Surveying scientific evidence of omega-3 benefits

More than three decades ago, the health benefits of omega-3 fatty acids were uncovered when researchers studied why the Inuits of Greenland -- whose diets consisted of whale, seal and fish -- had the lowest levels of heart disease in the world. The Japanese and Mediterranean diets are also associated with reduced risk of heart disease. After years of study, scientists realized the benefit of these diets likely came from marine food sources and their high content of the unsaturated fatty acid omega-3. Researchers began to investigate the potential health benefits of increasing these fatty acids in the diet, and today there are more than 14,000 scientific articles on the subject. Early studies showed that vegetables, seeds and nuts -- which contain high amounts of one type of omega-3, alpha-linolenic acid (ALA) -- as well as fish and seaweed that are rich in the other two types, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can benefit health.

The strongest evidence to date includes the use of EPA and DHA in lowering high triglyceride levels, and reducing the risk of sudden death and heart attacks (myocardial infarctions) in cardiovascular disease. Some evidence also suggests these omega-3s may help treat age-related macular degeneration and rheumatoid arthritis, and could aid brain health. Since DHA is found predominantly in the tissues of the eye and brain, some experts believe that supplementing with DHA may benefit the developing fetus and newborn. More study is needed to determine the full health benefits of EPA, DHA and ALA.

Omega-3 fatty acids can be obtained through foods and supplements. Food sources are the best way to increase omega-3 intake because they're also rich in vitamins, minerals and protein, but many people don't eat enough fish to obtain the high doses of EPA and DHA needed to treat some health conditions. That makes omega-3 supplements a good option for some consumers; in fact, more than $13 billion are spent each year worldwide on these products.

Primarily available as fish oil, cod liver oil, krill oil, algae or algal oil and flaxseed oil, omega-3s come in capsule or liquid forms that contain varying amounts. Fish oil is a rich source of EPA and DHA, but some people experience a fishy aftertaste. A highly concentrated prescription form of fish oil called Lovaza (omega-3-acid ethyl esters) allows for the same dose with fewer capsules, and its manufacture requires more oversight and regulation than with over-the-counter supplements. Cod liver oil is rich in EPA, DHA and vitamins, but taking too much can lead to health problems from excessive amounts of vitamins A and D. Krill oil also contains high amounts of EPA and DHA but is made from a small shrimplike crustacean, so it's a poor choice for anyone with a shellfish allergy. Relatively new on the market, algae or algal oil is a microalgae supplement that's the only vegan source of DHA. Flaxseed oil is a great source of ALA, but it doesn't contain EPA or DHA. (The body can convert a small amount of ALA to EPA and DHA, but it's less than 5 percent.)

For this buyer's guide ConsumerSearch relies heavily on medical and scientific journals. We focus primarily on review articles, which compile data from multiple studies and independent labs that test dietary supplements. We source articles from The American Journal of Clinical Nutrition, American Family Physician, The Journal of the American Medical Association, The New England Journal of Medicine and Mayo Clinic Proceedings, among others. We also use the Natural Medicines Comprehensive Database, the United States Pharmacopeia (USP) and ConsumerLab.com. The National Institutes of Health provide helpful websites with its Office of Dietary Supplements, MedlinePlus, and the National Center for Complementary and Alternative Medicine. MayoClinic.com, WebMD and the University of Maryland Medical Center also have useful overviews of omega-3 fatty acids and break down the evidence for their use in various health conditions. We list all the sources we consulted on the Our Sources page for this report.

The importance of omega-3 fatty acids

So what exactly are omega-3 fatty acids? These polyunsaturated fats come in four general types: saturated, monounsaturated, polyunsaturated and trans fats. Fatty acids are composed of chains of carbon atoms, and the more hydrogen atoms attached to the carbon, the more saturated the fat is. Saturated fats and trans fats can raise low-density lipoprotein (LDL) cholesterol, sometimes referred to as "bad" cholesterol, and increase the risk for heart disease. Unsaturated fats have had the opposite effect in clinical studies. The American Heart Association (AHA) recommends that a person get no more than 30 percent of their daily calories from fats, less than 7 percent of which should come from saturated fats and less than 1 percent from trans fats.

