Gamma Linolenic Acid
Other common name(s): GLA (also found in evening primrose oil, borage seed oil, black currant oil)
Scientific/medical name(s): gamma linolenic acid
Gamma linolenic acid (GLA) is an omega-6 unsaturated fatty acid made in the human body from linoleic acid, an essential fatty acid found in vegetable oils and egg yolks. The main supplemental sources of GLA are oils of the seeds of evening primrose, borage, and black currant plants. (For more information, see Evening Primrose.) Many companies sell these oils as good sources of GLA. It is also found in human breast milk.
Some studies have shown that GLA can slow or stop the growth of some types of cancer cells in tissue cultures in the laboratory. The same kinds of studies suggest that GLA may help some cancer drugs to work better. However, there is very little evidence as yet that GLA supplements work to prevent or treat cancer in humans. Human studies are under way to evaluate the role of GLA and other essential fatty acids on the growth of cancer.
How is it promoted for use?
Gamma linolenic acid is normally used by the body to make prostaglandins (hormone-like substances). Prostaglandins are believed to be involved in many processes in the body, including regulation of the immune system.
Most GLA in the human body is taken in as linoleic acid and then metabolized to GLA. Most people get plenty of linoleic acid in their diets and can convert it to GLA. Some researchers have suggested that some people (such as those with diabetes or skin allergies) do not make enough GLA from linoleic acid and may therefore benefit from taking GLA supplements.
It has been proposed that GLA supplements may stop or slow the growth of cancer cells. GLA and GLA-rich supplements have also been promoted to help people with breast pain, skin allergies, diabetes, obesity, rheumatoid arthritis, heart disease, high blood pressure, premenstrual syndrome, multiple sclerosis, attention deficit hyperactivity disorder (ADHD), and neurological problems related to diabetes.
What does it involve?
Gamma linolenic acid is available in liquid and capsule form, usually as a natural ingredient in black currant oil, borage oil, or evening primrose oil. The amount of GLA contained in the different types of supplements varies (for example, evening primrose supplements may contain about 10% GLA). Dosages of GLA as a supplement are generally in the range of 500 milligrams to 3,000 milligrams per day. An injectable form of GLA is being studied.
What is the history behind it?
Some of the plants with seeds that contain GLA have been used as folk remedies for hundreds, if not thousands, of years. However, the discovery of GLA and of these seed oils as a source of GLA is much more recent.
Research in the 1980s found that hormone-like substances called prostaglandins played a role in many of the body's processes. Prostaglandins play a role in making smooth muscles contract, controlling inflammation and body temperature, and in other body functions. Since GLA was known to be a building block for some prostaglandins, it was reasoned that GLA might be help treat human disease. While GLA is widely touted for its health benefits, research on its effectiveness in human diseases is still at an early stage.
What is the evidence?
Much of the research on GLA has been done using evening primrose oil. This oil has many components, including linoleic acid and vitamin E, which makes it hard to credit any effects to GLA alone. Studies of the ability of evening primrose oil and GLA to prevent or treat cancer in humans are still in the earliest stages.
Dietary GLA (most of which is consumed as linoleic acid) contributes to making and regulating prostaglandins. However, the exact role of the different prostaglandins in fighting cancer is still not clear.
Some research in the laboratory has suggested that GLA may prove to be helpful against certain cancers, but this research is still early. In laboratory tests, gamma linolenic acid slowed the growth of several types of human cancer cells. It has also been shown to make certain anti-cancer drugs better at killing cancer cells in laboratory studies.
There have been fewer clinical trials studying the effect of GLA on tumors. In a small English study of about eighty breast cancer patients, those who took GLA supplements in addition to tamoxifen responded more quickly to treatment than those who took tamoxifen alone. It is not clear if there were any longer term benefits.
An injectable form of GLA was studied in a clinical trial of 48 patients with pancreatic cancer. Those who got the highest doses of GLA were reported to live longer. However, a larger study of 278 patients did not find that those who got GLA (either by mouth or by vein) lived longer than expected. Some researchers have proposed that the injectable form of GLA may only be effective if injected directly into the tumor. Future studies may look at GLA combined with chemotherapy drugs.
Some studies have looked at the use of maglumine GLA (which is chemically different from the form sold in dietary supplements) against bladder cancer. It is used by infusing it directly into the bladder through a catheter. One small study found that about 43% of people with early-stage bladder cancer had their tumors shrink or completely disappear with this therapy. Clearly, more research is needed to learn which method of giving GLA is most effective, and whether GLA is useful in treating cancer, either alone or with standard treatments.
Neither GLA nor other GLA-rich supplements (such as evening primrose oil) have been convincingly shown to be useful in preventing or treating any other health conditions.
Are there any possible problems or complications?
This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the FDA that their products are safe or effective, as long as they do not claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.
Gamma linolenic acid does not appear to be toxic. However, it has been reported to aggravate a type of epilepsy and should not be used by people who take anti-seizure medicines. Long-term use of GLA may lead to inflammation, blood clots, or lowered immune system functioning.
Borage oil, which is sometimes used as a source of GLA, may contain toxins that can harm the liver or possibly cause cancer. If you take borage oil, be sure it is certified as free of unsaturated pyrrolizidine alkaloids (UPAs). Do not take more than the recommended dose.
Women who are pregnant or breastfeeding should speak with their doctors before using this treatment. 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).
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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: 05/13/2010