Fuente: "milk OR dairy products" J Hum Lact. 2026 Apr 20:8903344261431669. doi: 10.1177/08903344261431669. Online ahead of print.ABSTRACTOBJECTIVES: Breast milk is a sophisticated biological fluid that provides an ideal nutritional composition for infants and also exhibits variation in circadian rhythms. Breast milk has both bacteriostatic and bactericidal properties. Current research has not yet explored the potential influence of circadian changes in breast milk on its antibacterial activity. This study aimed to reveal the association between the antibacterial activity of breast milk and circadian rhythms.METHODS: The study was conducted with the participation of volunteer mothers who presented to our neonatal outpatient clinic between March and May 2024. Breast milk samples were classified based on the time of collection: Milk obtained between 04:00 and 22:00 was designated as daytime breast milk, whereas milk gathered between 22:00 and 04:00 was referred to as nighttime breast milk. A total of 60 breast milk samples were stored at 4°C, and the antibacterial effectiveness of these samples was assessed within 24 hours of collection.RESULTS: No significant difference was observed between day and night breast milk regarding their antibacterial activity against Escherichia coli (P = 0.819). Additionally, no correlation was found between the number of bacterial colonies in 60 breast milk samples and the storage time of the milk (r = 0.19, P = 0.1). A moderate positive correlation was found between the number of E. coli colonies in day breast milk and the storage time of breast milk (r = 0.431, P = 0.02).CONCLUSIONS: The general antimicrobial properties against E. coli showed a steady degree of effectiveness, with no major differences found between samples collected during the daytime and those obtained at nighttime.PMID:42007898 | DOI:10.1177/08903344261431669