Young children without consistent bedtimes in early childhood score lower on tests of intellectual performance at age 7, which may affect their health and wellbeing later in life, U.K. researchers said.
Children who went to bed at different times on school nights when they were 3, 5 and 7 years old did worse on tests of reading, math and spatial ability when they reached 7, the researchers at University College London wrote in a study published in the Journal of Epidemiology and Community Health. The findings were adjusted for factors such as socioeconomic status, and the effect didn’t differ for children in families with one or two working parents.
“It could be that consistent schedules are good for the patterns the body needs to establish,” Amanda Sacker, one of the authors and a professor in the epidemiology and public health department at University College London, said in a phone interview. “An irregular bedtime might mean that children are getting more sleep deprivation than children who go to bed at a regular time.”
The researchers said their study suggests age 3 may be a sensitive period and that the effects seem to build up over time.
The study analyzed data on bedtimes and test scores from 11,178 7-year-old children born from September 2000 to January 2002 who participated in the U.K. Millennium Cohort Study. When they were 3, 5 or 7, the children’s mothers were asked whether they always, usually, sometimes or never went to bed at a regular time.
Irregular bedtimes were most common at age 3, when almost 20 percent of children went to bed at inconsistent times, compared to less than 10 percent of the older children. Non-regular bedtimes at age 3 were associated with lower reading, math and spatial ability test scores.
At age 5, non-regular bedtimes were only linked to lower reading scores in girls and lower math scores in boys. Girls who never had consistent bedtimes at any age had significantly lower scores on all three tests, as did boys who didn’t have regular bedtimes at any two of the three ages.
“It seems to be additive as well,” Sacker said. “If you can’t get a schedule going by age 3, if you manage to get a regular routine by the time they start school at 5, that will still have positive effects.”
The study found that irregular bedtimes had more impact on girls than on boys. Sacker said it didn’t explain the reasons for the difference, which may be related to girls being more affected by psychosocial factors in their lives.
Previous studies have been smaller and haven’t followed children for as long a period, the authors said. Still, their findings echo several reports that linked inconsistent sleep with poor later cognitive performance in children.
“Previous research suggests all learning builds on previous learning,” Sacker said. “It’s more likely that children who aren’t doing well in early childhood will have more trouble catching up. There is a concern that this can have long-term implications.”
The UCL study’s findings may have been affected by missing test score data for 7 percent to 8 percent of participants, reports coming directly from parents rather than independent sources and the unavailability of data on bedtimes at weekends.
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