Omega-3 fatty acids (omega-3s, for short) are a group of polyunsaturated fatty acids that come from food sources, such as fish, fish oil, some vegetable oils (primarily canola and soybean), walnuts, wheat germ, and certain dietary supplements. As supplements, omega-3s are marketed as capsules or oils, often as fish oil.
Omega-3s are important in a number of bodily functions, including moving calcium and other substances in and out of cells, the relaxation and contraction of muscles, blood clotting, digestion, fertility, cell division, and growth. Omega-3s have been the subject of much media attention in recent years, because of studies finding they may be useful for such purposes as decreasing the rate of heart disease, reducing inflammation, and lowering triglyceride levels. Some countries and organizations have issued formal recommendations on the intake of omega-3s, through meals, oils, and possibly supplementation. Omega-3s have been of interest for diabetes primarily because having diabetes increases a person's risk for heart disease and stroke.
Summary of the research findings
Randomized clinical trials have found that omega-3 supplementation reduces the incidence of cardiovascular disease and events (such as heart attack and stroke) and slows the progression of atherosclerosis (hardening of the arteries). However, these studies were not done in populations that were at higher risk, such as those with type 2 diabetes.
With regard to studies on omega-3 supplementation for type 2 diabetes, there is somewhat more literature available than for most other complementary and alternative medicine therapies for this condition. A 2001 analysis was published by the Cochrane Collaboration, of 18 randomized placebo-controlled trials on fish oil supplementation in type 2 diabetes. The authors found that fish oil lowered triglycerides and raised LDL cholesterol but had no significant effect on fasting blood glucose, HbA1c, total cholesterol, or HDL cholesterol. (The authors did not identify and include studies with cardiovascular outcomes, but noted that this is an area for further research.) Another analysis was published in 2004 by the Agency for Healthcare Research and Quality, of 18 studies on omega-3 fatty acids for a number of measurable outcomes in type 2 diabetes. This study confirmed virtually all the Cochrane authors' findings, except for finding no significant effect on LDL cholesterol.
Additional studies are needed to determine whether omega-3 supplements are safe and beneficial for heart problems in people with type 2 diabetes. Studies that look specifically at heart disease outcomes in this population are needed.
Side effects and possible risks
Omega-3s appear to be safe for most adults at low-to-moderate doses. There have been some safety questions raised about fish oil supplements, because certain species of fish can be contaminated with substances from the environment, like mercury, pesticides, or PCBs. Fish oil is on the list of food substances that the U.S. Food and Drug Administration considers to be "generally recognized as safe." How well a product is prepared is another factor for consumers to consider. Women who are pregnant or breastfeeding should not take fish oil supplements. Fish oil in high doses can possibly interact with, and affect the action of, certain medications, including blood-thinning drugs and drugs for high blood pressure. Potential side effects of fish oil include a fishy aftertaste, belching, stomach disturbances, and nausea.
- There is limited scientific evidence on the effectiveness of dietary supplements as complementary and alternative medicine (CAM)A group of diverse medical and health care systems, practices, and products that are not presently considered to be part of conventional medicine. Complementary medicine is used together with conventional medicine, and alternative medicine is used in place of conventional medicine. for type 2 diabetes. The evidence that is available is not sufficiently strong to prove that any of the six supplements discussed in this report have benefits for type 2 diabetes or its complications. A possible exception may be the use of omega-3 fatty acidsEssential nutrients that the body cannot make on its own but can obtain from foods such as fish and flaxseed, or from dietary supplements. to lower triglyceridea levels.
- It is very important not to replace conventional medical therapy for diabetes with an unproven CAM therapy.
- To ensure a safe and coordinated course of care, people should inform their health care providers about any CAM therapy that they are currently using or considering.
- The dietary supplements reviewed in this section appear to be generally safe at low-to-moderate doses. However, each can interact with various prescription medications, affecting the action of the medications. People with type 2 diabetes need to know about these risks and discuss them with their health care provider. Prescribed medicines may need to be adjusted if a person is also using a CAM therapy.
Reviewed by Susan Weiner, R.D., M.S., C.D.E., C.D.N. 10/08
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