Do Fish-Oil Capsules Have Mercury in Them?

Q: I want to get the omega fatty acids from fish but avoid the mercury, so I've started taking fish-oil capsules. But now I've heard that those have mercury in them, too. Do they?

— Wary in Washington

A: Your concerns about mercury in fish oil are widely shared.

You'll find that mercury is just one of the major contaminants regularly found in seafood; exposure to polychlorinated biphenyls (PCBs), dioxin, DDT and other organochlorine pesticides are just as alarming.

Do these toxins find their way into fish-oil supplements? If they're in the source, they can be in the supplement. But supplements can be "cleaned," and properly purified supplements have lower levels of mercury and PCBs. Purification of fish oils by molecular distillation—a process that spins the oils around rapidly to separate the toxic metals from the fish—seems to be the method of choice. Also look for the oil's source: If it comes from a species known to be low in contaminants (e.g., sardines, anchovies, tilapia) that was fished sustainably from oceans known to be relatively clean, then you're probably safe.

How to Find Safe Supplements

The FDA says omega-3 supplements are "generally regarded as safe," but supplements aren't subject to review and approval requirements like prescription medicines are. Some fish-oil manufacturers are "USP-verified," which indicates compliance with standards set by the US Pharmacopeia — a seal of approval that's widely recognized. Many manufacturers also seek IFOS (International Fish Oil Standards) certification, but there are some claims that IFOS is a marketing tool for manufacturers, and that its standards are too low. Note that while some companies make the claim, there is no "pharmaceutical grade" standard in the United States for fish-oil supplements.

The Environmental Defense Fund surveyed 75 supplement companies to determine whether they purified their fish oil, what methods they use if so, and what standards they comply with. I'd start there.

Some other things to look for:

  • Fish oils are highly sensitive, and can go rancid quickly. Yuck. A supplement manufactured near where the oil is harvested has a better chance of being fresh.
  • The omega-3s found in plant foods like flaxseed are in the form of ALA (alpha-linolenic acid) and must be converted into EPA and DHA (the beneficial omega-3s). The conversion process is a complicated one, and only a small percentage of ALA will end up as EPA and DHA.
  • Many people use omega-3s to combat macular degeneration and prostate cancer, but the University of Maryland Medical Center cites studies that suggest omega-3s in the form of ALA may actually increase the risk of developing these two conditions. Far from conclusive, but something to keep in mind.
  • Make sure you're actually getting omega-3 fatty acids — not just "fish oil." The label should list the total amount of EPA and DHA and they should add up to the total amount of oils in the product. If they don't, you're being sold a bunch of fillers. Also, DHA is considered the most beneficial of the omega-3s, so you may want a higher percentage of DHA.
  • Although I've read some claims that molecular distillation ruins the oil by oxidizing it, I haven't seen any definitive evidence of that, and since molecularly distilled fish oils have lower levels of toxins, I consider them the safest kind.
  • You may run across oils in either ester or triglyceride form. The difference is in their "bioavailability," meaning how readily available the oils are for your body to absorb. Fish oils in triglyceride form have to convert to esters before your body can use them, so esters are considered superior but tend to be more expensive.

Getting Your Nutrients From Food

Looks like you've got some good options for safe supplements. But I just can't help myself ... We get into trouble when we start to think supplements can replace real or whole foods. We have come to think too often of food as a store of various independent benefits and dangers — fats, vitamins, fiber, carbohydrates — from which we should pick and choose. But there is a complexity to whole foods, a synergy between elements, that cannot be mimicked by the elements alone: Nutrients function differently as part of a whole than in isolated form. That's not to say supplements can't be beneficial. They certainly can — perhaps especially fish oils. Whether in the form of vitamin tablets or fortified drinks and snacks, however, supplements are expensive. It's a lot of money for something that may not be doing you much good.

Well, that's my daily homily out of the way. Once again, what started as a simple question ...

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