Is Fish Oil Healthy?

Medically Reviewed by Jabeen Begum, MD on November 14, 2023
Written by WebMD Editorial Contributor
8 min read

Fish oil is an oil taken from the tissues of fatty fish such as herring, mackerel, salmon, and tuna. The process involves pressing cooked fish, then separating the oil from the extracted fluid.

Half a century ago, Danish scientists noticed specific Inuit populations had lower rates of heart disease. Researchers believed that was due to their diet, which was rich in fatty fish. Fish and other seafood are excellent sources of long-chain omega-3 fatty acids (omega-3s), and the researchers thought that the lower rate of heart disease was because of the omega-3s in the fatty fish.

There is evidence from modern studies that omega-3s are good for your heart and blood vessels. Fish, especially cold-water fatty fish (such as salmon, mackerel, and tuna) are the best sources of omega-3s. Because of this, the Dietary Guidelines for Americans recommend 8 ounces of seafood per week for adults who aren't pregnant or nursing and who eat 2,000 calories per day. The American Heart Association recommends eating two 3-ounce portions of fish, especially fatty fish, per week. A 3-ounce portion is about the size of a deck of playing cards. 

What are omega-3 fatty acids?

Omega-3s are a group of polyunsaturated fats found in some foods. Polyunsaturated fats can help reduce bad cholesterol levels in your blood, which can lower your risk of heart disease and stroke. Omega-3s are critical for the proper development of the eyes and brain. They are also vital for heart and lung health and to keep your immune and endocrine systems working well. Your body can't make omega-3s, so, they must be taken in through food (or supplements if you don't eat fish and other seafood or plant sources of omega-3s). 

 

There are three types of omega-3s. Fatty fish have two important omega-3s called docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Plant-based foods have another omega-3 called alpha-linolenic acid (ALA), which the body can use to make DHA and EPA.  

According to the National Academy of Medicine, adequate intake of omega-3s (as ALA) per day for those assigned male at birth (AMAB) and those assigned female at birth (AFAB) is as follows:

  • From birth to 12 months, both AMAB and AFAB, 0.5 grams
  • From 1-3 years, both AMAB and AFAB, 0.7 grams  
  • From 4-8 years, both AMAB and AFAB,  0.9 grams
  • From 9-13 years, AMAB 1.2 grams, AFAB 1 gram  
  • From 14-50 years, AMAB 1.6 grams, AFAB 1.1 grams
  • 51+ years, AMAB 1.6 grams, AFAB 1.1 grams

If you're pregnant, adequate intake is 1.4 grams per day, and if you're nursing, adequate intake is 1.3 grams per day. 

Good food sources of omega-3s include:

  • Fatty fish, such as mackerel, salmon, sardines, trout, and tuna
  • Shellfish, such as crabs, mussels, and oysters
  • Flaxseeds and flaxseed oil
  • Soybeans (edamame) and soybean oil
  • Canola oil 
  • Chia seeds
  • Black walnuts

Some people, especially those who are pregnant and children aged 11 or younger, may want to watch out for mercury levels in fish. Too much mercury can damage the brain, nervous system, and other body systems. Some fish have higher levels of mercury than others. Those with higher levels are usually fish that eat other fish, such as shark, swordfish, bigeye tuna, and wild catfish. Eating up to 12 ounces a week of fish that are good sources of omega-3s (anchovy, mackerel, salmon, tuna, and so on) is believed safe for everyone.

It's better to get your omega-3s through food than fish oil supplements. This is because vitamins and minerals work best when they come from food. In food, they also come with many other helpful nutrients, such as antioxidants, that aren't in most supplements.

But not everyone eats fish, and some people may have food allergies that prevent them from eating foods high in omega-3s. Some people also have concerns about the amount of mercury in fish. Mercury is generally removed from fish oil when it's processed into supplements. If you don't or can't eat fish, fish oil may be an option to get your omega-3s. 

 

Fish oil supplements can come in liquid, capsule, and pill form.

In liquid form, 1 tablespoon contains:

  • Calories: 123
  • Protein: 0 grams
  • Fat: 13.6 grams
  • DHA: 0.573 grams
  • EPA: 0.853 grams
  • Carbohydrate: 0 grams
  • Fiber: 0 grams
  • Sugar: 0 grams

Typically, fish oil capsules and tablets have about 1,000 milligrams of fish oil, which gives 120 milligrams of DHA and 180 milligrams of EPA, but these amounts can vary widely depending on a number of things such as the brand. 

Cod liver oil supplements also have vitamin A and vitamin D as well as omega-3s. 

Many studies show that omega-3s may help improve your heart health when you eat them, but the data isn't as clear for fish oil supplements. 

Clinical trials on the benefits of fish oil supplements have mixed results. Some show supplements protect the heart or improve brain health, but others show no benefit. Research methods can be different between studies, and this may be why there are mixed results. 

Always talk to your doctor before taking over-the-counter supplements. They can advise you what's safe to take based on your medical history. Some supplements, like fish oil, may interfere with your prescription medicines, raise your chance of heart rhythm changes, and raise your risk of bleeding, especially if you take antiplatelets (such as aspirin, clopidogrel, or dipyridamole) or anticoagulants (such as heparin or warfarin). 

