Fish Oil (Omega-3 Fatty Acids)

Heart disease and cardiovascular events

There is some evidence that people with heart disease or high triglycerides may benefit from taking omega-3 supplements. A 2020 review of 86 studies involving 162,796 people found that increasing EPA and DHA slightly reduced the risk of coronary events and coronary death. A 2019 analysis of 13 major omega-3 supplementation studies (127,477 total participants) showed marine omega-3 supplementation lowered the risk of myocardial infarction (MI), coronary heart disease (CHD) death, and total CHD. A 2019 review of the VITAL, ASCEND, and REDUCE-IT trials concluded that the findings of each study showed that for the general population, consuming 1 gram per day of omega-3 fatty acids provides some benefits to cardiovascular health. (1)

Blood pressure

There's promising evidence that some complementary approaches, including meditation, tai chi, qigong, and yoga as well as garlic, fish oil, flaxseed, and green or black tea, may have small beneficial effects on blood pressure. (2)

Stroke

Eating seafood (fish and shellfish) has been linked to a moderate reduction in the risk of stroke. A 2020 review of 31 trials with 138,888 participants found increasing omega-3 supplements had little or no effect on reducing strokes. A 2021 analysis of 10 studies (73,124 participants) found that taking omega-3 supplements at low doses (1 capsule per day or less) was not associated with a reduced risk of stroke; however, a reduction in stroke risk was seen at high doses (three or more capsules per day), but only two of the studies used doses this high, so there isn't enough evidence to allow a definite conclusion to be reached. According to a 2016 report from the Agency for Healthcare Research and Quality (AHRQ), there is some evidence that omega-3s from marine sources (such as fish oil) may reduce the risk of one type of stroke (ischemic stroke), but omega-3s have not been shown to reduce total strokes or death from stroke. (1)

Triglyceride levels

A 2020 review of 23 studies (43,998 participants) showed that EPA and DHA reduce triglycerides by about 15 percent but do not affect body fat or other lipids. Several products containing omega-3s have been approved as prescription drugs to be used in combination with diet to reduce triglyceride levels in patients whose triglyceride levels are very high. The composition of these products is not the same as that of typical omega-3 supplements, and the testing and regulation of prescription drugs differ from those for dietary supplements. Therefore, the effects of these prescription products may not be the same as those of omega-3 dietary supplements. (1)

Depression

Although some studies have had promising results, it's uncertain whether omega-3 fatty acid supplements are helpful for depression. A 2021 review of 35 studies (1,964 participants) reaffirmed the conclusion from a 2015 review that if there is an effect, it may be too small to be meaningful, and the authors judged the quality of the evidence to be low or very low. Other reviews have suggested that if omega-3s do have an effect, EPA may be more beneficial than DHA and that omega-3s may best be used in addition to antidepressant medication rather than in place of it. Publication bias and key differences among the trials suggest the need for more high-quality studies. In a 2019 review of the effects of omega-3s on mental health during pregnancy and postpartum, 9 out of 14 studies (3,543 participants) showed that high consumption of DHA, either alone or with other fatty acids, may reduce symptoms of depression and anxiety during gestation; however, none of the studies showed omega-3s had an effect on depression or anxiety during postpartum, and the authors recommend further research. Depression can be a serious illness; if you or someone in your family may have depression, consult a health care provider. (1)

Attention-deficit hyperactivity disorder (ADHD)

There is some evidence that ADHD could be related to lower dietary intake of omega-3 and higher dietary intake of omega-6 fatty acids. However, research on omega-3 supplements for ADHD has had conflicting results, and it's uncertain whether omega-3s have any benefit for symptoms of this condition. A 2023 review of 36 studies compared supplements of polyunsaturated fatty acids (omega-3s, omega-6s, or both) to placebo for ADHD treatment in children and adolescents and did not find evidence that ADHD symptoms are likely to improve in children or adolescents with ADHD who receive polyunsaturated fatty acid supplements. The authors noted that more high-quality studies are needed due to small sample sizes, variations in types and dosage of supplements, and duration of the studies. (1)

