Naps in Children: 6 Months-7 Years

Transcription

1 Sleep, 18(2): American Sleep Disorders AssociatIon and Sleep Research Society Naps in Children: 6 Months-7 Years Marc Weissbluth Northwestern University School of Medicine, Chicago. Illinois. U.S.A. Summary: A cohort of 172 children was followed from 6 months to 7 years of age to determine how nap patterns change with age and whether there was individual stability of nap patterns. Results showed.that there were no differences in nap patterns based on gender, ordinal position, whether nap~ spontaneousl.y dlsappeare.d ~r.were stopped by the parents, and the number of naps at 6 months of. age. To.tal daytlme sle~p rem!med a stable mdlvldual characteristic between 6 and 18 months of age. Age was associated With hours nappmg (r , p < 0.001) and number of naps (r = -2, p < 0.001). A pattern of two naps per day was well estabhshed by 9-12 months. of age and one afternoon nap by months. Th: ~odal du~ation of naps from ~ to 6 years w~s 2 ~ours. ~unng the 3rd and 4th year, napping occurred in the majonty of children, but at decreasmg rates. A mmonty.of children were napping at 5 and 6 years and naps usually disappeared by age 7. Key Words: Naps-Infants-Children. Chronobiological features of daytime sleep/wake rhythms have been studied in different culture~ a~d across species and ages (1). However, for the pedlatnc age group, recent books contain little or no data ~n naps (2,3). Previously published research among children has utilized either a cross-sectional design, gathering data on different age groups at one point in time (4-6) or following one group of children for a relatively short period of time (7-13). One study observed that total sleep duration and the longest single period of sleep were stable individual characteristics, but that study examined three different groups of children at three different age intervals and did not specifically examine nap patterns (14). The purpose of this study was to longitudinally study a single group of children until they stopped napping in order to determine whether nap patterns were stable individual characteristics. Additionally, the study was designed to determine whether nap patterns in children might be associated with gender or ordinal position, and whether there were differences in nap patterns between children who were permitted to outgrow their naps compared with children whose naps were stopped by their parents. Data are presented which would assist clinicians in determining whether an abnormal nap pattern might be considered to be a sleep problem. The data will permit investigators to determine whether the evo- Accepted for publication September Address correspondence and reprint requests to Marc Weissbluth, M.D., 680 North Lake Shore Drive, # 123, Chicago, IL 60611, U.S.A. 82 lution of nap patterns in these children is similar to or different from children of other cultures or social classes. METHODS From September 1, 1984 to April 1, 1986, all consecutively born infants attending a general pediatrician's office (M.W.) were enrolled in the study and examined by the author. None were referred to the author for any problems. They were from white middle and upper-middle class families residing in an urban area. Beginning at the 6-month routine office visit, the parents were asked, "How many naps does your child take?", "Adding up the total time asleep during the day, how many hours does your child sleep?", and if there were no naps, "Did your child naturally stop taking naps or did you not allow, and why did you not allow your child to nap?". These questions were asked at all subsequent routinely scheduled office visits (9 months, 12 months, 15 months, 18 months, 24 months, and annually thereafter). At 21 months, when no office visit was scheduled, each family was contacted by the author. Sleep durations were rounded to the nearest 112 hour. Patients were included in this report if they remained in the pediatric practice at the time when they stopped napping or reached their seventh birthday. Patients were excluded if they left the practice at a time when they were still napping. Of 266 children enrolled in the study at 6 months of age, 172 children (65%) remained in the study until completion.

