Omega-3: the definitive guide

Omega-3: the definitive guide

Author Miriam Ferrer, PhD Last updated 22nd November 2019

  • Ingredients & Nutrition

Omega-3 fatty acids are a vital part of your diet, with important benefits for your body. Scientists have shown that they help you to maintain your brain, eyes, and cardiovascular system.

It’s no wonder that, along with multivitamins, fish oils containing omega-3 fatty acids are the most popular dietary supplement in the UK. In fact, a quarter of supplement users in the UK are taking a form of omega-3.1

We take a look at why these nutrients are so popular, and how you can make sure that you are getting enough.

  • What is omega-3?
  • How do I know if I'm deficient in omega-3?
  • How can I get enough omega-3?
  • What are the benefits of omega-3?
  • How much omega-3 do I need?
  • Summary

What is omega-3?

Omega-3 is the name for a group of polyunsatured fatty acids which are essential for the proper functioning of the body. The human body cannot create enough of its own omega-3 fatty acids, so they must be obtained from the diet.2

The three main types of omega-3 fatty acids required by humans are eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and alpha-linolenic acid (ALA) – a less potent form synthesized in plants.

EPA and DHA are produced by algae and are found in marine animals further up the food chain that have consumed it, including krill and cod. ALA is found in plant sources, including nuts and seeds like walnuts or chia.

  • DHA is very important in the development of foetuses, infants and children. It is found in high levels in the brain and parts of the eye, and aids in the development of these organs and the immune system. People who don’t get enough when they are young may suffer from conditions caused by poor brain and vision development, including neurological disorders and behavioural problems.2
  • EPA is believed to help lower inflammation, which means it may help to alleviate inflammatory conditions like arthritis and prevent other conditions that have an inflammatory component, like Alzheimer’s. It plays an important role in cardiovascular health thanks to a whole range of different effects, including a reduction in the buildup of plaques inside the blood vessels.2
  • ALA is a short-chain fatty acid found in plants. It is the precursor of DHA and EPA in the body, but recent studies suggest that it might also have an anti-inflammatory function on its own.26

The omega-3 fatty acids play an important role in forming the structures of cell membranes - in fact they are incorporated into the membranes of every cell in the body. Membranes are absolutely essential because they hold the cells together and allow molecules deemed helpful to pass into the cell while keeping out others. They are a source of energy and form signalling molecules called eicosanoids that are important for the cardiovascular, pulmonary, immune and endocrine systems.2

There is also some evidence that increasing the intake of omega-3 fatty acids may help to treat psychological issues, though much more research is needed on the topic.4

How do I know if I’m deficient in omega-3?

The human body cannot create enough omega-3 fatty acids on its own. That means we need to take in all the omega-3 that we need from our diet.

Unfortunately, many modern diets do not include foods that are rich in omega-3s such as oily fish. Instead they contain foods that have higher levels of omega 6 acids. Some research has shown that a higher ratio of omega 6 to omega-3 can increase the risk of becoming overweight or obese.5

Even diets that are thought of as ‘healthy’ can actually contribute to the problem. More and more people are now turning to vegetarian and vegan diets, which can also leave people more at risk of deficiency than the rest of the population because the ALA found in plants is not easily converted to DHA and EPA.6

There are a few signs that you might be deficient in omega-3, although you might not display any symptoms at all. For example, people deficient in fatty acids sometimes develop eczema (dermatitis) or rough skin.

At the more serious end of the spectrum, researchers have noted that severe deficiency is more common in people with psychiatric issues such as depression, bipolar disorder and ADHD.7

It is especially important that children and pregnant women get enough DHA, as it plays an important role in growth and development.

How can I get enough omega-3?

Omega-3 can only be obtained from dietary sources, so it is important to eat foods that are rich in these fatty acids.

Oily fish contain large quantities of long-chain omega-3 fatty acids. For example:

  • Mackerel
  • Salmon
  • Trout
  • Herring
  • Sardines

The NHS recommends eating at least one portion of oily fish a week.8

It also advises eating a portion of non-oily fish. White fish such as cod and haddock contain small quantities of omega-3. Some shellfish like mussels, crabs and oysters are a good source.

