Scientists reviewed research on how babies’ bones and minerals develop before and after birth. They found something surprising: vitamin D, which is super important for bone health in kids and adults, doesn’t seem to be as critical while babies are still in the womb. That’s because babies get minerals directly from their mothers through the placenta, not through their intestines like we do after birth. However, once a baby is born and starts breathing air, vitamin D suddenly becomes much more important for keeping bones strong and healthy. This review helps doctors understand why babies born to mothers with vitamin D deficiency can still have healthy bones at birth.

The Quick Take

  • What they studied: How vitamin D and a special protein called the vitamin D receptor affect bone and mineral development in babies before and after birth
  • Who participated: This was a review of many different studies, including research on animals and humans, clinical trials, case studies, and population studies. No single group of participants—instead, scientists looked at findings from many different research projects
  • Key finding: Babies in the womb don’t need vitamin D to develop healthy bones because they get minerals directly from their mothers. But after birth, vitamin D becomes essential for bone health and mineral balance
  • What it means for you: If you’re pregnant, vitamin D deficiency may not harm your baby’s bones before birth, but it could affect your own health. After birth, babies need adequate vitamin D for proper bone development. Talk to your doctor about vitamin D levels during pregnancy and infancy

The Research Details

This is a review article, which means scientists looked at many different studies already published on this topic and summarized what they found. They examined research from both animal studies (like mice and rats) and human studies, including clinical trials where doctors tested treatments, case reports about individual patients, and large population studies that looked at many people.

The researchers focused on understanding how mineral and bone development works differently in fetuses (babies in the womb) compared to newborns, children, and adults. They looked at how calcium, phosphorus, and magnesium move through the body at different life stages, and how vitamin D and a protein called the vitamin D receptor control these minerals.

By bringing together findings from many different types of studies, the authors could paint a complete picture of vitamin D’s role during fetal development versus after birth.

Understanding how fetal bone development works is important because it helps doctors know what to expect and what to worry about. If we know that vitamin D isn’t critical before birth, doctors won’t unnecessarily worry about every pregnant woman’s vitamin D levels affecting her baby’s bones. However, they can still focus on protecting the mother’s health and preparing for the baby’s needs after birth, when vitamin D becomes crucial

This is a review of existing research rather than a new study, so it depends on the quality of the studies it examined. The authors looked at multiple types of research (animal studies, human trials, and population studies), which gives a more complete picture. However, review articles are only as good as the research they summarize, so some findings may be stronger than others. The journal it was published in is respected for steroid and hormone research

What the Results Show

The main discovery is that fetuses develop healthy bones without needing much vitamin D. This happens because the placenta actively pumps minerals (calcium, phosphorus, and magnesium) directly into the baby’s bloodstream, bypassing the intestines. The baby’s blood mineral levels are actually higher than the mother’s, which helps bones grow quickly before birth.

Interestingly, vitamin D levels are kept very low in fetuses on purpose. The body breaks down vitamin D faster in the womb, and the hormone that usually triggers vitamin D production (called PTH) is also suppressed. This low vitamin D state doesn’t harm fetal bone development because the placenta is doing all the mineral-delivery work.

The research shows that babies born to mothers with severe vitamin D deficiency can still have normal bone mineralization and normal blood mineral levels at birth. This suggests the placenta is very efficient at getting minerals to the baby regardless of the mother’s vitamin D status.

Everything changes after birth. Once the baby takes its first breath and the umbilical cord is cut, blood calcium drops and phosphorus rises. This triggers the body to increase PTH and vitamin D production. Now the intestines become the main source of minerals, and vitamin D becomes essential for absorbing calcium and phosphorus from food.

The research also found that the vitamin D receptor (a protein that helps vitamin D do its job) doesn’t seem to be actively working in the fetus the way it does after birth. Babies born without a functioning vitamin D receptor or without the ability to make vitamin D still have normal bones at birth, but they may develop problems later in infancy and childhood. This shows that the fetal environment is fundamentally different from the newborn environment in how it handles minerals and vitamin D

This review confirms what some earlier research suggested but clarifies the picture. Previous studies hinted that vitamin D might not be critical before birth, but this comprehensive review explains why: the placenta takes over the job that vitamin D normally does after birth. The findings also align with observations that babies born in areas with very little sunlight (and thus low vitamin D) can still have healthy bones at birth, though they may develop problems later

This is a review of other studies, not original research, so it’s limited by what those studies found and how well they were done. Some of the animal studies may not perfectly reflect what happens in human babies. The review doesn’t provide new data on how common vitamin D deficiency in pregnancy actually is or how often it causes problems after birth. Additionally, most studies reviewed focused on severe vitamin D deficiency; we don’t know as much about mild to moderate deficiency

The Bottom Line

Pregnant women should maintain adequate vitamin D levels for their own health, even though it may not directly affect fetal bone development (moderate confidence). After birth, babies should receive adequate vitamin D through breast milk, formula, or supplements to support bone development and mineral absorption (high confidence). Healthcare providers should monitor vitamin D status in infants and young children, as this is when vitamin D becomes critical (high confidence)

Pregnant women should care about this research because it explains that while vitamin D is important for their own health, they don’t need to panic about vitamin D deficiency harming their baby’s bones before birth. New parents should care because it shows that vitamin D becomes very important right after birth. Healthcare providers should use this information to adjust their counseling—reassuring pregnant women about fetal bone health while emphasizing the importance of vitamin D after birth

Vitamin D’s importance shifts at birth. Before birth, the placenta handles mineral delivery. After birth, it takes a few weeks for the body to adjust and increase vitamin D production. Babies may start showing signs of vitamin D deficiency (like soft bones or poor growth) within weeks to months if they don’t get enough vitamin D after birth. Benefits of adequate vitamin D after birth appear gradually over months as bones strengthen

Want to Apply This Research?

  • Track your baby’s vitamin D intake sources: breast milk, formula type, supplemental drops, and sun exposure time. Record weekly to ensure baby is getting recommended amounts (400 IU daily for infants)
  • Set a daily reminder to give your baby vitamin D drops if recommended by your pediatrician. For pregnant users, track prenatal vitamin intake to ensure adequate vitamin D consumption for maternal health
  • Log your baby’s growth measurements (length and weight) monthly to monitor healthy bone development. Note any signs of poor growth or bone softness and share with your pediatrician. For pregnant users, track energy levels and bone health symptoms

This review summarizes scientific research on vitamin D’s role in fetal and infant development. It is not medical advice. Pregnant women and parents should consult with their healthcare provider about appropriate vitamin D supplementation for themselves and their babies. Individual needs vary based on diet, sun exposure, skin tone, and geographic location. Do not start or stop any supplements without discussing with your doctor first. If you have concerns about your baby’s bone development or growth, contact your pediatrician immediately