Alzheimer's disease and cognitive impairment

Some research indicates that people who eat more seafood may have a reduced risk of cognitive decline. A 2022 review of 33 studies suggests that dietary and supplemental omega-3s may have a protective effect against cognitive decline for healthy people without preexisting AD or dementia; however, there was no effect on cognition for people already diagnosed with AD. A 2018 review of 7 studies (795 participants) of men and women between the ages of 55 and 90 with mild to moderate AD found that omega-3 fatty acid supplementation may be beneficial in disease onset, when there is slight impairment of brain function, but the authors said there is not enough evidence to support omega-3 fatty acid supplementation for treatment of the disease. A 2017 research review suggested that people who carry a gene called APOE4, which is associated with an increased risk of AD, might benefit from taking DHA before developing signs of AD. (1)

Other conditions affecting the brain, nervous system, or mental health

Studies of omega-3s for multiple sclerosis have shown some beneficial effects on relapse rates, inflammation, and improving quality of life. Omega-3s have also been studied for autism spectrum disorders, with research to date suggesting no beneficial effects. Omega-3s may be a beneficial treatment for people with borderline personality disorder, particularly for impulsive behavioral dyscontrol and affective dysregulation. EPA has been found to reduce positive, negative, depressive, and anxious symptoms associated with schizophrenia and may reduce violent behaviors as well; medium- and long-term efficacy of omega-3 fatty acids in stable schizophrenia is not known. Additional evidence regarding their effects on these and other mental health conditions varies. (1)

Age-related macular degeneration (AMD)

Two major NIH-sponsored studies, AREDS and AREDS2, showed that dietary supplements containing specific combinations of vitamins, antioxidants, and zinc helped slow the progression of AMD in people who were at high risk of developing the advanced stage of this disease. AREDS2, which had more than 4,000 participants and was completed in 2013, also tested EPA and DHA. The results showed that adding these omega-3s to the supplement formulation didn't provide any additional benefits. Other studies of omega-3 supplements also haven't shown a beneficial effect on the progression of AMD. (1)

Dry eye disease

The results of several small studies suggested that taking omega-3 supplements might help relieve symptoms of dry eye disease. A 2022 review of 8 studies (1,107 participants) of omega-3 supplements, in either a capsule (6 studies) or eyedrops (2 studies), concluded that supplementation may improve symptoms in patients with dry eye disease, although the authors noted that sample sizes and durations varied as well as the possibility of bias. A 2018 NIH-sponsored study called the Dry Eye Assessment and Management (DREAM) study tested omega-3 supplements for a full year in 535 study participants with moderate-to-severe dry eye disease and found that the supplements were no more helpful than a placebo. At the end of their year in the DREAM study, 43 study participants agreed to participate in an extension study in which they were randomly assigned to continue using omega-3s or switch to a placebo; after 12 months, outcomes didn't differ between the two groups. (1)

Retinitis pigmentosa

Retinitis pigmentosa is a rare genetic disease that affects the retina. It causes loss of night vision and side (peripheral) vision and can lead to blindness. Only a few studies have been conducted on omega-3s for retinitis pigmentosa, and these studies have not shown any clear evidence of beneficial effects. (1)

Rheumatoid arthritis

A 2022 review of 30 studies (1,420 participants) found eating foods rich in polyunsaturated fatty acids (PUFAs), especially omega-3s, may improve symptoms such as pain and swollen and tender joints, and might be an appropriate addition to drug therapy for rheumatoid arthritis. A 2021 review of 12 studies (776 participants) found that diets rich in omega-3 fatty acids resulted in lower pain than ordinary diets, although the authors noted that evidence was low. Conventional medical treatment for rheumatoid arthritis can slow joint damage; if you have rheumatoid arthritis, don't change your use of prescribed medications without consulting your health care provider. (1)

Infant development and pregnancy outcomes

The nutritional value of seafood is important during early development. The Dietary Guidelines for Americans 2020-2025 and guidance from the FDA and EPA recommend that women who are pregnant or breastfeeding eat at least 8 ounces but no more than 12 ounces of a variety of seafood each week, from choices that are lower in methyl mercury; methyl mercury can be harmful to the brain and nervous system if a person is exposed to too much of it. A 2020 review of 15 trials, conducted for the Scientific Report of the 2020 Dietary Guidelines Advisory Committee, concluded there is limited evidence that omega-3 fatty acid supplementation during pregnancy has positive effects on cognitive development in children, and found insufficient evidence to evaluate effects on other developmental results such as language; social-emotional, physical, or visual development; academic performance; or risk of ADHD, autism, anxiety, or depression. A 2018 review of 70 studies with 19,927 pregnant women found preterm births (before 37 weeks) and early preterm births (before 34 weeks) were less likely among women who received omega-3 long-chain polyunsaturated fatty acid (LCPUFA) supplementation than those who did not, with fewer babies with low birth weight and lower risk of the babies dying or being ill and going to neonatal intensive care units. In 2016, AHRQ reviewed 143 studies and found that when women took omega-3 supplements during pregnancy, their babies' birth weight was slightly higher but the risk of an undesirably low birth weight did not change; pregnancies lasted a little longer but there was no effect on the risk of premature birth. Omega-3s were not found to have effects on other aspects of the mothers' or infants' health or the infants' long-term development, including growth after birth, visual acuity, long-term neurological and cognitive development, and the risks of autism, ADHD, learning disorders, and allergies. (1)

