Why is there no vitamin K in breast milk?

October 14, 2025 •

4 min read

Newborns are born with very low levels of vitamin K, with only small amounts passing from the mother through the placenta. A breastfed infant's primary nutrition source, human milk, is also naturally low in this essential nutrient, which is why there is no vitamin K in breast milk at sufficient levels to prevent a serious bleeding disorder.

Quick Summary

Breast milk is naturally deficient in vitamin K, a crucial nutrient for blood clotting, leaving newborns at risk for vitamin K deficiency bleeding (VKDB). Several physiological factors in infants contribute to this risk, making newborn supplementation via a single intramuscular injection the standard of care. This ensures the baby has adequate clotting ability until they can produce their own.

Key Points

Low Natural Levels: Human breast milk contains naturally low concentrations of vitamin K, insufficient to meet a newborn's needs.
Poor Placental Transfer: Only minimal amounts of vitamin K cross the placenta, resulting in very low reserves in the newborn at birth.
Sterile Infant Gut: Newborns lack the intestinal bacteria that adults use to produce their own vitamin K, compounding the deficiency.
VKDB Prevention: A single intramuscular vitamin K shot at birth is the most effective way to prevent Vitamin K Deficiency Bleeding (VKDB).
Maternal Diet is Ineffective: Increasing the mother's vitamin K intake does not reliably raise breast milk levels enough to protect the infant.
VKDB Risk in Breastfed Infants: Exclusively breastfed babies who do not receive a vitamin K shot are at a much higher risk for late-onset VKDB.

The Physiological Reasons for Low Vitamin K in Breast Milk

Understanding why breast milk lacks sufficient vitamin K is crucial for new parents and healthcare providers. It is not an oversight of nature but a combination of biological factors related to the newborn's development and the way the body handles this specific vitamin. Breast milk contains only small, natural amounts of vitamin K, not nearly enough to fulfill the newborn's needs, especially in the first weeks of life.

Inadequate Placental Transfer

One of the primary reasons for a newborn's low vitamin K stores is poor placental transfer. Even if the mother's dietary intake of vitamin K is sufficient during pregnancy, only a minimal amount is able to cross the placenta to the fetus. The vitamin is fat-soluble and does not move efficiently from maternal to fetal circulation. As a result, babies are born with very limited reserves, making them vulnerable from birth.

Sterile Newborn Gut

Adults produce a significant portion of their vitamin K2 (menaquinone) thanks to the bacteria in their gut. However, a newborn's gastrointestinal tract is relatively sterile at birth and takes time to develop the necessary bacterial flora. This means that newborns cannot produce their own vitamin K for several weeks to months, relying solely on external sources. This further compounds the risk posed by the low levels found in breast milk.

Low Vitamin K Concentrations in Human Milk

Breast milk contains naturally low concentrations of vitamin K, typically ranging from 1 to 9 micrograms per liter. This is simply not enough to provide the recommended daily intake for an infant, particularly an exclusively breastfed one. Numerous studies have confirmed this, and even maternal supplementation does not significantly increase breast milk vitamin K levels enough to be a reliable source for the baby.

The Serious Risk: Vitamin K Deficiency Bleeding (VKDB)

Because of the inherent physiological factors, all newborns are at risk for vitamin K deficiency bleeding (VKDB), a life-threatening condition also known as hemorrhagic disease of the newborn. This bleeding disorder can occur internally and externally, with the most severe cases involving intracranial (brain) hemorrhage.

Types of VKDB

Early-Onset: Occurs within the first 24 hours and is most often linked to mothers who took certain medications during pregnancy that interfere with vitamin K metabolism, such as some anti-seizure drugs.
Classical-Onset: Appears between day 2 and the first week of life, primarily in breastfed infants who did not receive the prophylactic vitamin K shot.
Late-Onset: Develops between one week and six months of age. It occurs almost exclusively in exclusively breastfed infants who did not receive vitamin K at birth and can be very dangerous, with a high rate of intracranial bleeding.

