Without this essential fatty acid, human life is hardly possible. DHA is abundant in neural tissues, important in terms of cognitive and visual function, and forms an integral part of the membranes of all the body's cells - including the cells of the brain.
If you're still not eating fish at least two times a week, read on. This article might convince you to stock up on the tuna and book that long overdue fishing trip.
Fatty acids explained
Let's first gloss over the basics:
Essential fatty acids (EFAs) are classified into two groups: the omega-3 fatty acids and the omega-6 fatty acids. These fats all fall into the category of long-chain polyunsaturated fatty acids, or PUFAs (vs. saturated and monounsaturated fatty acids).
While both the omega-3s and the omega-6s need to be included in the diet, we tend to eat more omega-6 fatty acids, and less omega-3 fatty acids, than we should. So, the general recommendation is to try to include more omega-3 fatty acids in the diet.
There are basically three omega-3 fatty acids to take note of: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and DHA.
Flaxseed is the richest source of ALA, which can be converted in the body to EPA and DHA. Fatty marine fish, such as salmon, tuna and mackerel, are rich in the omega-3 fatty acids EPA and DHA.
Although the brain needs a constant supply of EFAs throughout life, the two most sensitive periods are infancy and ageing.
Fatty acids and child development
A study conducted in 1992 reported that breastfed children had an 8,3 percent advantage in terms of IQ when they reached the ages of seven and eight.
This made researchers start to think that breastfeeding might have an impact on cognitive ability. They also started to wonder whether the omega-3 fatty acids in breast milk could be linked to this phenomenon.
More research followed and other positive results emerged.
Research showed that maternal omega-3 intake was critical for the development of the growing foetus and a landmark UK study indicated that Britain's mental health crisis could be tied to a 50-year decline in fish consumption.
A local study, conducted by the MRC, pointed to the importance of supplementing the diet with DHA prior to conception and during pregnancy. The study showed that a child born to a mother with a good DHA status is more advanced in terms of cognitive development at 18 months.
Research conducted in 2003 by the University of Stellenbosch showed that a fish flour-based spread, served with bread, possibly affected the learning and memory abilities of the primary-school children who participated in the study.
Fatty acids, ageing and dementia
From the above, it's clear that EFAs play an important role early in life. But dietary intake of these fatty acids also becomes increasingly important as we get older.
As we age, essential fatty acid deficiency can accelerate mental deterioration, according to Prof Nola Dippenaar, founder and owner of Health Insight, a company that consults to companies and individuals on the physiology and biochemistry of the human body.
"EFAs play a significant role in brain structure by determining membrane fluidity, while also contributing significantly to brain function," Dippenaar says.
She emphasises the fact that cell membranes aren't structures, but liquids, and that greater fluidity of the membranes improves the function of cells – also in the brain. This fluidity is thanks to the fatty acids that are incorporated in the cell membranes.
Although the brain has the ability to produce some of the long-chain polyunsaturated fatty acids (PUFAs) by itself, this process is limited and becomes even more limited as we age. So, as we grow older, more of these fatty acids should come from the diet.
The age-related decrease in the brain's essential fatty acid levels affects different parts of the brain in different ways. Unfortunately, the areas involved in memory and learning seem to be the first to suffer.
In terms of cell-membrane composition, the brain's cells respond to the omega-6 and omega-3 polyunsaturated fatty acid levels in the diet. The cells are particularly sensitive to the omega-3/omega-6 ratio.
Experts agree that by ensuring an adequate intake of the PUFAs as we age, the onset of neurodegenerative diseases, such as Alzheimer's disease, can possibly be delayed or even prevented.
Researchers have found that DHA, the fatty acid found in fish, has a particularly important role to play in terms of memory, giving us another good reason to ensure the adequate intake of this food throughout life.
Researchers found that among nearly 15 000 older adults living in China, India or one of five Latin American countries, the odds of having dementia generally declined as fish consumption rose.
Worldwide, 24 million people are affected by dementia, of which Alzheimer's disease is the most common form.
Mahan, L.K., Escott-Stump, S. (2000) Krause's Food, Nutrition & Diet Therapy: 10th Edition. W.B. Saunders.
Presentation by Dr Marius Smuts and others at the 21s Biennial Nutrition Congress of the Nutrition Society of South Africa, Port Elizabeth, September 2006.