162 Sharks: The Animal Answer Guide
in treating lung and ovarian cancers. Recent tests indicate squalamine may
also be effective against various virus-caused diseases; if this turns out to be
true, that would be a huge breakthrough in medicine because viral diseases
are notoriously difficult to treat. Squalamine is patented and produced by
reputable drug manufacturers. Most importantly, squalamine can be pro-
duced synthetically, so there’s no longer a need to kill sharks to obtain it
(see “Do sharks have diseases and are they contagious?” in chapter 9).
Before the 1950s, when it became possible to synthesize vitamin A,
shark liver oil was a major source of vitamin A as a dietary supplement.
“Shark liver oil is known to help strengthen and regenerate the immune
system while benefiting many other functions and organs of the body,” or
so read the claims of companies that sold the product. Although shark liver
oil has been used medicinally for centuries for ailments as diverse as wound
healing, respiratory and digestive tract irritation, and lymph node swelling,
none of these uses have been tested and proven medically, nor is shark liver
oil prescribed or used by American medical doctors.
Some over-the-counter (nonprescription) medications contain shark
liver oil. The most widely used of these is Preparation H for hemorrhoids.
(Wikipedia has a graphically illustrated explanation of hemorrhoids—or
ask any adult if you want the PG-13 version.) Shark liver oil is known to
shrink blood vessels by restricting blood flow. Hemorrhoids result from
inflamed blood vessels in the rectal region, so restricting blood flow to the
area reduces the swelling and itching. Because of its effect on blood vessels,
shark liver oil is also used in facial creams that target wrinkles.
Shark parts have proven useful in other medical procedures. One sur-
prising application is using shark corneas in human corneal transplants.
The cornea is the clear outer part of the eye in all vertebrates that light
must pass through first before focused by the lens on the retina. Corneal
disease causes the cornea to become cloudy, eventually blinding the victim.
Shark corneas have a number of unique properties. Most importantly, be-
cause the collagen layers making up a shark’s cornea are very dense, they
don’t swell in distilled water and remain transparent under a variety of sur-
gical conditions. These traits have been known since the late 1800s, based
on studies of the lowly Spiny Dogfish. Because shark corneas don’t swell
and human eyes don’t reject shark corneal tissue, shark corneas are a supe-
rior tissue for transplanting into diseased human corneas. As a result, shark
corneas have been used in corneal transplants for decades.
The usefulness of shark chondroitin sulfate for eye surgery and skin
grafts, squalamine for cancer treatment, shark liver oil for treating vari-
ous ailments, and shark corneas for transplants underscores another reason
we should do everything possible to protect sharks. Sharks are a potential
source of valuable products to cure human disease, including cures we have
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