The findings, submitted in a review written by Dr Robert White, suggest a number of these breast milk constituents vary in levels over the course of a 24-hour day.
Dr White’s conclusions may have future implications for makers of infant and baby formula, whose products offer a fixed nutritional composition primarily designed to ensure the child’s healthy development.
“Many components, such as cortisol and melatonin, are not present in the formula, and it has not been demonstrated that the infant suffers from their absence,” said Dr White, a neonatologist based at Beacon Children's Hospital in Indiana.
“Even those that are essential and demonstrate circadian variation in breast milk, such as fat content, may or may not have biological impact if they are delivered at constant concentrations over the course of the day as would occur in formula feeding.”
Studies that look into circadian stimuli contained in nutritional substances are less robust, but still credible.
Formula that used higher levels of protein and nucleotides and lower levels of tryptophan and carbohydrates during the day, with these amounts reversed at night led to improved sleep latency and duration when compared with a standard formula.
More findings with the same group subsequently showed that adding tryptophan, adenosine, and uridine to an infant cereal fed at night to infants 8–16 months of age with pre-existing sleep disorders led to an improvement in sleep patterns.
Passive transfer of nutrients
Dr White believes that individual compounds appear to enter the breast milk by passive transfer and that daytime changes mirror those changes seen in the serum and levels in breast milk, which were the same or lower.
In a few cases, this transfer appeared to have an active component, when the pattern deviated from or levels exceed those in the serum.
Fat content of human milk, in particular has shown stronger displays of circadian variation in term samples.
More recently, samples from mothers who delivered preterm, showed higher concentrations in evening samples.
However, circadian variability in protein and carbohydrate concentrations were less clear-cut, although higher nocturnal tryptophan level was a notable exception.
Some studies demonstrated circadian variability in calcium, phosphorus, and magnesium levels in breast milk, whereas others were unable to detect significant variation.
Several important micronutrients and hormones exhibit a daytime variation in breast milk, including some vitamins, iron, nucleotides, micro-RNA, cortisol, and melatonin.
“In utero, the foetus receives a rich milieu of circadian stimuli, including the mother's activity, body temperature, and probably most importantly, transplacental hormones, including cortisol and melatonin,” explained Dr White.
“At birth, these prenatal zeitgebers are lost and a new set of circadian stimuli are presented, most notably daylight, but there is also a continuation of certain maternal signals, including those in the breast milk, if the infant remains in extended intimate contact with her.”
In coming to his conclusions, he recommended a future research was necessary to determine whether high-risk infants will benefit if expressed breast milk is given matching the same circadian phase as it was expressed.
Source: Breastfeeding Medicine
Published online ahead of print: doi.org/10.1089/bfm.2017.0070
“Circadian Variation of Breast Milk Components and Implications for Care.”
Authors: Robert White