point bears great emphasis. All food is contaminated. For whatever reason, fish have drawn a greater-than-typical share of the examinations and analyses of contaminant burden. The second point has to do with the chemistry of the POPs as a class, and directly influences the first point.
Contamination of the environment by POPs begins with acute exposure. Someone spills a drum of chemical here, disposes of something there, incinerates waste some place else. These point-source releases are totally dispersed over time, via a mechanism which environmental toxicologists call fugacity, i.e. the ability of the chemical to flee (same root meaning as fugitive). Usually, that involves vapourization (volatility), and air movement is so random the whole Earth is readily exposed. The other major process is called partitioning, and is more of a solubility thing. That's what draws POPs into fatty tissues in animals exposed to them. So, you have these two counter-balancing influences. Volatility moves the chemicals around, but reduces concentration in an absolute sense, and partitioning, which increases the concentration all over again, but within an organism.
Once we realized how it was that e.g. DDT was found in huge concentrations in Arctic wildlife, where DDT had never been used (via volatility), manufacture and use of certain POPs has been drastically curtailed. In the environment, partitioning is constantly reducing the reservoir of POPs, leading to falling concentrations in the food chain. The predominant sink (where we say the contaminants disappear to) is marine sediment. The contaminants fall to the ocean floor partitioned into various forms of gunk, and get buried over time by other bits of debris. The Earth is "sweeping it all under the carpet", so to speak, and so long as the sediments remain undisturbed, those contaminants are no longer of concern to the living organisms in the rest of the environment.
Now, back to the risk/benefit consideration of fish consumption. I'm going to add some emphasis to certain terms in the following paragraph, and I want you to read it that way.
The fairly recent focus on promoting fish consumption has come from things like cohort dietary analyses correlated with health outcomes, and comparisons of regional dietary trends with disease incidence. You can be certain that the people upon whom those data depend were *not* eating pure and uncontaminated fish. Quite the contrary, fish consumed two decades ago were **more likely to be highly contaminated** than are fish of today. And yet, we attribute health benefits to a history of eating those **contaminated** fish. Let's not forget, this isn't a new problem. It's actually **a problem that is fading away**. I may well be a jaded old environmental toxicologist, but I eat farmed fish, without the slightest concern. Trust me, there are less publicized things that ought to worry you more.
Now, to fish oil specifically. I've found two government test documents that specifically refer to fish oil. The first one (it requires Adobe Acrobat to view it) deals with British fish oil supplements, but I don't think it matters much. Fish oil is a world commodity, just like wheat and pork bellies. You're eating the same stuff. Fish liver oils contain more toxic contaminants than do fish body oils, because the liver binds toxins to destroy them. You shouldn't use fish liver oils exclusively, anyway, because they contain such high concentrations of vitamins A and D that you can overdose. The take-home message is that fish oils contain less than the very conservative level of contaminants known as the TDI, or Tolerable Daily Intake, of POPs. Scientists know there is some intake, but it's not enough to raise concern.
The second report deals with fish meal and fish oil as used in aquaculture (farmed fish) in Canada. Fish oil sold for human consumption is purified from this crude oil used for fish feed supplements. So these contaminant loads are not representative of commercial fish oils sold for human consumption in North America, but you can get an idea of the scope of the world-wide pollution problem. You *are* being protected. Testing is being done.
http://www.foodstandards.gov.uk/multimedia/pdfs/26diox.pdf
http://www.inspection.gc.ca/english/anima/feebet/dioxe.shtml
Although it includes some exceedingly technical details, the following report completed by the Food Safety Authority of Ireland, "Investigation of Dioxins, Furans and PCBs in Farmed Salmon, Wild Salmon, Farmed Trout and Fish Oil Capsules", reaches the following conclusion:
"At the levels of dioxin identified in this study, the FSAI is of the opinion that there is no risk of consumers exceeding tolerable levels of dioxin from either the consumption of farmed fish or wild salmon as part of a balanced diet or fish oil capsule supplements when taken in accordance with the manufacturers instructions."http://www.fsai.ie/surveillance/food/surveillance_food_summarydioxins.asp
With respect to heavy metal contamination of fish oils....Just as POPs partition into fatty tissues, heavy metals partition into protein. The most basic purification of fish oil involves complete removal of protein. That also completely removes the heavy metals. There is no mercury in fish oil.
There are specific brands of fish oil which are said to have been fully purged of POP contaminants. Less purified fish oils do not breach the safety threshold, at least with respect to how we currently understand the risks. In conclusion, I am willing to recommend the use of fish oils for health reasons, without reservation or concern. The benefits far far exceed the risks. In those whose health is already compromised, perhaps as a direct result of omega-3 deficiency, the benefit is even greater.
For the geekier among you, here are a couple full-text articles on the health benefits of fish oils:
http://www.ijp-online.com/archives/1999/031/04/r0247-0264re.pdf
http://www.cnr.berkeley.edu/~jls/msc/varenna.pdf
Lar
poster:Larry Hoover
thread:356500
URL: http://www.dr-bob.org/babble/alter/20040613/msgs/361658.html