One main group of polyunsaturated fatty acids are omega-3s, of which there are several types. The three that are most beneficial are ALA, EPA and DHA. ALA is considered an essential fatty acid, which means the body is incapable of making it on its own so it must rely on dietary sources. A small percentage of ALA, estimated at less than 5 percent, can be converted into EPA and DHA, but the majority of EPA and DHA are obtained through the diet. Omega-3s are found in all cells and organs, with the highest concentration in the brain and eyes. They're important in creating eicosanoids, a group of chemicals that cells in the body use to communicate with one another. They also incorporate themselves into cell membranes and influence which substances can move in and out of the cells. Unlike other types of fats, omega-3 fatty acids can be stored in fat cells in only limited amounts, so we need to constantly resupply our bodies by eating foods or supplements that contain omega-3s.

Most research focuses on increasing the dietary intake of fatty fish or fish oil, which are rich in EPA and DHA. While small amounts of ALA can be converted into these fatty acids in the body, this conversion is minimal and it's unclear whether it provides the same health benefits as EPA and DHA. From the limited amount of research conducted, ALA hasn't demonstrated these same benefits. Further study is needed to determine what effects ALA has on health compared to EPA and DHA, as well as if there's any benefit to choosing EPA vs. DHA or if there's an optimal ratio when consuming both.

Another group of polyunsaturated fats are omega-6 fatty acids, the primary one being linoleic acid (LA). Many common cooking oils, such as corn, peanut, sesame and sunflower oils, contain predominantly omega-6s. Like omega-3 fats, omega-6s can be made into the chemical messengers eicosanoids, but they make different ones than their omega-3 counterparts. For example, LA makes eicosanoids that tend to promote inflammation, while EPA makes eicosanoids that may prevent inflammation or at least promote less of it.

Today, Americans tend to eat between 10 and 25 times more omega-6 fatty acids than omega-3s; before the advent of mass agriculture it's believed the human diet had a more equal ratio. In Japan, where there is less heart disease than in the U.S. despite a greater prevalence of smoking and higher average blood pressures, the typical diet contains closer to 60 percent omega-3s and 40 percent omega-6 fatty acids. Some research shows that reducing omega-6 intake while increasing omega-3 intake can reduce the symptoms of rheumatoid arthritis, a disease characterized by inflammation. While more research needs to be done before an optimal omega-6 to omega-3 ratio can be determined, The American Journal of Clinical Nutrition points out that reducing omega-6 fatty acid intake means you need less omega-3s to get the same healthful benefits.

Dosage, side effects and contamination

If you decide to increase your intake of omega-3 fatty acids for better health, how much should you take? The Food and Nutrition Board of the Food and Drug Administration (FDA), in conjunction with the Institutes of Medicine and the U.S. Department of Agriculture (USDA), hasn't set forth a reference daily intake -- the amount of a nutrient that will sufficiently satisfy the needs of 97 to 98 percent of the healthy population. Other organizations, however, provide recommendations. As a starting point, the average intake of EPA and DHA in the U.S. is 100 mg per day. The AHA advises consuming at least two 3.5-ounce servings of fatty fish each week or the equivalent of 500 mg of EPA and DHA every day. If you have heart disease, the AHA recommends consuming a 3.5-ounce serving of fish every day or 1 gram of EPA and DHA daily. If you have high triglycerides, the suggested intake is 3 to 4 grams per day. The FDA recommends speaking to your health care provider before taking more than 3 grams of omega-3s per day and before giving children omega-3 supplements.

Less than 5 percent of people who take omega-3 fatty acids experience side effects that commonly include belching, a fishy taste, nausea and diarrhea. Some of these adverse effects can be reduced by taking the supplements at bedtime or with meals, keeping them in the freezer or choosing enteric-coated capsules, which release their contents after they pass through the stomach. If you're allergic to fish or shellfish, make sure to read the supplement's ingredient list before taking it. Krill oil is derived from a small shrimplike crustacean and can potentially cause a reaction in patients with a shellfish allergy.

Omega-3s can potentially decrease clotting, so any patients with a bleeding disorder or liver disease or who takes blood thinners -- such as Coumadin (warfarin), Plavix (clopidogrel), Lovenox (enoxaparin) or aspirin -- should talk to a doctor before increasing their omega-3 intake. These fatty acids have also been known to decrease blood pressure and increase low-density lipoprotein (LDL "bad") cholesterol. Anyone who takes blood pressure or cholesterol medications, or who has problems with blood pressure or cholesterol, should speak to a doctor first as well. Birth control pills and Xenical (orlistat), also known as Alli, can potentially interfere with the effects and absorption of omega-3 fatty acids.

