Fish-oil capsules are to be given to children with learning and behavioural problems in a new study starting today to test if the supplement improves their condition.

A group of 38 pupils aged 10 to 16 at the Eaton Hall Special School in Norwich will be given the supplement daily for six months.

Children at the specialist school suffer from a range of conditions such as attention deficit disorder (ADD), attention deficit hyperactivity disorder (ADHD), autism, dyslexia and Asperger's syndrome.

Omega-3 fish oil - rich in fatty acids that help the brain send messages between cells - has been shown to improve memory, mood and concentration in previous studies.

Sales of cod-liver oil supplements, which are rich in vitamin A, D and omega-3, have soared in the past couple of weeks after an influential report in the US said recently that increased doses of vitamin D could reduce the chances of cancer.

The study by Durham County Council will also test if the fish-oil supplement could reduce the side effects of drugs already taken by some of the children. Drugs such as Ritalin, are used to treat ADD and ADHD but can lead to decreased appetite and insomnia.

Lianne Quantrill, project co-ordinator at Eaton Hall Special School, said: "There is already mounting evidence to suggest that there are benefits of taking omega-3 fish oils, particularly for those with behavioural problems who may already have fatty acid deficiencies. This trial will be a chance to look in detail at the effect on a particular group of children with special needs."

A study last year by Durham County Council found that adding a combination of omega-3 fish oil and omega-6 evening primrose oil improved the behaviour of unruly children.

Experts tracked 65 pupils in three childcare centres who were given the supplements for five months.