What are the levels of cortisol and melatonin in human breast milk?

From the Guidelines

Cortisol and melatonin are present in breast milk, with cortisol levels typically highest in the morning and lowest at night, and melatonin levels highest at night and lowest during the day, as supported by the most recent study 1. The levels of cortisol and melatonin in human breast milk vary throughout the day, following the mother's natural circadian rhythm.

• Cortisol levels in breast milk are typically highest in the morning and lowest at night, which helps regulate the infant's developing circadian rhythm and stress response system.
• Melatonin levels in breast milk, conversely, are highest at night and lowest during the day, supporting the baby's sleep-wake cycle. For breastfeeding mothers, it's essential to maintain consistent feeding schedules when possible, as this helps reinforce the natural hormonal patterns in breast milk.
• Nighttime feedings are particularly beneficial for transferring melatonin to the infant, potentially improving sleep quality. To support healthy cortisol and melatonin levels:

1. Maintain a regular sleep schedule to help regulate the natural hormonal patterns in breast milk.
2. Manage stress through relaxation techniques or exercise, as high stress levels can impact cortisol levels in breast milk.
3. Expose yourself to natural daylight, especially in the morning, to help regulate your circadian rhythm and cortisol levels.
4. Avoid bright lights and screens before bedtime, as this can suppress melatonin production and impact the infant's sleep-wake cycle. These hormones in breast milk play a crucial role in infant development, helping to establish circadian rhythms, regulate stress responses, and promote healthy sleep patterns, as discussed in the study 1. The natural variation in these hormone levels throughout the day is one reason why breast milk composition changes and adapts to meet the infant's needs at different times, highlighting the importance of breastfeeding and its benefits for infant development, as supported by the most recent study 1.

From the Research

Cortisol Levels in Human Breast Milk

• Elevated cortisol levels in breast milk are associated with immediate postpartum stressors, which can affect the performance of essential hormones in breast milk production 2
• Cortisol levels in breast milk can be influenced by perceived maternal stress, which can negatively impact exclusive breastfeeding rates 2
• Breast milk contains high levels of cortisol and amino acids that promote activity during the day 3

Melatonin Levels in Human Breast Milk

• Melatonin is present in breast milk, particularly in night milk, and plays a role in regulating the infant's circadian rhythm 4, 3, 5, 6
• Melatonin levels in breast milk vary in a circadian pattern, with higher levels at night and lower levels during the day 4, 5
• Melatonin in breast milk is stable for at least 4 hours after defrosting and up to 24 hours, making it a potential therapeutic agent 5
• Melatonin in human breast milk may play a critical role in circadian entrainment and optimizing neurodevelopmental outcomes in the neonatal setting 6

Comparison of Cortisol and Melatonin Levels

• Breast milk contains both cortisol and melatonin, but their levels vary throughout the day, with cortisol levels higher during the day and melatonin levels higher at night 3
• The balance between cortisol and melatonin in breast milk may be important for regulating the infant's circadian rhythm and overall health 4, 3