A guide to fish oil supplements

A guide to fish oil supplements

Does your desire to maintain brain, joint and heart health have you reaching for the fish oil capsules? Healthy Food Guide looks at the evidence behind these popular supplements.

The long-chain omega-3 oils found in fish have been linked to better heart health as well as improving memory and learning. Results from research show that it’s the omega-3 in fish eaten one to two times a week that has a positive effect on our cardiovascular risk.

Living in New Zealand we’re lucky to have easy access to good quality omega-3 packed seafood. But many of us still aren’t getting the recommended 430mg for women or 610mg for men of long-chain omega-3 daily. Taking a fish oil supplement may be a simple way to make sure we’re really getting enough.

The two main fatty acids found in fish oils are eicosapentanoic acid (EPA) and docosahexanoic acid (DHA). On the labels of fish oil supplements, you’ll see the total amount of omega-3 as well the amounts of EPA and DHA within that total. Some fish oil supplements also contain high levels of vitamin A, rosemary oil, vitamin E or flavourings. It’s worth remembering the upper limit for vitamin A for adults is 3000mcg daily. More than this can cause harm, so check the bottle to see how much you’re getting.

Evidence for …

Cardiovascular health

Current research indicates taking an omega-3 supplement doesn’t prevent heart attacks but there may be some benefit to your health if you’ve already had one. Also, fish oil supplements have been shown to reduce blood pressure, inflammation and triglyceride levels – all of which contribute to cardiovascular risk.


The anti-inflammatory effects of fish oils have been investigated in the management of pain in people with arthritis. While little effect was seen in people with osteoarthritis, taking daily 2600mg fish oil supplements may help reduce pain in people with rheumatoid arthritis.


Research on the use of fish oil supplements in Alzheimer’s disease has given mixed results. Taking 1000mg fish oil supplements in early stages of Alzheimer’s disease, or age-related memory problems, seems to be more successful at helping prolong memory than taking them later.
In children with ADHD, one of the fatty acids in fish oil, EPA, given at high doses (500mg+) daily, may help reduce symptoms and improve reading scores.

Too much fish oil

Taking high doses of fish oil can increase your risk of:

  • bleeding
  • low blood pressure
  • diarrhoea
  • reflux
  • vitamin A toxicity (if vitamin A is in your supplement too).


A 2015 study found 83 per cent of the New Zealand fish oil supplements tested were oxidised (rancid) and the amounts of EPA and DHA were considerably less than the amount on the label. The Ministry for Primary Industries then did a risk assessment, finding no evidence of food safety concerns when following recommended dose instructions and noting that fish oils will naturally oxidise over time.

What to look for in supplements

  • Added natural antioxidant such as vitamin E or rosemary oil
  • Sustainably and locally farmed fish
  • Concentrated fish oil if high doses are needed
  • If using to help focus, the amount of EPA should be 500mg+
  • Aim to purchase the freshest oil you can. This may mean shopping where the turnover is higher or where the product will be handled with care, although this may be easier said than done.

Think twice

Check with your GP before starting fish oil if you’re taking medications to lower blood pressure or blood thinners, such as warfarin.

Pregnant women need to avoid fish oil with vitamin A.

First published: Dec 2018

Article sources and references


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