Relationship between napping pattern and nocturnal sleep among Japanese nursery school children

It has been suggested that the daytime napping patterns of children differ according to racial and cultural backgrounds. The objectives of this study were to describe the daytime nap durations of Japanese nursery school children and to elucidate their relationship to nocturnal bedtimes.

The mothers of 967 children between 0 and 5 years of age recorded sleep logs for 9 consecutive nights. Considering the fact that the subject children were scheduled to take a nap on weekday afternoons, we investigated the proportion of children napping and the relationship between daytime nap duration and nocturnal bedtime on the basis of the data obtained on weekends when children were free from a specific nap schedule.

The percentage of children who habitually took a nap was 100% in those under 1 year old, and the percentages were 96.8%, 81.8%, 53.4%, 28.0%, and 9.0% in 1-, 2-, 3-, 4-, and 5-year-old children, respectively. There were significant relationships between nap duration and bedtime in the corresponding night in 2- to 5-year-old children. The "two hours or more" nap group showed a significantly later bedtime than the "no nap" and the "one hour or more but less than two hours" groups in the 2-year-old children (p<0.01 for both). The "two hours or more" nap group showed a significantly later bedtime than the other groups (p<0.01), and the "one hour or more but less than two hours" nap group showed a significantly later bedtime than the "no nap" group in the 3-year-old children (p<0.05). In the 4- to 5-year-old children, the "one hour or more but less than two hours" and "two hours or more" nap groups showed a significantly later bedtime than the "no nap" group (p<0.01 for both).

Daytime naps naturally become less common after the third birthday among Japanese nursery school children. The longer the nap durations in 2- to 5-year-old children, the later they went to bed on the corresponding night.