Taste, breath, and sweat effects

What to notice: Unpleasant taste, bad breath, bad-smelling sweat.

What to do: These effects are described as usually mild. Discuss persistent or troublesome effects with your health care provider. (1)

Headache

What to notice: Headache.

What to do: These effects are described as usually mild. Discuss persistent or troublesome effects with your health care provider. (1)

Gastrointestinal symptoms

What to notice: Heartburn, nausea, and diarrhea.

What to do: These effects are described as usually mild. Discuss persistent or troublesome effects with your health care provider. (1)

Not established by the sources used for this page

What to notice: The sources used describe side effects of omega-3 supplements as usually mild and list no specific symptoms requiring prompt clinician contact.

What to do: Ask your health care provider or pharmacist about any symptom that concerns you. (1)

Vitamin A and D excess from fish liver oil supplements — caution

Symptoms: Fish liver oil supplements, such as cod liver oil, contain EPA and DHA and also contain vitamins A and D, in amounts that vary from product to product. Vitamins A and D can be harmful in excessive amounts.

Action: Check with your health care provider about the supplements you take, and do not take a bigger dose than the label recommends. (1) (3)

Methyl mercury exposure from seafood during pregnancy or breastfeeding — caution

Symptoms: Methyl mercury can be harmful to the brain and nervous system if a person is exposed to too much of it.

Action: The Dietary Guidelines for Americans 2020-2025 and guidance from the FDA and EPA recommend that women who are pregnant or breastfeeding eat at least 8 ounces but no more than 12 ounces of a variety of seafood each week, from choices that are lower in methyl mercury. Discuss choices with your health care provider. (1)

Depression — caution

Symptoms: Depression can be a serious illness.

Action: If you or someone in your family may have depression, consult a health care provider. (1)

Rheumatoid arthritis and prescribed medicines — caution

Symptoms: Conventional medical treatment for rheumatoid arthritis can slow joint damage.

Action: If you have rheumatoid arthritis, don't change your use of prescribed medications without consulting your health care provider. (1)

Pregnancy and breastfeeding

The Dietary Guidelines for Americans 2020-2025 and guidance from the FDA and EPA recommend that women who are pregnant or breastfeeding eat at least 8 ounces but no more than 12 ounces of a variety of seafood each week, from choices that are lower in methyl mercury. On omega-3 supplementation in pregnancy, a 2020 review of 15 trials concluded there is limited evidence of positive effects on cognitive development in children and insufficient evidence to evaluate other developmental results; a 2018 review found preterm and early preterm births were less likely among women who received omega-3 LCPUFA supplementation; and a 2016 AHRQ review found babies' birth weight was slightly higher and pregnancies lasted a little longer, with no effect on the risk of premature birth and no demonstrated effects on other aspects of mothers' or infants' health or infants' long-term development. (1)

Infants and children

Smaller amounts of seafood are recommended for young children. Research on omega-3 supplements for ADHD in children and adolescents has had conflicting results, and a 2023 review of 36 studies did not find evidence that ADHD symptoms are likely to improve in children or adolescents with ADHD who receive polyunsaturated fatty acid supplements. Dietary supplements are sold as pills, capsules, powders, drinks, and energy bars; the sources used for this page give no dose for children. (1)

People with pre-existing disease or on prescribed treatment

A 2022 review found no effect of omega-3s on cognition for people already diagnosed with Alzheimer's disease. If you have rheumatoid arthritis, don't change your use of prescribed medications without consulting your health care provider. If you or someone in your family may have depression, consult a health care provider. (1)

People having surgery

Check with your health care provider about the supplements you take if you are going to have any type of surgery. (3)

United States

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