Omega-3 fatty acids are found in foods, such as fish and flaxseed, and in dietary supplements, such as fish oil.

The three main omega-3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is found mainly in plant oils such as flaxseed, soybean, and canola oils. DHA and EPA are found in fish and other seafood.

ALA is an essential fatty acid, meaning that your body can’t make it, so you must get it from the foods and beverages you consume. Your body can convert some ALA into EPA and then to DHA, but only in very small amounts. Therefore, getting EPA and DHA from foods (and dietary supplements if you take them) is the only practical way to increase levels of these omega-3 fatty acids in your body.

Omega-3s are important components of the membranes that surround each cell in your body. DHA levels are especially high in retina (eye), brain, and sperm cells. Omega-3s also provide calories to give your body energy and have many functions in your heart, blood vessels, lungs, immune system, and endocrine system (the network of hormone-producing glands).

Experts have not established recommended amounts for omega-3 fatty acids, except for ALA. Average daily recommended amounts for ALA are listed below in grams (g). The amount you need depends on your age and sex.

*As total omega-3s. All other values are for ALA alone.

Omega-3s are found naturally in some foods and are added to some fortified foods. You can get adequate amounts of omega-3s by eating a variety of foods, including the following:

• Fish and other seafood (especially cold-water fatty fish, such as salmon, mackerel, tuna, herring, and sardines)
• Nuts and seeds (such as flaxseed, chia seeds, and walnuts)
• Plant oils (such as flaxseed oil, soybean oil, and canola oil)
• Fortified foods (such as certain brands of eggs, yogurt, juices, milk, soy beverages, and infant formulas)

Omega-3 dietary supplements include fish oil, krill oil, cod liver oil, and algal oil (a vegetarian source that comes from algae). They provide a wide range of doses and forms of omega-3s.

Fish oil, which contains omega-3 fatty acids, is a commonly used dietary supplement. Omega-3s are promoted as “healthy” fats, and research shows that foods that contain omega-3s, such as fish and other seafood, have many health benefits. However, the potential benefits of fish oil and other omega-3 dietary supplements are not as clear. Below are answers to some commonly asked questions about fish oil and omega-3s.

1. I’m confused by all of the different terms such as ALA, EPA, and DHA that are used when referring to omega-3s from fish oil, flaxseed, or other sources. What are the differences?

There are two main types of omega-3 fatty acids—“short chain” and “long chain,” named for their somewhat different chemical structures. ALA is one of the most common short-chain omega-3s, while EPA and DHA are the most common long-chain omega-3s.

Plant foods such as flaxseed, soybean, and canola oils, as well as chia seeds and black walnuts, contain ALA. Fish and other seafood—especially cold-water fatty fish such as salmon, mackerel, and tuna—contain EPA and DHA.

Most omega-3 supplements, including fish oil, krill oil, cod liver oil, and vegetarian products made from algal oil, contain EPA and DHA. Flaxseed oil supplements contain ALA. Some foods, including certain brands of eggs, yogurt, milk, and soy beverages, contain added omega-3s. You can check product labels to determine which ones.

Most research on the potential health benefits of omega-3s involves EPA and DHA. Our bodies can convert ALA into EPA and DHA, but not very well. So if you want to increase the amount of EPA and DHA you consume, you need to get them from either foods or dietary supplements. If you eat about 8 ounces per week of a variety of seafood, you are getting about 250 mg of EPA and DHA each day. A typical fish oil supplement provides about 300 mg of EPA and DHA, but doses vary widely.

2. Are fish oil supplements recommended for cardiovascular disease? What does the latest research show?

Fish oil supplements help lower triglyceride levels, but their other effects on cardiovascular disease are less clear. Studies conducted 10 to 20 years ago found that fish oil reduced the risk of some heart problems such as sudden death and stroke, especially among people with heart disease. But many recent studies have not found the same thing. Some researchers believe that changes in people’s lifestyles, such as increased use of statins and higher consumption of fish over the last 10 to 20 years, might overshadow the potential benefits of fish oil. Research clearly shows that eating fish and other seafood as part of a healthy eating pattern reduces the risk of cardiovascular disease. Therefore, experts recommend consuming 8 or more ounces per week of fish and other seafood, including some varieties that have higher amounts of EPA and DHA (such as salmon, mackerel, and tuna).

3. I am pregnant and have heard that it’s important to get DHA in addition to prenatal vitamins. Should I take a supplement, eat more fish, or both?

