Shifts in sleep habits, rather than physical changes, may be the first sign that a child is hitting puberty, according to a study published Tuesday.

Puberty is known to be a time of not only bodily change, but also changes in the brain, behavior, emotional regulation and sleep patterns. The thinking has been that the physical developments come before, or around the same time as, the shifts in sleep habits.

“Our study shows that changes in sleep patterns appear earlier than body changes and can be considered as the earliest overt manifestation of puberty,” lead researcher Dr. Avi Sadeh, of Tel Aviv University in Israel, told Reuters Health in an email.

“For parents,” he said, “this means that if your child’s sleep patterns undergo significant changes around these ages your child is likely to show other pubertal changes soon after.”

It also means that parents should be on the lookout for potential sleep-related problems - such excessive daytime sleepiness or problems at school - at a relatively young age.

The study, reported in the journal Sleep, followed 94 children who were between the ages of 9 and 11 at the outset. The children were assessed three times over two years, which included wearing a wrist device that monitored their sleep patterns over one week.

Over time, the researchers found, the children started falling asleep later - by an average of 50 minutes - and sleeping less, with nightly sleep time falling by an average of 37 minutes. Some children also started to wake up more often during the night.

All of those sleep changes, the study found, generally predicted the beginnings of the physical changes of puberty. The reverse was not true, however.

According to Sadeh, sleep changes like the ones seen in this study - falling asleep later, more-fragmented sleep and less sleep overall - can affect kids’ behavior and ability to function during the day.

“From other studies we know that dramatic sleep changes at this age period are often also associated with excessive daytime sleepiness and compromised emotional, cognitive and academic functioning,” Sadeh said.

“Therefore, parents should be aware of the risks, and try to maintain some level of supervision to prevent development of chaotic sleep patterns which may exacerbate the problems,” added Sadeh.

Experts generally recommend that adolescents get nine hours of sleep each night. To achieve that, the American Academy of Sleep Medicine recommends that kids maintain a consistent bedtime routine, avoid sleeping in on weekends, and not read, watch TV or talk on the phone while in bed.

SOURCE: Sleep, December 1, 2009.