2 NAPS IN CHILDREN 83 Napping: Number Per Day 2.5 Naps Per Day j_mean NapslDay ~ # Children (N) Mean Naps/Day Std. Dev Minimum Maximum FIG. 1. Number of naps per day by age in months. Age In Months Data on the number of naps, duration of naps, whether the naps stopped spontaneously or were not allowed by the parents ("scheduled"), child's gender and ordinal position were analyzed by the Statistical Package for the Social Sciences computer program for MS WINDOWS Release 5.0. To determine whether or not there was individual stability of nap patterns, five groups of infants based on nap duration were created at 6 months of age. Repeated-measures analysis of variance (ANOV A) using multivariate analysis of variance (MANOV A) was performed to evaluate interactions between duration groups and age. One-way ANOV A was used to compare these five groups based on hours napped at each subsequent age. To determine whether those infants who at 6 months of age had more than two naps per day, when compared with those infants who had only two naps per day, continued to sleep more in terms of more naps or longer nap durations at subsequent ages, one-way AN OVA was performed. ANOV A using repeated measures utilizing MANOV A was performed to evaluate interactions between gender and nap patterns and also between ordinal position and nap patterns. One-way ANOV A was utilized to compare children who naturally stopped napping and children whose parents scheduled naps to stop. This analysis was performed first on all children in the study and second on groups of infants based on nap duration at 6 months of age. Pearson productmoment correlations were computed to determine the relationship between age and number of naps and age and duration of naps. Results are reported as significant ifp < RESULTS Of the 172 children in the study, 96 (56%) were boys and 134 (78%) were firstborn. At 7 years of age, 20 (12%) of children were still napping. Within a few months after their seventh birthday, only four children were still napping. Napping ended naturally in 112 (65%), napping was stopped by the parents in 56 (33%), and was unknown in 4 (2%). No differences were observed with regard to the number of hours napping per day, the number of naps per day or the age when napping stopped (whether natural or scheduled) between boys and girls, between firstborn and subsequent born children, or between infants at 6 months of age who had more than two naps per day compared with those who had two naps per day. Therefore, subsequent analyses were performed on the entire group. In Fig. 1, for Sleep. Vol. 18. No

3 84 M. WEISSBLUTH Percent of Children Taking 1, 2, or 3 Naps Per Day by Age Percent (among those still napping) ~- ----~ IlDay - 2IDay 1@@3IDay IDay 0 3.5' IDay IDay FIG. 2. Age In Months Percent of children taking one, two or three naps per day by age. Percent of those still napping by age in months. ages 3, 4, 5 and 6 years, the mean number of naps per day represents about six, five, four and three naps per week, respectively. Figures 1 and 2 show that at 6 months, infants nap two to three times per day and the third nap disappears by 9-12 months. Between 15 and 24 months, the morning nap disappears. At age 3 years, 92% of children are still napping 6 days per week, and at age 4, the majority of children (57%) are napping 5 days per week. At age 5, 27% of children are napping 4 days per week. Figure 3 shows that at 6 months, the mean number of hours per day napping is 3.5. The range is wide (1-6 hours), however 80% of these infants sleep hours per day, with 5% sleeping <2.5 and 15% sleeping >4 hours per day. At 9 and 12 months, 93% and 94% of infants, respectively, nap between 2 and 4 hours. With increasing age, infants' nap durations were restricted to narrower time frames; for example, at 15, 18,21 and 24 months, 91%, 98%, 97% and 99% ofinfants, respectively, napped -3.5 hours. The mode duration of the single nap from 2 to 6 years is 2 hours. The percent of children who are napping near the mode, -2.5 hours, is 76%, 80% and 80% at age 2, 3 and 4 years, respectively. At ages 5 and 6, most children who are still napping are sleeping 1-2 hours (89% at age 5 and 90% at age 6). Figure 4 shows that at 3 years, parents reported that only 1.8% of these children had stopped napping during their 2nd year. However, during their 3rd and 4th year, 18.5% and 34.5% of the children, respectively, naturally stopped napping. From the data shown in Fig. 5, repeated measures ANOV A using MANOV A showed significant interactions between duration groups and age (F = 1.73, df = 36, p = 0.005). Statistically significant differences were observed between these groups at 9 months (p < 0.001), 12 months (p < 0.001), 15 months (p < 0.05) and 18 months (p < 0.05). At 21 months (p = 0.08) and 24 months (p = 0.07) there is a tendency for children to maintain their initial nap duration pattern. The Pearson product-moment correlation of age by hours of napping was significant (r = -0.73, p < 0.001), as was the correlation of age by number of naps (r = -2, p < 0.001). DISCUSSION Ontogenetic development of sleep processes has matured into a consolidated circadian rhythm of wakefulness and sleep by 6 months of age (15-20). Among infants and children no consistent relationship has been reported between the duration of daytime sleep and

