PRACTICAL ASPECTS

Eating fish will not provide the levels of nutrients that are found in cod liver oil. Even in heavy fish-eating populations, the addition of cod liver oil improves health.^42-43 And taking fish oils is not the same as taking cod liver liver oil. One tablespoon of regular cod liver oil and one-half tablespoon of high-vitamin cod liver oil provide the amount of elongated omega-3 fatty acids found in twelve 1,000 mg fish oil capsules.

As for vitamin D, body oils of fish can be good sources as long as you are willing to eat a lot of them. One-half pound of fatty herring or sardines gives a dose of vitamin D equal to that of about one tablespoon of cod liver oil. But salmon oil has one-fifth the potency of cod liver oil.

One concern about taking cod liver oil is the presence of contaminants--heavy metals (such as mercury, cadmium and lead), PCBs and so forth. Fortunately, consumers need not worry when it comes to cod liver oil. All cod liver oils in the US must be tested according to protocols of the Association of Analytical Communities (AOAC) and approved free of detectable levels of 32 contaminants before they can be imported into this country. Furthermore, mercury is water soluble. It may be present in the flesh of fish, but it is not present in the oil.

Another concern is rancidity. Cod liver oil can become rancid if improperly handled. In a 1988 study, peroxide values (indicating rancidity) ranged from a low of 2 to a high of 44.7.⁴⁴ Nevertheless, properly handled cod liver oil is relatively stable. It contains 21 percent saturated fatty acids and 57 percent monounsaturated fatty acids, which provide stability. The fishy smell of cod liver oil is due to the presence of small amounts of fish protein and is not a sign of rancidity. To ensure that your cod liver oil is fresh, avoid buying the large economy size or the end-of-season sale item. Buy cod liver oil in small dark bottles and keep them in a cool dark place. Cod liver oil need not be refrigerated after opening if it is used up quickly--within two months.

Virtually all cod liver oil imported into the US comes from Norway, and while all of it is safe, there are different grades, depending on vitamin levels. The lighter oil from the "top of the barrel" has a lower molecular weight, goes rancid more quickly and has lower levels of vitamins, while the heavier oil, which sinks, is richer in vitamins. The heavier oil is what Dr. Price referred to as high-vitamin cod liver oil. It contains double the amounts of vitamin A and D as regular cod liver oil. Virtually all cod liver oil imported into the US is the lighter, "top of the barrel" variety. The Norwegians keep the best for themselves!
Whenever taking cod liver oil, remember the findings of Dr. Price. He noted that he did not get good results from cod liver oil unless he gave it concurrently with high-vitamin butter. Just why this is so is a matter of speculation, but we do know that the very unsaturated fatty acids found in cod liver oil cannot be effectively assimilated and stored in the tissues without the presence of adequate saturated fatty acids, the kind that would be provided by butter. This means that even regular butter would help support cod liver oil therapy; but Price found that the combination of cod liver oil with high-vitamin butter, from cows eating rapidly growing green grass, was nothing short of miraculous, reversing tooth decay and bringing patients back from the brink of death.

I do not find it hard to take Carlson's cod liver oil on a spoon, but for many, the big challenge is how to get this oily substance down. One technique is to add cod liver oil to a small amount of water or fresh juice, stir and then quickly send it down the hatch. If you can't bring yourself to take cod liver oil on a spoon or in water, then use the capsules. For babies and small children, use an eye dropper.

OLD RESEARCH BROUGHT TO LIGHT

In researching this article, I had the great fortune to stumble upon a book published in the 1930s--it is truly exciting to come upon material found and lost and found again. Ultraviolet Light and Vitamin D in Nutrition, by Katharine Blunt and Ruth Cowan, published by the University of Chicago, contains fascinating material, including a chapter on the research of Mrs. May Mellanby published in 1918 in The Lancet II, page 767.

The book describes the work of scientists E. M. Honeywell, A. F. Hess and C. E. Bills (after which the Bills's Scale for determining antirachitic value for vitamin D is named) who studied all aspects of fish oil potency, production and seasonal distribution. Early in their research they discovered that oil extracted from cod when the fish were fat in the summer contained much lower amounts of vitamin D. Summer oil scored 100 on the Bills scale but winter oil scored above 1,000 and some oils scored 20,000. Their conclusion: "For a fish of a given size, antirachitic potency varies inversely with the amount of fat or oil in the liver." In other words, the less oil in the fish, the more concentrated it was.

In one fascinating study, they found that fish kept in darkened aquariums and fed on trimmed raw veal muscle had the same amount of vitamin D as free-swimming fish exposed to sunlight. So how the fish obtain vitamin D remains a mystery. Perhaps they are able to extract it from microscopic plankton and algae.
It is important to note that the amount of vitamin A in cod liver oil does not have any consistent relation with the amount of vitamin D. In numerous samples, oils rich in vitamin A were poor in vitamin D, and oils rich in vitamin D were poor in vitamin A.
According to the book, in 1922 the US imported about 1.8 million gallons of cod oil and cod liver oil. By 1927 this amount grew to almost 5 million gallons based on data from the Bureau of Foreign and Domestic Commerce of the United States Department of Commerce. Cod oil is rancid oil used in the tanning industry, not for human consumption. The figures don't distinguish the difference, but most of the increase was in the edible cod liver oil due to research showing its benefit in preventing rickets. According to the Commerce Yearbook of 1928, "Medicinal oil production has increased greatly, and the advance in its price has lessened the supply of common cod oil for tanning."

In 2000, America imported only about one tenth that amount (less than half a million gallons), indicating a huge decline in use.

In 1930, when the book was compiled, the technology was just being developed to determine vitamin D potency. The accepted value as of August 31, 1929 was " one rat unit of vitamin D," defined as "that amount of vitamin D which, when uniformly distributed into the standard vitamin D deficient diet-ration, will produce a narrow and continuous line of calcium deposits on the metaphyses of the distal end of the radii and ulnae of standard rachitic rats." "Potent cod liver oil" is defined as that containing one of these rat units per 0.75 mg. The International Units started out as rat units!

Testing of 18 oils in use at that time showed great variations in potency. Luckily today we have methods of standardization and much better methods of transportation and storage to improve the amount of vitamin D and freshness of our cod liver oil.