Lactation Physiology and Hormones

Lactation Physiology

• The mammary gland, commonly known as the breast, provides milk for offspring and is a characteristic feature of mammals.
• Alveoli are rounded or oblong cavities in the breast where milk is produced.
• Secretory cells in the acinus (milk gland) secrete milk components into the ducts.
• Myoepithelial cells line the alveoli and contract to secrete milk into the duct.
• Oxytocin released during letdown causes milk ejection.
• Lactogenesis is another term for human milk production.
• Mammogenesis is another term for mammary growth.

Hormones in Breast Development and Lactation

• Estrogen promotes ductal growth during mammary gland differentiation with menstruation.
• Progesterone stimulates alveolar development after the onset of menses and throughout pregnancy.
• Human growth hormone aids development of terminal end buds leading to mammary gland development.
• Human placental lactogen supports alveolar development during pregnancy.
• Prolactin enables alveolar development and milk secretion during pregnancy and breastfeeding (from the third trimester to weaning).
• Oxytocin facilitates letdown by ejecting milk from myoepithelial cells, from the start of milk secretion to weaning.

Hormonal Control & Stages

• Luteal and placental hormones (placental lactogen and chorionic gonadotropin) prepare for breastfeeding during pregnancy.
• Estrogen stimulates milk-producing glands.
• Progesterone is responsible for tubule elongation and epithelial cell duplication.
• Prolactin is needed to complete lobular-alveolar development of mammary gland.
• Mammary gland development and lactation occur in stages: mammogenesis, lactogenesis I, lactogenesis II, and lactogenesis III (galactopoiesis/full lactation).
• Involution occurs approximately 40 days after the cessation of breastfeeding.

Lactogenesis Stages

• Lactogenesis I begins during pregnancy at ~12–16 weeks before delivery, when milk starts to form and lactose and protein levels increase, resulting in large gaps between alveolar cells.
• Colostrum is produced during Lactogenesis I; it is the first milk and it is rich in antibodies.
• Lactogenesis II begins 2–8 days postpartum with increased blood flow to the mammary glands and a drop in progesterone levels.
• Tight junctions between alveolar cells close (3–4 days postpartum), preventing leakage between cells
• In Lactogenesis II, copious milk secretion begins (“milk comes in”), with significant increase in volume and composition.
• Delayed lactogenesis II can lead to breastfeeding issues.
• Lactogenesis III begins approximately 9 days postpartum with a maintained milk supply, stabilized milk composition, and production adjusted based on infant demand.

Lactogenesis Impact Factors

• Premature delivery.
• Delivery method.
• Maternal BMI > 30.
• Presence of diabetes.
• Maternal or infant complications.
• All of the above factors may lead to incomplete milk supply (< 25–35 oz/day).

Hormones for Milk Supply

• Prolactin stimulates milk production.
• Prolactin is stimulated by suckling (doubles prolactin levels), stress, sleep, and sexual intercourse.
• The hypothalamus releases Prolactin-inhibiting factor, which inhibits prolactin.
• Prolactin also prevents milk production during pregnancy, despite high prolactin levels and peaks during lactogenesis III.
• It is linked to nipple stimulation in lactogenesis II and nighttime breastfeeding or pumping increases prolactin secretion.
• Blood prolactin level does not determine milk volume, but it is essential for milk synthesis.
• Oxytocin triggers milk letdown and ejection.
• Nipple stimulation and sensory input (e.g., baby crying, thinking about nursing) stimulate oxytocin release.
• Oxytocin contracts milk ducts to push milk out and may cause tingling or sharp pain during letdown.
• It also stimulates uterine contractions during and after delivery to help seal blood vessels and reduce uterus size postpartum.

Milk Secretion

• Lactose is made in the secretory cells and secreted into milk ducts by exocytosis.
• Milk fat comes from triglycerides in the mother's blood and fatty acids produced in the breast and these form fat droplets, and a portion of the cell membrane surrounds the fat droplets to secrete into the milk duct.
• Sodium, potassium, and water are actively transported from cells into milk.
• Proteins (immunoglobulins, hormones, albumin, and plasma proteins) are pulled from the mother’s blood into alveolar cells through transcytosis and then secreted into the ducts.
• Leukocytes and other components from the mother’s plasma pass directly between cells through the paracellular pathway.
• This occurs before tight junctions between alveolar cells close.

