The surprising conclusion is bound to prove controversial, according to the Lancet, which published the research.
But the finding - a spin-off from a study aimed at establishing whether breast-fed babies are likely to be more intelligent - appeared independent of social class, of how many brothers and sisters the children had and of how young the mother was.
The good news from the research - which involved testing the IQ of almost 1,000 men and women is that the long-suggested link between breast- feeding and high IQ does not stand up. "Mothers who cannot or who chose not to breast-feed need no longer worry that their children may be less intelligent," the Lancet said.
But the finding that babies given dummies ended up with lower IQs is more puzzling. Catherine Gale and Dr Christopher Martyn, the study's authors, say there are several possible explanations. Babies willing to take dummies may be slightly less intelligent. Those who took them may have received less stimulation. And dummy-sucking possibly makes babies less interested in their surroundings.
A leading article in the Lancet, however, says other variables are probably at play. The best evidence, it argues, is that "intelligent, loving and caring mothers are likely to have intelligent children, irrespective of how they chose to feed their babies."Reuse content