A different rhythm of life: sleep patterns in the first four years of life and associated socio-demographic characteristics in a large Brazilian birth cohort.

Background: Sleep is an important marker of healthy development and has been associated with emotional, behavioral and cognitive development. There is limited longitudinal data on children’s sleep with only few reports from low and middle income countries (LMIC). We investigate sleep parameters and associated socio-demographic characteristics in a population-based longitudinal study in Pelotas, Brazil. Methods: Data from the Pelotas 2004 Birth Cohort were used (n=3,842). Infant sleep was collected through maternal report at 3, 12, 24 and 48 months: sleep duration, bed and wake time, nighttime awakenings, co-sleeping and sleep disturbances (24 & 48 months). Findings: Compared to children in high income countries (HIC), children in Brazil show a substantial shift in rhythms with later bed and wake times by approximately 2 hours. These remain stable throughout the first four years of life. This population also shows high levels of co-sleeping which remain stable throughout (49.0-52.2%). Later bedtime was associated with higher maternal education and family income. Higher rates of co-sleeping were seen in families with lower income and maternal education and for children who were breastfed. All other sleep parameters was broadly similar to data previously reported from HIC. Interpretation: The shift in biological rhythms in this representative community sample of children in Brazil, challenges our understanding of optimal sleep routine and recommendations.