Breast milk composition changes pending time of day, as you read about in my previous article. Breast milk contains higher levels of cortisol and activity-promoting amino acids during the day, to promote alertness, feeding behaviour, and catabolic processes in infants. Night milk contains high levels of melatonin and tryptophan to foster sleep, relax digestion, and support cell restoration (Sanchez, 2013, Hahn-Holbrook, 2019). Other nutrients fluctuate through the post partum phases, either increasing or decreasing. Today, we will delve into these changing nutrients a little more deeply.
Breast milk protein has been shown to contain a relatively high concentration of tryptophan, compared with other mammalian milks, such as cows’ milk and goats’ milk. Tryptophan is an essential amino acid. It must be consumed as part of the diet. It is a precursor of the neurotransmitter serotonin and of the hormone melatonin (Cubero, 2007). Oral consumption of tryptophan modifies the circulating levels of serotonin and melatonin. Absorption is dependent on presence of carbohydrate. Adequate carbohydrate results in easier absorption of tryptophan, and transport into the brain (Cubero, 2007; Cubero 2006; Lien, 2003).
When examining the overall cycle of tryptophan in breast milk, lowest levels are found mid-afternoon. Tryptophan in breast milk peaks at around 3am. This affects 6-sulfatoxymelatonin, a metabolite of melatonin, which subsequently peaks approximately 3 hours later in breast fed infants. The rhythm of this metabolite seems to be influenced by the rhythm of tryptophan found in breast milk (Cubero, 2005). As is expected, the level of melatonin itself is highest overnight, dropping during the day.
As melatonin levels fluctuate due to varying levels of tryptohpan, cortisol levels also fluctuate with the circadian rhythm. Highest levels are seen at approximately 6am, and lowest levels at 6pm (Italianer et al, 2020).
Circadian variation is seen in fat levels of breast milk, with highest fat content seen early evening, and lowest early morning (Italianer et al, 2020). Fats play a role in breast milk as they are necessary for growth and development of a healthy baby, in particularly development of a healthy gut (Ramiro-Cortijo et al, 2020). They also play a role in controlling appetite.
Diagram from Italianer et al, 2020
Nucleotides are compounds that play a key role in numerous intracellular chemical processes. These are made by the body, and play an important role in DNA and RNA. These components of co-enzymes NAD, FAD and coenzyme A; as biological regulators and as an energy source. Studies have also shown potential benefits to intestinal flora, immunity, iron absorption, lipid metabolism and gut development (Lerner & Shamir, 2000). Key nucleotides include adenosine, guanosine and uridine. These excite or relax the central nervous system, promoting restfulness and sleep. Highest nucleotides concentrations are found in samples taken between 8pm and 8am, with lower quantities seen during the day (Sanchez, 2009).
Concentration of B vitamins in breast milk change through the early post partum period. This highlights breast milk ability to change based on infant requirements. Thiamin (B1) and B12 increases over the first few months, whilst B6 increases during first weeks, then a gradual decline is seen, whilst folate peaks at 2-3 months into the lactating period.
B Vitamins play varying roles in body systems and development. Interestingly, no circadian variation has been identified for B vitamins, with levels remaining stable, regardless of time of day (or night) (Italianer et al, 2020).
Iron is an important mineral, who’s ability to meet the infant requirements dwindles from around 6 months of age. Levels of iron in breast milk are also influenced by the circadian rhythm. Iron levels are lowest around 6pm, and at their peak 12 hours later (Italianer et.al, 2020).
As can be seen, many important nutrients found in breast milk vary pending time of day or night. Why is this important? If you breast feed your baby expressed breast milk, this adds further evidence that feeding the infant milk from the same time of day it was expressed is likely to have positive benefits, due to the changing composition of breast milk, pending time of day.
This post was sponsored by NiMera.
From time to time I write sponsored posts such as this, however views are entirely my own, and I only ever collaborate with companies and brands who resonate with me.
Italianer, M. F., Naninck, E., Roelants, J. A., van der Horst, G., Reiss, I., Goudoever, J., Joosten, K., Chaves, I., & Vermeulen, M. J. (2020). Circadian Variation in Human Milk Composition, a Systematic Review. Nutrients, 12(8), 2328. https://doi.org/10.3390/nu12082328
Lerner, Aaron and Shamir, R, (2000). Nucleotides in infant nutrition: An update. IMAJ, Vol2, p772-773.
Sánchez et al. The possible role of human milk nucleotides as sleep inducers. Nutritional Neuroscience, 2009; 12 (1): 2 DOI: 10.1179/147683009X388922
Ramiro-Cortijo, D., Singh, P., Liu, Y., Medina-Morales, E., Yakah, W., Freedman, S. D., & Martin, C. R. (2020). Breast Milk Lipids and Fatty Acids in Regulating Neonatal Intestinal Development and Protecting against Intestinal Injury. Nutrients, 12(2), 534. https://doi.org/10.3390/nu12020534