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.
EAT YOUR EGGS

In 1929, researchers tested a variety of foods for vitamin D content and found the second most potent source of vitamin D was egg yolk. The book describes studies in which Hess both cured and prevented rickets in rats by giving them egg yolks. He also gave prophylactic treatment to 12 infants to forestall development of rickets in the winter months, which his experience had taught him to expect in the great majority of bottle-fed infants. He gave them one egg yolk added to their regular formula starting in December. None of the 12 developed rickets in March as expected and, unlike prior years, blood phosphates remained stable at summer values.

About this same time, Johns Hopkins University investigators cured seven African-American children of rickets, in most cases severe, by adding one or two eggs daily to their diet of milk and cereal.

Like the vitamin D in cod liver oil, the amount of vitamin D in egg yolks also varies. Researchers in Kansas looked at four groups of hens: one group got sunlight in the yard plus 30 minutes under a quartz mercury vapor lamp producing UV-B light; another got sunlight through glass plus 30 minutes under the lamp; the third group got sunlight alone; and the fourth group got sunlight under glass alone. Eggs from hens under glass produced rickets in rats. Those with considerable UV-B prevented rickets completely and those with less (no lamp) caused the development of slight rickets. Only the sunlight plus lamp completely prevented rickets, showing that the natural UV-B in Kansas did not provide sufficient light for optimal vitamin D. Giving cod liver oil to the chickens had the same effect as exposure to UV-B light. Cod liver oil as two percent of the ration increased levels of vitamin D in the egg yolks fivefold.
The surprising conclusion is that chickens should either be given sunlamp treatment or cod liver oil. Poultrymen and consumers alike need to recognize that the axiom "an egg is an egg" is a mistaken one. Rather, "an inadequate ration may yield impoverished eggs as well as animals." The authors suggest that eggs be graded by vitamin content. What a concept! Too bad no one listened. What would they think of our so-called "organic" eggs from hens raised in barns, never exposed to light and given "all-vegetarian" feed?
MEET MRS. MELLANBY

The most fascinating part of this little book is the chapter describing the experiments done in England by a Mrs. May Mellanby. Her husband, Dr. E. Mellanby, was the author of over 400 studies and the first to control rickets with diet. Cod liver oil had been used for centuries as a remedy but the specific application to rickets was first demonstrated by Dr. Mellanby. (Control of rickets using UV-B light was demonstrated almost simultaneously by investigators at Columbia and Johns Hopkins University in 1921.) In his research into rickets in dogs, he discovered the mineral-blocking effect of phytic acid in grains and legumes. Dr. Mellanby demonstrated that diets containing high levels of cereals, especially oatmeal, and lacking vitamin D, are the most effective producers of rickets. If vitamin D is inadequate there is poor tooth development, but Mrs. Mellanby then went on to prove that no matter how much cereal is fed, if vitamin D is adequate tooth formation is normal. Mrs. Mellanby believed that as cereals increase in the diet, vitamin D must also be increased to offset their anticalcifying effects—think of the implications of this research on today's baby-feeding habits, where infants are given cereals as their first food but denied egg yolks until they are one year old!

Mrs. Mellanby also determined that vitamin D must be present from conception in order for proper tooth formation to occur. If vitamin D is absent during the early gestational period, the enamel cannot form properly, and it cannot be repaired by giving vitamin D later.

In her initial studies Mrs. Mellanby used dogs as the source of data but she later examined more than one thousand "baby" teeth from children. She divided these teeth into four categories—normal, hypoplastic (slightly underdeveloped), moderately underdeveloped and grossly underdeveloped. Only 149, or about 14 percent, of the total 1,036 were sound. About one-quarter were slightly underdeveloped, but nearly two-thirds were moderately or grossly underdeveloped.

It is more difficult to examine teeth in place, but of 266 adult teeth examined by Mrs. Mellanby, not one was sound. The teeth were extracted only for purposes of straightening the teeth, which means that they were erupting in a jaw that was underdeveloped. Thus, children with narrow faces most likely have underdeveloped teeth. Tooth structure and later decay are directly related. Prevention of cavities must start in the womb.
CURING CAVITIES

A final plum from this most fruitful book regards secondary dentine. Secondary dentine, a less well-organized form of tubular dentine, is produced throughout life as a patching material where cavities have begun, where the overlying enamel has been worn away, and within the pulp chamber as part of the aging process. Sometimes when cavities occur, production of secondary dentine can "heal" the decayed spot or rebuild portions of the tooth that have worn away. If vitamin D is adequate, secondary dentine will be well calcified. If vitamin D is lacking, dentine will be of poor quality or not present at all.

