People afflicted with chronic, painful and/or terminal diseases are understandably eager to take all possible steps to alleviate their symptoms, cure their conditions or prevent recurrences. This anxiety makes them susceptible to the lure of so-called "alternative" or unconventional therapies that may not be effective or safe. One item in the health-food industry's array of unproved cancer/AIDS/arthritis remedies is shark cartilage.
Shark cartilage was first introduced to the public in the 1992 publication Sharks Don't Get Cancer, by I. William Lane and Linda Comac. The story received wide media coverage, especially after a shark cartilage report was featured on 60 Minutes in 1993. And the public has gotten the message: They're taking the pills and getting the treatments that Lane and other shark cartilage proponents suggest in the hope that this "natural" substance will help or protect them.
In spite of the claims made by Lane and Comac, the most avid proponents of shark cartilage, there is still no sound scientific support for the efficacy of this substance when used as they recommend. There are sound scientific data suggesting that some cartilage-derived compound(s) could be useful in treating at least some types of cancer, however. On the basis of these data, shark cartilage proponents have spun a pseudoscientific web of evidence to support their claims and sell their products. In this article we will separate scientific fact from fantasy and will show how the shark cartilage camp has gone beyond the limits of rationality.
Since the early 1970s, some researchers have focused their efforts to combat cancer on interfering with a process known as angiogenesis the formation of new blood vessels. Angiogenesis is necessary for tumor growth and spread; interfering with the process aims to slow or halt the growth of malignant tumors.
The cells in a tumor, like normal cells, must receive nutrients and oxygen from the blood in order to survive and grow. Cancer cells depend initially on the network of blood vessels supplying the surrounding normal cells. After a malignant tumor reaches a certain size, however, its blood supply must increase. If new blood vessels don't form, the tumor cannot grow and the cancer will be less likely to spread.
While malignant tumors have been found in most parts of the body, they are not equally distributed among different types of tissues and organs. It has been observed that cartilage the pliable substance found on the surfaces of joints, at the ends of ribs, in the ears and in the nose is much less likely to be invaded by cancer cells than are many other tissues. Cartilage itself has no blood vessels nutrients, oxygen and waste products simply diffuse through the cartilage.
These observations inspired researchers to investigate whether cartilage contains some inhibitory substance that prevents the invasion by or growth of cancerous cells. Early investigations, utilizing cartilage from calves, established that there was, indeed, an inhibitor made partly of protein that prevented the invasion of cartilage by cancer cells.
There was a problem, however. Obtaining large quantities of calf cartilage was difficult because calves, like all mammals, don't have much cartilage. As a mammal develops before birth, its skeleton is initially made of cartilage, not bone. Late in prenatal life, calcium, phosphorus and other minerals are incorporated into the skeletal cartilage; and specialized cells called osteoblasts replace the cartilage with bone. This replacement process is mostly complete by birth, and only relatively small amounts of cartilage remain in the body.
In contrast, in Chondrichthyes, the class of fish to which sharks belong, the skeleton never completely calcifies. It remains predominantly cartilaginous throughout the animal's life. Because of this developmental difference between mammals and sharks, and because sharks can grow to be much larger than calves, sharks provide much more cartilage per animal. This, rather than any magical properties of sharks, per se, is why researchers first started to use shark cartilage in their experiments.
In experiments performed on rabbits, mice or chick embryos, investigators found that shark cartilage also contained an angiogenesis inhibitor. The inhibitor was either placed close to an implanted tumor or infused into the animal's bloodstream, and the growth (or lack thereof) of blood vessels was measured. Although this inhibitor was not exactly the same as the one found in calf cartilage, it seemed more effective at inhibiting blood vessel growth.
It's important to emphasize that none of the animals in the experiments actually ate the cartilage. In spite of this fact, Lane and others claim that feeding shark cartilage to humans is an effective treatment. This is doubtful, primarily because of the chemical nature i.e., the protein content of the cartilage-derived inhibitor.
Proteins are not absorbed from the intestines as whole molecules. Proteins are usually large molecules, and they may contain thousands of amino acids, the building blocks that make up all proteins. When a protein is eaten, stomach acid starts to break it apart. This disassembly continues in the small intestine, where digestive enzymes work on the ingested proteins until they are broken down into much smaller pieces. These pieces, usually consisting of only one or two amino acids, are then absorbed from the small intestine into the bloodstream.
This absorption process has been known and understood for many years. To suggest that a protein can be absorbed and still function as an entire unit after being broken down by the digestive process is disingenuous. The fact that a protein has been "pulverized" and suspended in a solution (as Lane claims to have done for shark cartilage) does not mean that that protein will be protected from digestion if it is eaten.
