In a large randomized trial of human lactation, researchers have found evidence that prolonged breast-feeding is associated with improved scores on some intelligence tests in childhood.

The results, published in the May issue of The Archives of General Psychiatry, appear to confirm those of previous observational studies.

Researchers in Belarus trained 8,457 mother-infant pairs with an extensive breast-feeding educational program, while a control group of 7,856 received standard care. At three months, 73 percent of the trained mothers, but only 60 percent of the controls, were still exclusively breast-feeding. By six months, exclusive breast-feeding had declined substantially in both groups, to 7.9 percent for the education group and 0.6 percent for the controls.

At 6 ½ years, the breast-fed group scored significantly higher on tests of vocabulary, word matching and verbal I.Q., although the differences in several other tests of intelligence were not significant. Teacher ratings of the children were consistently higher for those who were breast-fed.