ALA is found in nuts, seeds and some vegetables including:

  • Chia seeds
  • Flax seeds
  • Walnuts
  • Spinach
  • Seaweed

Some people don’t like the taste of fish or foods that naturally contain omega-3. Fortunately, there are fortified versions of common foods available for purchase, including eggs, butter and milk.

Food supplements containing omega-3 are another popular option. The most common omega-3 supplement is made of cod liver oil or fish oil, but krill oil is an increasingly popular alternative because it also contains choline, which is important for liver health, and the helpful nutrient astaxanthin.

Vegans might wish to consider a plant-based supplement containing omega-3 extracted from algae.

What are the benefits of omega-3?

Heart and cardiovascular health

Studies have demonstrated that omega-3 fatty acids can help to maintain good cardiovascular health.

A 2018 review found that it may have benefits for heart disease,9 and studies have shown that it is associated with a lower risk of cardiovascular events like heart failure.10,11,12

It is also believed to help reduce the buildup of harmful plaques in the blood vessels that are associated with atherosclerosis.13

The World Health Organisation says there is convincing evidence that replacing other fatty acids in your diet with omega-3s reduces the risk of heart disease and that there is a possibility it can reduce the risk of developing diabetes.14

Many heart and cardiovascular issues are linked to chronic inflammation, so the anti-inflammatory effects of omega-3s are often cited as a reason for its positive effects.15

In addition, obesity is a major risk factor for cardiovascular diseases. There is evidence that taking in more omega 6 fatty acids (found in meat, for example) while decreasing omega-3s actually increases the risk of becoming obese.5

Brain health

Omega-3 fatty acids are very important for brain health. DHA, in particular, contributes to the maintenance of normal brain function.

Studies have shown that omega-3 supplementation can improve memory in older people.16

Other studies suggest that omega-3 supplementation can be used in the treatment of conditions like Parkinson’s and dementia/Alzheimer’s.17 Any benefits might be due to the role of inflammation in these diseases and the anti-inflammatory properties of omega-3 fatty acids.3

However, more studies are needed on the relationship of omega-3 to these conditions.

Psychological health

Researchers at the University of Amsterdam and University of Leiden found that people with depression and anxiety had lower levels of omega-3 in their bodies. Those without the conditions had consistently higher levels.18 Omega-3 supplementation has been suggested as a therapeutic option for the treatment of conditions including depression, schizophrenia, PTSD and ADHD.3

Immune system

Animal studies have shown that omega-3 fatty acids help to modulate immune responses, which could be important for the treatment of autoimmune diseases like arthritis and asthma. However, the evidence for humans is inconclusive at the moment.19

Foetal development

Omega-3 is essential for the proper development of cell membranes, the brain and retinas in the womb.20 omega-3 supplementation during pregnancy has been correlated with proper brain and eye development and normal immune response after birth.21,22

EPA and DHA supplementation may also help mothers to carry children to term. This is important because premature birth is associated with a range of health issues.22,23

How much omega-3 do I need?

The amount of omega-3 you need depends on your age, sex and health, however, there are currently no UK recommendations on how much omega-3 you should consume. The World Health Organisation suggests that adults need 0.25 grams of EPA and DHA per day,14 while the National Institutes of Health (NIH) in the United States suggests 1.6 g of ALA for adult men and 1.1 g of for adult women on top of DHA/EPA. Pregnant or breastfeeding women and babies/children require different amounts.14

The NHS recommends eating at least one portion of oily fish and one of non-oily fish per week. This will contribute to maintaining healthy levels of omega-3s.

It is best to eat a varied diet so that you are incorporating all three kinds of omega-3 (EPA, DHA and ALA) into your diet. If you have a restricted diet it may be a good idea to consider taking a supplement to ensure you get enough.

There are no UK Government recommendations on omega-3 supplements, but the Association of UK Dieticians suggests that if you decide to take them you should look for an omega-3 oil rather than fish liver oil. Children, teenagers and pregnant women should check to make sure the supplement is appropriate for them.25


Omega-3 fatty acids are a vital part of a healthy diet. They help us through our lives, from developing properly in the womb all the way through to adulthood.

Research suggests that they play an important role in a whole range of biological processes, and that they can aid with brain, cardiovascular, psychological and immune health.

Make sure you are getting enough in your diet by following NHS dietary recommendations. You might also like to consider taking a supplement, particularly if you are on a restricted diet or do not enjoy foods that contain large amounts of omega-3.


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