Fish Oil

What is it?

Fish oil comes from many types of fish. It is rich in two important omega-3 fatty acids called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

The benefits of fish oil seem to come from its omega-3 fatty acid content. Fish that are especially rich in these oils include mackerel, herring, tuna, and salmon. The body doesn’t produce many of its own omega-3 fatty acids. Omega-3 fatty acids reduce pain and swelling, and also prevent the blood from clotting easily.

Some fish oil products are approved by the FDA as prescription medications to lower triglycerides levels. Fish oil is also available as a supplement. Fish oil supplements do not contain the same amount of fish oil as prescription products, so they cannot be used in place of prescription products. Fish oil supplements are sometimes used for heart health and mental health, but there is no strong evidence to support most of these uses.

Do not confuse fish oil with EPA, DHA, cod liver oil, flaxseed oil, krill oil, or shark liver oil. See the separate listings for these topics.

Is it effective?

NatMed Pro rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

Effective for …

High levels of fats called triglycerides in the blood (hypertriglyceridemia). Taking certain fish oil prescription drugs by mouth, including Lovaza, Omtryg, and Epanova, reduces very high triglyceride levels. These products are most often taken at a dose of 4 grams daily. While some non-prescription fish oil supplements might also help, these products contain less omega-3 fatty acids than the prescription fish oil products. People would need to take as many as 12 capsules of fish oil supplements daily to get the same effect as prescription fish oil.

Possibly Effective for …

A procedure to open a blocked or narrowed blood vessel (angioplasty). Taking fish oil by mouth decreases the rate of blood vessel re-blockage by up to 45% when taken for at least 3 weeks before an angioplasty and continued for one month after.
Involuntary weight loss in people who are very ill (cachexia or wasting syndrome). Taking a high dose of fish oil by mouth seems to slow weight loss in some cancer patients. Low doses of fish oil don’t seem to have this effect.
Kidney damage caused by the drug cyclosporine. Taking fish oil seems to prevent kidney damage in people taking cyclosporine. Fish oil also seems to improve kidney function in people who recently rejected a transplanted kidney and are taking cyclosporine.
Menstrual cramps (dysmenorrhea). Taking fish oil, alone or with vitamin B12 or vitamin E, can improve painful periods and reduce the need for pain medications for menstrual cramps.
Nausea and vomiting caused by an infection of the intestines. Taking fish oil during pregnancy seems to reduce the risk of the child having nausea and vomiting from an infection of the intestines.
Heart failure. Consuming higher amounts of fish oil from foods has been linked with a lower risk of heart failure. Eating 1-2 servings of non-fried fish per week is recommended. It’s too soon to know if taking fish oil supplements helps prevent heart failure. But taking fish oil supplements by mouth might reduce the risk of death or hospitalization in people that already have heart failure.
Abnormal levels of blood fats in people with HIV/AIDS. Taking fish oil supplements by mouth reduces triglyceride levels in people with abnormal cholesterol levels caused by HIV/AIDS treatment.
High blood pressure. Taking fish oil by mouth seems to slightly lower blood pressure in people with moderate to very high blood pressure. It’s not clear if it helps people with slightly high blood pressure or those who are already on blood pressure-lowering medications.
A condition that slowly leads to kidney disease (IgA nephropathy). Taking fish oil by mouth for 2-4 years can slow the loss of kidney function in high-risk patients with IgA nephropathy. It’s not clear if it helps when taken short-term, or in low-risk patients.
Build up of fat in the liver in people who drink little or no alcohol (nonalcoholic fatty liver disease or NAFLD). Taking fish oil by mouth might reduce liver fat and improve liver health in people with NAFLD.
Rheumatoid arthritis (RA). Taking fish oil by mouth, alone or together with the drug naproxen, seems to help improve symptoms of RA. However, taking fish oil does not seem to prevent RA.

