- There has been a substantial amount of research on supplements of omega-3s, particularly those found in seafood and fish oil, and heart disease. The findings of individual studies have been inconsistent. In 2012, two combined analyses of the results of these studies did not find convincing evidence these omega-3s protect against heart disease.
- There is some evidence that omega-3s found in seafood and fish oil may be modestly helpful in relieving symptoms in rheumatoid arthritis. For most other conditions for which omega-3s have been studied, definitive conclusions cannot yet be reached, or studies have not shown omega-3s to be beneficial.
- Omega-3 supplements may interact with drugs that affect blood clotting.
- It is uncertain whether people with fish or shellfish allergies can safely consume fish oil supplements.
- Fish liver oils (which are not the same as fish oils) contain vitamins A and D as well as omega-3 fatty acids; these vitamins can be toxic in high doses