More from last year’s Skeptics conference.
A Relatively recent development in Western society has been the increased popularity of health foods and dietary supplements. While initially these health foods could only be purchased through a sparse number of “alternative retail outlets” manned by the converted, as sales have grown and the realisation of the potential profit has become obvious to more people, availability has become easier. There has been a mushrooming of “Health Food Shops”, an increasing number of supermarkets have established “Health Food Bars” and many conventional pharmacies have made the sale of these products a feature of their business.
Claims for beneficial effects of these products have also increased. There are those that provide increased energy or are especially suitable for better skin tone, others boost the immune system. Some offer unique benefits to female reproductive function.
In most instances, when an attempt is made to evaluate them using the information supplied by the manufacturer or marketer, the customer is grossly disappointed. Usually the compositional analysis is provided, but there is no information about the bioactivity or the reason why it is believed to be beneficial for certain conditions.
Knowing that there is a certain level of sodium or that there is 25% protein in an item does not say anything about whether it will be effective for treating piles! It is not too difficult to find two quite different products with similar compositional properties which are claimed to have very different effects.
Additionally it is not unknown for marketers to mix their natural product with fillers. These compounds add bulk to the sample, and are generally innocuous but ineffective. The consequence is that the product the customer purchases from the retailer is really of somewhat unknown composition. As this is seldom mentioned in the labelling, one doesn’t know what percentage of the product is actually active material.
In view of the expansion of interest in these health products, one may ask about the level of evidence supporting the claims made for them. Have sound scientific experiments been performed which justify some of the claims? Have these results been subjected to peer review and critical assessment?
In general, it has to be said that there is very little convincing data that substantiates many of the contentions. In most instances this is probably because very little good experimental work has been undertaken. After all, if one can make money by promoting something with claims that do not breach any therapeutic drug and legal requirements, then there is little incentive to invest money to determine what the properties are. There is the risk that one might not get the answer that is sought and as a result the hen that is laying the golden egg is lost.
There are exceptions to this. Ones that readily come to mind are taxol, which is obtained from the Pacific yew tree and is used as a treatment of cancer, the green-lipped mussel extract which can be shown to have efficacy in treating arthritis and, recently, the use of St John’s wort for the relief of depression.
Cartilage is widely available through health food outlets usually as 400mg or 500mg capsules. The two most common sources are cattle and shark. A number of claims have been made about its benefits, the most frequent being anti-cancer activity.
The price range of these capsules is wide, ranging from the equivalent of $450 per kilogram to over $3,300 per kilogram. Does one know whether the more expensive ones are more beneficial? A recent survey showed only one of nine different forms of the shark cartilage capsules stated the percentage of cartilage in each capsule.
Are the others pure cartilage or do they contain bulking constituents? These are serious considerations when it was reported that shark cartilage sales in the US in 1995 exceeded $US30 million and the growth rate was exponential.
What do we know about shark cartilage? Many of the brands state the composition. The levels of protein, chondroitin sulphate, calcium, etc are itemised on the labels, but that is not particularly helpful in evaluating what effect the product may have on tumours. There is no indication as to which of the components are likely to be beneficial. None of the labels of the products retailing in New Zealand describe any proven biological effect.
This is disconcerting in view of the widespread promotion of shark cartilage as being beneficial for the prevention of tumour growth and spread. There is substantial evidence, both in the US and in other countries, that an increasing number of cancer patients are using “alternative remedies”. When the evidence supporting the claims of efficacy is minimal, the logic of such approaches is questionable.
The promoters of cartilage purport that it is an anti-angiogenic material, ie, it prevents the growth of new blood vessels. New vessels are required for tumours to continue to grow and for them to “take” at secondary sites. Thus, the inhibition of new vessel production will have an anti-cancer effect. Cartilage is suggested as being especially advantageous because it is virtually free of blood vessels and so possibly contains compounds that inhibit their growth. Sharks are suggested as a superior source because of their very low incidence of cancers. This idea has been widely promoted through several popular books by Dr William Lane1,2.
But to emphasise the statements above about beneficial claims being unsubstantiated claims, a survey of promotional material for shark cartilage has revealed at least 22 human conditions which are claimed by various entrepreneurs to be ameliorated by it (Table 1).
Conditions Amenable to Shark Cartilage Therapy
This number of diverse benefits from the one product may lead a sceptic to think that in due course, and with a few more benefits, it may become a universal panacea and thereby save the human race!
The potential purchaser is also left with the dilemma of whether shark or bovine cartilage is likely to be more useful. There have been claims and counter-claims about the relative merits of each source, but these are largely propounded by promoters who obviously have vested interests to protect. There is no published evidence comparing their relative merits.
Another difficulty in interpreting the limited data on the biological effects of consuming shark cartilage is that the few experiments reported in the refereed literature have been in vitro studies. As most people are taking it as a food additive, it is quite possible that an active anti-angiogenic principle demonstrated in one of these assays is destroyed by the digestive system, eliminating any biological effect. This is particularly relevant if the active ingredient is a protein.
In order to address some of these questions, we devised an experimental model where shark cartilage was fed as a dietary supplement to rats and its effect on the growth of new blood vessels was evaluated. Shark cartilage was included in the powdered diet, while control animals received an unsupplemented diet. The outcome was that growth of the new vessels was retarded by up to 50% at the optimal dose (Table 2). This effect was dependent on the dose given up to a maximum of about 6g per kilogram of food, above which there was no added benefit (Figure 1). This has been shown to be reproducible and has been published in the peer-reviewed literature3.
|Days after Induction||Normal Diet (%)||Shark Cartilage Supplemented Diet (%)||Statistical Significance|
|16||50.2 ± 2.6
|23.4 ± 2.6 (n=42)||p<0.0001|
|25||37.2 ± 2.2
|17.5 ± 1.9
|TABLE 2: Percentage of mesenteric window area occupied by blood vessels 16 and 25 days after stimulation with Compound 48/80. (Mean ± SEM)|
This experiment indicates that there is an anti-angiogenic constituent in shark cartilage which survives the degradation processes characteristic of the mammalian digestive system. Thus, in rats at least, shark cartilage can inhibit blood vessel growth. This does not prove that such a mechanism also operates in humans. Nor does it show that it has any benefit for the retardation of the tumour progression, despite one manufacturer claiming that our published paper shows that.
The controlled experiments that we reported showed that there is potential for shark cartilage to have an anti-cancer effect, but that will require further research. Finding investors for such an investigation is the greatest hindrance to rapid progress in this determination. These problems are characteristic of much of the health food industry. However, the overcoming of the myths and claims surrounding many of these products will only be achieved by rigorous scientifically sound investigations.
3)Davis, P.F., He, Y., Furneaux, R.H., Johnston, P.S., Ruger, B.M., Slim, G.C. Inhibition of Angiogenesis by Oral Ingestion of Powdered Shark Cartilage in a Rat Model. Microvasc. Res. 54: 178-182 (1997).
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