Possibly Ineffective for …

An eye disease that leads to vision loss in older adults (age-related macular degeneration or AMD). People who eat fish more than once weekly have a reduced risk of developing age-related vision loss. But taking fish oil by mouth for up to 6 years does not prevent vision loss or slow down its progression.
Chest pain (angina). Taking fish oil supplements by mouth does not reduce the risk of death or improve heart health in people with chest pain.
Hardening of the arteries (atherosclerosis). Taking fish oil by mouth doesn’t slow the progression or improve symptoms of atherosclerosis.
Eczema (atopic dermatitis). Taking fish oil supplements doesn’t help treat or prevent eczema. But children who eat fish at least once weekly from the age of 1-2 years seem to have a lower risk of developing eczema.
Irregular heartbeat (atrial fibrillation). Eating fatty fish or taking fish oil supplements by mouth does not reduce the risk of irregular heartbeat. In fact, the risk of irregular heartbeat might be increased in some people taking fish oil supplements.
A lung disease that affects newborns (bronchopulmonary dysplasia). Giving fish oil by mouth to premature infants doesn’t seem to reduce the infant’s risk of developing this lung disease.
Long-term blood flow problems in the brain (cerebrovascular diseases). Eating fish might reduce the risk of cerebrovascular disease. But taking fish oil supplements by mouth doesn’t have this effect.
Memory and thinking skills (cognitive function). Taking fish oil supplements by mouth does not improve most memory or thinking skills in older people, young adults, or children.
A digestive tract infection that can lead to ulcers (Helicobacter pylori or H. pylori). Taking fish oil supplements by mouth does not seem to improve H. pylori infections when compared to standard medications.
Kidney transplant. Taking fish oil by mouth doesn’t help people live longer after a kidney transplant. It also doesn’t seem to prevent the body from rejecting the transplant.
Breast pain (mastalgia). Taking fish oil by mouth doesn’t seem to reduce long-term breast pain.
Multiple sclerosis (MS). Taking fish oil by mouth doesn’t seem to improve symptoms in people with MS.
Osteoarthritis. Taking fish oil by mouth doesn’t improve pain or function in people with osteoarthritis. But it might help overweight people with osteoarthritis-like pain.
High blood pressure during pregnancy. Taking fish oil by mouth does not seem to prevent high blood pressure during pregnancy.
A pregnancy complication marked by high blood pressure and protein in the urine (pre-eclampsia). Taking fish oil by mouth does not seem to prevent pre-eclampsia.
A mental disorder marked by hallucinations and delusion (psychosis). Taking fish oil by mouth does not seem to prevent or reduce symptoms of psychosis.
Sudden chest pain that may occur while resting (unstable angina). Taking fish oil by mouth does not seem to prevent this condition.
Abnormal rapid heart rhythms (ventricular arrhythmias). Taking fish oil by mouth does not affect the risk for abnormal heart rhythms or reduce the risk of death in people with abnormal rapid heart rhythms.

Probably Ineffective for …

Diabetes. Taking fish oil by mouth doesn’t lower blood sugar in people with type 2 diabetes. It also doesn’t reduce the risk of certain complications of diabetes, such as heart attack and stroke. But taking fish oil by mouth might lower blood fats called triglycerides in people with diabetes.

There is interest in using fish oil for a number of other purposes, but there isn’t enough reliable information to say whether it might be helpful.

Is there concern for the safety of its use?

When taken by mouth: Fish oil is likely safe for most people in doses of 3 grams or less daily. Taking more than 3 grams daily might increase the chance of bleeding. Fish oil side effects include heartburn, loose stools, and nosebleeds. Taking fish oil supplements with meals or freezing them can reduce these issues.

Consuming high amounts of fish oil from DIETARY sources is possibly unsafe. Some fish are contaminated with mercury and other chemicals. Fish oil supplements typically do not contain these chemicals.

When applied to the skin: There isn’t enough reliable information to know if fish oil is safe or what the side effects might be.

Special Precautions & Warnings:

Pregnancy and breast-feeding: Fish oil supplements are likely safe when taken by mouth. Taking fish oil does not seem to affect the fetus during pregnancy or the baby while breast-feeding. But swordfish, king mackerel, and tilefish should be avoided during pregnancy, by those who may become pregnant, and while breast-feeding. These fish might contain high levels of mercury and may contain other toxins. Limit consumption of other fish to 12 ounces/week (about 3 to 4 servings/week). Consuming fatty fish in high amounts is possibly unsafe.

Children: Fish oil supplements are possibly safe when taken by mouth. In adolescents, fish oil has been used safely in doses of up to about 2.2 grams daily for 12 weeks. But young children should not eat more than two ounces of fish per week. Consuming fish oil from DIETARY sources in large amounts is possibly unsafe. Fatty fish contain toxins such as mercury. Eating contaminated fish frequently can cause serious adverse effects in children.

Bipolar disorder: Taking fish oil might increase some of the symptoms of this condition.

Liver disease: Fish oil might increase the risk of bleeding in people with liver scarring due to liver disease.

Diabetes: Taking high doses of fish oil might make it more difficult to control blood sugar levels.

Familial adenomatous polyposis: There is some concern that fish oil might further increase the risk of getting cancer in people with this condition.

Conditions in which the immune system response is lowered (including HIV/AIDS): Higher doses of fish oil can lower the body’s immune system response. This could be a problem for people whose immune system is already weak.

An implanted device to prevent irregular heartbeat: Fish oil might increase the risk of irregular heartbeat in patients with an implanted defibrillator. Stay on the safe side and avoid fish oil supplements.

Fish or seafood allergy: Some people who are allergic to seafood such as fish might also be allergic to fish oil supplements. There is no reliable information showing how likely people with seafood allergy are to have an allergic reaction to fish oil. Until more is known, advise patients allergic to seafood to avoid or use fish oil supplements cautiously.