The Letdown Reflex

• Infant suckling triggers the letdown reflex, sending signals to the hypothalamus, which then signals the posterior pituitary to release oxytocin.
• Oxytocin causes the myoepithelial cells around secretory cells to contract, pushing milk from the glands into the ducts.
• Hearing a baby cry, sex, or thoughts of nursing can also trigger letdown, possibly causing milk leakage.

Human Milk Composition

• Human milk is the only food most healthy infants need for the first 6 months of life.
• It provides complete nutrition and protects against infections and chronic diseases like celiac disease, inflammatory bowel disease, diabetes, and leukemia.
• Composition is dynamic and changes based on stage of lactation, time of day, infant age, gestational age at delivery, infection in the breast, maternal nutritional status, and maternal menses. It also varies by geographical location.
• Composition matches the changing needs of the infant.

Species-Specific Composition

• Human milk is species-specific and tailored to human infant needs.
• Milk in other mammals differs based on species, environment, and genetics.
• Higher fat and nutrient density in mammal milk facilitates faster growth and earlier doubling of birthweight.
• Human milk has hundreds of components with nutritive and non-nutritive roles, but many components are still being studied.

Standards and Substitutes

• Codex Alimentarius Commission (FAO and WHO) sets global standards for human milk substitutes.
• Composition differs between brands and changes over time.
• See Tables 6.2, 6.3, and 6.4 for comparisons of nutrients in milk across species, colostrum vs. mature milk, and mature milk vs. human milk substitutes.

Colostrum

• Produced during Lactogenesis I (days 1–3 postpartum).
• Is thick and yellowish.
• Infants drink 2–20 mL per feeding in the first 2–3 days.
• Provides 580–700 kcal/L (average 670 kcal/L).
• Higher in protein and minerals and is lower in carbohydrates, fats, and vitamins than mature milk.
• The key proteins are secretory IgA and lactoferrin.
• Lacks some proteins found in mature milk and contains highest levels of mononuclear cells for immune protection.
• Is also higher in sodium, potassium, vitamin E, carotenoids, and chloride.

Macronutrients & Bioactive Components

• Breast milk is isotonic with plasma.
• Babies do not need additional water, even in hot or dry climates.
• Water suspends sugars, proteins, immunoglobulin A, sodium, potassium, citrate, magnesium, calcium, chloride, and water-soluble vitamins.

Energy Composition

• Human milk provides approximately 0.65–0.75 kcal/mL.
• Energy content varies with fat, protein, and carbohydrate composition.
• Breastfed infants consume fewer calories than formula-fed infants.
• Exclusively breastfed infants experience early enhanced growth in the first 3–4 months.
• By 8-11 months, breastfed infants are thinner when compared to formula-fed infants.
• Differences in weight disappear by 12–23 months.

Lipids Composition

• Lipids are the second-largest component of breast milk at a concentration of 3–5%.
• They provide about half of the energy in human milk, primarily in the form of triglycerides.
• Fat content varies by time of day and within a single feeding, with foremilk being lower in fat and hindmilk being higher.
• Maternal BMI, age, gestational age, parity, breastfeeding frequency, and lactation stage influence milk's fat content.
• Energy from lipids ranges from 20.9 to 26.2 kcal/oz or 65 to 75 kcal/dL.
• Total milk fat quantity is not influenced by diet, but fatty acid profile reflects maternal diet and fat stores.
• Very low-fat diets lead to increased medium-chain fatty acid synthesis in the breast

DHA

• DHA, essential for retinal development, accumulates in the last months of pregnancy and is especially important for preterm infants.
• Milk DHA levels depend on maternal diet, supplementation, and fat stores.
• Cod liver oil (high in DHA, vitamins A and D) may improve cognitive outcomes, but must be used with caution.

Trans Fatty Acids

• Trans fatty acids are derived from the maternal diet and present in human milk.
• Concentrations were higher in North American women but are decreasing due to regulatory bans.
• Trans fat levels have declined after the FDA ban in 2015 in Canada and the U.S.