During pregnancy, experts recommend eating 8 to 12 ounces of a variety of seafood per week, choosing from varieties that are lower in methyl mercury. These include salmon, herring, sardines, light tuna, and trout. Pregnant women should not consume certain types of fish—such as king mackerel, shark, swordfish, and tilefish—that are high in methyl mercury.

Some studies show that taking DHA or other omega-3 dietary supplements during pregnancy might slightly increase a baby’s weight at birth and the length of time the baby is in the womb, both of which might be beneficial. However, it is not clear whether taking these supplements during pregnancy affects a baby’s health or development. We recommend talking with your health care provider for advice.

Most people in the United States get enough ALA from the foods they eat. They also get small amounts of EPA and DHA. Recommended amounts of EPA and DHA have not been established.

A deficiency of omega-3s can cause rough, scaly skin and a red, swollen, itchy rash. Omega-3 deficiency is very rare in the United States.

Scientists are studying omega-3s to understand how they affect health. People who eat fish and other seafood have a lower risk of several chronic diseases. But it is not clear whether these health benefits come from simply eating these foods or from the omega-3s in these foods. Here are some examples of what the research has shown.

Cardiovascular disease
Many studies show that eating fatty fish and other types of seafood as part of a healthy eating pattern helps keep your heart healthy and helps protect you from some heart problems. Getting more EPA and DHA from foods or dietary supplements lowers triglyceride levels, for example.

The American Heart Association (AHA) recommends eating one to two servings of seafood per week to reduce your risk of some heart problems, especially if you consume the seafood in place of less healthy foods. For people with heart disease, the AHA recommends consuming about 1 g per day EPA plus DHA, preferably from oily fish, but supplements are an option under the guidance of a health care provider. The AHA does not recommend omega-3 supplements for people who do not have a high risk of cardiovascular disease.

Infant health and development
During pregnancy and breastfeeding, eating 8 to 12 ounces per week of fish and other seafood may improve your baby’s health. However, it is important to choose fish that are higher in EPA and DHA and lower in mercury. Examples are salmon, herring, sardines, and trout. It is not clear whether taking dietary supplements containing EPA and DHA during pregnancy or breastfeeding affects a baby’s health or development. However, some studies show that taking these supplements may slightly increase a baby’s weight at birth and the length of time the baby is in the womb, both of which may be beneficial. Breast milk contains DHA. Most commercial infant formulas also contain DHA.

Cancer prevention
Some studies suggest that people who get more omega-3s from foods and dietary supplements may have a lower risk of breast cancer and perhaps colorectal cancer. But a large clinical trial found that omega-3 supplements did not reduce the overall risk of cancer, or the risk of breast, prostate, or colorectal cancers. Other clinical trials in progress will help clarify whether omega-3s affect cancer risk.

Alzheimer’s disease, dementia, and cognitive function
Some—but not all—research shows that people who consume more omega-3s from food such as fish may have a lower risk of developing Alzheimer’s disease, dementia, and other problems with cognitive function. More study of the effects of omega-3s on the brain is needed.

Age-related macular degeneration (AMD)
AMD is a major cause of vision loss among older adults. Studies suggest that people who get higher amounts of omega-3s from the foods they eat may have a lower risk of developing AMD. But once someone has AMD, taking omega-3 supplements does not keep the disease from getting worse or slow down vision loss.

Dry eye disease
Dry eye disease occurs when tears don’t provide enough moisture, causing eye discomfort and vision problems. Some studies show that getting more omega-3s from foods or supplements—mainly EPA and DHA—helps relieve symptoms of dry eye disease. But a large, recent study found that the symptoms of people with dry eye disease who took fish oil supplements of 2,000 mg EPA plus 1,000 mg DHA daily for 1 year did not improve any more than those who took a placebo (a dummy pill). Another study in healthy people found that daily supplements of 460 mg EPA plus 380 mg DHA for 5.3 years did not affect the risk of getting dry eye disease. More research on the effects of omega-3s on dry eye disease is needed.

Rheumatoid arthritis (RA)
RA causes chronic pain, swelling, stiffness, and loss of function in the joints. Some clinical trials have shown that taking omega-3 supplements may help manage RA when taken together with standard RA medications and other treatments. For example, people with RA who take omega-3 supplements may need less pain-relief medication, but it is not clear if the supplements reduce joint pain, swelling, or morning stiffness.

Other conditions
Researchers are studying whether taking omega-3 dietary supplements may help lessen some of the symptoms of attention-deficit/hyperactivity disorder, childhood allergies, and cystic fibrosis. But more research is needed to fully understand the potential benefits of omega-3s for these and other conditions.

