MONDAY, May 27 (HealthDay News) -- A new study of twins suggests
that genes may play a big role in how long babies and toddlers
sleep at night, while environment is key during nap time.
Researchers found that among nearly 1,000 twins they followed to
age 4, genes seemed to explain much of the difference among
youngsters' nighttime sleep habits. In contrast, napping seemed
mainly dependent on the environmental setting -- especially for
toddlers and preschoolers.
So does this mean the amount of sleep your little one gets at
night is out of your control?
No, said the lead researcher on the study, which was published
online May 27 in the journal
"[Parents] should not give up on trying to correct inadequate sleep duration or bad sleep habits early in childhood," said Evelyne Touchette, of Laval University in Quebec, Canada.
For one, the study found that environment did matter in babies'
and toddlers' nighttime sleep -- and even seemed to overshadow
genes by the age of 18 months.
The reasons for the findings are unclear, Touchette said. But
she said it makes sense that environment would matter more at the
age of 18 months versus 6 months, when the maturation of the brain
may be key in infants' ability to sleep for longer stretches at
There's no clear explanation, though, for why genetic influences
became stronger again after the age of 18 months, Touchette
A sleep researcher not involved in the study said it's not
really possible to break down children's sleep into "nature or
"Everything is a complex interaction between genes and environment," said Hawley Montgomery-Downs, an associate professor of psychology at West Virginia University in Morgantown.
It's not possible, she said, to parse out what proportion of
young children's sleep duration is due to genes, and what
proportion is environment.
For the study, Touchette's team followed nearly 1,000 Canadian
twins whose mothers reported on their sleep habits from the ages of
6 months through 4 years. About 400 children were identical twins,
which means both twins share all of the same genes; the rest were
fraternal twins, who are no more genetically similar than non-twin
In general, such studies can help researchers sort out the
influences of genes versus "shared environment," which could
include anything from a mom's diet during pregnancy to family
When it came to hours slept at night, genes seemed to explain
more than half of the variance among children at the ages of 30
months and 4 years. Genes were nearly as important at the age of 6
The exception was the age of 18 months, when environment seemed
to account for about half of the variance among the children.
As for napping, environment became a bigger influence as kids
got older, explaining most of the differences in children's habits
by age 4, Touchette said.
What can parents take away from all of this? "We've still got a
lot to learn about children's sleep," Montgomery-Downs said.
For many parents, bedtime is anything but peaceful. Getting your
child to settle down and fall asleep may be a battle, and then
there are the questions: How much sleep is enough? Is your child
waking up too often at night? Is he napping too much or too
There are no clear-cut answers, Montgomery-Downs said.
Experts have tried to come up with some general advice, based on
what's typical for young children. According to the National Sleep
Foundation, babies aged 3 months to 11 months sleep for an average
of nine to 12 hours at night (total, not straight through), and
take one to four naps during the day -- fewer as they approach 1
year. The average toddler gets about 12 to 14 hours of sleep over
24 hours, with most taking at least one daytime nap.
But that doesn't mean parents should worry if their child gets a
little less sleep than that, or is stubborn about napping,
Montgomery-Downs said. "Just because most kids average a certain
amount of sleep doesn't mean that's the 'normal' amount," she
"We know that with adults, there's a lot of individual variation in how much sleep a person needs," Montgomery-Downs said. So children, too, may vary in how much sleep is enough, she said. But the research isn't there to know for sure.
There are things parents can do to help their little ones sleep
at night, Touchette said. In one study, her team found that
5-month-olds were less likely to sleep for six straight hours at
night when their parents fed them each time they woke.
Staying with your child until he falls asleep and picking him up
each time he fusses are not good ideas, either, Touchette said.
Setting routines, including a consistent bedtime and a soothing
activity such as reading a story, is important, Montgomery-Downs
Many parents try to keep their toddler awake during the day,
thinking that will help them fall asleep at night. But that can
backfire, she said, since overly tired kids may become irritable or
hyperactive. "We know that nap deprivation is not good," she
If your child refuses to nap, however, you can't force him,
Montgomery-Downs said. For a 3-year-old, it may signal that he's
outgrown his need for an afternoon snooze. And the general rules
are the same as for bedtime: Set up a consistent, quiet sleep
environment and see what happens.
The National Sleep Foundation has
sleep tipsfor parents.
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