Fish-oil and omega-3 supplements are popular because they are believed to have health benefits. The American Heart Association (AHA) recommend eating oily fish and omega 3 to promote heart health. However, studies have produced mixed results.

White fish also contain oils, but at lower concentrations, and mainly in the liver. Cod is a white fish, and its oil is concentrated in its liver. Cod liver oil contains less omega-3 fatty acid but more vitamin A and D.

Here are some key points about fish oils.

• Fish oils contain omega-3 fatty acids and vitamins A and D.
• Omega-3 fatty acids found in fish oils may protect the heart and offer other health benefits, but research results have been mixed.
• Eating fish is a better way of getting fish oil or omega 3 than taking supplements.

Multiple sclerosis

Fish oils are said to help people with multiple sclerosis (MS) due to its protective effects on the brain and the nervous system. However, at least one study concluded that they have no benefit.

Prostate cancer

May reduce the risk of developing prostate cancer. However, another study linked higher omega-3 levels to a higher risk of aggressive prostate cancer.

Research published in the Journal of the National Cancer Institute suggested that a high fish oil intake raises the risk of high-grade prostate cancer by 71 percent, and all prostate cancers by 43 percent.

Post-partum depression

Consuming fish oils during pregnancy may reduce the risk of post-partum depression. Researchers advise that eating fish with a high level of omega 3 two or three times a week may be beneficial. Food sources are recommended, rather than supplements, as they also provide protein and minerals.

Mental health benefits

An 8-week pilot study carried out in 2007 suggested that fish oils may help young people with behavioral problems, especially those with attention deficit hyperactivity disorder (ADHD).

The study demonstrated that children who consumed between 8 and 16 grams (g) of EPA and DHA per day, showed significant improvements in their behavior, as rated by their parents and the psychiatrist working with them.

Memory benefits

Omega-3 fatty acid intake can help improve working memory in healthy young adults, according to research reported in the journal PLoS One.

However, another study indicated that high levels of omega-3 do not prevent cognitive decline in older women.

Heart and cardiovascular benefits

Omega-3 fatty acids found in fish oils may protect the heart during times of mental stress.

Findings published in the American Journal of Physiology suggested that people who took fish oil supplements for longer than 1 month had better cardiovascular function during mentally stressful tests.

Meanwhile, a review of 20 studies involving almost 70,000 people, found "no compelling evidence" linking fish oil supplements to a lower risk of heart attack, stroke, or early death.

People with stents in their heart who took two blood-thinning drugs as well as omega-3 fatty acids were found in one study to have a lower risk of heart attack compared with those not taking fish oils.

The AHA recommend eating fish, and especially oily fish, at least twice a week, to reduce the risk of cardiovascular disease.

Alzheimer's disease

For many years, it was thought that regular fish oil consumption may help prevent Alzheimer's disease. However, a major study in 2010 found that fish oils were no better than a placebo at preventing Alzheimer's.

Meanwhile, a study published in Neurology in 2007 reported that a diet high in fish, omega-3 oils, fruit, and vegetables reduced the risk of dementia and Alzheimer's.

Vision loss

Adequate dietary consumption of DHA protects people from age-related vision loss, Canadian researchers reported in the journal Investigative Ophthalmology & Visual Science.

Epilepsy

A 2014 study published in the Journal of Neurology, Neurosurgery & Psychiatry claims that people with epilepsy could have fewer seizures if they consumed low doses of omega-3 fish oil every day.

Schizophrenia and psychotic disorders

Omega-3 fatty acids found in fish oil may help reduce the risk of psychosis.

Findings published in Nature Communications details how a 12-week intervention with omega-3 supplements substantially reduced the long-term risk of developing psychotic disorders.

Health fetal development

Omega-3 consumption may help boost fetal cognitive and motor development. In 2008, scientists found that omega-3 consumption during the last 3 months of pregnancy may improve sensory, cognitive, and motor development in the fetus.

Sources

The fillets of oily fish contain up to 30 percent oil, but this figure varies. White fish, such as cod, contains high concentrations of oil in the liver but less oil overall. Oily fish that are rich in omega-3 fatty acids include anchovies, herring, sardines, salmon, trout, and mackerel.

Other animal sources of omega-3 fatty acids are eggs, especially those with "high in omega-3" written on the shell.

Vegetable-based alternatives to fish oil for omega 3 include:

Fish is not the only food source of omega-3 oils.

• flax
• hempseed
• perilla oil
• spirulina
• walnuts
• chia seeds
• radish seeds, sprouted raw
• fresh basil
• leafy dark green vegetables, such as spinach
• dried tarragon

A person who consumes a healthful, balanced diet should not need to use supplements.