Busy mothers might be sending their babies confusing signals if they feed evening breast milk that was expressed in the morning, according to new research.
Breast milk’s composition changes throughout the day, including hormones believed to influence babies’ wake and sleep patterns, researchers reported today in Frontiers in Nutrition.
A mother might unintentionally disrupt her infant’s rest if she stores breast milk in the morning and then provides it in the afternoon or evening, researchers cautioned.
Lead researcher Melissa Woortman, a recent doctoral graduate in nutritional sciences at Rutgers University in New Brunswick, N.J., stated in a news release: “Breast milk is a dynamic food: Consideration should be given to the time it is fed to the infant when expressed breast milk is used.”
Senior investigator Maria Gloria Dominguez-Bello, a professor in biochemistry and microbiology at Rutgers, added in a news release: “The timing of these cues would be particularly critical in early life, when the infant’s internal circadian clock is still maturing.”
Breast Milk as a Dynamic Food
Doctors consider breast milk a baby “super food” packed with vitamins, minerals, and compounds that help build the young immune system and nourish the growing body, researchers noted.
It’s widely considered the best source of infant nutrition, but many mothers aren’t able to directly breastfeed multiple times throughout the day and night. Instead, they use pumps to express and store milk for later feedings.
Study Methods
Researchers collected 10 milliliter breast milk samples from 21 women at specific intervals on two days, roughly a month apart: 6 a.m., noon, 6 p.m., and midnight. Another 17 participants provided one day’s worth of samples taken at the same times.
Researchers analyzed the samples for levels of three hormones: melatonin, cortisol, and oxytocin. Melatonin and cortisol are involved in regulating wake and sleep cycles.
The breast milk samples were also examined for levels of immunoglobulin A, an antibody protein produced by the immune system, and the milk protein lactoferrin. These influence the baby’s digestive system.
Key Findings
Results showed that melatonin and cortisol varied throughout the day. Melatonin peaks at midnight, while cortisol reaches its highest levels in the early morning.
Woortman explained: “We all have circadian rhythms in our blood, and in lactating mothers, these are often reflected in breast milk. Hormones like melatonin and cortisol follow these rhythms and enter milk from maternal circulation.”
The other breast milk components remained mostly stable throughout the day. This might be because they aren’t as strongly influenced by signals dictating circadian rhythms, researchers suggested.
Practical Recommendations
The results suggest that mothers should try to feed their expressed milk at times that reflect when it was collected and stored, researchers said.
Dominguez-Bello stated: “Labeling expressed milk as ‘morning,’ ‘afternoon,’ or ‘evening’ and feeding it correspondingly could help align expressing and feeding times and preserve the natural hormonal and microbial composition of the milk, as well as circadian signals.”
For busy mothers, that adjustment represents a practical step, Woortman noted.
She concluded: “In modern societies where it may not be feasible for mothers to stay with their infants throughout the day, aligning feeding times with the time of milk expression is a simple, practical step that maximizes the benefits of breast milk when feeding expressed milk.”
This research suggests a straightforward modification to breast milk storage and feeding practices that could help support babies’ developing circadian rhythms and sleep patterns.