Do sharks really not get cancer, and if not why?
haifisch at cats.ucsc.edu
Thu Feb 20 19:23:28 EST 1997
In article <Pine.SOL.3.91.970218102047.9795C-100000 at general3.asu.edu>,
natural at imap1.asu.edu wrote:
> There is book entitled 'Sharks don't get cancer." Its not too bad, but
> actually, it is due to several factors, one being they do not have
> calcium, only cartilage. Second, they produce a compound called squalamine.
This book is a hype-piece written buy a guy who sells shark cartilage products.
I guess the market fell out of snake oil.
Sharks DO get cancer - though at a low frequency of occurance. Most
cold-blooded animals have lower cancer rates than do warm-blooded mammals
like us. (The warming system of lamnoid sharks is not the same as
warm-blooded.) Of course sharks do not indulge in the social carcinogens
that humans do either.
This mythos arose when it was found that cartilage secretes a trace
substance which inhibits the formation of blood vessels (anti-angiogenesis
factor). Since tumors often stimulate blood vessel development to supply
their increased growth rates, it is hoped that this factor may be used to
treat (not prevent) cancer by restricting the blood flow to the tumor.
The factor is found in all vertebate cartilage - there is nothing special
about the cartilage from sharks, but since their (almost) entire skeleton
is cartilagenous, they provided an easy source for testing the factor.
The effect is very localized - consuming cartilage orally accomplishes
nothing but the encouragement of shark slaughtering. Eat the gristle off
your chicken bones if you must.
Squalamine is a high quality lubricant extracted from shark liver, but has
no special health promotion. The idea that shark liver extracts are
medicinal lingers from World War II when the war closed down the North
Atlantic cod fishery. Shark liver oil was sold as a replacement for cod
liver oil for a source of dietary vitamin A. Other sources of vitamin A
are readily available. Several shark populations impacted by the fishery
of the 1940's have yet to recover.
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