Nighttime Sleep

Study reports that the duration of infant nighttime sleep is most affected by long nap duration and the time of day the nap ends.


Sleep is undeniably critical to the optimal health and development of a child in the first 5 years of their life. The basic sleep structure of children is established at approximately one and a half years of age and remains similar until they are five, characterized by afternoon naps that eventually give way to a sleep pattern where they sleep only at night. Previous studies have demonstrated that nighttime sleep quality deteriorates when children nap for a long time during the day. However, these studies have been based mainly on parent reports and not independent, physiological measurements of sleep behaviours. A research group from Japan examined the daytime napping patterns of infants and nocturnal sleep-wake patterns using actigraphy to determine what napping factors affect sleep quality at night.

Fifty 1.5 year old infants from full-term pregnancies and without physical or mental disabilities participated in the study. Activity and sleep levels were measured using actigraphy, a technique that uses a miniature accelerometer to record continuous movement. Actigraphs were attached to each child’s waist with an elastic belt for 7 consecutive days. Parents kept a sleep diary for the duration, noting the time of nap, going in/out of bed, bathings, and night awakenings of which they were aware.

The average nap time of infants in this study was 1 hour, 55 minutes (± 48 minutes). Actigraphic data demonstrated that two significant napping factors affected the nighttime sleep of infants – nap duration and nap-end time. Long daytime naps that cause infants to go to sleep later at night are already well documented based on parent questionnaires from previous studies. A novel finding of the study was that infant nighttime sleep duration was positively correlated with later nap-ending time, or naps that finish later in the day. This observation suggests that parents should have their infant nap early in the afternoon.

To further strengthen their results, the researchers of this study can opt to repeat the same experiment with a larger sample size, and conduct a random control trial where children are exposed to different nap durations. Overall, however, the study supports the strategy of controlled-duration naps starting in the early afternoon for infants to maximize the amount of nighttime sleep.




Written By: Fiona Wong, PhD

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