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
- Several types of dietary supplements 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.
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 for Depression?
It’s uncertain whether omega-3 fatty acid supplements are helpful for depression. Although some studies have had promising results, a 2015 evaluation of 26 studies that included more than 1,400 people concluded that if there is an effect, it may be too small to be meaningful. Other analyses 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.
Omega-3s have not been shown to relieve symptoms of depression that occur during pregnancy or after childbirth.
Depression can be a serious illness. If you or someone in your family may have depression, consult a health care provider.
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.
Sourced from a National Center for Complementary and Integrative Health publication on May 23, 2019.