Nutrition During Lactation (Part 1)

Nutrition During Lactation (Part 1)

• General Outcome:

  • Understand physiological changes during lactation and their relation to nutrition.
  • Summarize the benefits of breastfeeding.
  • Understand factors affecting breastfeeding.

• Specific Outcomes:

  • Describe the development, structure, and functional components of the mammary gland.
  • Describe key hormonal influences on development and function.
  • Describe the benefits of breastfeeding for mother and infant.
  • Describe barriers to breastfeeding and ways to overcome them.

Development of Mammary Gland

• Estrogen and progesterone increase during puberty, influencing pubertal breast development.
• During pregnancy, estrogen stimulates the development of milk-producing mammary glands.
• Breasts produce milk from water and nutrients.
• Milk is stored in lobules until oxytocin signals muscles to contract and push milk through ducts.

Functional Units of the Mammary Gland

• Alveoli are the functional units of the mammary gland.
• Each alveolus contains secretory cells and a duct.
• Ducts are arranged like branches of a tree.
• Myoepithelial cells surround secretory cells and contract under oxytocin influence, ejecting milk into the ducts.

Lactogenesis

• Lactogenesis is another term for human milk production.
• Lactogenesis has three stages:
  • Stage I: Begins at the end of the last trimester (12 weeks before delivery), milk begins to form, and lactose & protein in milk increase.
  • Stage II: Occurs 2-5 days after birth with increased blood flow to the mammary gland. Delayed stage II is associated with breastfeeding failure.
  • Stage III: Occurs about ten days after birth, also called galactopoiesis, where milk composition becomes stable.

Hormonal Control of Lactation

• Prolactin: Stimulates milk production, stimulated by suckling, and influenced by stress, sleep, and exercise. Prolactin level in the blood isn't directly related to the amount of milk produced. If breasts aren't stimulated, prolactin levels can drop.
• Oxytocin: Involves in the ejection of milk from the milk glands, stimulated by suckling, also acts on the uterus during and after delivery – causing it to contract, seal blood vessels and shrink.

Secretion of Milk

• Lactose: Made in the secretory cells.
• Milk fat: Comes from maternal triglycerides and fatty acids produced in the breast. Actively transported from the cell into milk.
• Sodium, potassium & water: Actively transported from the cell into milk.
• Proteins: Captured from the mother's bloodstream through transcytosis.
• Leukocytes: Pass directly between cells (paracellular pathway)
• Milk components are secreted into ducts through exocytosis.

Letdown Reflex

• Also called the milk ejection reflex.
• A natural response during breastfeeding when the body releases milk from the breasts.
• Stimulation: Baby sucking on the breast stimulates sensory nerve endings in the nipple and areola.
• Hormonal response: Signals are sent to the brain to release oxytocin. Oxytocin causes the muscles around the alveoli to contract.
• Milk release: Muscle contractions push milk through the milk ducts and out of the nipple.

Human Milk Composition (Summary)

• Human milk: the only food needed by infants for the first six months
• Composition: changeable over a feeding, dependent on infant age, maternal nutritional status, and location.
• Variations: colostrum and mature milk have different compositions.

Human Milk Composition - Colostrum

• A thick, yellow fluid produced during lactogenesis II (days 1–3 after birth).
• Infants may drink only 2-20 mL (0.5–4 tsp) per feeding.
• High in protein and immunoglobulin A (provides antibodies). High in lactoferrin (regulates iron absorption).

Human Milk Composition - Water & Energy

• Human milk is isotonic with maternal plasma.
• Provides 0.65–0.75 kcal/mL. Fewer calories than milk substitutes. Enhanced growth in the first 3-4 months in exclusively breastfed infants.
• At 8-11 months, breastfed infants are thinner than infants who consume human milk substitutes.

Human Milk Composition - Lipid, Protein, Carbohydrate, and Fat-soluble Vitamins

• Lipid: Contributes half of the calories in human milk, with variations in foremilk and hindmilk. Contains DHA, trans fatty acids, and cholesterol.
• Protein: Protein content is relatively low, and influenced by infant age. Contains casein and whey proteins.
• Carbohydrate: Dominant carbohydrate is lactose, which enhances calcium absorption. Other carbohydrates include oligosaccharides, which stimulate the growth of beneficial bacteria, and inhibit harmful ones.
• Fat-soluble Vitamins:
• Vitamin A: Higher concentration in colostrum, often in beta-carotene form. Important for calcium absorption and bone metabolism.
• Vitamin D: Content reflects maternal exposure to sunlight.
• Vitamin E: Protects cells, crucial for neurological and muscle function.
• Vitamin K: Used in blood clotting, with some newborns at risk of deficiency and needing intramuscular supplementation.

Human Milk Composition - Water-soluble Vitamins

• Content reflects maternal diet and supplements.
• Well-nourished mothers provide infants with appropriate amounts of nutrients – minerals like magnesium, calcium, iron, and zinc are highly available.
• Vitamins like vitamin C and lactose promote iron absorption.

Taste of Human Milk

• Human milk taste is important to newborns.
• The taste is slightly sweet, carrying flavors of ingested compounds (e.g., mint, garlic, vanilla).
• Transfer of flavors is selective.
• Variation in flavor can influence infant interest in consumption.