Omega-3 and fish oil supplements

Key points about Omega-3 and fish oil supplements

  • Omega-3 fats are found in many cells in your body, especially in cells in your brain and eyes.
  • They play an important role in helping your blood vessels, heart, immune system and lungs work properly.
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Omega-3 fatty acids are a type of polyunsaturated fats. Polyunsaturated fats are often referred to as ‘good fats' as they are important in your diet. The main omega-3 fatty acids are:

  • docosahexaenoic acid (DHA)
  • eicosapentaenoic acid (EPA)
  • alpha-linolenic acid (ALA).

These are found naturally in some foods.

Diagram of different types of omega-3 fatty acids

ALA is an essential fatty acid, meaning your body can’t make it. Your body can convert some ALA into EPA and then to DHA, but only in very small amounts. Therefore you need to get most of your EPA and DHA from food.

Omega-3s can reduce your triglyceride levels, a type of fat found in your blood. DHA and EPA/DHA combination products can increase LDL cholesterol levels, while pure EPA products do not. Read more about cholesterol and fats and oils

Omega-3 fats are found in many cells in your body, especially in cells in your brain and eyes. They play an important role in helping your blood vessels, heart, immune system and lungs work properly. This is why including foods that are high in the omega-3 fats EPA and DHA, such as oily fish, is encouraged as part of a healthy balanced diet. 

The New Zealand Heart Foundation recommends that to get sufficient omega-3 for a healthy heart you need to eat fish or seafood twice a week, preferably oily fish. Examples of oily fish are salmon, mackerel, sardines, kahawai and warehou.

The amount of omega-3 in fish varies between species and whether they are farmed or fresh fish. Oily fish like fresh tuna, fresh or tinned salmon, sardines, pilchards and mackerel are higher in omega-3. White fish and sea food (oysters, eel and prawns) have a lower omega-3 content.

  • Tinned salmon, mackerel, sardines and pilchards can be a great way to get more omega-3.
  • Fish tinned in brine is high in sodium which can increase blood pressure and increase your risk of heart disease.
  • Choose fish tinned in spring water, or rinse the fish thoroughly to remove the brine and sodium.
  • Remember that flavoured tinned fish may also contain added sugar and sodium.

There is a variety of omega-3 and fish oil supplements that can be bought from pharmacies, supermarkets, health shops and online. They are available as capsules, tablets and liquid. There are currently no New Zealand recommendations for taking omega-3 and fish oil supplements.

It is best to get omega-3 from food. A well-balanced diet that includes 2 serves of oily fish per week will provide an adequate amount of omega-3 that your body needs.

Not all fish oil supplements are created equally. Unlike medicines, fish oil supplements do not need to be approved by Medsafe, the medicines regulatory organisation in New Zealand. This means that manufacturers can sell supplements simply with claims of safety and effectiveness.

A recent analysis of 10 fish oil supplements available in New Zealand highlighted the ongoing challenges associated with the regulation of health claims associated with dietary supplements. The authors confirmed that the literature on health effects is contradictory and clearer definitions of the types of health statements that can be made and the research necessary to support them requires regulatory clarification.

Fish oil can slightly reduce blood pressure and heart rate. However, statin medicines are much more effective in lowering cholesterol and the risk of heart problems in people with heart disease or those at high risk of developing heart disease. There is no benefit to taking a fish oil supplement if you are already on a statin. Read more about statins

Randomised trials have not shown a benefit for fish oil supplement reducing dementia risk, but high-dose DHA supplementation may be beneficial to those carrying the APOE4 gene. Fish oil may slightly reduce inflammation, and very high dose fish oil (5.5 grams) can be helpful in rheumatoid arthritis in certain situations.

When choosing fish oil supplements
Look at the amount of EPA and DHA contained in the capsule, tablet or liquid, rather than the fish oil content. For example, the product label on a fish oil supplement may say the following: 

Each capsule contains: Fish oil – Natural 1.5g equiv. 
Eicosapentaenoic acid (EPA) 270mg, Docosahexaenoic acid (DHA) 180mg.

  • In this example, each capsule has EPA + DHA = 270mg + 180mg = 450mg of omega-3. 
  • If you are unsure about how to read the labels of fish oil supplements, ask your pharmacist for advice.
  • EPA content is the most important for heart health, but very high doses are required (above 1800mg daily) for any benefit.
  • Meanwhile the DHA in fish oil supplements can increase LDL cholesterol (‘bad cholesterol’), and high doses can increase the risk of atrial fibrillation, bleeding, stomach upset, abnormal liver tests and rash. 

Not all fish oil supplements are created equally. It is possible that omega-3 fatty acids might be lower than those stipulated on the labels because unsaturated fatty acids are susceptible to oxidation and degradation. 

Interactions with medicines 
Omega-3 can have blood thinning effects when taken in high doses. Seek medical advice before taking doses of omega-3 supplements, especially if you are taking anticoagulant medication such as warfarin.

Seafood allergy
Although the risk of allergic reactions to fish oil supplements is considered to be low in people allergic to fish due to the method of purification, it is recommended that you seek medical advice before taking fish oil supplements. Read more(external link)

The following links have more information about omega-3. Be aware that websites from other countries may have information that differs from New Zealand recommendations.

Omega-3 fatty acids(external link) National Institutes of Health, US
Omega-3(external link) The Association of UK Dietitians, UK 
Fats, oils and heart health(external link) Heart Foundation, Australia
Omega-3 and mood disorders(external link) Black Dog Institute, Australia
Allergic and toxic reactions to seafood(external link) Australasian Society of Clinical Immunology and Allergy


5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


  1. Omega-3 fatty acids(external link) National Institutes of Health, US
  2. Omega‐3 fatty acids for the primary and secondary prevention of cardiovascular disease(external link) Cochrane Library, 2018
  3. Guide to eating for a healthy heart(external link) Heart Foundation, NZ
  4. Are over-the-counter fish oil supplements safe, effective and accurate with labelling? Analysis of 10 New Zealand fish oil supplements(external link) NZMJ September, 2020
  5. Association of docosahexaenoic acid supplementation with Alzheimer disease stage in apolipoprotein E ε4 carriers: a review.(external link) JAMA Neurol. 2017 Mar 1;74(3):339-347. 
  6. Fish oil in recent onset rheumatoid arthritis: a randomised, double-blind controlled trial within algorithm-based drug use.(external link) Ann Rheum Dis. 2015 Jan;74(1):89-95. 
  7. Kai moana – food from the sea(external link) Heart Foundation, NZ

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Dr Jeremy Steinberg, FRNZCGP; Katrina Pace, New Zealand Registered Dietitian

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