4 NAPS IN CHILDREN Napping: Hours Per Day 4.0 Hours Per Day ~.Mean Naptime # Children (N) Mean Naptime Std. Dev. Minimwn Maximum Age in Months FIG. 3. Number of hours per day spent napping by age in months. Percent of Children Who Stopped Napping By Age Stopped and Natural vs Scheduled* Percent Mo 36Mo 48Mo 60Mo Age Napping Stopped Natural fbi Scheduled... ' ' 72+Mo *These are percents of all children, e.g., 345% of all children stopped napping naturally in their 4th year. FIG. 4. Percent of children who stopped napping by age (months) when napping stopped and natural vs. scheduled end to napping ~..

5 86 M. WEISSBLUTH Napping: By Duration Groups At 6 Months Hours Per Day "'1-2.5 Hrs (Mean).3 Hrs (Mean) +3.5 Hrs (Mean) +4 Hrs (Mean) +> 4 Hrs (Mean) Hrs (Mean) Hrs (Mean) Hrs (Mean) Hrs (Mean) > 4 Hrs (Mean) Age In Months FIG.S. Napping by duration groups at 6 months (hours per day by age in months). Number per duration group = 31 (1-2.5 hours), 40 (3 hours), 41 (3.5 hours), 3S (4 hours) and 2S (>4 hours). nighttime sleep (13,21-24). Thus, it was decided to begin at 6 months and focus on daytime sleep; because of the time constraints imposed by the context of a busy general pediatric office, data were not gathered on night sleep or temporal patterns of sleep. Newborns were enrolled in the study before the publication of the author's parent advice book on sleeping (25); thus, it is unlikely that parents selected the author for pediatric care based on expectations regarding sleeping. Parent education regarding sleep habits has been shown to produce better sleep patterns (26), and advice was given to parents regarding napping based on generally available published information. Therefore, the data may reflect optimum napping. The age-specific decrease for nap duration observed in this survey is the same as previously reported in 1981 and 1927 (27). Other studies of young infants (14), children (17), and adults (1) showed a tendency for individual stability of sleep patterns. Intrasubject stability, despite the intersubject variability, was also observed in this study between 6 and 18 months. Stable age-specific trends and individual stability may reflect biological processes. Finally, the fact that the range of nap duration around the mode is narrow and the mode stays constant from 2 to 6 years despite variation in caretaking and social activities suggests that nap duration in children has a biological basis. Another study reported similar results regarding the ages and percent of children when daily naps stopped: 21f2-3 years (20%), 3-4 years (17%) and 4-5 years (40%) (4). Thus, it appears that naps naturally become less common after the third birthday. Some parents stop their child from napping, but, as a group, their children did not have different nap patterns from those children who naturally outgrew naps. There were three reasons why parents stopped their children from napping. Among 3-6-year-old children, scheduled preschool or school activities conflicted with the nap (60%) and parents of 5-year-olds wanted the child to go to sleep earlier at night (30%) because the children were fighting going to sleep or falling asleep around 9-10 p.m. Stressful events that disorganized home routines, such as death of a parent, divorce, move to a new home or birth of twin siblings, caused an additional 10% of parents to stop a child's napping. Simply having a new sibling was not associated with a change in napping. Furthermore, there were three children between 21f2 and 31/2 years of age who stopped napping for about a year