Cholesterol

• Cholesterol is needed for cell membrane growth and replication.
• Cholesterol ranges from 6.5 to 18.5 mg/100 mL, and varies by woman and day.
• Maternal diet does not affect milk cholesterol levels.
• Breastfed infants consume more cholesterol and have higher serum cholesterol early on, but by 18 months, levels are similar between breastfed and formula-fed infants.
• Adults who were breastfed tend to have lower cholesterol levels.

Proteins

• Human milk protein content is 0.8–1.0%, which is lower than other mammals like cows milk.
• Protein content in human milk is more affected by infant age than maternal intake.
• Protein concentration changes with hormones that regulate gene expression and has both nutritive and non-nutritive functions such as antiviral, antimicrobial, and anti-inflammatory properties.

Casein

• It combines with calcium phosphate, magnesium, and citrate to give milk its white color.
• Its digestion produces casein phosphopeptides, which aids calcium absorption.
• Casein levels are low early in lactation and increase over time.

Whey Proteins

• Soluble in water after casein is removed.
• Highest in early lactation and decreases over time.
• Whey:casein ratio is 90:10 early, 60:40 in mature milk, and 50:50 in late lactation.
• Ratios impact glucose metabolism and hormone release
• Includes lysozyme, immunoglobulins, lactoferrin, and other binding proteins.
• Lysozyme increases over time and protects against E. coli and Salmonella.
• Enzymes in whey support digestion and immunity.

Mucins

• Found in the milk fat globule membrane (MFGM).
• Provide antiviral and antimicrobial protection.

Nonprotein Nitrogen

• Provides 20–25% of nitrogen in milk.
• Urea accounts for 30–50%, nucleotides for around 20%.
• Supports synthesis of nonessential amino acids, hormones, growth factors, nucleic acids, and carnitine.
• Nucleotides support immune function, GI development, and disease resistance.

Milk Carbohydrates

• Lactose is the dominant carbohydrate and enhances calcium absorption.
• Other carbohydrates include monosaccharides, polysaccharides, oligosaccharides, and protein-bound carbohydrates.
• Oligosaccharides are the second largest group of carbohydrates in human milk with over 200 HMOs (human milk oligosaccharides) identified.
• They are free or bound to proteins (glycoproteins) or lipids (glycolipids)
• Oligosaccharides promote bifidus bacteria growth, prevent attachment of harmful bacteria to the gut lining and contribute to innate immune protection.
• Oligosaccharides contribute calories at low osmolality, stimulate bifidus bacteria growth, and inhibit harmful bacteria like E. coli
• Human Milk Oligosaccharides (HMOs) are medium length carbohydrates with lactose on one end that can be free, bound to proteins (glycoproteins), or lipids (glycolipids)
• HMOs promote beneficial bacteria growth and are considered part of innate immune protection provided by breastfeeding.

Fat-Soluable Vitamins

• Colostrum has about twice as much vitamin A as mature milk
• Some vitamin A is present as beta-carotene, which gives colostrum a yellow color, and mature milk vitamin A is adequate for infant growth and development through 6 months.
• Vitamin A deficiency increases risk of eye problems, infection, iron-deficiency anemia, and growth failure.
• Maternal intake influences vitamin A levels, but supplementation does not show significant benefits.
• Vitamin D is important for calcium absorption and bone health.
• Vitamin D content in milk reflects maternal status, and deficiency in breastfeeding mothers can lead to infant hypocalcemia and rickets.
• Primary form of Vitamin D in milk is 25-OH vitamin D and D3, and sunlight exposure increases vitamin D3 levels in milk.
• Vitamin E is a potent antioxidant that supports neurological function and protects cells.
• Vitamin E is related to fat content in milk (40 µg vitamin E per gram of lipid).
• Alpha-tocopherol decreases from colostrum to mature milk, while beta and gamma tocopherols remain stable across lactation stages.
• It is usually adequate for full-term infants, but low for preterm infants
• Vitamin K supports development of clotting factors with about 5% of breastfed infants at risk for vitamin K deficiency without supplementation.
• Intramuscular vitamin K at birth has been standard in the U.S. since 1961.