There is some evidence that the mineralization of dentine may depend on calcium derived from saliva rather than blood; in other words, it is deposited from the exterior rather than the interior of the tooth. The book describes studies by Dr. C. L. Pattison who, working with Mrs. Mellanby, determined that the calcium content of saliva doubled or even tripled when the diet contained adequate vitamin D from cod liver oil.
DOWNSIDE

Now that I have told you all this good news about cod liver oil, I need to comment on the research surrounding its possible toxicity. Over-elevated serum levels of vitamin D are a possibility if you combine summer or southern sun and cod liver oil. So if you are spending a lot of time out in the sun during the summer months, it's probably best to cut back on the dose. If you are unsure, you should test your blood levels of vitamin D.

Cod liver oil is no longer recommended in Great Britain and in the US pregnant women are advised to avoid most vitamin A and vitamin A-containing foods, including cod liver oil. Both countries have adopted this policy because of the recognized teratogenicity (may cause birth defects) of retinoic acid, a synthetic form of vitamin A. But low vitamin A also causes birth defects. In the developing countries, such as Brazil, Pakistan and India, vitamin A deficiency is widespread, afflicting millions. A 1992 survey of the US population determined that 50 percent of Americans consume 19 percent or less of the Recommended Daily Allowance (RDA) or 400 IU.

The original study showing birth defects associated with intake of mostly synthetic vitamin A exceeding 5,000 IU daily was published November 23, 1995 in the New England Journal of Medicine.46 Other studies showing an association of birth defects with vitamin A concerned topical creams containing vitamin A derivatives such as Accutane, or extremely high doses of A used in animal studies.47-52

A later study, less well publicized, from the National Institute of Child Health and Human Development (NICHD), found no association with birth defects in women who took up to 10,000 IU of vitamin A during pregnancy. Because few women took more than 10,000 IU, researchers could not determine whether higher doses were a problem. Later Mills and others continued their research and determined that after serum testing and determining safe serum levels, women taking 30,000 IU of preformed vitamin A from animal foods (not beta-carotene) daily had the same blood levels of A as healthy pregnant women in the first trimester who had healthy babies. The conclusion is that a dosage over 30,000 IU vitamin A daily may be teratogenic for a certain few, but anything up to that amount is safe.53-54

Thus if you are or may become pregnant, limit cod liver oil intake to not more than a total vitamin A value of 30,000 IU. If using my favorite brand, Carlson Labs cod liver oil, that would equal the amount of vitamin A found in 12 teaspoons or 4 tablespoons, more than anyone would ever take. If using high-vitamin cod liver oil, the limit would be 2 tablespoons. Two tablespoons of regular cod liver oil provide 15,000 IU vitamin A, 2600 IU vitamin D and 6 grams of mixed omega-3 fatty acids, safe for pregnancy and good for mom and baby.

There is one situation in which high levels of vitamin A are not recommended and that is the condition of certain types of liver disease in which there is altered vitamin A metabolism. This is frequently the case with alcoholism. Alcoholics should not take high doses (not more than 1-1.5 tablespoons of regular cod liver oil) and what they do take should be accompanied by zinc supplements. The enzymes needed for vitamin A metabolism in the liver are zinc dependent.

The most likely culprits for production of birth defects in humans are topical and oral vitamin A analogs, not cod liver oil. Researchers have criticized the original 1995 study, from which governmental policy has been derived, for overstating the negative effect. Only 1.4 percent took supplements exceeding 10,000 IU a day, not a large enough sample from which to draw conclusions. However, it is important to never combine cod liver oil or vitamin A from supplements with oral or topical medications for acne or other skin disorders treated with retinoic acid derivatives.

If you sunbathe regularly and have found that your vitamin D levels are within the normal range, do not use cod liver oil unless you are willing to test and retest to determine that your blood levels of vitamin D have not gone too high. We do not know enough to say whether or not sunbathing and cod liver oil work synergistically or antagonistically. If you decide to get lots of sun and also use cod liver oil, please send me your vitamin D tests for my continued research. Cod liver oil use is safe in most of the US and all of Canada in winter but it should not be combined with other sources of vitamin D without careful testing and monitoring.