Sharks have been swimming in the Earth's oceans for about 400 million years. They predate humans, dinosaurs and just about anything that walks, crawls or swims. The average shark lives to be about 25, and it's believed that some sharks can live up to 100 years or more. This places them next to the whale as one of the longest-living sea creatures. The fact that they have such a long lifespan has prompted a great deal of research into the secret to their longevity.
Sharks have been studied closely for more than 100 years, mainly because of their low likelihood of contracting disease. Fish with bones have a pretty high rate of growing tumors. For a long time, scientists believed that sharks were immune to cancer and tumors. So what makes sharks different? They don't have bones. Their skeleton is made up entirely of cartilage. This is one reason that shark teeth are collectible -- it's the only fossil you can find from dead sharks. Their cartilage dissolves over time, and nothing is left but the hard-enameled teeth. Many researchers think that this cartilage holds the secret to the cure for some human medical conditions -- namely cancer.
The shark-cartilage industry is booming, to say the least -- some statistics place earnings at about $25 million per year [source: McGraw Hill]. Most of this money comes from the sale of over-the-counter supplements and vitamins containing shark cartilage. You can walk into any health supplement store or browse the Internet and find dozens of shark-cartilage products. It's typically sold in powdered form or packaged in an oral capsule. It's estimated that 100 million sharks are killed every year by humans. We can't know for sure how many are killed for their cartilage, but the vast amounts of shark products on the market give us a pretty good idea.
But could sharks really help cure disease? And can they aid in the fight against cancer? We'll get to the bottom of these questions on the following page.
It was once believed that sharks didn't get cancer. Recent studies, including one conducted by Johns Hopkins University, have disproved those claims. Hopkins professor Gary Ostrander and his research team found 40 cases of tumors in sharks and other elasmobranchs -- sea creatures with skeletons made of cartilage instead of bones. Proponents of using shark cartilage for human medication claim that it helps prevent something called angiogenisis. This is when a tumor continues to grow because of the formation of new blood vessels.
That sharks can and do get cancer makes it clear that ingesting their cartilage in a health-food supplement won't cure the disease in humans. To verify this, researchers have undertaken specific studies on the effects of shark cartilage in cancer patients. Studies on mice and on humans in 1998 and 2005 found that taking an oral shark-cartilage supplement had no effect on cancerous tumors. Results indicated that it didn't prevent the spread of cancer to other organs either. The study also found that taking the supplements led to some gastrointestinal side effects like diarrhea, nausea and vomiting. Shark cartilage also contains mercury, something doctors warn against because of its negative effects on the brain and kidneys.
But that hasn't stopped people from taking it. The media is quick to jump on a "miracle cancer cure" and did just that in 1993 when a "60 Minutes" episode featured a book that touted the use of the cartilage, titled "Sharks Don't Get Cancer." Professor Ostrander characterized the book's research as "overextensions" of some early experiments with shark cartilage.
Ostrander acknowledges that shark cartilage could help fight tumors if the key elements of the cartilage were isolated and administered to the tumor itself -- but a lot of research needs to take place first in order to determine any positive correlations. So while shark-cartilage supplements won't cure cancer, there may be some things we can learn by studying the predator.
Some of this research is already being performed at the Mote Marine Laboratory's Center for Shark Research in Sarasota, Fla., with the help of Clemson and South Florida Universities. Sharks have a tremendous resistance to disease, and much of the Mote laboratory research is centered on their immune system.
Most animals produce disease-fighting cells in their bone marrow. There's a delay from the time the disease appears to when the cells are produced and sent out to fight the disease. Since sharks have no bones, they produce immune cells mainly in their spleen and thymus. The Mote research indicates that because of this, the shark's immune cells are more readily available in the bloodstream and the lag time is eliminated. Their antibodies are also the smallest in the animal kingdom and are more able to penetrate tissue and get to the disease faster.
Although there may not be any evidence to suggest that ingesting shark products can have an effect on our own immune systems, we may be able to learn more about how immune cells behave by studying sharks.
For more on sharks and cancer research, please visit the links on the next page.
We may be fascinated by sharks, but they can cause trouble for other species. Learn what Earth would be like if there were no sharks at HowStuffWorks.
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More Great Links
- "Laboratory/Animal/Preclinical Studies." National Cancer Institute, 2008. http://www.cancernet.gov/cancertopics/pdq/cam/cartilage/HealthProfessional/page5
- "Metro Business; 2 Cartilage Concerns Settle Federal Suit." The New York Times, July 12, 2000. http://query.nytimes.com/gst/fullpage.html?res=9906E3D91138F931A25754C0A9669C8B63
- "Putting the bite on cancer." elasmo-research.org, 2008. http://www.elasmo-research.org/education/topics/p_bite_on_cancer.htm
- "Shark cancer claims rubbished." BBC, April 6, 2000. http://news.bbc.co.uk/1/hi/health/703082.stm
- "Shark Cartilage Cancer 'Cure' Shows Danger of Pseudoscience." Science Daily, December 3, 2004. http://www.sciencedaily.com/releases/2004/12/041201082202.htm
- "Shark Cartilage Quackery." elasmo-research.org, 2008. http://www.elasmo-research.org/education/topics/p_quack.htm
- "Shark Gets a Bad Rap." McGraw Hill Publishers, 2008. http://www.mhhe.com/biosci/genbio/casestudies/sharks.mhtml
- "Sharks Get Cancer." American Cancer Society, April 25, 2004. http://www.cancer.org/docroot/NWS/content/NWS_1_1x_Sharks_Get_Cancer.asp
- Handwerk, Brian. "Do Sharks Hold Secret to Human Cancer Fight?" August 20, 2003. http://news.nationalgeographic.com/news/2003/08/0820_030820_sharkcancer.html
- Luer, Carl A. "Sharks and Cancer." Florida Museum of Natural History, 2008. http://www.flmnh.ufl.edu/fish/sharks/nsrc/sharksandcancer.html