New study reveals breast milk is like a ‘dynamic superfood’

By Stephen Beech

Storing breast milk for specific times of the day could boost babies’ body clocks, according to a new study.

The findings showed that human breast milk is a "dynamic" food, containing different hormone levels at different times of the day.

Labeling expressed milk could be a way to ensure tots receive important cues at the right time - helping busy mums support the development of their child, say scientists.

They explained that breast milk is the first "super food" for many babies.

Full of vitamins, minerals, and other bioactive compounds, it helps build the young immune system and is widely considered the optimal source of infant nutrition.

But not all mothers have the chance to directly breastfeed multiple times during the day and night, and might use expressed milk stored for later.

Previous research has shown that breast milk delivers a range of cues from mother to baby, including signals that are thought to influence infants’ circadian rhythms.

But scientists say the hormones and proteins involved in circadian signaling may vary in breast milk concentration over 24 hours.

To discover more about such fluctuations, researchers in the United States investigated expressed breast milk samples taken during different times of the day.

Study first author Dr. Melissa Woortman, of Rutgers University, said: “We noted differences in the concentrations of bioactive components in breast milk based on time of day, reinforcing that 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.”

Study senior author Professor Maria Gloria Dominguez-Bello, also of Rutgers University, said: “The timing of these cues would be particularly critical in early life, when the infant’s internal circadian clock is still maturing.”

The research team took 10 milliliters of breast milk samples from 21 participants at 6 am, 12 pm, 6 pm, and 12 am on two different days, which were about a month apart.

A further 17 participants provided samples taken at the same times once, resulting in 236 samples included in the analysis.

The samples were examined for levels of melatonin, cortisol, and oxytocin – all hormones – as well as immunoglobulin A (IgA), an antibody protein part of the immune system, and lactoferrin, a milk protein.

Melatonin and cortisol are involved in the regulation of the circadian rhythm, whereas the other examined components influence intestinal development and gut microbiome dynamics.

The findings, published in the journal Frontiers in Nutrition, showed that some breast milk components - especially melatonin and cortisol - varied over the course of the day.

Melatonin peaked at midnight, whereas cortisol was at its highest levels in the early morning.

Dr. Woortman said, “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.”

She said the other examined components were mostly stable throughout the day.

The researchers believe that might be because they may not be as strongly influenced by signals dictating circadian rhythms.

The research team also found that as babies got older, the levels of different compounds in breast milk varied. For example, the levels of cortisol, IgA, and lactoferrin were highest when babies were less than one month old.

They believe higher levels of the compounds likely support immune defence and gut colonisation in very young babies.

Dr. Woortman said: “When it comes to differences in day/night variations by infant age, this could reflect the stabilising of the maternal circadian clock that occurs with time after giving birth, as well as the maturing and stabilization of the infant’s circadian rhythm.”

The researchers say their findings suggest that feeding expressed milk could be timed to maximize natural biological alignment so that circadian signals that support infant sleep, metabolism, and immune development – adaptations shaped through evolution – could be maintained.

Dominguez-Bello said: “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."

Dr. Woortman added: “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."