Docosahexaenoic acid (DHA)
|Description||Docosahexaenoic acid (DHA) is a long-chain omega-3 polyunsaturated fatty acid (PUFA); it has 22 carbons in its chain compared to the 18 carbons of alpha-linolenic acid (ALA), its precursor omega-3 fatty acid. Eicosapentaenoic acid (EPA) is the other important long-chain omega-3. Although DHA can be formed in the body through the conversion of ALA, the conversion rate is very limited meaning that we must have a source in our diet to obtain appropriate amounts.|
|Function/ Used for||DHA has many functions in the body including as a significant component of phospholipid cell membranes in cells found throughout the body; DHA is especially concentrated in cells in the retina, brain and sperm.
DHA provides a rich source of energy and is also used to form eicosanoids – signalling molecules used within the cardiovascular, pulmonary, immune and endocrine systems. Eicosanoids formed from omega-3s such as EPA are generally more anti-inflammatory than those formed from omega-6s, meaning they could have an anti-inflammatory effect in the body if consumed in greater amounts.
DHA is needed for maintaining good heart health by contributing to normal heart function and supporting normal blood pressure and blood triglycerides levels1.
DHA is important in infant development, particularly in prematurely born infants1. It is believed to be necessary to early eye and brain development in the foetus and breastfed babies. DHA is also thought to support brain development throughout childhood and to support normal brain function and vision throughout life.These beneficial effects are obtained with a daily intake of1:
• 3g EPA + DHA for normal blood pressure;
• 2g EPA + DHA for blood triglyceride levels;
• 250mg EPA + DHA for normal heart function;
• 250mg DHA for brain function and vision and
• 200mg DHA plus 250mg EPA + DHA for development of brain and eye in the foetus and breastfed babies.
|Intake||The European Food Safety Authority makes recommendations for combined EPA and DHA intake2:
• 250mg of EPA/DHA per day for adults and children over the age of 2;
• 100mg DHA per day for infants and young children aged 7-24 months;
• 100-200mg DHA per day in addition to general adult requirements for pregnant and lactating women from sources such as fish body oils (fish liver oils should be avoided -see ‘use in pregnancy and breastfeeding’).In the UK long-chain omega-3 fatty acid intake has been recommended to increase from 200mg per day to 450g per day; equating to one portion of white and one portion of oily fish per week3.UK average daily intake: Average intake of omega-3 fatty acids as a percentage of dietary energy increases with age from 0.8% for 4–10-year-olds up to 1% in adults (19-64 years of age)3.
|As a supplement||There are currently no UK recommendations for omega-3 supplements and recommendations are to get it from food. However, common supplements providing DHA (and EPA) include cod liver oil and fish oil supplements available as capsules and liquids. It’s also possible to get vegan long-chain omega-3 supplements made from algae oil.
The British Dietetic Association (BDA) advises taking a supplement providing the recommendation for EPA+DHA of 450mg/day4. Some supplements provide doses much greater than this.
Supplements made from fish liver oils also contain other nutrients such as vitamin A so it advised to check how much it’s providing if you’re also taking a vitamin A supplement. The SACN advises that you should have no more than 1500ug of vitamin A from food and supplements combined5. Also see ‘use in pregnancy and breastfeeding’.
People should always check the label for information about a specific product.
|Found in (dietary sources)||Good sources of DHA include oily fish (e.g. salmon, mackerel, trout), fish body and fish liver oil, white fish (e.g. cod, haddock, pollock), algae oil, eggs (particularly from chickens fed an omega-3 enriched diet).|
|Deficiency||A deficiency of omega-3s can cause rough, scaly skin and a red, swollen, itchy rash; however obvious symptoms of deficiency such as this are rare in the UK2.|
|Precautions and contraindications||Patients with blood clotting disorders or those taking anticoagulants such as warfarin should be monitored while taking cod liver oil or other fish oils6.|
|Use in pregnancy and breastfeeding||Cod liver oil or other fish liver oil supplements should not be taken by women who are pregnant or planning a pregnancy because high amounts of vitamin A may be present.
Women who are pregnant or breastfeeding, or likely to become pregnant, and girls who may become pregnant in the future, can safely have up to two portions of oily fish a week.
|Interactions e.g. with other medications||Taking cod liver oil or other fish oils with anticoagulants (such as warfarin), aspirin, dipyridamole (a vasodilator), ginkgo biloba or ginseng, may increase the risk of bleeding. Medical supervision in these cases is required6.|
|Adverse effects||When consumed in amounts consistent with dietary intake DHA is likely very safe. Fish liver oils contain vitamins A and D, fat soluble vitamins that can be toxic when consumed in excessive amounts6.
Reflux or “burping up” of fish oil may occur in some individuals. Take with food to avoid this occurring.
|References||1 EU Community Register of Nutrition and Health Claims
2 EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol. EFSA Journal 2010; 8(3):1461.
3 SACN; Saturated fats and health (2019)
4 British Dietetic Association (BDA); Omega-3: Food Fact Sheet
5 SACN; Advice on Fish Consumption: Benefits and Risk (2004)
6 Mason, P. Dietary Supplements. Pharmaceutical Press, London, 2001.