The U.S. Food and Drug Administration recommends consuming no more than 5 g/day of EPA and DHA combined from dietary supplements. Any side effects from taking omega-3 supplements are usually mild. They include an unpleasant taste in the mouth, bad breath, heartburn, nausea, stomach discomfort, diarrhea, headache, and smelly sweat.

Omega-3 dietary supplements may interact with the medications you take. For example, high doses of omega-3s may cause bleeding problems when taken with warfarin (Coumadin®) or other anticoagulant medicines.

Talk with your health care provider about possible interactions between omega-3 supplements and your medications.

What’s the Bottom Line?

How much do we know about omega-3 fatty acids (omega-3s)?
Extensive research has been done on omega-3s, especially the types found in seafood (fish and shellfish) and fish oil supplements.

What do we know about the effectiveness of omega-3 supplements?

• Research indicates that omega-3 supplements don’t reduce the risk of heart disease. However, people who eat seafood one to four times a week are less likely to die of heart disease.
• High doses of omega-3s can reduce levels of triglycerides.
• Omega-3 supplements may help relieve symptoms of rheumatoid arthritis.
• Omega-3 supplements have not been convincingly shown to slow the progression of the eye disease age-related macular degeneration.
• For most other conditions for which omega-3 supplements have been studied, the evidence is inconclusive or doesn’t indicate that omega-3s are beneficial.

What do we know about the safety of omega-3 supplements?

• Omega-3s usually produce only mild side effects, if any.
• There’s conflicting evidence on whether omega-3s might influence the risk of prostate cancer.
• If you’re taking medicine that affects blood clotting or if you’re allergic to fish or shellfish, consult your health care provider before taking omega-3 supplements.

What Are Omega-3s?

Omega-3s (short for omega-3 fatty acids) are a kind of fat found in foods and in the human body. They are also sold as dietary supplements.

Types of Omega-3s and Foods That Contain Them

• The omega-3s EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are found in seafood (fish and shellfish).
• Because of their chemical structure, EPA and DHA are sometimes referred to as long-chain omega-3s.
• A different type of omega-3, ALA (alpha-linolenic acid), is found in certain plant oils such as flaxseed, soybean, and canola oils and also in some other foods of plant origin, such as chia seeds and black walnuts.
• Most of the research discussed in this fact sheet focuses on EPA and DHA.

Supplements That Contain Omega-3s

• Fish oil supplements contain EPA and DHA.
• Fish liver oil supplements, such as cod liver oil, contain EPA and DHA, and they also contain vitamins A and D, in amounts that vary from product to product. Vitamins A and D can be harmful in excessive amounts.
• Krill oil contains EPA and DHA.
• Algal oils are a vegetarian source of DHA; some also contain EPA.
• Flaxseed oil contains ALA.

Seafood vs. Supplements

• For some health conditions, the evidence for benefits from seafood (fish and shellfish) is stronger than the evidence for omega-3 supplements.
• How could this happen? Here are some possibilities:
  • Seafood may provide enough omega-3s; more may not be better.
  • Other nutrients in seafood besides omega-3s may play a role in its benefits.
  • Some of the benefits of seafood may result from people eating it in place of less healthful foods.
  • There’s evidence that people who eat seafood have generally healthier lifestyles.

The Federal Government’s Dietary Guidelines for Americans 2015–2020 recommends that adults eat 8 or more ounces of a variety of seafood (fish or shellfish) per week for the total package of nutrients seafood provides, and that some seafood choices with higher amounts of EPA and DHA be included. Smaller amounts of seafood are recommended for young children.

Use of Omega-3 Supplements in the United States

According to the 2012 National Health Interview Survey, which included a comprehensive survey on the use of complementary health approaches in the United States, fish oil supplements are the nonvitamin/nonmineral natural product most commonly taken by both adults and children. The survey findings indicated that about 7.8 percent of adults (18.8 million) and 1.1 percent of children age 4 to 17 (664,000) had taken a fish oil supplement in the previous 30 days.

What Do We Know About the Effectiveness of Omega-3s?