Comparison: Vitamin K in Breast Milk vs. Formula


Feature	Breast Milk	Infant Formula (US)
Vitamin K Source	Trace amounts transferred from maternal diet.	Fortified with supplemental vitamin K.
Concentration	Naturally low (1-9 mcg/L) and insufficient for newborns.	High enough to reduce VKDB risk significantly.
Infant Requirement	Requires newborn supplementation to prevent VKDB.	Provides higher amounts, but supplementation is still standard for all newborns.
Maternal Diet Influence	Maternal vitamin K supplementation does not raise breast milk levels sufficiently to protect the infant.	Levels are consistent and not dependent on maternal diet.
Gut Flora Role	Infant must rely on developing gut flora for production, which takes weeks to months.	Higher content compensates for the sterile newborn gut.

Why Maternal Supplementation is Not a Solution

Some parents wonder why increasing the mother's vitamin K intake wouldn't solve the problem, rather than needing to supplement the baby directly. Several studies have shown that even large maternal doses do not result in a significant enough increase in breast milk to protect the infant from VKDB. The body simply does not transfer it effectively into human milk. This is why major health organizations, such as the American Academy of Pediatrics, maintain that the single, prophylactic vitamin K shot for the newborn is the only proven method to prevent VKDB.

The Recommended Solution: Prophylactic Vitamin K

Due to the severe and often devastating consequences of VKDB, the American Academy of Pediatrics has recommended the universal administration of a single intramuscular dose of vitamin K for all newborns since 1961. This shot is the most effective and safest way to ensure the baby has adequate clotting factors and protects them throughout the vulnerable early months of life. While some oral alternatives have been explored in other countries, they are often less effective, poorly absorbed, and require multiple doses, leading to potential issues with compliance.

The CDC provides excellent information on this topic for parents and caregivers. You can learn more about vitamin K recommendations and newborn health by visiting the CDC's Vitamin K factsheet.

Conclusion: The Importance of Supplementation

In summary, the reason there is no vitamin K in breast milk in sufficient quantities is due to a natural biological limitation. Newborns are born with inadequate stores, and their bodies cannot yet produce their own. Breast milk, despite being the ideal nutrition source for numerous reasons, simply does not contain enough to compensate. As a result, the risk of VKDB is very real for unsupplemented, exclusively breastfed infants. Prophylactic vitamin K administration at birth is a safe and highly effective intervention that has virtually eliminated this life-threatening condition in countries where it is standard practice. It is a critical component of newborn care that provides protection during the crucial first few months of life.

Frequently Asked Questions

Breast milk is naturally low in vitamin K for several biological reasons. Primarily, vitamin K does not pass efficiently through the placenta from mother to fetus during pregnancy, so newborns are born with very limited stores. The infant's gut is also sterile at birth and does not yet have the bacteria needed to produce its own vitamin K.

No, studies show that a mother's dietary intake or even high-dose supplements do not significantly increase the vitamin K concentration in breast milk to a level that can protect a newborn from deficiency. The body does not transfer it effectively into the milk.

Yes, it is highly recommended by all major health organizations, including the American Academy of Pediatrics. Since breast milk is a poor source of vitamin K and newborns have low stores, the shot is the best way to prevent the life-threatening condition of Vitamin K Deficiency Bleeding (VKDB).

VKDB is a serious bleeding disorder that can occur in newborns and young infants due to insufficient vitamin K. It can cause uncontrolled bleeding in various parts of the body, including the brain, which can lead to severe and sometimes fatal consequences.

Refusing the vitamin K shot significantly increases a newborn's risk of developing VKDB. Late-onset VKDB, which often affects exclusively breastfed infants, has a high rate of severe brain hemorrhage and can result in permanent damage or death.

While some countries use multi-dose oral vitamin K regimens, the intramuscular injection is considered the most effective and reliable method. Oral doses are less consistently absorbed, require better compliance, and are not approved for newborns in the United States.

Yes, the vitamin K shot has been safely administered to millions of newborns for decades. Any potential side effects, such as mild pain or bruising at the injection site, are very minimal compared to the life-threatening risks of VKDB.

Yes, infant formula sold in the United States and many other countries is fortified with vitamin K. This provides a more consistent level of the vitamin than breast milk, though newborn supplementation is still the standard of care for all infants.