Going to bed at different times every night curbs children’s brain power and may affect health in adult life, suggests new research using Millennium Cohort Study data.
Researchers at University College London (UCL) looked at whether bedtimes in early childhood were related to brain power in more than 11,000 seven-year-olds. They compared the children’s bedtimes at ages 3, 5 and 7 to their test scores in reading, maths and spatial awareness at seven years.
The UCL study found that both boys and girls with irregular bedtimes at age 3 had lower scores in reading, maths and spatial awareness at age 7.
However, regular bedtimes at age 5 were not associated with poorer brain power in either boys or girls, which suggests that age 3 is a particularly sensitive period for cognitive development.
Girls who had irregular bedtimes at age 7 scored lower in all three test areas than those with regular bedtimes even after taking account of other potentially influential factors, although this pattern did not emerge in seven-year-old boys.
The study revealed that irregular bedtimes were most common at age 3, when around one in five children went to bed at varying times every night. By age 7, more than half of the children went to bed regularly between 7.30 and 8.30pm.
Children whose bedtimes were irregular or who went to bed after 9pm were likely to come from more socially disadvantaged backgrounds.
The findings indicate that the impact of irregular bedtimes is cumulative. Girls who did not have regular bedtimes at either 3, 5 or 7 had significantly lower reading, maths and spatial awareness scores than girls who had consistent bedtimes at all three ages. The impact was the same in boys, but for any two of the three time points.
The researchers point out that irregular bedtimes could disrupt natural body rhythms and cause sleep deprivation, which undermines the plasticity of the brain and the ability to acquire and retain information.
“Sleep is the price we pay for plasticity on the prior day and the investment needed to allow learning fresh the next day,” they said. “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.”
‘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, was published online in the Journal of Epidemiology and Community Health in July 2013.
Professor Amanda Sacker
ESRC International Centre for Lifecourse Studies in Society and Health (ICLS), University College London
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