The study, authored by Jacques Montplaisir, MD, of the Sleep Disorders Center at Sacre-Coeur Hospital in Montreal, Quebec, Canada, focused on 1,492 children, who were studied annually from five months of age to six years. A questionnaire, filled out by the children's mothers, measured each child's hyperactivity-impulsivity (HI), inattention and daytime sleepiness scores for each of those years.

Four developmental sleep duration patterns were identified in the study: short persistent (six percent), composed of children sleeping less than 10 hours per night until the age of 6 years; short increasing (4.8 percent), composed of children who slept fewer hours in early childhood but whose sleep duration increased around 41 months of age; 10-hour persistent (50.3 percent), composed of children who slept persistently approximately 10 hours per night; and 11-hour persistent (38.9 percent), composed of children who slept persistently around 11 hours each night.

According to Dr. Montplaisir, the study found no difference in sleep duration between weekdays and weekends, indicating that children were not compensating on the weekend for sleep loss occurring during the week, even in the group of short persistent sleepers. Short increasing sleepers, who had evidence of a nocturnal sleep consolidation problem before the age of 41 months, did not compensate their short nighttime sleep duration by more daytime sleep at 29 months, added Dr. Montplaisir.

The results indicate that a modest but chronic reduction of just one hour of sleep nightly in early childhood can affect the child's cognitive performance at school entry. Short sleep duration multiplied by 3.1 the risk of low performance on the Peabody Picture Vocabulary Test--Revised. This suggests that language acquisition and the consolidation of new words into memory could be significantly impeded by chronically shortened sleep duration throughout childhood, said Dr. Montplaisir.

Low performance on the Block Design subtest was also observed in the short increasing sleep group. This means that, although sleep duration improved at three years of age, the risk of scoring low on the Block Design subtest at six years of age remained more than 2.4 times higher. This finding points to an early critical period for cognitive development that may be jeopardized by short sleep duration, noted Dr. Montplaisir.

The results also demonstrate a significant relationship between high HI scores at six years of age and a short increasing sleep duration pattern. Although sleep duration improved at three years of age, the risk for high HI scores at six years of age remained 3.2 times higher. There is a critical period in early childhood where the lack of sleep is particularly detrimental on various aspects of development even if the sleep duration normalizes later on, warned Dr. Montplaisir.

"The results of this paper highlight the importance of giving a child the opportunity to sleep at least 10 hours a night throughout childhood, especially before the age of three-and-a-half years, to ensure optimal cognitive performance at school entry," said Dr. Montplaisir.

It is recommended that children in pre-school sleep between 11-13 hours a night, and school-aged children between 10-11 hours of sleep a night.

The American Academy of Sleep Medicine (AASM) advises children to follow these steps to get a good night's sleep:

• Follow a consistent bedtime routine.
• Establish a relaxing setting at bedtime.
• Get a full night's sleep every night.
• Avoid foods or drinks that contain caffeine, as well as any medicine that has a stimulant, prior to bedtime.
• Do not go to bed hungry, but don't eat a big meal before bedtime either.
• The bedroom should be quiet, dark and a little bit cool.
• Get up at the same time every morning.

Parents who suspect that their child might be suffering from a sleep disorder are encouraged to consult with their child's pediatrician or a sleep specialist.

The article, entitled, "Associations Between Sleep Duration Patterns and Behavioral/Cognitive Functioning at School Entry",  was published in the September 1 issue of the journal Sleep.

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