Contamination is a common concern with seafood, and methyl mercury, polychlorinated biphenyls (PCBs) and dioxins cause the most worry. Being water-soluble, mercury isn't found in any significant amounts in the oils extracted from fish. PCBs are usually found in trace amounts in supplements, but below the maximum suggested intake. While the FDA doesn't monitor supplements as strictly as it does medications, the USP independently tests supplements to verify their contents and whether they're properly labeled, and to determine if they're contaminated. Finally, the Environmental Protection Agency has issued a joint advisory with the FDA for pregnant women and young children to limit their intake of mercury. For more information, see the agency's Fish Consumption Advisories.

Omega-3 fatty acids and their uses

For the past 30 years, the scientific community has studied omega-3 fatty acids to determine what health benefits can be obtained by increasing one's dietary intake. While an immense amount of research has been done, there's an equal amount still left to do. Here we list the various health conditions for which omega-3 supplementation has been researched and the results. Keep in mind that the medical community requires rigorous testing and has very high standards for stating that a medication or supplement is "proven" effective. Depending on the resource, you'll find variable answers as to whether omega-3 fatty acids are effective, likely effective or ineffective for a given health condition.

Cardiovascular disease. Substantial evidence indicates that increased intake of omega-3 fatty acids can lower various risk factors for cardiovascular disease, also known as heart disease. This includes lowering triglyceride levels (see below) and blood pressure, and slowing the progression of atherosclerosis (the buildup of plaque in arteries). Studies find that omega-3s decrease the ability of blood platelets to group together and form clots, and reduce levels of the amino acid homocysteine. (Elevated homocysteine levels have been linked to cardiovascular disease, but there isn't enough evidence showing that lower homocysteine levels reduce risk.) However, the research evaluating the ability of omega-3s to prevent an initial heart attack is minimal and conflicting. The EURAMIC (European Community Multicenter Study on Antioxidants, Myocardial Infarction and Breast Cancer) showed that increased fish intake did not reduce chances of having a first heart attack, but another study saw a 50 percent decrease in first-time heart attacks with subjects who took 5.5 grams of omega-3s each month. The Japan Eicosapentaenoic Acid Lipid Intervention Study (JELIS) saw an 18 percent decrease in heart-related events in patients without heart disease.

The most significant benefit has been seen in preventing recurrent events for patients who already have heart disease or who have had a heart attack. One aspect of JELIS looked at the use of EPA in conjunction with statins -- a group of cholesterol-lowering drugs -- in patients with high cholesterol. Those who took both EPA and statins had a 19 percent reduced risk of having a major coronary event than patients who took a statin alone. In the Diet and Reinfarction Trial, men who were told to eat at least two servings (3 ounces) of fatty fish per week over a two-year period had a 29 percent reduction in mortality. And the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico Prevenzione Trial found that patients who took EPA and DHA had a 45 percent decrease in sudden death due to an irregular heart rhythm. However, these studies and others didn't show any reduction in nonfatal heart attacks. Although there's some evidence that EPA and DHA can prevent some irregular heartbeats, called arrhythmias, studies that examined patients with atrial fibrillation (an abnormal heartbeat) without heart disease showed that EPA and DHA didn't prevent its recurrence.

High triglycerides. Hypertriglyceridemia is an elevated level of triglycerides, a type of cholesterol, in the blood. There's very strong evidence that EPA and DHA can treat this condition, especially for those with very high levels of >/= 500 mg/dL. In fact, studies show that doses of 3 to 4 grams per day of EPA and DHA can lower triglycerides by as much as 20 to 50 percent. Since this high dosage requires taking a large number of pills, GlaxoSmithKline created a prescription omega-3 fatty acid called Lovaza, which has a higher concentration of EPA and DHA than over-the-counter supplements. Numerous studies indicate that when combined with a class of cholesterol-lowering drugs known as statins, Lovaza can further reduce triglycerides by 20 to 30 percent. See our page on Lovaza.

Omega-3s can also affect other types of cholesterol. With both supplements and Lovaza, studies show a small increase in low-density lipoprotein (LDL "bad") cholesterol as well as high-density lipoprotein (HDL "good") cholesterol. The overall benefit of taking omega-3s is substantial because the increases in HDL and LDL balance each other out. And when you consider the drop in triglyceride levels, there's an overall net benefit. Nevertheless, have your cholesterol monitored by a physician if you choose to take an omega-3 supplement or Lovaza.

