Mercury and fish oil

As time passes, the dose of fish oil advocated in the Track Your Plaque program is going upward.

While epidemiologic studies, like the Chicago Western Electric Study and the Nurses' Health Study suggest that decreases in mortality from heart disease begin by just eating fish a couple times per month, there are newer data that suggest greater quantities confer greater benefits.

In the last Heart Scan Blog post, I discussed the recently-released ERA JUMP Study that demonstrated a relationship between higher omega-3 fatty acid blood content and reduced quantities of carotid and coronary plaque. The JELIS Study demonstrated a 19% reduction in cardiovascular events when fish-consuming Japanese added 1800 mg of EPA (only).

However, the suggestion that increased quantities of fish oil potentially yield greater protection from heart attack and facilitate coronary plaque regression is also stirring up worries about mercury exposure. So I dug up a Heart Scan Blog post from a year ago that discussed this issue and reprint it here.

I often get questions about the mercury content in fish oil. I've even had patients come to the office saying their primary care doctor told them to stop fish oil to avoid mercury poisoning.

Manufacturers of fish oil also make claims that this product or that ("super-concentrated", "pharmaceutical grade", "purified", etc.) is purer or less contaminated than competitors' products. The manufacturers of the "drug" Omacor [now Lovaza], or prescription fish oil, have added to the confusion by suggesting that their product is the most pure of all, since it is the most concentrated of any fish oil preparation (900 mg EPA+DHA per capsule). They claim that "OMACOR is naturally derived through a unique, patented process that creates a highly concentrated, highly purified prescription medicine. By prescribing OMACOR® (omega-3-acid ethyl esters), a prescription omega-3, your doctor is giving you a concentrated and reliable omega-3. Each OMACOR capsule contains 90% omega-3 acids (84% EPA/DHA*). Nonprescription omega-3 dietary supplements typically contain only 13%-63% EPA/DHA."

How much truth is there in these concerns?

Let's go to the data published by the USDA, FDA, and several independent studies. Let's add to that the independent (and therefore presumably unbiased) analyses provided by Consumer Reports and Consumer Labs ( How much mercury has been found in fish oil supplements?


This is different from the mercury content of whole fish that you eat. Predatory fish that are at the top of the food chain and consume other fish and thereby concentrate organic methyl mercury, the toxic form of mercury. Thus, shark, swordfish, and King mackerel are higher in mercury than sardines, herring, and salmon.

The mercury content of fish oil capsules have little to do with the method of processing and much more with the animal source of oil. Fish oil is generally obtained from sardines, salmon, and cod, all low in mercury. Fish oil capsules are not prepared from swordfish or shark.

Thus, concerns about mercury from fish oil--regardless of brand--are generally unfounded, according to the best information we have. Eating whole fish--now that's another story for another time. But you and I can take our fish oil to reduce triglycerides, VLDL, IDL, small LDL, and heart attack risk without worrying about mercury.

I am not advocating ad libitum eating of fish. Sadly, this may be related to excessive accumulation of contaminants. I am suggesting that greater quantities of omega-3 fatty acids from relatively contaminant- and mercury-free fish oil capsules.

More on this in an upcoming webinar on the Track Your Plaque website: Fish Oil and the Track Your Plaque Program - Is More Better?

Comments (9) -

  • Anne

    8/2/2008 2:39:00 PM |

    I take omega-3 fish oil supplements and I eat lots of oily fish, generally around 400g salmon, 200g sardines and 200g trout per week. I'm not worried about the mercury content of the fish I eat, partly because these are fish low in mercury anyway but also because I did a fair bit of research and discovered that a lot of the mercury content of fish and how it affects a person depends on the age of the person and how many years they have been eating fish. I, for example, only started to eat fish a couple of years ago in my early 50s, and by the time any serious level of mercury might have built up in my body I will be an extremely old lady...but I'm not worried.

