Short for docosahexaenoic acid, it is one of the most important omega-3 fatty acids needed for optimal health.
The brain is 60% fat, of which DHA is one of the most important components essential for brain and eye function. DHA is also present in every other cell in your body, in the membrane of the tiny structures (mitochondria) that make energy. These are especially concentrated in heart muscle cells.
Why it is important
DHA is a highly unsaturated, long-chain polyunsaturated fatty acid (LCP). In chemical terms, this means there are lots of gaps in its molecular structure where hydrogen atoms are missing. These gaps make DHA very flexible and, when optimum amounts are present in cell membranes, it allows electrical signals to pass more easily from one brain cell to another. Because of its structure, DHA also keeps the membranes surrounding each synapse – the communication gap between two nerve cells – in a more fluid state. This helps nerve cells release chemicals into the gap more quickly, and for the detector sites (receptors) on the other side of the gap to recognise messenger chemicals more readily. Brain cells whose membranes are rich in DHA therefore seem to communicate more quickly with each other.
When DHA is in short supply, other fatty acids – especially saturated fats – are incorporated into the nerve cell membranes instead. As these are more rigid, however, nerve cell membranes become less flexible and less efficient in passing on electrical and chemical messages. As a result, the speed of communication between one brain cell and another is slowed.
Very small amounts of DHA may be made in the body from an essential fatty acid, linolenic acid, but the amount made is probably low and most DHA comes from our diet. DHA is mainly found in animal products such as fish, eggs and meats.
Oily fish, such as mackerel, herring, salmon, trout, sardines, pilchards, are the richest dietary source of EFAs, containing 10 to 100 times more DHA than non-marine food sources such as nuts, seeds, wholegrains and dark green, leafy vegetables. Those who follow a strict vegetarian are most likely to have a low DHA level. The only rich vegetable source of DHA is algae.
People who follow a low fat, low fish diet often also miss out on beneficial LCPs. The fact that intakes are low is illustrated by the finding that average DHA concentrations in the breast milk of British Mothers is only 0.2%, six times lower than that of North American Inuit women (1.2%) who eat plenty of fish. Pure DHA can now be extracted from algae to yield a highly purified form that does not contain other LCPs present in fish – this is ideal as another LCP found in fish (eicosapentaenoic acid, EPA) may not be as suitable for pregnant women. DHA extracted from algae is also free of pollutants that may be present in certain fish oils.
DHA is vital for development of a baby’s eyes and brain, especially during the last three months of pregnancy. DHA makes up 10% – 15% of the weight of a baby’s cerebral cortex. DHA is also concentrated in the light-sensitive cells at the back of a baby’s eyes where it makes up 50% of the weight of each retina. DHA is so important to a developing baby that, during late pregnancy, the placenta extracts it from the mother’s own blood and concentrates them in her baby’s circulation. As a result, a baby’s levels of DHA are twice as high as his mother’s. If maternal levels of DHA are low, some DHA is also obtained from the mother’s richest store – her own brain. This may account for the slight shrinkage (2% – 3%) in maternal brain size seen in some pregnant women, and account for the poor concentration, forgetfulness and vagueness that many women experience during the last few months of pregnancy. A newborn baby is unable to produce DHA from essential fatty acids until he is at least 4 months old. He therefore depends on what he can obtain from breast milk or enriched formulas. Research has shown that, by the age of nine months after birth, babies fed on mother’s milk or a formula milk enriched with LCPs have better visual acuity than those receiving formula that does not contain LCPs.
Recent research suggests the benefits of early LCP enrichment may last into childhood. A group of 6 year olds were asked to find a picture identical to the one they were given among several that were slightly different. While there was no difference in the number of mistakes made, children who had received LCP-enriched formula during the first 4 months of life were able to perform the task more quickly than those not receiving enriched formulas. For example, in a test that took an average of 8 seconds, those who had received LCPs were able to complete it around one and a half seconds faster. Other tests also found that those who had received LCPs as babies were able to perform other mental tasks more quickly, although overall there was no difference in IQ.
DHA and mental performance
In older people, low levels of DHA have been linked with memory loss, mood swings and conditions such as dyslexia, attention deficit hyperactivity disorder and autism. Dyslexia is a common condition in which there is difficulty in learning to read and write plus impaired night vision (dark adaptation), poor peripheral vision and difficulty in processing rapid changes in visual stimulation (eg flicker, motion). Although the exact cause is unknown, it is believed to be linked with deficiency of certain essential fatty acids so that nerve cells in the brain transmit certain information more slowly. Research is under way to see if giving DHA-rich supplements to pregnant women with a family history of dyslexia can help to prevent the condition. Researchers have already found that fatty acid metabolism is abnormal in people with dyslexia, with increased turnover of two lipids – phosphethanolamine and phosphocholine. This may be a genetic difference which is made worse by lack of dietary EFAs and improved by a diet rich in EFAs.
DHA and the heart
DHA is one of the omega-3 fatty acids that makes fish oils so beneficial for heart health. It has beneficial effects on cholesterol and triglyceride levels and may also have beneficial effects on blood pressure and heart rhythm. Ideally we should all eat fish at least twice a week. Sadly, however, because of the levels of pollutants such as mercury, dioxins and PCBs, the Food Standards Agency recently advised that only one of these portions should be oily fish. Taking a fish oil or DHA supplement that is known to have low levels of pollutants is one way to obtain the benefits of a fish-rich diet. Another option is to eat fish that is classed as organic (Currently organic salmon and trout are available).
Recommended daily amounts:
- For adults who obtain some DHA from their diets: 100mg daily.
- For adults who obtain little dietary DHA: 200mg daily (eg vegetarians, those following a low fat diet).
- Breast-feeding: 200mg DHA daily.
- Children: 100mg DHA daily.
Did Einstein’s mother eat fish?
The size of a baby’s brain, and its head circumference are linked to its blood levels of DHA during the first year of life. By the age of nine months after birth, babies fed on mother’s milk (which contains DHA) or formula enriched with DHA seem to have significantly better visual acuity than baby’s receiving formula that does not contain DHA. As a result, most formula milks are now enriched with long-chain polyunsaturated fatty acids.