Nature Versus Nurture in Babies' Sleep

Child sleep influenced mostly by environment in daytime and by genetics in nighttime

(RxWiki News) It can be tough to pick out what influences a child's sleeping patterns. Some of it is probably genetic, and some is probably environmental. The trick is knowing which is which.

A new study recently found that children's daytime sleep appeared to be influenced more by the child's environment.

The child's nighttime patterns, however, appeared to be strongly influenced by genetics.

"Discuss your child's sleep with a pediatrician."

The study, led by Evelyne Touchette, PhD, of the Research Unit on Children’s Psychosocial Maladjustment at Laval University in Québec, Canada, aimed to pick apart the genetic and environmental influences on kids' sleep at different ages.

The researchers studied 995 twins, a little less than half of whom were identical twin pairs while the rest were fraternal (non-identical) twins.

The researchers gathered information on the children's sleeping habits from their mothers when the kids were 6 months, 18 months, 2.5 years and 4 years old.

The researchers then made calculations to estimate how much environmental factors affected the kids' sleep compared to how much their genes affected sleep.

They were able to do this by comparing the sleep pattern differences between identical twins compared to the differences between non-identical twins.

The sleeping patterns studied included how many total hours the children slept and how frequently they fully woke up enough to cry out for their parents or without self-soothing to return to sleep.

The researchers found that the sleeping patterns of children during the daytime, such as naps, were most strongly influenced by their environment.

Meanwhile, children's nighttime sleeping patterns appeared more influenced by their genetics.

The exception was found among children aged 18 months and among children who were getting increasingly less sleep as they got older.

However, only 4.3 percent of the children were in the group who began rapidly losing sleep time. For 73 percent of them, this rapidly decreasing sleep time appeared to be mostly due to environmental factors.

Environmental factors could involve regularity of bedtimes, schedules, lights in the room or similar factors.

Most of the kids (75.7 percent) only gradually decreased their amount of sleep at a normal rate expected for aging.

For about 71 percent of the children who had short sleep at night, the researchers determined this sleeping pattern was predominantly due to genetics.

"This study is the first to show that daytime sleep duration in early childhood is strongly influenced by environmental factors," the authors wrote.

"In contrast, consolidated nighttime sleep duration is largely influenced by genetic factors," they wrote.

However, "at 18 months, it could suggest a good timing for parental interventions on nighttime sleep," the authors added.

"Future studies will be needed to understand which family settings seem to play a role in daytime sleep duration during early childhood," they wrote.

William Kohler, MD, the director of Pediatric Sleep Services at Florida Hospital Tampa and a dailyRx expert, noted that the study's most valuable contribution is to help parents realize that environmental factors do a play a part in how well children sleep.

"The article points out the need to be aware of the environmental and genetic factors involved in sleep, both daytime and nighttime in children," Dr. Kohler said.

"There are some parts of sleep that we cannot change - the genetic aspects - but we can change the environmental ones," he said. "I think we need to practice good sleep hygiene because we are able to influence that aspect of sleep."

Good sleep hygiene includes having a regular bed time, reducing use of artificial light or screen time before bed and waking up at a regular time.

The study was published May 27 in the journal Pediatrics.

The research was funded by the Canadian Institutes of Health Research, Social Sciences and Humanities Research Council of Canada, Canada Research Chair Program, Canadian Institute of Advanced Research, National Health Research and Development Program, Quebec Research Funds (FCAR, FQRSC, and FRSQ), Quebec Ministries of Health, Social Services and Families, Lucie and André Chagnon Foundation, Ste-Justine Hospital, University of Montreal and Laval University.

The authors declared no conflicts of interest.

Review Date: 
May 24, 2013