2.5 Biochemical factors
2.5.1 Highly unsaturated fatty acids
As we saw in Section 1, ‘medical’ approaches to some psychological conditions have focused on biochemistry and the use of corresponding drug treatments. Very little research of this kind has been applied to dyslexia. However, emerging evidence suggests that there may be a biochemical contribution involving abnormal metabolism of highly unsaturated fatty acids (HUFA) – essential substances that play a key role in brain development and the maintenance of normal brain function. In fact, just two fatty acids make up 20 per cent of the brain's dry mass, as they are essential components of the membranes surrounding every cell (and structures within each cell). HUFA are also needed to produce other substances that are crucial for regulating a very wide range of brain and body functions including cell signalling, immune system responses and cardiovascular function.
These essential fatty acids – from the so-called omega-6 and omega-3 series – are found in a wide range of natural foods. However, they are often seriously lacking from modern diets, especially if these are high in saturated fats or processed foods with a high level of artificial fats. In fact, only fish and seafood provide significant quantities of the crucial omega-3 fatty acids. Most of us therefore rely on being able to build our own HUFA from simpler compounds. However, this conversion process may be inefficient in some people, who would therefore have a higher dietary requirement. There is some evidence that this (and/or other inefficiencies in fatty acid metabolism) may be a factor in the biological predisposition to dyslexia, as well as related conditions such as ADHD and dyspraxia (Richardson et al., 1999; Richardson and Ross, 2000).
Fatty acid deficiency leads to minor physical symptoms such as excessive thirst, frequent urination, rough dry skin and hair, and soft or brittle nails. Research has shown that these characteristics are common in children with ADHD, and adults and children with dyslexia. Magnetic resonance (MR) imaging is a safe and non-invasive technique involving the use of radiowaves within a very strong magnetic field. It can be used to obtain either structural images (the well-known MRI) or information on the chemical composition of tissues (magnetic resonance spectroscopy, or MRS). MR brain imaging has also revealed differences in lipid metabolism in dyslexic versus non-dyslexic adults that are consistent with HUFA deficiency, and increased levels of an enzyme that removes HUFA from cell membranes have been reported from blood biochemical studies of dyslexia. If some features of dyslexia and related conditions like ADHD reflect fatty acid deficiency, then supplementing the diet with these fatty acids could be helpful in the management of these conditions. We will return to this in Section 3.