Do sharks really not get cancer, and if not why?

Jim Barron jdbarron at cphl.mindspring.com
Sat Feb 22 10:57:04 EST 1997


Bruce Heyer wrote:
> 
> 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.


I have read that there is an oil in shark liver that acts to chelate
mercury.  Would this be Squalamine?   Since sharks are so high on the
marine food chain and mercury is known to be  a problem in things like
tuna, etc. presumeably they must have SOME method for dealing with it.

jdbarron at cphl.mindspring.com





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