How human breast milk composition contains somnogenic nucleotides that help infants sleep | Biology of Breast Milk
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The composition and consistency of breast milk changes markedly during the first few weeks and months of lactation in response to an infant's needs. Notable differences between the macronutrient content of breast milk and cow's milk drive home the fact that breast milk is a highly dynamic, species-specific fluid that provides proteins, carbohydrates, fats, vitamins, and minerals to support and nourish a human infant. In this episode, Dr. Rhonda Patrick describes the different types of fluids produced by the human breast during lactation and explains how the nutritional content of these fluids meet the infant's needs.
Let's start with some of the basics, breast milk production and composition. The first fluid that a mother produces is colostrum, a thick, sticky fluid that typically is yellow, orange, or white in color. Since colostrum contains a slew of immune factors, its primary role is immunological rather than nutritional. Some women can express colostrum in the last few months or weeks of pregnancy.
Next comes transitional milk, which arrives during the first few days to two weeks after childbirth and is high in lactose. By four to six weeks after childbirth, the mother's milk is considered mature. Mature milk that is expressed during the early part of a single feeding session is called foremilk. It's high in lactose and has a watery consistency. The milk expressed during the latter part of this feeding is called the hindmilk. It's high in fat and has a creamy consistency. Breast milk is an incredibly dynamic substance. It changes in composition during a single feeding from day to night and throughout the lactation period in response to the growing infant's needs. It's also influenced by circadian rhythms. Breast milk contains several components that transmit circadian signals to help the infant regulate its own sleep/wake cycle with the nighttime breast milk containing higher levels of melatonin and somnogenic amino acids like tryptophan.
Breast milk nucleotides, which are important structural components of DNA and RNA, also show circadian rhythmicity. Some of the nucleotides peak during the day while others peak at night, suggesting a potential role for these nucleotides as sleep inducers. This data suggests that if an infant is fed expressed breast milk, the milk should be provided at the same time of day that it was expressed to maintain the infant circadian rhythm.
It's important to note that things you eat, drink, supplement, but even more importantly, smoke, can end up in your breast milk. Breast milk is species-specific. Human breast milk contains proteins, carbohydrates, fats, vitamins, and minerals to nourish a human infant. One of the biggest differences you'll see between human milk and other types of milk is the protein content. The total protein content in human breast milk is quite a bit lower than milk from other species, one of the reasons human infants grow so slowly compared to say a calf. There are roughly 415 different proteins in human breast milk. These proteins provide nutrition of course, but they also aid in the infant's digestion and supply both anti-microbial and immunological factors that compensate for deficiencies in the infant's immune system, which I'll talk about a little bit later.
Breast milk contains a variety of complex carbohydrates. The most abundant of which is lactose, which provides necessary energy for the infant's brain.
The body’s 24-hour cycles of biological, hormonal, and behavioral patterns. Circadian rhythms modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, metabolism, and others, ultimately influencing body weight, performance, and susceptibility to disease. As much as 80 percent of gene expression in mammals is under circadian control, including genes in the brain, liver, and muscle.[1] Consequently, circadian rhythmicity may have profound implications for human healthspan.
A thick, sticky fluid produced during the first stage of lactogenesis, the production of milk. Colostrum is rich in immunomodulatory factors, and its primary role is immunological, rather than nutritional. Relative to a mother's later milk, colostrum is low in lactose, potassium, and calcium and high in sodium, chloride, and magnesium. It is commonly yellow, orange, or white in color.
Complex carbohydrate foods provide vitamins, minerals, and fiber that are important to the health of an individual. As opposed to simple or refined sugars, which do not have the vitamins, minerals, and fiber found in complex and natural carbohydrates. Simple sugars are often called "empty calories" because they have little to no nutritional value.
Breast milk that is expressed during the early part of a single feeding session. Foremilk is high in lactose and has a watery consistency.
Breast milk expressed during the latter part of a single feeding session. Hindmilk is high in fat and has a creamy consistency.
An essential mineral present in many foods. Iron participates in many physiological functions and is a critical component of hemoglobin. Iron deficiency can cause anemia, fatigue, shortness of breath, and heart arrhythmias.
The processes of synthesis and secretion of milk from the mammary glands. Lactation requires both mechanical and hormonal inputs. Nipple stimulation and subsequent milk removal promote the continued release of prolactin and oxytocin. In turn, these hormones drive ongoing production and release of milk (respectively).
A hormone that regulates the sleep-wake cycle in mammals. Melatonin is produced in the pineal gland of the brain and is involved in the expression of more than 500 genes. The greatest influence on melatonin secretion is light: Generally, melatonin levels are low during the day and high during the night. Interestingly, melatonin levels are elevated in blind people, potentially contributing to their decreased cancer risk.[1]
One of four nitrogen-containing molecules that comprise DNA. A nucleotide consists of one of four chemicals, called a “base,” plus one molecule of sugar and one molecule of phosphoric acid. Nucleotides are typically identified by the first letter of their base names: adenine (A), cytosine (C), guanine (G), and thymine (T). They form specific pairs (A with T, and G with C), and their bonds provide the helical structure of the DNA strand.
Sleep-promoting substances or activities. Somnogenic entities include exercise, meditation, and illness, among others.
An essential amino acid. Tryptophan plays key roles in the biosynthesis of proteins and is a precursor to several molecules with physiological significance, including melatonin, niacin, and the neurotransmitter serotonin. Inflammation causes tryptophan to be reallocated from serotonin synthesis to that of kynurenine, which then converts to the neurotoxin quinolinic acid, leading to depression. Dietary sources of tryptophan include most protein-based foods, such as meat, beans, or nuts.
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