There has been much media coverage suggesting the health benefits of eating cold water oily fish, such as mackerel, lake trout, herring, sardines, anchovies, salmon, halibut, and albacore tuna. What is the scientific evidence?

Likely to help protect against high blood pressure, high cholesterol, longer term heart attack and stroke if you are currently healthy (although not necessarily if you already have chronic heart disease – see further below). Dr Mike Knapton of the British Heart Foundation, advises, "Until now, medical research has demonstrated a benefit from omega 3 fats in protecting people from heart and circulatory disease.” Similarly the American Heart Association recommends eating oily fish at least twice a week.

The health benefits are in line with other aspects of the Mediterranean diet, which contains much food rich in omega-3 fatty acids, such as fresh fruit and vegetables, oily fish, whole grains and garlic. Interestingly, Inuit Eskimos, whose diet is very clearly non Mediterranean but who get large amounts of omega-3 fatty acids from eating fatty fish, tend to have increased levels of ‘good’ cholesterol and reduced levels of fats in the blood.  

Likely to protect against colon cancer. The University of Maryland Medical Center reports that laboratory studies, animal studies, preliminary studies with humans and epidemiological research (among Eskimos, who have a high fat diet but eat a lot of fish and have low rates of colon cancer) suggest that eating foods rich in omega-3 fatty acids appears to reduce the risk of colon cancer.

May protect against Alzheimer’s. This is according to a French study published in the journal Neurology. Researchers from the French National Institute for Health and Medical Research in Bordeaux found that regular consumption of fish reduced the risk of Alzheimer’s by 35% in people who did not have a known genetic predisposition – and also that a diet rich in omega-3 oils reduced the risk of dementia by 60%.

May protect against macular degeneration. NHS Choices advises caution here, arguing that underlying evidence used in meta-analysis undertaken by Dr Elaine Chong and colleagues in Australia and Singapore and widely reported in the media is weak and that the researchers themselves say it is too soon to draw definitive conclusions. Hopefully further research will reveal whether or not the initial promise suggested is justified.

Unlikely to slow the progress of Rheumatoid Arthritis but may help treat the symptoms

Why oily fish may have health benefits Webmd reports that oily fish contains omega-3 polyunsaturated fatty acids, and these fatty acids help in a number of different ways:If you already have atherosclerosis (narrowing of the arteries), they may stop it getting worse; they make platelets (the cells that help blood to clot) less sticky so that you are less likely to get blood clots blocking your blood vessels; they lower blood pressure; they reduce levels of triglycerides (a type of fat in your blood that can be harmful); and they raise the levels of good cholesterol (also called HDL cholesterol) in your blood.

Mixed results from research into a range of other conditions. According to a recent study plublished in Nutrient 2019 there have been mixed results when considering the use of oily fish in relation to: Asthma, Attention deficit/hyperactivity disorder (ADHD), Breast cancer, Depression, Inflammatory Bowel Disease (IBD), Lupus, Osteoporosis, Schizophrenia, Skin disorders.

Mixed results in relation to prostate cancer. Oily fish can help protect againts prostate cancer according to epidemiological studies reported by the University of Maryland Medical Center and to research conducted at the University of California, San Francisco and reported in Clinical Cancer Research. However, a recent study reported in the Journal of the National Cancer Institute suggested that oily fish increased the risk of prostate cancer.  

NB. Bipolar reports epidemiological research from countries such as Finland and Japan suggesting that eating more fish reduces the risk of depression and suicidal thoughts, as well as benefits from a number of controlled studies but concludes, ‘This means that it is a very good idea to take fish oil in addition to your regular medication. As yet, there is not enough research to prove fish oil alone can treat either bipolar disorder or unipolar depression.’

Should be avoided and/or taken in small amounts only and/or medical advice taken if you

  • are pregnant (because of potentially harmful contaminants such as mercury which can harm an unborn child’s developing nervous system , particularly in mackerel, shark, swordfish and marlin – with the US Environmental Protection Agency, the US Food and Drug Administration and the UK Food Standards Agency all recommending caution here)
  • have angina (in a large scale trial at the where 3,114 men with stable angina were given high amounts of oily fish in 2003, an increased number of cardiac deaths were recorded -although a number of possible factors may have been at work here, such as mercury levels increasing as more fish is eaten and large amounts of omega-3 fatty acids increasing the risk of bleeding and potential hemorrhagic stroke)
  • bruise easily or have a bleeding disorder
  • are taking blood thinning medication, such as aspirin or warfarin
  • have diabetes 2 (as some people with Diabetes 2 may experience a slight increase in fasting sugar as a result of taking fish oil)

The US National Institutes of Health confirms that fish oil is likely to have a range of health benefits and that normal doses of fish oil should not normally present a risk but advises caution in relation to identified groups ie pregnant women, nursing mothers, patients already having elevated risks of bleeding and diabetics (although the risk here is considered very unlikely). The NIH also confirms that very high doses may increase the risk of bleeding

May help enhance or mitigate the adverse effects of certain medication ie Cyclosporine; Etretinate and topical steroids; and Cholesterol -lowering medications (according to the University of Maryland Medical Center).

 In conclusion

  • As with most natural substances fuller and more rigorous clincial trials will often be needed to provide a definitive picture
  • Very high consumption of oily fish should be avoided and caution exercised by at risk groups such as pregant women, nursing mothers and people with angina and diabetes
  • With these caveats, for most healthy people the advice to eat at least a couple of portions of oily fish a week appears well founded and likely to produce a number of protective health health benefits. 

Update and reviewed February 2020, next review date 2024