Omega-3 and fish oil supplements

Easy-to-read medicine information about omega-3 and fish oil supplements.

Key points

  1. Omega-3 fatty acids are found in food such as oily fish, flaxseed, walnuts and pumpkin seeds, and in dietary supplements such as fish oil.
  2. The main omega-3 fatty acids are docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and alpha-linolenic acid (ALA). You need to get most of your EPA and DHA from food as your body can only make very small amounts from ALA.
  3. Omega-3 fats are found in many cells in your body, but 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. 
  4. In New Zealand it’s recommended that adults have 2 servings of oily fish a week to provide omega-3 fatty acids, which may help to reduce the risk of heart disease.  
  5. It is best to get omega-3 fatty acids from your diet. Most supplements are highly degraded, containing much less omega-3 content than claimed on the label. In addition, supplements contain very low doses of mixed DHA/EPA content and are unlikely to provide any benefits for health.
  6. Taking fish oil supplements in high doses can cause a slightly increased risk of atrial fibrillation, swelling of your legs, bleeding, stomach upset and abnormal liver tests.

What are omega-3 fatty acids?

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. Fish sources of omega-3 are also called long-chain omega-3 fatty acids. These work differently in your body to ALA. You need to get most of your DHA and EPA from food as your body can only make very small amounts from ALA.

  • Sources of DHA and EPA – these are found in oily fish, such as sardines, salmon, trout and mackerel.
  • Sources of ALA – ALA is found in plant foods such as flaxseeds, soybean, chia seeds, walnuts, pumpkin seeds and canola oil.

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

The amount of omega-3 in fish varies between species of fish 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.

Why are omega-3 fatty acids important?

Omega-3 fats are found in many cells in your body, but 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. 

How often should I eat oily fish?

In New Zealand it’s recommended that men have 610mg of long chain omega-3 daily and women have 430mg daily to reduce the risk of heart disease. This is 2 servings of oily fish a week.3 A serving of fish is:

  • 125–150g raw fish, which is about the size of your hand (palm and fingers)
  • a 95g tin of tuna, which has about 100mg of omega-3
  • a 105g tin of pink salmon, which has about 120mg of omega-3.

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.

Omega-3 and fish oil supplements 

There are 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 medications, fish oil supplements do not need to be approved by the medicines regulatory organisation in New Zealand, Medsafe. This means that manufacturers can sell supplements simply with "claims" of safety and effectiveness. Fish oil supplements in New Zealand are highly degraded (oxidised) and may contain significantly less omega-3 content than claimed on the label.4

Fish oil supplements – what is the evidence?

Fish oil can slightly reduce blood pressure and heart rate. However, statin medications 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.5 

Fish oil may slightly reduce inflammation, and very high dose fish oil (5.5 grams) can be helpful in rheumatoid arthritis in certain situations.6

Tips about using omega-3 and fish oil supplements

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. 

Fish oil supplements in New Zealand are highly degraded and contain far less omega-3 content than claimed on the label. Best-before dates, cost and country of origin are poor markers of quality and it is not possible for consumers to detect non-degraded products.

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

Learn more

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 National Institutes of Health, US
Omega-3 The Association of UK Dietitians, UK 
Sources of  omega-3 Heart Foundation, Australia
Omega-3 and mood disorders Black Dog Institute, Australia
Allergic and toxic reactions to seafood Australasian Society of Clinical Immunology and Allergy


  1. Omega-3 fatty acids National Institutes of Health, US
  2. Omega‐3 fatty acids for the primary and secondary prevention of cardiovascular disease Cochrane Library, 2018
  3. Guide to eating for a healthy heart Heart Foundation, NZ
  4. Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA. Sci Rep 5, 7928 (2015) 
  5. Association of docosahexaenoic acid supplementation with Alzheimer disease stage in apolipoprotein E ε4 carriers: a review. 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. Ann Rheum Dis. 2015 Jan;74(1):89-95. 
  7. Kai moana – food from the sea Heart Foundation, NZ

Reviewed by

Katrina Pace is a New Zealand Registered Dietitian. As a freelance nutrition, health and wellness writer she specialises in making complex health concepts easy to understand.
Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr Jeremy Steinberg, FRNZCGP; Katrina Pace, New Zealand Registered Dietitian Last reviewed: 19 Feb 2020