6 NAPS IN CHILDREN 87 during a period of marital discord or problems with caretakers. After resolution of the conflicts, all three children resumed napping and continued to nap for years. Additionally, there were many other children whose families experienced deaths (including Sudden Infant Death Syndrome), divorces or moves but there were no napping problems. It appears that when parents and caretakers maintain nap routines, despite potentially disruptive stressful events, children continue to nap. REFERENCES 1. Dinges DF, Broughton RJ, eds. Sleep and alertness. Chronobiological, behavioral, and medical aspects of napping. New York: Raven Press, Guilleminault C, ed. Sleep and its disorders in children. New York: Raven Press, Touitou Y, Haus E, eds. Biologic rhythms in clinical and laboratory medicine. Berlin: Springer Verlag, Dales RJ. Afternoon sleep in a group of nursery-school children. J Genet Psychol1941 ;58: Moore T, Ucko Le. Night waking in early infancy. Arch Dis Child 1957;32: Holliday J, Sibbald B, Tooley M. Sleep problems in two-yearolds. Family Practice 1987;4: Wooding AR, Boyd J, Geddis DC. Sleep patterns in New Zealand infants during the first 12 months of life. J Paediatr Child Health 1990;26: Bramford FN, Bannister RP, Benjamin CM, Hillier VF, Word BS, Moore WM. Sleep in the first year of life. Dev Med Child NeuroI1990;32: Wladimirova G. Study of cyclic structure of daytime sleep in normal infants aged 2 to 12 months. Acta Physiol Pharmacol Bulg 1983;9: Traisman AS, Traisman HS, Coatti RA. The well-baby care of 530 infants. A study ofimmunization, feeding, behavioral, and sleep habits. J Pediatr 1966;73: Crowell J, Keener M, Ginsburg N, Anders T. Sleep habits in toddlers months old. JAm Acad Child Adolesc Psychiatry 1987;264: Koch P, Soussignan R, Montagner H. New data on the wakesleep rhythm of children aged from 21h to 41h years. Acta Paediatr Scand 1984;73: Klackenberg G. The development of children in a Swedish urban community. A prospective longitudinal study. VI. The sleep behavior of children up to three years of age. Acta Paediatr Scand 1968;Suppl 187: Jacklin CN, Snow ME, Gahart M, Maccoby EE. Sleep pattern development from 6 through 33 months. J Pediatr Psychol1980; 5: Harper RM, Leake B, Miyahara L, et al. Temporal sequencing in sleep and waking states during the first 6 months oflife. Exp NeuroI1981;72: Coons S, Guilleminault C. Development of sleep-wake patterns and non-rapid eye movement sleep during the first six months of life in normal infants. Pediatrics 1982;69: Hoppenbrowers T, Hodgman J, Arakawa K, Geidel SA, Sterman MB. Sleep and waking states in infancy; normative studies. Sleep 1988;11 : Louis J, Zhang JX, Revol M, Debilly G, Challamel MJ. Ontogenesis of nocturnal organization of sleep spindle: a longitudinal study during the first 6 months oflife. Electroencephalogr Clin NeurophysioI1992;83: Salzarulo P, Fagioli I. Post-natal development of sleep organization in man: speculations on the emergence of the 'S process'. Neurophysiol Clin 1992;22: de Roquefeuil G, Djakovic M, Montagner H. New data on the ontogeny of the child's sleep-wake rhythms. Chronobiollnt 1993; 10: Koch P, Soussignan R, Montagner H. New data on the wakesleep rhythm of children aged from 21h to 41h years. Acta Paediatr Scand 1984;73: Weissbluth M. Sleep duration and infant temperament. J Pediatr 1981;99: Michelsson K, Rinne A, Paajanen S. Crying, feeding and sleeping patterns in I to 12-month-old infants. Child Care Health Dev 1990; 16: Weissbluth M. Sleep duration, temperament, and Connors' ratings of three-year-old children. Dev Behav Pediatr 1984;5: Weissbluth M. Health, sleep habits, happy child. New York: Ballantine, Wolfson A, Lacks P, Futtman A. Effects of parent training on infant sleeping patterns, parents' stress, and perceived parental competence. Clin PsychoI1992;60: Weissbluth M, Poncher J, Given G, Schwab J, Mervis R, Rosenberg M. Sleep duration and television viewing. J Pediatr 1981;99:486-8.