Irregular bedtimes during early childhood are linked to lower cognitive performance, a large longitudinal UK study finds.
Researchers from the ESRC International Centre for Lifecourse Studies in Society and Health at University College London examined whether the time and regularity of bedtimes in early childhood are associated with intellectual performance at age seven. Given the well-established importance of early development for later health and wellbeing, the authors warn these sleep-related differences could have lasting consequences across the life course.
The analysis used data from more than 11,000 seven-year-old children who took part in the Millennium Cohort Study (MCS), a nationally representative longitudinal study of children born in the UK between September 2000 and January 2002. Information was collected during home visits and surveys when the children were aged 3, 5 and 7, including questions about family routines and bedtimes.
The study assessed cognitive performance using validated tests of reading, mathematics and spatial awareness. The researchers looked not only at whether bedtime timing mattered, but also whether consistency across ages 3, 5 and 7 made a difference, and whether any specific age represented a particularly sensitive period for cognitive development.
Key patterns emerged. Irregular bedtimes were most common at age 3, when about one in five children experienced varying sleep schedules. By age 7, a majority of children typically went to bed between 7:30 and 8:30 pm. The analysis also found that children who had irregular bedtimes or who regularly went to bed after 9 pm were more likely to come from socially disadvantaged backgrounds.
When the children were assessed at age 7, girls who had experienced irregular bedtimes scored lower on all three cognitive measures even after adjusting for a range of potentially influential factors. The same strong association across all three test domains was not observed for boys at age 7. However, irregular bedtimes at age 3 were linked to lower reading, maths and spatial awareness scores for both boys and girls, which suggests that around three years old may be a particularly sensitive developmental window.
The effects also appeared cumulative. Girls who never had regular bedtimes at ages 3, 5 and 7 showed significantly lower scores in reading, mathematics and spatial awareness compared with girls who maintained consistent bedtimes across those ages. For boys, similar cumulative effects were evident when irregular bedtimes occurred at any two of the three assessment points.
The authors propose plausible mechanisms: irregular sleep schedules can disrupt circadian rhythms and reduce overall sleep quantity or quality. Reduced or fragmented sleep may impair brain plasticity, weakening the processes necessary to consolidate learning and to retain new information. Disrupted sleep at key early stages of development could therefore undermine the building blocks of later cognitive and educational attainment.
Professor Amanda Sacker, Director of the ESRC International Centre for Lifecourse Studies in Society and Health at UCL and senior author of the study, commented: “Sleep is the price we pay for plasticity on the prior day and the investment needed to allow learning fresh the next day. Early child development has profound influences on health and wellbeing across the life course. Therefore, reduced or disrupted sleep, especially if it occurs at key times in development, could have important impacts on health throughout life.”
Notes about this research
The study is published online in the Journal of Epidemiology and Community Health. Contact: Media Relations Office – University College London. Source: UCL press release. Image: painting of a sleeping baby credited to Tojetti, Virgilio (1851–1901) and released into the public domain by Boston Public Library. Original research: “Time for bed: associations with cognitive performance in 7-year-old children: a longitudinal population-based study” by Yvonne Kelly, John Kelly and Amanda Sacker, Journal of Epidemiology and Community Health. Published online July 8, 2013 (doi:10.1136/jech-2012-202024).