Are cortisol concentrations in human breast milk associated with infant crying?

Area of Science:

• Endocrinology
• Developmental Psychology
• Human Lactation

Background:

• Human breast milk contains cortisol, a stress hormone.
• The role of breast milk cortisol in infant behavior, particularly crying, is not well understood.
• Previous research has not investigated the longitudinal association between breast milk cortisol and infant crying patterns.

Purpose of the Study:

• To investigate the association between human breast milk cortisol concentrations and infant crying behaviors (fussing and crying) during the first three months of life.
• To examine potential sex differences in the relationship between breast milk cortisol and infant crying.
• To analyze changes in breast milk cortisol levels over the first 12 weeks of an infant's life.

Main Methods:

• A longitudinal study involving 70 mothers and their infants.
• Mothers collected morning breast milk samples at 2, 6, and 12 weeks postpartum.
• Infant fussing and crying were recorded via 3-day diaries, and milk cortisol was quantified using established methods.

Main Results:

• Breast milk cortisol concentrations showed a significant increase from 2 to 12 weeks of infant age.
• No significant association was found between breast milk cortisol levels and the total duration, frequency, or bout length of infant fussing and crying.
• These findings were consistent for both male and female infants.

Conclusions:

• Breast milk cortisol levels increase during the first three months of life but do not appear to influence infant crying behaviors.
• Further research is needed to explore the biological functions of milk cortisol and its potential impact on infant development.
• The study highlights the complexity of factors influencing infant crying and stress responses.