Water-Soluable Vitamins

• Levels in milk are responsive to maternal diet or status for thiamin, riboflavin, B6, B12, and choline.
• Milk from well-nourished U.S. women typically meets estimated infant needs.
• B12 deficiency from conditions like vegan diet or pernicious anemia can lead to long-term infant neurological deficits.
• Folate is bound to whey proteins and is less influenced by maternal intake than other vitamins.

Minerals in Human Milk

• Minerals contribute to milk’s osmolality.
• Monovalent ions are balanced by alveolar cells with lactose to maintain isosmotic composition.
• Compared to cow's milk, mineral content in human milk is lower, it declines over the first 4 months postpartum (except magnesium), and its lower mineral content is easier on infant kidneys and supports growth well.
• Minerals like magnesium, calcium, iron, and zinc are highly bioavailable in human milk due to efficient mineral packaging, which reduces the amount needed and supports infant absorption.
• Human milk has 49% zinc availability from, while cow milk or formula only have 10%.
• Breastfed infants are at low risk for anemia despite low iron concentration due to absorption being supported by vitamin C and lactose.
• Iron status is similar to formula-fed infants for up to 9 months.
• Longer periods of exclusive breastfeeding (6.5 months) decreased anemia risk.

Zinc & Trace Minerals

• Zinc is highly available in human milk due to protein binding.
• Zinc needs and intake per kg decline after the first months, it is maintained even with low maternal intake, and rare deficiencies may cause dermatitis or diaper rash due to zinc transport defects in mammary gland.
• Zinc supplementation resolves deficiency if present.
• Trace minerals include copper, selenium, chromium, manganese, molybdenum, nickel, and fluorine, which are essential for growth and development, and are generally not influenced by maternal diet or supplements except fluoride.
• DRI for fluoride is 0.1 mg/day for infants under 6 months and fluoridated water is safe for breastfeeding mothers and infants.

Breast Milk Taste

• Flavor of milk is affected by maternal diet (e.g., mint, garlic, vanilla, alcohol).
• Flavors transfer selectively and in small amounts.
• Infants respond more to new flavors, showing more interest and nursing longer and exposure to varied flavors may support acceptance of new solid foods.
• Longer exclusive breastfeeding results in a greater preference for umami flavor at 6 months

Milk Supply Demands

• Establishing a good milk supply in the first month involves putting the baby to the breast within 30 minutes after birth; encourage frequent rooming and feeding (10–12 times in 24 hours); providing breast pump if mother is separated from baby; offering lactation support for proper positioning; encouraging hydration and a nutrient-dense diet (vegetables, fruits, whole grains, lean protein); feeding from both breasts while nursing on demand; starting on the favored breast before switching to the other when sucking slows; and using skin-to-skin contact to help encourage longer feeding.
• Milk production averages 600 mL/day in first month, increasing to 750–800 mL/day by 4–5 months, but range can vary from 450 to 1,200 mL/day.
• Influenced by infant weight, milk energy density, and age which increases with twin/triplet nursing or pumping.
• Milk removal signals breast to make more milk with 24% of milk left in after feeding.
• Daily synthesis rate is 64% of the maximum, indicating the capability to produce more.
• Mothers of twins will also produce more than needed for a singleton.
• Breast size is determined mostly by fat, not milk-producing tissue, so small breasts can produce as much milk as large breasts.

Milk Production

• Larger breasts may allow less frequent feeding due to higher storage capacity.
• Feeding frequency is not consistently linked to milk supply.
• Milk production varies by breast and feeding session.
• Daily milk volume is related to total milk removed in 24 hours.

Milk Quality

• More complete emptying increases milk synthesis according to Daly’s theory.
• Milk quantity (not quality) is regulated by feedback inhibitor of lactation(FIL), which is a whey protein that inhibits milk production through autocrine signaling
• Higher concentration of milk = high FIL = low milk production therefore if more milk is left, synthesis slows; if emptied, synthesis increases

Breastmilk After Surgery

• Expressing milk may be more necessary due to illness or separation and can be done via manual expression, hand pumps, electric pumps, and hospital-grade pumps.
• Double pumping for 10 minutes is more efficient than single pumping for 20 minutes
• Electric pumps may raise prolactin more than manual methods.
• Around 8-12+ pumping sessions per day may be needed for full milk supply, but individual needs vary based on emptying efficiency and breast storage capacity.
• Breast reduction surgery may impair lactation due to tissue removal or duct damage, while 91.8% of women with prior reduction report breastfeeding issues.
• Incision type such as periareolar incisions affect outcome and are more likely to disrupt ducts with augmentation compressing ducts and reduce milk flow.

