Babies given formula milk are noticeably deficient in a particular fatty acid.

Researchers from the Royal Hospital for Sick Children in Glasgow studying the brain tissue of infants who'd died from cot death found that the percentage of docosahexaenoic acid in the brain was "significantly greater" (9.7 per cent) in breastfed babies, compared to those fed formula milk (7.6 per cent).

Docosahexaenoic acid (DHA) is a phospholipid (chemical compound), which makes up about one fourth of brain matter. "Because rapid brain growth and phospholipid incorporation occurs during foetal and early neonatal life, lipid nutrition during pregnancy and early postnatal life may be especially important to subsequent development," said the research team.

In a follow up letter to the study, two researchers from the Institute of Brain Chemistry and Human Nutrition at Hackney Hospital in London concluded that this new data together with other studies comparing cognitive development and visual function, "demonstrate that milk formulae do not match breast milk for optimum neurovisual development."

The study's author, Dr J Farquharson and his colleague, responded to their results by calling for supplementation of formula milks with DHA. However, the Hackney team, represented by Keb Ghebremeskel, said that their own unpublished study shows that DHA in formula milk substantially "inhibits" the conversion of lineoleic acid, causing a marked insufficiency of arachidonic acid, another essential fatty acid (EFA) in the blood.

The Hackney team suggest that the composition of formula milk should more closely imitate that of breast milk with regard to all the EFAs. However, in the same breath they list a few of the ways that human milk can be tailored to order: breast milk contains DHA and arachidonic acid, even when these fatty acids are absent form the mother's diet, and the milk of mothers with preterm infants contains more EFAs than those with full term infants.