Food and Behaviour Research

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A meta-analysis of blood fatty acids in people with learning disorders with particular interest in arachidonic acid

Morse NL (2009) Prostaglandins Leukot Essent Fatty Acids. 81(5-6) 373-89. doi: 10.1016/j.plefa.2009.09.00 

Web URL: View this and related abstracts via PubMed here


Small individual studies report that people with learning disorders have lower than normal blood concentrations of docosahexaenoic acid and arachidonic acid. The origin and consequence of the subnormal docosahexaenoic acid have been much speculated. However, relatively little attention has been paid to the significance of the low arachidonic acid concentration.

Studies were identified through a literature search including subjects with various learning disorders or symptoms thereof and age-matched controls. A meta-analysis of pooled data from the red blood cell and plasma/serum showed that red blood cell arachidonic acid and docosahexanoic acid concentrations were significantly lower than normal [-3.93 and -18.92, respectively (weighted mean difference as a % of weighted mean control)]. Plasma/serum arachidonic acid and docosahexaenoic acid concentrations were also significantly lower than normal [-6.99 and -15.66, respectively (weighted mean difference as a % of weighted mean control)].

However, in absolute amounts the arachidonic acid was as severely depressed as docosahexanoic acid within red blood cells 0.57mg/100mg of fatty acid below normal verses 0.59mg/100mg for docosahexaenoic acid. Plasma/serum arachidonic acid was even lower; 0.71mg/100mg of fatty acid below normal verses 0.34mg/100mg for docosahexaenoic acid.

The origin, consequences and relative importance of subnormal arachidonic acid to brain function bears further investigation.


This study found significantly lower blood concentrations of omega-6 AA, as well as omega-3 DHA, in children with various behaviour and learning disorders compared with controls. This finding was from a meta-analysis combining data from published studies to date (involving over 400 children in total).

Increasing evidence indicates that fatty acid abnormalities can play a role in childhood behaviour and learning difficulties such as ADHD, dyslexia, dyspraxia and autistic spectrum disorders.

In blood fatty acid studies, low concentrations of the long-chain omega-3 fatty acids (EPA and DHA) have most commonly been reported. This is in keeping with the apparent benefits of dietary supplementation with fish oils (which contain these omega-3) shown in some clinical trials of children with these kinds of conditions. However - as this review points out, the most successful trials in this area have also included some omega-6 AA, as well as omega-3 EPA/DHA, in the active treatment formulations.

To date, very little attention has been paid to the potential role of the main omega-6 fatty acid - arachidonic acid (AA) - in child behaviour and learning difficulties.  Like omega-3 DHA, omega-6 AA is a key component of brain and nerve cell membranes, and (like EPA and DHA) it also gives rise to numerous other substances that help to regulate blood flow, hormonal balance, immune function, gene expression and many other aspects of cell signalling in the body and brain.

Modern western-type diets are very rich in the short-chain omega-6 (linoleic acid, or LA), found in vegetable oils. And because this can (at least in theory) be converted within the body to omega-6 AA, it is generally assumed that AA deficiencies are unlikely.  

The low AA levels reported here in children with behaviour and learning difficulties call that assumption into question. 

Individual differences in conversion efficiency, and/or other factors (such increased loss via oxidative stress), may affect dietary needs for AA.  Deficiencies of this key omega-6 have already been implicated in some mental health conditions such as schizophrenia.

In addition to detailed analyses of the blood fatty acid findings to date, this paper also provides a summary of treatment studies in this area, and a comprehensive, detailed review of what is currently known about dietary sources of, and requirements for, arachidonic acid.