Breastfeeding

• Surgery type, incision site, and history of breastfeeding should be reviewed, furthermore infants should be monitored for growth and signs of insufficient intake.
• Silicone or saline breast implants are not contraindications for breastfeeding and the research shows no toxic effects or elevated silicone in milk since levels in breast milk are lower in formula or cow's milk.

Post Pregnancy Diet

• U.S. Dietary Guidelines have been adapted for pregnant and breastfeeding women.
• Moderate weight loss is possible without compromising infant weight gain if a diet is healthy and balanced, and assessment should focus on ○​ Maternal energy intake for weight management​ ○​ Potential food triggers of infant colic​ ○​ Supplement and food intake​ ○​ Medical and breast health history ○​ Common diagnoses: altered weight status, inadequate milk supply, B12 needs (vegan), lack of knowledge, WIC eligibility​
  • Nutrition intervention may include: adjusting energy intake, education on milk production and feeding/pumping, and recommendations for food or nutrient supplements (e.g., calcium, B12).
• Monitor maternal weight, infant growth, and nutrient status.
• DRI assumes 540 kcal/day energy cost for exclusive breastfeeding for the first six months, subtracting 140 kcal/day mobilized from fat stores, meaning a net of about 400kcal/day.
• EER = Total Energy Expenditure + milk production cost – energy mobilization
• Adult EER equations are used for women 19+ and teen equations for those under 19
• For 7-12 months postpartum (partial breastfeeding), the recommendation is 380 kcal/day and 2020-2025 recommends +330 kcal/day for 0–6 months and +400 kcal/day after 6 months to support 0.8 kg/month weight loss
• Individualized assessment based on maternal weight and infant growth is needed for recommendations

Milk Composition

• Mild calorie deficits reduce milk volume but not water content.
• Over a longer period animal studies showed a threshold effect (e.g., 60% energy → reduced milk production and 80% energy → maintained milk production)
• Studies show to lose weight while breastfeeding diets of 1500 kcal/day is generally accepted while more strict plans are viable with support.

Micronutrients

• 1800 kcal/day is the generally accepted minimum calorie recommendation for post partum mothers

• High-fat macronutrient diets will result in higher milk-fat content and an energy deficit

• Deficiencies observed in vitamins C and E and, calcium and vitamin D may also be low

• In response recommend a diet of low-fat dairy for calcium and vitamin D and fruits, vegetables, and whole grains is recommended

• Moderate exercise is safe alone.

• When combined with a mild energy restriction improvements to fat loss and metabolic health have been shown. Vitamin and Mineral Supplements:​

• Routine supplementation is not needed for well-nourished women and supplement is only specified for needs.

• The supplements Calcium (1200 mg) and vitamin D (10 µg) and B12 are crucial for clients that are vegan or at risk of deficency.

Vitamin Intakes

• Common low intakes are of folate, thiamin, vitamin A, calcium, iron, or zinc
• Low vitamin intake rarely affects maternal or infant status
• Overemphasis may discourage breastfeeding, and no adverse effects comes from consuming fortified foods.
• Also, no evidence that a high fluid increases milk supply is backed, and you should only drink to quell thirst and the urine color should be the indicator.
• The RDI for water = 3.8 L/day but it should be noted than excess fluid may negatively affect supply​
• Vegetarian diets can meet nutritional needs with consideration of calories, protein, calcium, vitamins D and B12, iron, zinc intake and can supplemented with fortified food.

Infant conditions

• Defined as crying >3 hours/day, and >3 weeks and associated with maternal intake of cow milk, onions et al.
• Elimination diet from allergens reduced symptoms.
• In summary one should replace nutrients, and reduce maternal intake of food.