    I've also read that the mercury in the bodies of children growing up in the Pacific who eat a lot of fish is much higher than the rest of the world but they are not damaged by it, and the beneficial effects of the fish outweigh the effects of the mercury. Here's one comment about that:  'Mercury, fish and you: what to do ?':


  • Jim

    8/2/2008 2:53:00 PM |

    I have been increasing the amount of salmon in my diet, but it is getting harder to find wild salmon in my area (Tulsa, Oklahoma), and when I do find it, it is much higher in price than farmed salmon. So, as a result, I eat a lot of farmed salmon, which probably does not offer much of a health benefit.

  • Jenny

    8/2/2008 2:54:00 PM |

    Are there good quality large scale studies linking the use of fish oil capsules with improved outcomes?

    Studies like the Japanese one you cited are of people eating fish, not taking the oil separately, and it's worth noting that the Japanese who are always cited as the good health example for fish do eat shark and just about anything else that swims.

    It is also a fact that the people I mentioned who needed chelation therapy for proven mercury poisoning were eating mostly salmon and cod.

    I do use fish oil capsules. But so many nutrients have proven ineffective when taken apart from the foods they are embedded in that one has to wonder.

    Vitamins A, C and E supplementation has not tested out but foods high in those nutrients do.

    So that makes me wonder how much of the benefit of eating fish is from the oil and how much from  other factors associated with fish eating. Has the benefit of fish oil eaten without the rest of the fish and not as part of a meal been shown in high quality research not funded by fish oil merchants?

  • Ross

    8/2/2008 7:19:00 PM |

    What you want is molecularly distilled fish oil.  The molecular distillation process reduces the amount of mercury to a level that is not detectable with modern instrumentation.  Since our bodies can tolerate detectable quantities of mercury without harm, using molecularly distilled fish oil is pretty much mercury free.

    So which brands use molecular distillation?  Carlson's, LEF, and pretty much all of the major brands do.  If you're not sure, take a look at the label.  It should be written somewhere on there.

    Any product claiming to have "lower mercury levels" than other quality sources is just blowing smoke.  None of them contain measurable amounts of mercury.

  • Red Sphynx

    8/2/2008 9:29:00 PM |

    Is rancidity a significant problem with capsules?

  • Anne

    8/3/2008 8:37:00 AM |

    The omega-3 fish oil I take is not in capsule form but a liquid - Eskimo-3. It says it has been purified so that mercury and other environmental contaminants are well below current acceptable levels and this has been confirmed by independent studies. It has not been chemically modified. You have to store it in the fridge once opened. They press the oil from sardines caught in deep seas from the Antarctic and south Atlantic.


  • Dr. Brad

    8/3/2008 11:28:00 PM |

    the data on mercury toxicity from fish is very interesting- basically, the toxicologist (in lieu of epidemiologists) defined the 'upper limits'. Toxicologists routinely assume 1/10th the level where problems were identified as their upper limit threshold-- if you look at the original data, however, you'll find that it was based on people who's primary food was pilot whale and another group and in both cases there was at best, minimal cognitive changes noted.  they then took this threhold and lowered the limit by 10 fold--- the result of this national public policy--- 3/4 of all pregnant woman eat insufficient amounts of omega3FAs-- had epidemiologist looked at this issue and been involved in creating the recommended guidelines you would have seen 5-10x higher levels of mercury consumption permitted.  i'll find the original data on this and send it your way abit later.

  • buy jeans

    11/3/2010 2:54:54 PM |

    The mercury content of fish oil capsules have little to do with the method of processing and much more with the animal source of oil. Fish oil is generally obtained from sardines, salmon, and cod, all low in mercury. Fish oil capsules are not prepared from swordfish or shark.

  • moseley2010

    12/6/2010 6:09:56 PM |

    I also get these mercury remarks or concerns every time I encourage friends to start taking fish oil supplements. I always explain that as long as they come from clean waters, like the ones surrounding New Zealand, it's ok. I guess I gave them the wrong explanation. Now I know what to tell them.