The research, by Dundee University team, indicates that infants who are not breast fed might need supplements of long-chain polyunsaturated fatty acids (LCPUFA). One source would be the old favourite, cod liver oil - which is particularly rich in such acids.
Many commercial infant formulas do not contain LCPUFA, according to Dr Peter Willatts, the psychologist at Dundee who led the research, published tomorrow in The Lancet.
LCPUFA, that occur in foods such as fish oils, eggs and vegetable oils, are known to be important for visual and brain development: rats brought up on a diet which lacks the necessary components for their bodies to make LCPUFA, have learning impairments.
However, although those fatty acids are known to be present in breast milk, they have been omitted from almost all infant formul as it was thought babies could synthesize enough from fatty acids already in the body. The few feeding formul that include these fatty acids say so in accompanying leaflets.
Dr Willatts led a research team that tested the effect of including or excluding LCPUFA on 44 infants. From birth, 21 were given LCPUFA while the rest got a formula without it, until both were four months, when they were weaned. At 10 months their thinking was assessed, using a three-step problem which they had to solve to find and retrieve a hidden toy.
Dr Willatts' team found the LCPUFA babies scored significantly higher. One reason may be that accumulating LCPUFA in the cell membranes of the central nervous system speeds up information processing.
"People have been arguing about whether formula should contain LCPUFA for about 20 years," said Dr Willatts yesterday. "But it's only in the past 10 years that proper research has been carried out.
"There were some early suggestions from the United States that including it could lead to language problems, but we didn't find that in our tests."
By the time infants are about six months old and eating solids, babies can synthesize the fatty acids from their foods.
"We don't know what the long-term effects could be," he said. "It may be that this is just a short-term gain." He is continuing the study with children up to the age of five, but says it could take "a couple of years" for the results to emerge.
As for the cod liver oil as a source of LCPUFA, Dr Willatts says: "It's revolting, but it might turn out that this really is one good reason for feeding it to your child."