July 8th, 2013
06:35 PM ET
If your children are throwing temper tantrums because sleep seems unappealing, consider that it may be OK to let them stay up a little longer, as long as bedtime happens around the same time every night.
A new study suggests that consistency of young children's bedtime is associated with positive performance on a variety of intellectual tests. The study was published in the Journal of Epidemiology and Community Health.
"If the child prefers to go to sleep a little bit later, but it’s done regularly, that’s still OK for them, according to the evidence," said Amanda Sacker, professor in the Department of Epidemiology and Public Health at University College London.
Researchers looked at information about bedtimes and standardized test scores for more than 11,000 children who were part of the UK Millennium Cohort Study, a nationally representative study of children in the United Kingdom.
The Millennium Cohort Study followed children when they were aged 3, 5 and 7, and included regular surveys and home visits. Researchers asked parents about family routines such as bedtimes.
Children also took standardized tests in math, reading and spatial abilities when they were 7 years old.
Researchers controlled for socioeconomic status in addition to other factors such as discipline strategies, reading to children and breakfast routines.
The study found that, in general, consistent bedtimes were linked to better performance across all subject areas. This was especially true for 7-year-old girls, regardless of socioeconomic background - they tended to do worse on all three intellect measurements if they had irregular bedtimes. Boys in this age group did not show the effect.
In both girls and boys, non-regular bedtimes at age 3 were linked with lower test scores, but not at age 5.
Bedtimes that had never been consistent for girls at ages 3, 5, and 7 were associated with lower scores than regular bedtimes. For any two of these ages, boys also tended to do worse on the tests if they didn't go to sleep at a routine time.
These results "showed that it wasn’t going to bed late that was affecting child’s development, it was the irregular bedtimes that were linked to poorer developmental scores," Sacker said.
Why did girls appear to be more strongly affected by irregular bedtimes than boys? "It might be that girls are more susceptible to elements of the psychosocial environment than boys, and hence also more easily perturbed by inconsistent bedtime schedules," the study authors wrote.
Sacker and colleagues had initially suspected that late bedtimes would also be associated with poor cognitive test performance, but this turned out to not matter, when other factors such as socioeconomic status were controlled for.
Researchers found that, in general, children who had irregular bedtimes or went to bed after 9 p.m. tended to come from lower socioeconomic backgrounds than other study participants. These were the children more likely to be from poor homes and have mothers with poorer mental health. They were also less likely to have breakfast and be read to daily.
The study used a large group of participants but still only draws correlations, not causes. It is not proof that irregular sleep is a direct driver of lower test scores.
Also, information about bedtimes came from parents' self-reporting, and were not independently verified.
Researchers also did not assess the length of sleep that the children typically had. Parents reported on what time their children went to bed or whether there was no regular bedtime, but did not state exactly how much sleep they received.
The answers to the questions of exactly what represents a "regular" bedtime - is it OK to vary lights-out by an hour? A half an hour? - are still unknown.
There are a few possible explanations for the observations in the study. One is that children with an irregular bedtime may not be getting good quality sleep. Also, the body's circadian rhythms can be disrupted when a person doesn't have consistent sleep schedules.
Each day, as environmental stimuli influence changes in the brain, we need sleep to allow fresh learning for the day to come, according to the study. Cognitive impairment and lack of concentration are two possible consequences of limited or disrupted sleep. Given the importance of childhood development, study authors say, low-quality sleep in this critical period could have long-term health effects.
The study supports other research showing that adults also benefit from having consistent bedtimes.
"It not only helps with what’s gone on the day before, but it also sets you in good stead for the day to come," Sacker said.
That makes it worth finding a consistent time to tuck in the little ones - and yourself.
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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.