Conditions Affecting the Circulatory System

• Heart Disease
• Stroke
• Triglycerides

Conditions Affecting the Brain, Nervous System, or Mental Health

• Depression
• Attention-Deficit Hyperactivity Disorder (ADHD)
• Alzheimer’s Disease/Cognitive Impairment
• Other Conditions Affecting the Brain, Nervous System, or Mental Health

Eye Diseases

• Age-Related Macular Degeneration
• Dry Eye Disease
• Retinitis Pigmentosa

Other Conditions

• Rheumatoid Arthritis
• Infant Development
• Miscellaneous Conditions

What Do We Know About the Safety of Omega-3s?

• Side effects of omega-3 supplements are usually mild. They include unpleasant taste, bad breath, bad-smelling sweat, headache, and gastrointestinal symptoms such as heartburn, nausea, and diarrhea.
• Several large studies have linked higher blood levels of long-chain omega-3s with higher risks of prostate cancer. However, other research has shown that men who frequently eat seafood have lower prostate cancer death rates and that dietary intakes of long-chain omega-3s aren’t associated with prostate cancer risk. The reason for these apparently conflicting findings is unclear.
• Omega-3 supplements may interact with drugs that affect blood clotting.
• It’s uncertain whether people with seafood allergies can safely take fish oil supplements.

Omega-3 fatty acids are a group of polyunsaturated fatty acids that are important for a number of functions in the body. The omega-3 fatty acids EPA and DHA are found in seafood, such as fatty fish (e.g., salmon, tuna, and trout) and shellfish (e.g., crab, mussels, and oysters). A different kind of omega-3, called ALA, is found in other foods, including some vegetable oils (e.g., canola and soy). Omega-3s are also available as dietary supplements; for example, fish oil supplements contain EPA and DHA, and flaxseed oil supplements contain ALA. Moderate evidence has emerged about the health benefits of consuming seafood. The health benefits of omega-3 dietary supplements are unclear.

Here are 7 things you should know about omega-3s:

1. Results of studies on diets rich in seafood (fish and shellfish) and heart disease provide moderate evidence that people who eat seafood at least once a week are less likely to die of heart disease than those who rarely or never eat seafood. The Dietary Guidelines for Americans, 2010 includes a new recommendation that adults eat 8 or more ounces of a variety of seafood per week because it provides a range of nutrients, including omega-3 fatty acids. (Smaller amounts are recommended for young children, and there are special recommendations for pregnant or breastfeeding women. See Tip #4.)
   
2. Evidence suggests that seafood rich in EPA and DHA should be included in a heart-healthy diet; however, supplements of EPA and DHA have not been shown to protect against heart disease. In 2012, two groups of scientists analyzed the research on the effects of EPA/DHA supplements on heart disease risk. One group analyzed only studies in people with a history of heart disease, and the other group analyzed studies in people both with and without a history of heart disease. Neither review found strong evidence of a protective effect of the supplements.
   
3. A 2012 review of the scientific literature concluded that EPA and DHA, the types of omega-3s found in seafood and fish oil, may be modestly helpful in relieving symptoms of rheumatoid arthritis. In the studies included in the review, many of the participants reported that when they were taking fish oil they had briefer morning stiffness, less joint swelling and pain, and less need for anti-inflammatory drugs to control their symptoms.
   
4. The nutritional value of seafood is of particular importance during fetal growth and development, as well as in early infancy and childhood. Women who are pregnant or breastfeed should consume 8 to 12 ounces of seafood per week from a variety of seafood types that are low in methyl mercury as part of a healthy eating pattern and while staying within their calorie needs. Pregnant or breastfeeding women should limit the amount of white tuna (labeled as “albacore”) to no more than 6 ounces per week. They should not eat tilefish, shark, swordfish, and king mackerel because they are high in methyl mercury.
   
5. There is ongoing research on omega-3 fatty acids and diseases of the brain and eye, but there is not enough evidence to draw conclusions about the effectiveness of omega-3s for these conditions. DHA plays important roles in the functioning of the brain and the eye. Researchers are actively investigating the possible benefits of DHA and other omega-3 fatty acids in preventing or treating a variety of brain- and eye-related conditions.
   
6. There is conflicting evidence about whether a link might exist between the omega-3 fatty acids found in seafood and fish oil (EPA/DHA) and an increased risk of prostate cancer. Additional research on the association of omega-3 consumption and prostate cancer risk is under way.
   
7. The bottom line: Including seafood in your diet is healthful. Whether omega-3 supplements are beneficial is uncertain. If you are considering omega-3 supplements, talk to your health care provider. It’s especially important to consult your (or your child’s) health care provider if you are pregnant or breastfeeding, if you take medicine that affects blood clotting, if you are allergic to seafood, or if you are considering giving a child an omega-3 supplement.