RESUMO
BACKGROUND: The relationship between infant colic and breast milk beta-endorphin (BE) and relaxin-2 (RLX-2) has not been studied before. METHODS: Thirty colic infants and their mothers constituted the study group, and the same sex, similar age and healthy infants and their mothers formed the control group. Maternal predisposing factors were analysed with questionnaires. RESULTS: The frequency of headache and myalgia in the mothers was significantly higher in the study group compared to the control group. Sleep quality of mothers in the study group was worse than in the control group (p = 0.028). While breast milk RLX-2 level in the study group was not different from the control group, breast milk BE level in the study group was significantly higher than the control group (p = 0.039). A positive correlation was found between breast milk BE levels and crying times, and between sleep quality scores and crying times. Headache, myalgia, sleep quality and breast milk BE levels were found to have a significant effect on infant colic. CONCLUSIONS: Breast milk RLX-2 has no role on infant colic. Breast milk BE may act as a biological mediator in transmitting of maternal predisposing factors such as poor sleep quality, headache and myalgia from mother to infant. IMPACT: The relationship between infant colic and breast milk beta-endorphin (BE) and elaxin-2 (RLX-2) has not been studied before. Maternal sleep quality, headache, and myalgia are predisposing factors associated with infant colic. Breast milk RLX-2 has no effect on infant colic. Breast milk BE may play a role as a biological mediator in transmitting the effects of predisposing factors from mother to infant. Breast milk BE may be a mediator in biological communication between mother and infant.