Here's a breakdown of some of the most recent claims and research about fish oil:

Prevention of Heart Disease and Heart Attacks

Overall, studies show that eating fish and other types of seafood as part of your balanced diet helps improve your heart health, especially when you eat seafood in place of less healthy foods. Fish oil supplements lower triglyceride levels and might reduce your chance of having a heart attack or stroke, especially if you don't eat much food with omega-3s. The evidence for omega-3 supplements improving heart health is stronger for people who have heart disease than for healthy people.

Some studies suggest that omega-3s may also reduce blood pressure. Two studies in people with high blood pressure showed that both the systolic (upper or first number) and diastolic (lower or second number) blood pressure numbers came down when people took more than 3 grams per day of fish oil supplements. But since taking more than 3 grams per day of fish oil supplements can raise your chance of bleeding, you shouldn't take this much fish oil unless you are being watched by your doctor. 

Improved cognitive function

Some early studies led researchers to think that omega-3 supplements could help brain function in people with Alzheimer's disease and prevent dementia in healthy older people. But further research hasn't shown that so far. One systematic review found that for older people with mild cognitive impairment, omega-3s may help some aspects of cognitive function, such as attention, immediate recall, and processing speed, but these results need to be confirmed with more tests.

Alleviation of rheumatoid arthritis

Data that support the benefits of omega-3s for people with rheumatoid arthritis is mixed. The systematic reviews don't show that they make the overall symptoms better, but they do seem to lower the amounts of nonsteroidal anti-inflammatory drugs (NSAIDs) and steroids that may be needed for pain and morning stiffness. Omega-3s may be a good add-on to help manage pain if you have rheumatoid arthritis, but more research is needed. 

Eye health support

Results from some early studies suggest that eating higher amounts of omega-3s could lower your chance of developing age-related macular degeneration (AMD). AMD is an eye disease that causes blurring in the center of your vision and is a major cause of vision loss in older people. One randomized, controlled trial showed that people who said they had a high omega-3 intake were about 30% less likely to develop some types of AMD than other people. Two systematic reviews that included trials of people with early AMD showed that omega-3 supplements don't reduce the chance of progressing to advanced AMD or prevent vision loss.

Fish oil may help relieve symptoms of dry eye disease, but findings from clinical trials have been mixed. Dry eye disease is a long-term condition that lowers the amount and quality of your tears, which can cause vision trouble and be painful. One trial showed that taking 1,000 milligrams of omega-3 supplements every day for 3 months reduced dry eye symptoms. But another large trial didn't find any difference.

Help with depression

Early studies suggest that people who take fish oil supplements may have less depression. One systematic review that included 26 trials showed that people with high fish intake had a slightly lower risk of depression. But although another study found a small benefit of omega-3s for symptoms of depression, they didn't find enough evidence to say that omega-3s benefit people with major depressive disorder.

Defense against prostate cancer

Some studies in animals suggest that omega-3s may stop cancers from growing. But researchers haven't been able to repeat these results in humans. Early studies in humans have been mixed, with some studies showing that omega-3s in supplements raise the chance of getting prostate cancer and other studies showing that eating more fish and other foods high in omega-3s lower the chance. Overall, researchers don't think the studies so far show that omega-3s affect the chance of getting or dying from prostate cancer.

Always consult with your doctor before taking any new supplements.

The National Academy of Medicine hasn't set an upper limit for omega-3s, but they do say that high amounts (such as 900 milligrams a day for EPA and 600 milligrams a day for DHA or more for a few weeks) might reduce your immune system function. Amounts of 2-15 grams a day of fish oil may also lower the function of platelets and raise your chance of bleeding. 

Both the FDA and the European Food Safety Authority say that omega-3 supplements (EPA and DHA) up to 5 grams a day appear safe. Two large trials did show that taking 4 grams a day of omega-3 supplements for several years slightly raised the chance of an abnormal heart rhythm in people with heart disease or people with a high chance of getting heart disease.

It's not clear whether fish oil is safe for people who are allergic to seafood. If you are allergic to seafood, talk to your doctor before you take fish oil supplements.

Common side effects of omega-3 supplements are generally mild and may include:

  • An unpleasant taste in the mouth
  • Fishy-smelling breath or sweat
  • Heartburn
  • Nausea
  • Stomach ache or indigestion
  • Diarrhea
  • Headache

Cod liver oil supplements can also have high levels of vitamin A. Vitamin A is toxic in large amounts. 

Consider the following before taking fish oil:

Medication interference

Avoid fish oil if you are taking anticoagulant medication. Fish oil decreases blood clot formation, increasing the risk of bleeding for those on warfarin or low-dose aspirin.

Cancer and disabilities at birth

Be sure to research brands of fish oil, as not all are created equal. The FDA doesn't regulate supplements, so it's important that you only buy supplements from sources you know and trust.

Certain brands are certified free from polychlorinated biphenyls (PCBs), which are believed to cause cancer and disabilities at birth.