A study in the Aug. 1 issue of SLEEP suggests that poor sleep consolidation during the first two years of life may be a risk factor for language learning. The longitudinal study involved 1,029 twins from the Quebec Newborn Twin Study.
Sleep consolidation was measured by parental report at 6, 18 and 30 months of age. Language skills were measured with the MacArthur Communicative Development Inventory at 18 and 30 months, and with the Peabody Picture Vocabulary Test at 60 months.
Results show that the day/night sleep ratio decreased significantly from 6 to 30 months of age. Children with language delays at 60 months had less mature sleep consolidation at both 6 and 18 months than children without delays and those with transient early delays.
Genetic analyses found that the sleep ratio at 6 months of age was highly heritable (64%). It also predicted language learning at 18 months and 30 months, mainly through additive genetic influences. At 18 months, the sleep ratio was mainly due to shared environment influences (58%) and predicted language learning at 60 months.