I've recently posted this over in the supplements area.
I would like to caution those choosing cod liver oil.
Cod liver oil is slightly less rich in EPA than is fish oil, although it is much cheaper. About 9 percent of the fatty acids in cod liver oil are EPA, whereas about 18 percent of the fatty acids in fish oil are EPA. Therefore on a gram-for-gram basis, fish oil will give you about twice the amount of EPA as cod liver oil. Any oil, and especially fish oils, should be stored away from light to prevent oxidation of the polyunsaturated fatty acids. If the oils are in soft gelatin capsules, then this acts as another barrier to oxidation of the oils.
However, both cod liver oil and fish oil CAN be contaminated with PCB's. This is why they should be purified by molecular distillation which removes PCB's. These molecular distilled brands are slightly more expensive, but their health benefits are dramatically better.
I've been doing a lot of research on fish oil. I'm trying to figure out why the prices are so all over the board ~ anywhere from $10/mo to $80/mo. One would think quality has a lot to do with it. Not necessarily! Here's what I have learned so far.
There are three grades of fish oil. The first is cod liver oil. The second is health-food grade fish oil. And finally there is pharmaceutical-grade fish oil. What distinguishes one from another is the purity and concentration of the long-chain omega-3 fatty acids Each step in the refining process adds additional cost to the final product.
The term ‘pharmaceutical-grade’ seems to be only used by Dr. Sears (Zone), however, there is really no standard definition for it. I’ve been able to find products which meet his criteria, but don’t necessarily use that term.
Total long-chain omega-3 fatty acids should be more than 60% of the total fatty acids and PCBs/gram oil should be less than 10 ppb (parts per billion). Molecular distillation ensures the contaminants have been removed.
Vitamin E is often included in fish oils as a preservative. At low levels, approximately 5 I.U./gram of fish oil, it is protective. At higher levels, such as 20 I.U./gram of fish oil, it can actually speed up the oxidative process.
Since the NOW brand (Omega-3 1000mg-Cholesterol Free) is the least expensive (about $9.00) and the most easily obtained (for me), I focused my attention on that brand. Seems it fits. It’s actually manufactured in Canada by a company that private labels for many companies world wide. I’m going to stick with this product unless I find compelling evidence to not to. (
http://www.nowfoods.com/?action=itemdetail&item_id=3374)
For those who might be interested, Dr. Barry Sears came out with a book called The Omega Rx Zone. Regardless of the Zone diet, there is great information regarding the use of fish oil. You'll note from above, I am not advocating his product. I believe there are other, more cost effective, high quality products available.