The authors of the largest study of its kind believe it has answered sceptics with definitive proof that vitamin and mineral supplements can substantially improve the intelligence of children.

The Anglo American study, of 6l5 teen aged children in four Californian schools, showed that 25 per cent of children on ordinary diets would boost their intelligence by taking supplements.

Forty five per cent of the test children gained at least l5 IQ points in their non verbal tests scores, compared to only 20 per cent of the control group. The children were divided into three groups, with one taking l00 per cent of the US Recommended Daily Allowance, one taking 200 per cent of the RDA, and a third taking a placebo.

The researchers, who included London Professor of of nutrition John Yudkin, and vitamin C champion Professor Linus Pauling in California, found that the most significant improvements were in the children taking the supplement containing l00 per cent of the RDA.

The study backs up the claims of Swansea senior psychology lecturer Dr David Benton who first conducted a similar smaller study and obtained similar results, thereby setting off a medical furore and the scorn of television shows like BBC's Food and Drink.

Dr Yudkin emphasized that the results don't necessarily advocate the use of vitamins so much as demonstrate "that many children are consuming diets that do not completely meet their total needs."

Benton also believes it points up a fundamental flaw in the way that RDAs are calculated.