That is the conclusion of a paper published in the British Journal of Developmental Psychology today, Thursday 22 November, by Trine Flensborg-Madsen and Erik Lykke Mortensen from the University of Copenhagen.

Their paper looks at a sample of 938 people from the Copenhagen Perinatal Cohort (CPC). The CPC has followed a group of 9125 people born in the city between 1959 and 1961 through their lives. Between 2009 and 2011, when they were aged around 50, 1698 members of the group completed IQ tests. Flensborg-Madsen and Mortensen’s sample was drawn from those 1698 group members.

The researchers compared the results of those tests with studies made of the same participants when they were young children. They found a significant relationship between the speed with which the participants had reached a number of developmental milestones in childhood and their IQ scores 50 years later.

The strongest associations with IQ in middle age were with reaching the milestones ‘Naming objects/animals in pictures’, ‘Forming a sentence’ and ‘Sharing experiences’ more quickly than other children.

On analysing the results further, the researchers found that milestones related to language explained 6.7 per cent of the variance in midlife IQ, while milestones related to social interaction explained 3.1 per cent.

Trine Flensborg-Madsen said: