Oral Session 2
Saturday, April 28, 2018 | 4:00pm-5:30pm | Room 342B
CIRCADIAN RHYTHM DEVELOPMENT DURING THE FIRST YEAR OF AGE – THE CHILD-SLEEP COHORT
Juulia Paavonen (Finland)*
Isabel Morales-Muñoz (Finland)
Tarja Stenberg (Finland)
Pirjo Pölkki (Finland)
Tiina Paunio (Finland)
Anneli Kylliäinen (Finland)
Timo Partonen (Finland)
Outi Saarenpää-Heikkilä (Finland)
Circadian rhythms refer to biological rhythms that have an endogenous period length of approximately 24 hours. The rest-activity rhythms are the most important circadian rhythms humans. The development of the circadian system starts after birth, so that during first two or three months of life, daytime sleep begins to diminish and the longest sleep periods start to accumulate in the night. The aims of the present study were 1) to describe the normative variation in development of sleep-wake rhythm at the ages of 3 and 8 months 2) to assess whether slow development is related to sleep quality either based on parental reports or on actigraph measurements and 3) to evaluate how slow development of sleep-wake rhythm is related to age, gender, and season of birth.
Materials and methods
The study is based on the CHILD-SLEEP birth cohort. We utilised parental questionnaires at the ages of three (N=1427) and eight months (N=1282) and actigraph measurement at eight months (N=343). The study protocol has an approval of the local ethical committee. We excluded infants with significant developmental delays (N=11). The results are based on statistical testing and multivariate modelling.
Three-month-old infants slept an average of 5.1 hours during the day (35.9%), 9.1 hours during the night and 14.2 hours totally, while at 8 months they slept an average of 3.4 hours during
daytime (25.6 %), 9.9 hours during night time and 13.3 hours totally. Slow circadian rhythm development was found in 28.4% at the age of three months and in 14.6% at the age of eight
months. At three months, infants with slow development of circadian rhythms were reported to have less sleep during the night, and more sleep during daytime. More importantly, they also had longer total sleep per 24 hours and longer sleep-onset latency; they also spent longer time awake during the night, and had longer sleep onset latencies after wake-up at night. At eight months, the infants with slow development of circadian rhythm showed expectedly less sleep during the night, and more sleep during daytime. They also had longer total sleep per 24 hours, longer sleep onset latency, longer time awake during night, later bedtime, and later sleep onset.
According to actigraph registrations at the age of 8 months, we obtained that the infants with slow development of circadian rhythm spent less time in bed, had less assumed night sleep,
later sleep start and ending, and less actual night sleep than the infants without slow development of circadian rhythm. In multivariate modelling, we found that sleeping difficulties at three and eight months of age were explained by slow development of circadian rhythm. However, the differences regarding total sleep per 24 hours and bedtime were also explained by season of birth (p=0.042) and gender (p=0.007).
To conclude, infants sleep-wake rhythm development is highly variable. Infants with slower circadian rhythm development have poorer sleep quality as reflected by the parental reports as well as the actigraphs measurement. Intervention studies are needed to find out whether sleep-wake rhythm modifications improve sleep quality in infants with slower sleep-wake development.