Shark Liver Oil
Other common name(s): none
Scientific/medical name(s): alkylglycerols, alkoxyglycerols, squalene, squalamine
Shark liver oil is promoted as a complementary or alternative form of treatment for cancer and other diseases. The oil is taken from the liver of cold-water sharks. Shark liver oil is a rich source of alkylglycerols, chemicals that may have anti-cancer properties. Alkylglycerols are also found in human bone marrow and in breast milk. Other chemicals in shark liver oil being studied against cancer are squalamine and squalene.
Shark liver oil is widely used alongside conventional cancer treatment in northern Europe and is sold as a dietary supplement in the United States. Available scientific evidence does not support claims that shark liver oil supplements are effective against cancer in humans. Recent research has focused on certain components of shark liver oil (alkylglycerols, squalamine, and squalene). Early laboratory studies suggest that they may have anti-tumor effects in animals, but their effects in humans are not yet known. Clinical trials are currently under way.
How is it promoted for use?
Shark liver oil is promoted as a dietary supplement used to boost the immune system, fight off infections, heal wounds, and to treat cancer and lessen the side effects of conventional cancer treatment.
Alkylglycerols, one of the components found in shark liver oil, are thought to be helpful in several ways. It has been suggested that they fight cancer by killing tumor cells indirectly. Proponents claim they activate the immune system in two ways: by stimulating immune system cells called macrophages, which consume invading germs and damaged cells; and by inhibiting protein kinase C, which is a key regulator of cell growth. Proponents also claim that alkylglycerols reduce the side effects of chemotherapy and radiation treatment, supposedly because of their ability to protect cell membranes.
Because of their supposed immune-boosting effects, alkylglycerols are also claimed to help against colds, flu, chronic infections, asthma, psoriasis, arthritis, and AIDS. Since macrophages are also important in wound healing, alkylglycerols are said to have healing effects. These claims have not been studied in controlled clinical trials.
Other compounds in shark liver oil, such as squalamine and squalene, have also been promoted to have anti-cancer effects. Because some early studies have shown that squalamine can slow the growth of tumor blood vessels, proponents claim it may help to treat cancer, either alone or combined with chemotherapy. It is also being studied for use against macular degeneration, an eye condition that results in loss of vision. Squalene has been promoted as having cell-protecting abilities, which may reduce the side effects of chemotherapy.
These claims are currently being studied. Depending on the commercial preparation, shark liver oil may also be rich in omega-3 fatty acids and vitamin A. Shark liver oil has also been used in some moisturizing skin creams and lotions, although several cosmetics companies have recently removed this ingredient because of concern regarding the decline of some shark species.
What does it involve?
Shark liver oil is available as a dietary supplement in capsule and liquid forms. There are no standardized dosages. These supplements are available at health food stores and over the Internet.
What is the history behind it?
Shark liver oil has been used as a folk remedy by people on the coasts of Norway and Sweden for hundreds of years. It was mainly used to promote wound healing and as a general remedy for conditions of the respiratory tract and the digestive system.
In the 1950s, a young Swedish doctor suggested that extracts of bone marrow helped boost the recovery of white blood cells in children undergoing radiation therapy and chemotherapy for leukemia. The active ingredient in the bone marrow extract was identified as alkylglycerols. Shark liver oil was found to be one of the richest sources of alkylglycerols. Around 1986, the first commercially purified shark liver oil with a "standard dose" of alkylglycerols was marketed. It is still widely used in many northern European countries.
What is the evidence?
Available scientific evidence does not support claims that shark liver oil supplements are effective against cancer in humans. Most of the studies on alkylglycerols and cancer have been done in the laboratory. A few studies showed some benefit in women with cervical cancer who were also undergoing radiation therapy. These studies were published by a single group of Scandinavian researchers in the 1970s and 1980s and have not been confirmed by other research groups. There appears to be very little recent research on the benefits of alkylglycerols in preventing or treating cancer.
More recently, research has focused on squalamine, a substance found in shark liver oil that stops the growth of tumor blood vessels. Researchers found that squalamine decreased the number of lung metastases—tumors that spread to the lung from a primary cancer elsewhere in the body—found in laboratory animals. Early studies in people with cancer have shown that squalamine can safely be combined with chemotherapy, but whether it helps shrink tumors or prolongs survival is not clear. It is currently being studied with other treatments for lung and prostate cancer.
Squalene, a substance found in olive oil and some types of shark liver oil, has been studied in the laboratory. One laboratory study found that squalene seemed to protect normal bone marrow cells from the effects of some chemotherapy drugs while still allowing the drugs to affect cancer cells. It is not yet clear whether this protective effect will extend to animals and humans.
Are there any possible problems or complications?
Although many people have taken shark liver oil, the issue of potential toxicity at the usual doses has not been well studied. Some mild digestive problems such as nausea, upset stomach, and diarrhea have been reported. Some animal studies have found that shark liver oil and its components may raise blood cholesterol levels. A Japanese study found some shark liver oil supplements to be contaminated with polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). PCBs can have harmful effects in humans and may increase the risk of some types of cancer. People with seafood allergies may also react to shark liver oil.
Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.
More information from your American Cancer Society
The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).
The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management
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Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.
Last Revised: 11/01/2008