Researchers studied breast milk from 98 mothers to understand special proteins called osteocalcin that may help babies develop strong bones and healthy brains. They found these proteins are present in breast milk and change over time as mothers continue breastfeeding. The amount of one type of protein was especially high in the first milk mothers produce after birth. While scientists still need to learn exactly how these proteins help babies, this discovery suggests breast milk contains even more beneficial compounds than previously known.

The Quick Take

  • What they studied: Whether special bone-related proteins called osteocalcin are found in breast milk and if they change as mothers continue breastfeeding
  • Who participated: 98 mothers with an average age of about 32 years old who provided breast milk samples at different times during their breastfeeding journey
  • Key finding: Two types of osteocalcin proteins were found in breast milk. One type was twice as high in the first milk (colostrum) compared to mature milk produced later. First-time mothers had slightly higher levels than mothers who had breastfed before.
  • What it means for you: Breast milk contains special proteins that may support your baby’s bone development and brain health. This is another reason why breastfeeding provides unique benefits, though scientists are still learning exactly how these proteins help babies grow.

The Research Details

Researchers collected breast milk samples from 98 mothers at four different times: within the first 3 days after birth, at 1 week, at 2 weeks, and at 3 months. They measured the amounts of two types of osteocalcin proteins in each sample using laboratory tests. They also asked mothers about their diet, exercise habits, weight, age, and how many children they had previously given birth to.

This approach allowed scientists to track how these proteins change as breastfeeding continues and to see if a mother’s lifestyle affected the protein levels in her milk. By collecting samples at multiple time points, researchers could understand the natural pattern of these proteins throughout the breastfeeding period.

Understanding what’s in breast milk helps explain why it’s so beneficial for babies. By measuring these proteins at different stages, researchers can see if they’re most important early in breastfeeding or throughout. This information could eventually help scientists understand how to support infant development better.

This study measured actual breast milk samples using established laboratory methods, which is reliable. The sample size of 98 mothers is reasonable for this type of research. However, the study only describes what’s present in breast milk—it doesn’t yet prove how these proteins actually help babies develop. More research is needed to understand the real benefits.

What the Results Show

The researchers found that both types of osteocalcin proteins are present in breast milk throughout the breastfeeding period. One type, called undercarboxylated osteocalcin (ucOCN), was particularly interesting: it was twice as concentrated in colostrum (the first milk produced) compared to mature milk produced later. This suggests the first milk may be especially rich in compounds that support early infant development.

The other type, called carboxylated osteocalcin (cOCN), remained relatively stable throughout breastfeeding, though it decreased slightly as the total amount of protein in milk decreased over time. This pattern suggests different roles for each protein type.

First-time mothers had slightly higher levels of both proteins in their colostrum compared to mothers who had breastfed before, though this difference was small. This finding suggests that a mother’s breastfeeding experience may influence the composition of her milk.

The study examined whether a mother’s lifestyle factors—such as diet quality, exercise frequency, body weight, age, or number of previous pregnancies—affected the osteocalcin levels in her milk. Interestingly, most lifestyle factors showed no clear connection to these protein levels. This suggests that osteocalcin in breast milk may be naturally regulated by the body rather than significantly influenced by what mothers eat or how much they exercise.

This is one of the first studies to specifically measure osteocalcin proteins in human breast milk. Previous research has identified many other beneficial compounds in breast milk, but these bone-related proteins hadn’t been thoroughly studied in this context. The finding that these proteins are present adds to our growing understanding of breast milk’s complexity and suggests it contains more specialized compounds than previously documented.

The study describes what proteins are present in breast milk but doesn’t explain what they actually do for babies or mothers. Scientists still need to conduct additional research to understand the real health benefits. The study also didn’t measure whether these proteins are actually absorbed and used by babies’ bodies. Additionally, all participants were relatively similar in age and background, so results may not apply to all populations of breastfeeding mothers.

The Bottom Line

If you’re breastfeeding, this research suggests that your milk naturally contains beneficial proteins that may support your baby’s bone and brain development. Continue breastfeeding as recommended by health professionals. No specific dietary or lifestyle changes are needed based on this study, as the research shows these proteins are naturally present regardless of lifestyle factors. (Confidence level: Moderate—more research is needed to confirm health benefits.)

Breastfeeding mothers and parents interested in infant nutrition should know about this research. Healthcare providers may find this information useful when counseling families about breastfeeding benefits. This research is less relevant for families using formula, though formula manufacturers may eventually use these findings to improve their products.

These proteins are present from the very beginning of breastfeeding, with the highest concentrations in the first milk. Babies would receive these compounds immediately, though scientists still need to determine how long it takes to see any health effects.

Want to Apply This Research?

  • Track breastfeeding duration and timing (especially noting when you started) to correlate with your baby’s developmental milestones like bone strength assessments or cognitive development checks at pediatric visits.
  • Use the app to log breastfeeding sessions and note any questions about your milk composition to discuss with your healthcare provider. Set reminders to maintain consistent breastfeeding practices, as the research suggests milk composition naturally adapts over time.
  • Monitor your baby’s growth and development through regular pediatric checkups, which can assess bone health and developmental progress. Use the app to record these checkup results and any observations about your baby’s growth patterns over the first three months and beyond.

This research describes proteins found in breast milk but does not yet prove specific health benefits for babies. The study is preliminary and more research is needed to understand how these proteins affect infant development. This information should not replace advice from your pediatrician or healthcare provider. If you have questions about breastfeeding or your baby’s nutrition, consult with your doctor or a lactation specialist. This research does not provide medical advice and should not be used to diagnose or treat any condition.