If this sort of "protection" were possible, millions of diabetics would not have to inject the protein hormone insulin they could simply take it in a pill. But insulin, like any other protein, is broken down during digestion and is thus rendered inactive by the time its constituent amino acids are absorbed into the bloodstream. It is more than likely that the same digestive processes that inactivate insulin would also inactivate any anticancer activity of shark cartilage.
Lane also suggests in his book that the shark cartilage can be administered by enema into the lower gastrointestinal tract. But the same absorption problem remains. In normal digestion, this area of the intestine absorbs water and some minerals, but not whole proteins. The probability that an effective amount of inhibitor could be absorbed by this route is virtually nil. And since Lane himself, on page 57 of his book, states that "The potency of shark cartilage as an angiogenesis inhibitor increases with its increasing protein content," the inability of protein to be absorbed whole presents an insurmountable barrier to oral or rectal administration.
Perhaps the weakest link in Lane's chain of evidence about shark cartilage is the lack of substantiated clinical data to support that this is indeed a safe and efficacious treatment. While Lane does cite a small study in Cuba (also described in the 60 Minutes presentation) that he says "proves" his points about shark cartilage, researchers have stated that the results of this study were dubious at best. X-ray films purporting to show tumor shrinkage were described by one authority as unclear and hard to interpret.
Scientists at the National Cancer Institute (NCI), after reviewing data that Lane presented to them, did not think his results were of sufficient caliber to support further investigation. Lane accuses the NCI scientists of being "anti-alternatives"; but if that were truly the case, they could simply have refused to look at his data at all.
Dr. Mary McCabe of the Cancer Therapy Evaluation Program at the NCI pointed out that she and colleagues had attended informal presentations of clinical data by Lane and a Cuban physician well after Lane's book was published. McCabe stated that none of the data presented warranted the NCI's funding clinical trials of shark cartilage at the present time. Dr. McCabe was quick to point out, however, that the NCI is supporting research into the possible use of other, more promising, anti-angiogenesis factors; this is not a research area that is being neglected.
In his book, Lane also emphasizes that shark cartilage is a naturally occurring product, as though this fact alone increases its effectiveness. It is true that many of our most effective and widely used pharmaceuticals were originally derived from "natural" products. For example, vincristine and vinblastine are anticancer agents found in the periwinkle, a species of myrtle, and the recently discovered taxol, effective against ovarian cancer, is derived from the bark of the Pacific yew tree. But when oncologists use these compounds to fight cancer, they don't feed their patients myrtle or yew-bark tea or powder they use the purified or synthesized active compounds and inject them.
Similarly, if the anti-angiogenesis factor from shark cartilage is to be truly useful, it will likely have to be administered in a highly purified form that has been carefully tested. We need to know which types of cancer it is effective against as well as what, if any, side effects it has. It is fine to speculate (as Lane and Comac do) that shark cartilage would only work against highly vascularized tumors, such as those found in breast, cervical, prostate and pancreatic cancers, but not against leukemia. But wouldn't it be better to know if this is true?
Lane states that the angiogenesis inhibitor from shark cartilage is probably most useful as a preventive measure or against tumors in the early stages of development, when blood vessels are forming. This is because once a tumor is well established, it already has a network of existing blood vessels. But Lane also repeatedly cites "evidence" that shark cartilage is effective in patients who are terminally ill with various types of cancer. Presumably, their tumors are well established, so how could their purported cures possibly result from the shark cartilage angiogenesis inhibitor? Lane never really explains.
Like many other remedies touted as "natural," "used for generations," "nontoxic" or "organic," shark cartilage has not been examined sufficiently to allow us to say that this is a useful compound or even to say what the most useful dosage would be. As shown in the sidebar, anywhere from 2.25 to 4.44 grams per day are recommended, depending on which manufacturer's product and directions one chooses to follow. Similarly, cost varies from $26 to $79 per month depending on the product and dosage schedule. If the substance had really been properly tested, it would now be clear how much is needed to do the job.
Lane does make a point in his book that a substance that limits angiogenesis should not be taken by pregnant women, since the growing infant needs to make new blood vessels, or by patients recovering from surgery or with healing wounds that require formation of new blood vessels. But these caveats are not on the labels of all shark cartilage preparations. How is the consumer supposed to know about them?
Whether taken as pill or powder, orally or rectally, shark cartilage may not hurt you, since it won't be absorbed but it won't help you, either. The most effective thing about shark cartilage seems to be its marketing.
Ruth Kava, Ph.D., is Director of Nutrition at the American Council on Science and Health.
| Cost of Three Shark Cartilage Preparations in New York City, January 1995
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(From Priorities Vol. 7, No. 2, 1995)
