Sleep is essential for infant's cognitive, motor and comportamental development. The hypothalamus' suprachiasmatic nucleus is responsible for the generation of several circadian rhythms including the synthesis of the hormone melatonin, variations in temperature and sleep-wake transition that undergo external interferences such as dark-light cycle. Melatonin, wich is synthesized and released at night time, acts like an important transducer of photic information for the organism. Infants up to 12th week of life did not properly establish the circadian rhythm of melatonin and, consequently, there is still no synchronization of the sleep-wake cycle. Breastfeeding acts in order to establish infant's circadian rhythms through melatonin's passage from breast milk, since melatonin production starts at about 3 to 5 months of age, thus can have a positive impact on infant sleep patterns and, consequently, positive effects on child development. Considering that sleep disorders are among the most prevalent childhood problems, including the range around 12 months of age, and that when early detected and treated the developmental consequences that such disorders cause can be minimized, it is important to characterize the main sleep problems in this population and their relationship with the breastfeeding method and with the daytime and nighttime melatonin contents. The objectives of the present study are (1) assess sleep quality through the Brief Screening Questionnaire for Infant Sleep Problems (BISQ), (2) assess the presence of melatonin day/night content variation by salivary melatonin dosage in full-term infants born at 12 months of age - of both genders, randomly recruited from child care centers (3) investigate the correlation between sleep quality, the presence melatonin content day/night variation and breastfeeding method received by these children up to 6 months of age (exclusively breastfed and predominantly non-breastfed). It is hypothesized that there are better sleep patterns and the melatonin day/night rhythm establishment in children who are exclusively breastfed compared to those who have not been exclusively breastfed.
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