The relations between sleep patterns, breastfeeding and early language development A part of the project: StarWords: a study of parental report on words

The project is a part of the StarWords: a study of parental report on words. The current project focuses on the relations between the sleep patterns, breastfeeding and language development of young children. We will investigate whether sleep patterns (consecutive daytime sleeping durations, consecutive nighttime sleeping durations, ratio of consecutive daytime sleeping durations to consecutive nighttime sleeping durations, total length of sleeping) and breastfeeding patterns (whether the child is breastfed at a given age, total length of breastfeeding) are related to the very early language development (emergence of the bubbling, earliest words and multiword utterances, CDI scores) in monolingual and bilingual children. The study has a longitudinal design. The families will be invited to join the study as soon as the children are born (but they will be also allowed to join later until the children are younger than 24 months). The families will be asked to download and use the mobile application developed for the purposes of the StarWords project (see: https://multilada.pl/en/projects/starwords/). In the application, the families will be asked to type in the gestures, words and multiword combinations used by the children. Additionally to the frequent regular reports about the new gestures, words and multiword combinations, the caregivers will be asked to complete MacArthur Communicative Development Inventories (CDIs) when the children are about 16 months old (CDI - Words and Gestures) and when the children are about 26 months old (CDI - Words and Sentences). During the project, each month the families will be asked about the sleep patterns, and once the child is 12 months old, the family will be asked about breastfeeding (and if the child is breastfed at the age of 12 months, they will be asked every three months whether breastfeeding is continued). Previous studies have analysed the effects of breastfeeding and sleep patterns on language (and broader cognitive) development only separately. Generally, breastfeeding has a positive impact on language development, especially in populations under the risk of developing language impairment (see Smith, 2015, for review). In particular, parents of children who were breastfed longer than 3 months were less concerned about their language development, and the effect was particularly pronounced if breastfeeding was longer than 9 months (Dee at al., 2007). The length of breastfeeding was also positively correlated with the likelihood of polysyllabic babbling at the age of 8 months (Vestergaard et al., 1999), as well as with expressive and receptive communication scores at the age of 18 months (Leventakou et al., 2015). Another study showed that even breastfeeding for more than 12 months was beneficial for toddlers' language development (Iqbal et al., 2017). Regarding the sleep patterns, it appears that sleep consolidation is associated with maturation of sleep-wake rhythms. In other words, the day/night sleep duration ratio which is naturally decreasing with child development (i.e. in development children tend to sleep more at night and less during day) may be a good index of sleep maturation (Dionne et al., 2011). It was shown that the day/night sleep duration ratio at the age of 6 and 18 months (but not 30 months) is weakly related to the language outcomes (CDI scores) at the age of 18 and 30 months, and to receptive vocabulary scores at the age of 60 months (Dionne et al., 2011). Dearing et al. 2001 also found positive influence of sleep patterns on language development (comprehension and production). They focused on children’s circadian sleep regulation (rhythms in sleep and wakefulness during the 24 hour cycle) and found that children who were more rhythmic in their sleep at 7 and 19 months had higher mental development scores at 24 months and higher language scores at 36 months. On the other hand, although Dionne et al., 2011, showed that the total number of hours slept has no impact on the language scores (in contrast to the day/night sleep ratio), some studies showed that children who slept less than 10 or 11 hours per day at the age of 29 months presented lower receptive vocabulary scores at the age of 5 years (Touchette et al., 2007). Finally, the sleep patterns and breastfeeding are not independent. At the age of 6 months, breastfed children are more likely to wake up during the night (Galabally et a., 2013), although the total number of slept hours does not necessarily differ between breastfed and non-breastfed infants (Demrici et al., 2012). Another study on 1.5-year-old toddlers showed however that whereas daytime naps induce a longer nighttime sleep, nighttime breastfeeding may decrease the duration of nighttime sleep (Nakagawa et al., 2021). It appears that the relations between breastfeeding, sleep patterns and language development may not be clear: whereas both breastfeeding and longer sleep increase vocabulary scores, breastfeeding may decrease the sleep duration. Also, it has not been studied whether the patterns of the relations across sleeping, breastfeeding and language development are stable or change with child development. This study is related to the StarWords project (full title: “New perspectives on assessing early language development in mono- and bilingual context: a web-based interactive parental report in a longitudinal study”). Dearing, E., McCartney, K., Marshall, N. L., & Warner, R. M. (2001). Parental reports of children’s sleep and wakefulness: Longitudinal associations with cognitive and language outcomes. Infant Behavior and Development, 24(2), 151–170. https://doi.org/10.1016/S0163-6383(01)00074-1 Dee, D. L., Li, R., Lee, L.-C., & Grummer-Strawn, L. M. (2007). Associations Between Breastfeeding Practices and Young Children’s Language and Motor Skill Development. Pediatrics, 119(S92). https://doi.org/10.1542/peds.2006-2089N Demirci, J. R., Braxter, B. J., & Chasens, E. R. (2012). Breastfeeding and short sleep duration in mothers and 6-11-month-old infants. Infant behavior & development, 35(4), 884–886. https://doi.org/10.1016/j.infbeh.2012.06.005 Dionne, G., Touchette, E., Forget-Dubois, N., Petit, D., Tremblay, R. E., Montplaisir, J. Y., & Boivin, M. (2011). Associations Between Sleep-Wake Consolidation and Language Development in Early Childhood: A Longitudinal Twin Study. Sleep, 34(8), 987–995. https://doi.org/10.5665/SLEEP.1148 Galbally, M., Lewis, A. 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