Sore Nipples

• Affects over 90% of women but subsides with breastfeeding or correct latch and positioning.
• In general correct latch & positioning with consults is accepted.
• Air-dry and expressed milk is needed along with pump only after sore is healed.
• Is often due to stress with the counteraction relaxing with relaxation techniques such as music. Also avoid caffeine.

Letdown Failure

• Is the combination of stress, distraction etc. that results to management issues. ○​ Use relaxation techniques (e.g. music, deep breathing).​ ○​ Oxytocin nasal spray (short-term).​

Hyperactive Letdown

• Is the result of infants choking due to strong flow which should be solved by stopping feeding early or reducing supply. ○​ Remove baby until flow slows.​ ○​ Express some milk before feeding.​ ○​ Ensure hindmilk is reached to prevent colic.​

Postpartum Pain

• Is caused by full breasts where treatment is needed to apply warm/cold compress of frequent feeding. ○​ Warm compress before, cold compress after.​ ○​ Express to soften breast before latching.​

Breastfeeding Points

Human Milk is the most important food source from 6 months - several years as long as certain supplements that help diet that affects milk fat are applied.

• Human milk is optimal; exclusive for 6 months.
• Breastfeeding benefits both infant and mother.
• Breastfeeding possible on vegetarian/vegan diets with attention to B12.
• Breastfeeding support reduces disparities and improves outcomes.

Low Milk & Nipple Types Chart

• In breastfeeding certain levels help ensure that the patient is well informed

• It is vital to diagnose problems such as low-quality nipple that requires pumping and monitoring

    Perceived or Real Causes:​
    ○​ Infrequent nursing/pumping or hormones.
    ○​ The recommendation is Galactogogues.
  

Breastfeeding & Medication

• Breastfeeding should be the number one solution and the FDA has a list of ingredients within the PLLR.

Risk & Herble Safety

Risk Factors

• Cytotoxic drugs causes problems and all drugs are recorded in charts that are safe and compatible
• There are contraindications based on what is stated in documentation
• Reduce drugs by cutting duration and scheduling a time after to feed the baby
• Key herbs in US such as echninacae which helps avoid Gi distress

Herbs that affect Body

• Promote Milk Flow*: Fenugreek, milk thistle, goat’s-rue, fennel, etc.
• Reduce Milk Flow*: Sage, parsley, jasmine, castor bean In this chart only 5 different products provide safe herbal teas:
  • Rose hips:Vitamin C, immune support
  • Raspberry: Uterine tone, milk flow, nausea
  • Red bush: Beverage
  • Peppermint: Relieve nausea (limit use)
  • Orange: Flavor
  • Chicory: Constipation, digestion

Effects

• Alcohol should be well planned to reduce feeding but there are several solutions
• Nicotine has several down sides
• The drugs can lead to DNA/RNA disprutions for marijuana
• Also, Environmental pollutants can have sever contamination with what is stated for each category:
  • Risk Reduction:​ table 7.8 can help reduce risks ○​ Avoid high-mercury fish​ ○​ Reduce fat intake​

Newborn Education & Jaundice Chart

-Educating of newborns and signs can help lead to great parenting that is proven to show more signs of caring The following lists issues that come with premature Jaundice

    ○​ Inadequate feeding→ ↑ bilirubin​
     ○​ Risk: low Apgar, prematurity is major​
    ○​ Treatment:improve breastfeeding/phototherapy​

Breastfeeding Twins Chart 7.7 and below

    ○​ Exclusive BF = 3–4 months​
    ○​  If mothers take bad allergen this increases risk.
    ○​ A high diet of allericncs will effect everything so maintain a low-allergen diet.

Interventions

• There are several options to combat allergies and ensure that the best results are being followed by the parents ○​ Interventions:​ ○​ Pumping if poor latch​

AAP recommendation

○​ Breastfeeding=high-risk to Galactosemia = (High glucose)

Formula

○​ AAP recommendation, all pre-mature infants should receive Milk (not over lactate levels)

List Chart

Below is a list chart of what to collect and maintain storage ○ Methods: Hand/Manual, Electric pumps, hospital pumps ○​ Fridge: 4–7 days

Model program

​ BPPOP (Breastfeeding Promotion) ensures that the practice is great, there is also a hear campaign and Milk clubs