Micronutrients in Breastmilk

Breast milk is the "gold standard" for infant nutrition, providing a unique matrix of bioavailable nutrients, bioactive factors, and immunological components tailored to the human infant's needs. While macronutrients (proteins, fats, carbohydrates) provide the energy for growth, micronutrients (vitamins and minerals) in breast milk play critical roles in metabolic regulation, enzymatic function, bone mineralization, and neurodevelopment.

A defining characteristic of micronutrients in breast milk is their high bioavailability. Although the absolute concentration of certain minerals (like iron and zinc) may be lower in human milk compared to animal milk, their absorption rates are significantly higher due to the presence of specific carrier proteins and favorable ratios of other constituents,.

I. Fat-Soluble Vitamins in Breast Milk

The concentration of fat-soluble vitamins in breast milk can be influenced by maternal stores and dietary intake.

1. Vitamin A

• Content: Human milk contains approximately 53 $\mu$g/100 ml of Vitamin A.
• Colostrum: Colostrum is particularly rich in Vitamin A, which is essential for immune function and retinal development.
• Maternal Influence: Levels are generally adequate in well-nourished mothers. However, in Vitamin A deficient mothers, the levels may be compromised, necessitating supplementation.
• Preterm Milk: Preterm milk generally has higher Vitamin A concentrations than term milk.

2. Vitamin D

• Content: Breast milk is a poor source of Vitamin D, containing only 0.4–10 IU/100 ml (approximately 12–60 IU/L),,.
• Deficiency Risk: This level is insufficient to meet the daily requirement of 400 IU/day. Consequently, exclusively breastfed infants are at risk for Vitamin D deficiency and rickets if they do not receive adequate sunlight or supplementation,.
• Management: It is recommended that all exclusively breastfed infants receive 400 IU of supplemental Vitamin D per day starting from the first few days of life,.

3. Vitamin E

• Content: Human milk contains approximately 0.2 mg/100 ml.
• Function: It acts as an antioxidant, protecting cell membranes (especially red blood cells) from oxidative stress.
• Preterm Infants: Preterm infants are susceptible to Vitamin E deficiency (hemolytic anemia) because placental transfer occurs late in pregnancy. While breast milk provides some, preterm formulas or supplements are often needed to match the high oxidative stress environment.

4. Vitamin K

• Content: Breast milk is a poor source of Vitamin K, containing only 15 ng/100 ml, compared to 60 ng/100 ml in cow's milk.
• Clinical Implication: Due to low transfer across the placenta and low levels in breast milk, newborns are at risk for Hemorrhagic Disease of the Newborn (HDN),.
• Prophylaxis: All newborns should receive Vitamin K prophylaxis (0.5–1 mg IM) at birth to prevent bleeding, regardless of feeding method, but it is critical for breastfed infants due to delayed gut colonization,.

II. Water-Soluble Vitamins in Breast Milk

Water-soluble vitamins in breast milk are strongly correlated with maternal dietary intake. Deficiencies in the mother can lead to deficiencies in the infant.

1. Vitamin B-Complex

• Vitamin B12 (Cobalamin):
  • Content: 0.18 $\mu$g/100 ml.
  • Risk: Levels are dependent on maternal intake. Infants of strict vegetarian (vegan) mothers are at high risk for Vitamin B12 deficiency, which can present as megaloblastic anemia, hypotonia, and infantile tremor syndrome,.
• Vitamin B1 (Thiamine):
  • Content: 16 $\mu$g/100 ml.
  • Risk: Breastfed infants of mothers consuming polished rice diets (low thiamine) are at risk for Infantile Beriberi.
• Folate:
  • Content: 0.18 $\mu$g/100 ml. Folate is bound to folate-binding proteins in milk, which aids absorption.
• Other B Vitamins: Riboflavin (43 $\mu$g), Niacin (172 $\mu$g), and Vitamin B6 (11 $\mu$g) are present in adequate amounts for a healthy term infant if the mother is well-nourished.

2. Vitamin C (Ascorbic Acid)

• Content: Human milk contains 4.3 mg/100 ml, which is significantly higher than cow's milk (1.8 mg/100 ml).
• Adequacy: This amount is sufficient to prevent scurvy in infants. Pasteurization or boiling of animal milk destroys Vitamin C, putting artificially fed infants at risk if not fortified, whereas breastfeeding protects against this.

III. Minerals and Trace Elements

While the total mineral content (ash) of human milk is lower than that of cow's milk (0.2 g vs. 0.7 g), the bioavailability is superior.

1. Iron

• Content: Iron content is low, approximately 0.05–0.15 mg/100 ml.
• Bioavailability: Despite the low quantity, iron in breast milk has very high bioavailability (~50% absorption) compared to cow's milk or formula (~4-10%).
• Mechanism: This is largely due to Lactoferrin, an iron-binding protein in breast milk that facilitates absorption and sequesters iron from bacteria (bacteriostatic effect),.
• Duration: The iron stores of a term, breastfed infant are usually sufficient for the first 6 months. After 6 months, iron-rich complementary foods are required to prevent Iron Deficiency Anemia (IDA),.

2. Zinc

• Content: 0.53 mg/100 ml.
• Bioavailability: Zinc in human milk is highly bioavailable due to the presence of zinc-binding ligands (like citrate or picolinic acid).
• Clinical Relevance: This high bioavailability protects infants against zinc deficiency. In contrast, cow's milk contains phytates that inhibit absorption. However, zinc levels in breast milk decline sharply over the first few months, necessitating zinc-rich complementary foods after 6 months.
• Acrodermatitis Enteropathica: Infants with this genetic defect in zinc absorption typically do not manifest symptoms while exclusively breastfed due to the superior absorption of zinc from human milk.

3. Calcium and Phosphorus

• Calcium: 33 mg/100 ml.
• Phosphorus: 15 mg/100 ml.
• Ca:P Ratio: Breast milk has a highly favorable Ca:P ratio of > 2:1.
• Significance: This ratio ensures optimal calcium absorption and prevents hypocalcemic tetany. Cow's milk has a high phosphorus load (Ca:P ratio < 2:1), which can hinder calcium absorption and lead to neonatal hypocalcemia.

4. Other Trace Elements

• Copper: 0.04 mg/100 ml. Levels are higher in preterm milk.
• Selenium: Important antioxidant; levels correlate with maternal intake.
• Iodine: 7 $\mu$g/100 ml. Levels depend on maternal iodine status. Deficiency in the mother can lead to hypothyroidism in the infant.

IV. Variations in Breast Milk Composition

1. Preterm Milk (PTM) vs. Term Milk

Micronutrient composition varies significantly based on the gestational age of the neonate.

• Electrolytes and Minerals: Preterm milk has higher concentrations of Sodium, Chloride, Magnesium, Iron, Copper, and Zinc compared to term milk to meet the higher metabolic needs of the preterm infant.
• Decline: The high protein and mineral content in preterm milk declines to term milk levels by about 4–6 weeks.
• Need for Fortification: Despite higher initial levels, the rapid growth rate of Very Low Birth Weight (VLBW) infants exceeds the provision from breast milk alone. Human Milk Fortifiers (HMF) are added to expressed breast milk to provide additional Calcium, Phosphorus, Zinc, Vitamin D, and other nutrients to prevent osteopenia of prematurity and ensure adequate growth.

2. Comparison with Cow's Milk (Micronutrient Perspective)

Table: Comparison of Micronutrients (per 100 ml),