Rheumatoid arthritis. While it isn't strong, overall evidence suggests that omega-3 fatty acids may benefit those who suffer from rheumatoid arthritis (RA), an autoimmune disease that primarily affects the joints. Small studies show that taking at least 3 grams per day of EPA and DHA reduces the occurrences of morning stiffness, the number of painful swollen joints, and the use of nonsteroidal anti-inflammatory drugs and corticosteroids after 12 weeks. Similar studies with ALA showed no change in symptoms. In other research, reducing omega-6 intake while increasing omega-3 intake was shown to help patients with RA. For more on the omega-6 to omega-3 ratio, see the "Importance of Omega-3s" section. Overall, omega-3 supplementation hasn't been shown to slow the progression of RA.

Eyes. One primary tissue in which high levels of EPA and DHA can be found is the eye. Not many studies have been done, but in surveying populations about their diets, researchers found that those who report eating a diet high in EPA and DHA are 30 percent less likely to develop a disease of the retina. Similar research shows that increased consumption of EPA and DHA also reduces the risk of developing age-related macular degeneration. More research needs to be done to determine if these observed eye disease decreases are due specifically to EPA and DHA intakes.

Infant and maternal health. Scientists theorize that omega-3s are helpful to the developing fetus and infant, but few studies offer definitive proof that they provide notable benefits. The brain and eyes are known to contain significant amounts of DHA, so DHA may be important in their development. Various infant formulas are now fortified with DHA, and some experts encourage a modest increase in omega-3 fatty acids, 200 to 300 mg per day, for women who are pregnant or breast-feeding. Some studies suggest that an increase in EPA and DHA can lead to improved vision and cognitive development in children, but an equal number of studies show no effect. In addition, there are conflicting study results on whether increased omega-3 intake can reduce miscarriages and prevent preterm deliveries. If you're pregnant or breast-feeding and decide to consume more omega-3 fatty acids, use only sources that are low in contaminants like mercury.

Stroke. The evidence for using omega-3s to prevent strokes is mixed. One study shows that eating two servings of fish per week reduces the overall risk of stroke by 50 percent, but there was an increase in the risk of hemorrhagic stroke. A stroke is either ischemic, where blood flow is blocked from getting to the brain by a clot, or hemorrhagic, where a blood vessel bursts and blood leaks into the brain. Given the studies on heart disease, it's believed that omega-3s can decrease the formation of clots, resulting in a protective effect against ischemic stroke.

Mental health. Some evidence suggests that EPA and DHA can improve symptoms of psychosis, depression, attention deficit and hyperactivity disorder, anxiety and aggression, but more research is needed.

Dementia. Studies that survey populations on their diets indicate that increased omega-3 fatty acid intake may decrease the risk of developing dementia or Alzheimer's disease. While more research is needed, it's clear that omega-3 supplementation provides no benefit for patients who already have Alzheimer's disease.

Chemotherapy. Some studies look at whether taking more omega-3 fatty acids can minimize weight loss during chemotherapy. The evidence is conflicting, but a 2011 study published in the journal Cancer showed a significant reduction in weight loss when patients took 4 grams of fish oil per day. More research is needed to confirm these results.

Cancer. A recent comprehensive review in The Journal of the American Medical Association showed that when all studies are considered together, taking omega-3s doesn't prevent the development of cancer. This held true no matter what form of cancer was evaluated.

Everything else. The list is extensive of health conditions for which there may be some benefit to using omega-3 fatty acids. These include inflammatory bowel disease, systemic lupus erythematosus, renal disease, asthma, Raynaud's disease, chronic fatigue syndrome, organ transplantation, cystic fibrosis and osteoporosis.

There are also multiple conditions for which omega-3 fatty acids show no benefit, including migraines, multiple sclerosis, psoriasis, male infertility and improving immune system function in patients with HIV.

For more information on how omega-3 fatty acids relate to various health conditions, see MayoClinic.com and MedlinePlus.

