Language development and intelligence in midlife.

Individual differences in early language skills have been found to be associated with other cognitive outcomes in childhood and adolescence. However, research is limited on whether these associations persist into adulthood. In this study, we examined potential associations of the timing of early language milestones with cognitive ability in a prospective cohort study of 938 singletons from the Copenhagen Perinatal Cohort (CPC), who participated in a 50-year follow-up examination in 2009-2011. Later attainment of a number of milestones was associated with lower midlife IQ with the strongest associations found for 'Naming objects/animals in pictures', 'Forming a sentence', and 'Sharing experiences'. Milestones related to language explained 6.7% of the variance in midlife IQ, while milestones related to social interaction explained 3.1%. The study provides evidence that individual differences in language development during the first years of life are associated with intelligence in midlife. Statement of contribution What is already known on this subject? Differences in early language skills are associated with other cognitive skills in childhood and adolescence. No study has examined this association from childhood through midlife in a large community-based sample. What does this study add? Early language development is associated with intelligence in midlife. A total of 6.7% of the variance in midlife IQ is explained by milestones related to language. Adjustment for potentially confounding factors did not change the associations.