Oxford University researchers explained the findings, recently published in the journal PLOS One, at a conference in London on 4 September.

The study was presented at the conference by co-authors Dr Alex Richardson and Professor Paul Montgomery from Oxford University's Centre for Evidence-Based Intervention in the Department of Social Policy and Intervention. It is one of the first to evaluate blood Omega-3 levels in UK schoolchildren. The long-chain Omega-3 fats (EPA and DHA) found in fish, seafood and some algae, are essential for the brain's structure and function as well as for maintaining a healthy heart and immune system. Parents also reported on their child's diet, revealing to the researchers that almost nine out of ten children in the sample ate fish less than twice a week, and nearly one in ten never ate fish at all. The government's guidelines for a healthy diet recommend at least two portions of fish a week. This is because like vitamins, omega-3 fats have to come from our diets -- and although humans can in theory make some EPA and DHA from shorter-chain omega-3 (found in some vegetable oils), research has shown this conversion is not reliable, particularly for DHA, say the researchers.

Blood samples were taken from 493 schoolchildren, aged between seven and nine years, from 74 mainstream schools in Oxfordshire. All of the children were thought to have below-average reading skills, based on national assessments at the age of seven or their teachers' current judgements. Analyses of their blood samples showed that, on average, just under two per cent of the children's total blood fatty acids were Omega-3 DHA (Docosahexaenoic acid) and 0.5 per cent were Omega-3 EPA (Eicosapentaenoic acid), with a total of 2.45 per cent for these long-chain Omega-3 combined. This is below the minimum of 4 per cent recommended by leading scientists to maintain cardiovascular health in adults, with 8-12 per cent regarded as optimal for a healthy heart, the researchers reported.

Co-author Professor Paul Montgomery said: 'From a sample of nearly 500 schoolchildren, we found that levels of Omega-3 fatty acids in the blood significantly predicted a child's behaviour and ability to learn. Higher levels of Omega-3 in the blood, and DHA in particular, were associated with better reading and memory, as well as with fewer behaviour problems as rated by parents and teachers. These results are particularly noteworthy given that we had a restricted range of scores, especially with respect to blood DHA but also for reading ability, as around two-thirds of these children were still reading below their age-level when we assessed them. Although further research is needed, we think it is likely that these findings could be applied generally to schoolchildren throughout the UK.'

Co-author Dr Alex Richardson added: 'The longer term health implications of such low blood Omega-3 levels in children obviously can't be known. But this study suggests that many, if not most UK children, probably aren't getting enough of the long-chain Omega-3 we all need for a healthy brain, heart and immune system. That gives serious cause for concern because we found that lower blood DHA was linked with poorer behaviour and learning in these children. 'Most of the children we studied had blood levels of long-chain Omega-3 that in adults would indicate a high risk of heart disease. This was consistent with their parents' reports that most of them failed to meet current dietary guidelines for fish and seafood intake. Similarly, few took supplements or foods fortified with these Omega-3.'

The current findings build on earlier work by the same researchers, showing that dietary supplementation with Omega-3 DHA improved both reading progress and behaviour in children from the general school population who were behind on their reading. Their previous research has already shown benefits of supplementation with long-chain omega-3 (EPA+DHA) for children with ADHD, Dyspraxia, Dyslexia, and related conditions. The DHA Oxford Learning and Behaviour (DOLAB) Studies have now extended these findings to children from the general school population.

'Technical advances in recent years have enabled the measurement of individual Omega-3 and other fatty acids from fingerstick blood samples. 'These new techniques have been revolutionary -- because in the past, blood samples from a vein were needed for assessing fatty acids, and that has seriously restricted research into the blood Omega-3 status of healthy UK children until now,' said Dr Richardson.

The authors believe these findings may be relevant to the general UK population, as the spread of scores in this sample was within the normal population range for both reading and behaviour. However, they caution that these findings may not apply to more ethnically diverse populations as some genetic differences can affect how Omega-3 fatty acids are metabolised. Most of the children participating in this study were white British.