Tips on how to boost your intake of omega-3s

When choosing an omega-3 fatty acid supplement or increasing your dietary intake, here are some important things to remember:

  • Talk with your health care provider. He or she can explain how boosting your intake of omega-3 fatty acids could potentially benefit you, and make sure you choose a source that's compatible with your health needs and any allergies you might have. It's also important to prevent interactions with any of your medications or health conditions, especially if you have a bleeding disorder or liver disease, or are on blood thinners such as Coumadin (warfarin), Plavix (clopidogrel), Lovenox (enoxaparin) or aspirin. If you have high cholesterol, your doctor may also want to order blood tests to ensure your levels aren't increasing.
  • Determine your reasons. Your motivation for increasing your omega-3 intake will dictate how much to consume and in what forms. While there's no official recommended intake from the USDA, the AHA suggests consuming a 3.5-ounce serving of fish every day or 1 gram of EPA and DHA daily. If you have high triglycerides, the recommendation is 3 to 4 grams of EPA and DHA per day.
  • Eat food. When increasing your intake of omega-3s by changing your diet rather than adding a supplement, the benefits are many. Omega-3 food sources are also rich in vitamins and minerals.
  • Read the ingredients. Different fish oil supplements contain oil from different types of fish. Look for a ratio of three parts EPA to two parts DHA. In addition, some supplements labeled as krill oil may contain both krill and fish oil. Check the ingredient list before choosing a supplement, especially if you have any food allergies.
  • Be aware of vitamin content. All oil supplements include a small amount of vitamin E as a preservative, but cod liver oil has high amounts of vitamins A and D. The fat-soluble vitamins A, D, E and K can be stored in fat tissue and may build to toxic levels over time if you continually take more than what's recommended. Know how much of a vitamin is supplied with each serving and how many servings you need to reach the desired level of omega-3s.
  • Keep the supplements fresh. Make sure to reseal the container tightly, refrigerate after opening (especially liquids), and keep out of heat and light. Omega-3 fatty acid supplements, especially fish and krill oil, can spoil easily; avoid getting more than a month's supply at a time.
  • Watch out for false or misleading claims. Manufacturers of omega-3 supplements may make claims that sound good but aren't true. For instance, there's no such thing as "pharmaceutical grade" fish oil. And it means nothing if a label says a supplement was tested in an "FDA approved lab." The FDA registers and inspects labs, but does not approve them.
  • Lessen unpleasant side effects. None of fish oil's major side effects are life-threatening, but they can be disagreeable. To reduce burping, nausea and the fishy taste, try taking the supplement with meals or at bedtime. Keeping fish oil in the freezer can reduce the flavor. Or look for an enteric-coated capsule, which will release the supplement in the small intestine instead of the stomach.
  • Look for independent testing seals like USP. Unlike with prescription medications, there's very little regulation of over-the-counter vitamins and supplements. Pharmaceutical companies are required to prove to the FDA that their products are safe and effective before they reach the market, but with supplements, the FDA has to prove whether they're harmful after they're available to consumers. Supplement manufacturers don't need FDA approval; instead, they rely only on themselves to ensure their supplements are safe and contain what they say on the labels.

Fortunately, the nonprofit USP sets standards for dietary supplements and will verify a product if the manufacturer requests that it do so. Supplements that pass inspection are considered USP-verified and are assured to contain what's listed on the label in those amounts, that they aren't contaminated, that they'll break down and release what they contain appropriately, and that they've been manufactured according to the FDA's Good Manufacturing Practices (GMPs). For more on USP verification and a list of USP-verified products, see USP Dietary Supplements. In addition, the Natural Products Association provides GMP certification to companies that request it; they're listed here. ConsumerLab.com performs similar independent testing and verification of dietary supplements. The omega-3 products it has tested can be found at Product Review: Fish Oil and Omega-3 Fatty Acid Supplements, but the site requires a membership fee.

More resources on omega-3 fatty acids

United States Department of Agriculture's (USDA) Nutrient Data Laboratory is a searchable database where you can find the nutrient content of any food.

United States Pharmacopeia (USP) is a nonprofit organization that sets standards for dietary supplements and will verify their contents if a manufacturer submits its product. Supplements that are verified will have a USP verification seal on their labels.

ConsumerLab.com provides independent testing and verification of dietary supplements.

NSF is another nonprofit organization that verifies dietary supplements.

MayoClinic.com's article Dietary Fats: Know Which Types to Choose discusses which fats to include and avoid in your diet.

MayoClinic.com's article Omega-3 fatty acids, fish oil, alpha-linolenic acid is a good overview of omega-3s. It includes an easy-to-understand guide of the evidence available for the use of omega-3 fatty acids in various health conditions.

WebMD provides a basic guide to omega-3s with Omega-3 Fatty Acids: Fact Sheet.

The Natural Products Association offers third-party testing to its members. Manufacturers can apply for three certifications: Good Manufacturing Practices, TruLabel and Purity Testing Services for Chinese Raw Materials.

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