Chapter Six – Lactation

Physiology of the Breast

The mammary gland is composed of several structures that support milk production:

• Alveoli: Rounded or oblong-shaped cavities where milk is produced.

• Secretory Cells: Cells responsible for milk secretion.

• Myoepithelial Cells: Surround the secretory cells and help eject milk into the ducts.

Breast development is typically complete 12-18 months after menarche.

Stages of Lactogenesis

1. Lactogenesis I: Milk formation begins in the last part of pregnancy and continues until a few days postpartum.

2. Lactogenesis II: 2-5 days postpartum, increased blood flow to the breast occurs and milk “comes in.”

3. Lactogenesis III: 9 days postpartum onward, milk composition stabilizes.

Hormones Involved in Lactation

• Prolactin: Promotes milk synthesis and alveoli development; stimulated by suckling.

• Oxytocin: Responsible for milk ejection or the ‘let-down’ reflex; stimulated by suckling, nipple stimulation, and even the thought of the baby.

Human Milk Composition

Human milk is the sole nutritional source for most infants for the first 6 months and provides both nourishment and immune protection.

Colostrum – “Liquid Gold”

• First milk secreted during the first few days postpartum.

• Thicker, buttery-yellow appearance.

• Higher in proteins (secretory IgA and lactoferrin), minerals, and white blood cells compared to mature milk.

• Lower in carbohydrates, fats, and vitamins.

Immune Factors in Human Milk

• Lactoferrin: Binds free iron, preventing bacterial growth and supporting iron absorption.

• Secretory IgA: Protects mucosal surfaces and supports immune system development.

Macronutrients in Human Milk

Lipids

• Provide ~50% of calories.

• Foremilk is lower in fat; hindmilk is richer in fat.

• DHA (omega-3): Essential for retinal and brain development.

• ARA (omega-6): Supports growth and brain function.

• Cholesterol: Needed for hormone production and nerve development.

Proteins

• Total protein content is lower than cow’s milk but easier to digest.

• Casein (~40% of total protein): Helps with calcium absorption.

• Whey proteins (~60% of total protein): Provide antiviral and antimicrobial effects.

• Non-protein nitrogen: Used for producing non-essential amino acids.

Carbohydrates

• Lactose: Dominant carbohydrate, supports CNS development and calcium absorption.

• Oligosaccharides: Promote growth of beneficial gut bacteria and prevent pathogen binding.

Micronutrients in Human Milk

Fat-Soluble Vitamins

• Vitamin D: Low in breast milk; supplementation recommended.

• Vitamin K: Newborns receive an injection at birth to prevent clotting disorders.

Minerals

• Lower mineral concentration than cow’s milk, reducing strain on infant kidneys.

• Iron: Although low in quantity, it is highly bioavailable (50% absorption vs. 12% in formula).

• Zinc: Bound to protein for better absorption.

Bioactive Cells and Bacteria in Human Milk

• Contains living cells that help shape the infant’s gut microbiome.

• Diverse bioactive components adjust in response to maternal and infant needs.

Dynamic Nature of Breast Milk

• Changes daily, within feedings, and across developmental stages.

• Foremilk is lower in fat; hindmilk is higher in fat and calories.

• Maternal diet influences milk taste, exposing infants to varied flavors.

Benefits of Breastfeeding

For Infants

• Lower infant mortality.

• Reduced risk of SIDS, gastrointestinal infections, ear infections, asthma, allergies, and chronic diseases.

• Cognitive benefits: Higher IQ scores in breastfed children.

• Pain reduction (analgesic effect).

For Mothers

• Hormonal benefits: Increased oxytocin helps the uterus contract.

• Physical benefits: Delayed ovulation, potential weight loss, lower risk of breast and ovarian cancer.

• Psychological benefits: Enhanced bonding, reduced stress.

Breast Milk Supply and Demand

• Suckling sends signals to increase milk production.

• Frequent nursing is essential to maintain supply.

• Breast size does not determine milk supply.

Feeding Patterns and Infant Hunger Cues

• Hunger signs: Hand-to-mouth movements, sucking, head-turning, crying (late sign).

• Feeding frequency: 10-12 feedings per day for newborns.

• Weight loss up to 7% in the first 5 days is normal.

• 6 wet diapers and 3-4 soiled diapers per day indicate adequate intake.

Tooth Decay and Breastfeeding

• Human milk has protective components, but nursing at night after 1 year increases risk.

• Dental check-ups recommended 6 months after the first tooth erupts.

Vitamin & Mineral Supplementation for Infants

• Vitamin K: Given at birth.

• Vitamin D: Supplementation from 2 months onward.

• Iron: Needed from 4-6 months onward.

Nutrient Needs for Breastfeeding Mothers

• Energy needs:

  • 0-6 months: Additional 500 kcal/day (330 kcal from diet, 170 kcal from fat stores).

  • 7-12 months: Additional 400 kcal/day.

• Protein-calorie malnutrition affects volume but not quality of milk.

• Vegan mothers may need B12 supplementation.

MyPlate and Dietary Guidelines for Breastfeeding

• Supports balanced nutrition and adequate hydration.

• Reinforces the importance of iron-rich foods for infants after 4-6 months.

WIC and Breastfeeding Support

• Provides education, lactation counseling, and food assistance for breastfeeding mothers.