Teaching Chrononutrition When Promoting Breastfeeding: How Breastmilk Can Help Tune Infant Sleep Cycles
The existence of rhythms can be seen throughout biology, often termed chronobiology. The tempo of our daily life, our cycles of behavior and physiology, is directed by the suprachiasmatic nucleus within the hypothalamus. This is the timekeeper or central circadian clock that produces the body’s circadian rhythms. We also have peripheral circadian clocks in tissues of the gut, liver, heart, pancreas, and adipose and muscle tissue. Chrononutrition is the intersection between nutrition and the body’s circadian rhythms.
During early infancy, the baby’s circadian clock is not yet fully functional—just ask any parent! The newborn’s circadian rhythm is typically established by 12-16 weeks of age through external factors such as light/dark exposure and the timing of feedings.
Did you know, however, that breastmilk has rhythm too?
Human milk components, especially the bioactive ones, exhibit a circadian variation in their concentrations. The fluctuation of breastmilk ingredients facilitates how information on time of day is transferred from the mother to the infant. This mechanism contributes to the development of stable circadian rhythms in the infant that regulate physiological functions such as sleep, respiratory rate, body temperature, metabolism, hormone release, and immune function.
For example, melatonin is a primary circadian hormone, seen in high concentrations in breastmilk at night while being almost undetectable during the day. Melatonin extends its reach to all biological fluids and organs and synchronizes the body’s peripheral clocks. Because of its circadian pattern in breastmilk, melatonin introduces one of the first circadian messaging systems within the infant’s body during the time when their own melatonin rhythmicity is not yet functioning.
Following birth, the heart and vascular system continues to develop and grow. Cardiac fibroblasts continue to proliferate, such that the first months of life represent a critical period for cardiac health programming by environmental factors. The receipt of melatonin through breastmilk helps maintain the infant’s physiological mechanisms in a circadian manner. Melatonin acts directly on cellular pathways, synchronizes the peripheral clocks, and entrains rhythms in the cardiovascular system that are vital to homeostasis and function, programming future cardiovascular health. However, melatonin is not the only breastmilk component that’s got rhythm.
Cortisol levels are 330% higher in morning milk. Daytime milk has increased cortisol and activity-promoting amino acids, promoting alertness, feeding behavior, and catabolic processes. Nighttime milk—with its increased melatonin and tryptophan—fosters sleep, relaxes digestion, and supports cell restoration.
Higher levels of activity-promoting neuroactive amino acids, promoters of wakefulness, are all at peak levels in daytime milk compared to night milk. These include tyrosine, a precursor of norepinephrine and epinephrine; methionine, an essential amino acid and precursor to acetylcholine (a neurotransmitter); phenylalanine, an essential amino acid; and aspartic acid and glycine, neurotransmitters implicated in activity.
This may have implications for infants with phenylketonuria, as phenylalanine (PHE) seems to peak around noon. Clinicians could advise mothers (when appropriate) to breastfeed or express milk when PHE levels are lower and feed the specialty formula when PHE levels are highest. Key immune factors are generally higher during the day such as IgA, C3, C4, and phagocytes.
So, what does this mean in terms of infant health and clinical recommendations? The implications of consuming asynchronous breastmilk on infant health are not well studied. However, some mothers may be exclusively expressing milk and may wish to label the milk with the time of day it was expressed.
Storing all of a day’s worth of milk in a pitcher may be easier but does not provide the rhythmicity of breastmilk components. We also do not know what the implications are on the circadian variations of breastmilk components in mothers who work night or rotating shifts. One thing we can be confident about is the importance of the promotion, protection, and support of breastfeeding in our practices. We have much to learn about human milk!
Jones & Bartlett Learning invites qualified instructors to request a review copy of my text, Breastfeeding Management for the Clinician: Using the Evidence, in consideration of course adoption.
About the author:
Marsha Walker, RN, IBCLC, is the Vice President of the Federal Policy Committee for the National Lactation Consultant Alliance. She is a registered nurse and international board certified lactation consultant. She has been assisting breastfeeding families in hospital, clinic, and home settings since 1976. As such, she advocates for breastfeeding at the state and federal levels. She served as a vice president of the International Lactation Consultant Association (ILCA) from 1990-1994 and in 1999 as president of ILCA. She is a previous board member of the US Lactation Consultant Association, Baby Friendly USA, the Massachusetts Lactation Consultant Association, and the Massachusetts Breastfeeding Coalition. She serves as Associate Editor of Clinical Lactation and a board member of the National Lactation Consultant Alliance. Marsha is an international speaker, and an author of numerous publications including ones on the hazards of infant formula use, Code issues in the United States, and Breastfeeding Management for the Clinician: Using the Evidence, Fifth Edition.