Babies born very early and very small often don’t get enough vitamin D, which is important for building strong bones. Researchers studied 215 tiny premature babies in a hospital and gave some of them twice as much vitamin D as others. The babies who received the higher dose had stronger, denser bones when they left the hospital. This suggests that giving premature babies more vitamin D might help protect their bones during this critical early period when they’re growing rapidly but can’t eat normally yet.

The Quick Take

  • What they studied: Whether giving premature babies twice the standard amount of vitamin D (800 IU instead of 400 IU per day) would help them develop stronger bones by the time they left the hospital.
  • Who participated: 215 very premature babies (born weighing less than 1,500 grams or about 3.3 pounds) admitted to a hospital’s intensive care unit over a 14-year period. These babies were too small and sick to eat normally when born.
  • Key finding: Babies who received 800 IU of vitamin D daily had noticeably stronger bones (measured by a special X-ray scan) compared to babies who received 400 IU, even after accounting for differences in their birth weight and how long they needed IV nutrition.
  • What it means for you: If you have a very premature baby in the hospital, talk to your doctor about vitamin D supplementation. The higher dose appears safe and may help your baby’s bones develop better during this vulnerable time. However, this finding needs to be confirmed with more research before it becomes standard practice everywhere.

The Research Details

This was a retrospective study, meaning researchers looked back at medical records of babies who had already been treated at the hospital between 2010 and 2023. They compared two groups: babies who received 400 IU of vitamin D daily and babies who received 800 IU daily, starting when the babies were two weeks old. The vitamin D was given once the babies could tolerate some nutrition through their feeding tubes.

To measure bone strength, doctors used a special type of X-ray called DEXA (dual-energy X-ray absorptiometry), which is like taking a picture that shows how dense and strong bones are. This scan was done when each baby was ready to leave the hospital. The researchers carefully analyzed the data to account for differences between the two groups, such as how much the babies weighed at birth and how long they needed IV nutrition.

This research approach is important because very premature babies face a unique problem: they miss out on the last few months of pregnancy when bones normally get much stronger. They also can’t eat enough food to get vitamin D naturally. By looking at real patient records over many years, researchers could see what actually happened in practice and whether the higher vitamin D dose made a real difference in bone development.

Strengths of this study include a reasonably large sample size (215 babies) and a long time period of data collection (14 years), which makes the findings more reliable. The researchers also adjusted their analysis to account for differences between the two groups. However, this was a retrospective study looking at past records rather than a carefully controlled experiment, so we can’t be completely certain the vitamin D caused the stronger bones—other factors might have played a role. The study was conducted at a single hospital, so results might differ in other settings.

What the Results Show

The main finding was clear: babies receiving 800 IU of vitamin D daily had stronger bones at discharge than babies receiving 400 IU. Specifically, when researchers measured bone mineral apparent density (BMAD)—essentially how tightly packed and strong the bone material is—the higher-dose group showed significantly better results across the whole body.

When the researchers focused on the thighbone (femur), the difference was even more striking. Babies in the 800 IU group had noticeably denser thighbone material. This is particularly important because the thighbone is one of the body’s largest and most important bones.

Interestingly, the two groups started out slightly different: babies in the 800 IU group were born slightly heavier on average and had mothers who were slightly older. They also needed IV nutrition for a longer period. The researchers used statistical methods to account for these differences, and the vitamin D benefit remained significant even after these adjustments.

The study found that vitamin D supplementation was associated with improved bone mineralization throughout the baby’s entire body, not just in one location. This suggests that the vitamin D was having a widespread positive effect on bone development. The fact that the benefit was particularly strong in the femur (thighbone) is noteworthy because this bone bears weight and is critical for future mobility and health.

Previous research had already shown that 400 IU of vitamin D daily could safely raise vitamin D levels in premature babies to adequate amounts. This new study builds on that knowledge by asking whether an even higher dose (800 IU) could provide additional benefits for bone development. The findings suggest that doubling the dose may offer real advantages without apparent safety concerns, though more research is needed to confirm this.

This study has several important limitations. First, it looked backward at medical records rather than randomly assigning babies to receive different doses in a controlled experiment, so we can’t be completely certain the vitamin D caused the stronger bones. Second, it was conducted at a single hospital in South Korea, so the results might not apply to all premature babies everywhere. Third, the study didn’t follow babies after they left the hospital, so we don’t know if the stronger bones at discharge led to better long-term health outcomes. Finally, the two groups had some differences at the start (birth weight, mother’s age, duration of IV nutrition), which could have influenced the results even though researchers tried to account for these differences statistically.

The Bottom Line

Based on this research, there is moderate evidence that 800 IU of vitamin D daily may be beneficial for very premature babies’ bone development compared to 400 IU. However, parents and doctors should know this is based on one study at one hospital. The recommendation would be: discuss vitamin D supplementation with your baby’s neonatal team, and if supplementation is recommended, 800 IU appears to be a safe and potentially more effective dose than 400 IU. More research is needed before this becomes a universal standard.

This research is most relevant to parents of very premature babies (born before 32 weeks of pregnancy and weighing less than 1,500 grams) who are in neonatal intensive care. It’s also important for neonatologists and pediatricians who care for these vulnerable babies. If your baby was born at a normal weight or after 32 weeks of pregnancy, this specific research may not apply to you, though vitamin D is still important for all babies.

The benefits measured in this study were visible by the time babies left the hospital, which is typically 2-4 months after birth for very premature infants. However, the long-term effects on bone health, growth, and development are unknown and would require follow-up studies to determine.

Want to Apply This Research?

  • For parents of premature babies in the NICU: track the daily vitamin D dose received (in IU) and note the date supplementation began. Record any bone density measurements or X-ray results if available. This creates a record to discuss with your pediatrician at follow-up appointments.
  • If your baby is prescribed vitamin D supplementation, set a daily reminder to ensure the supplement is given at the same time each day. Use the app to log when the dose was given and note any changes in feeding tolerance or other observations to share with your medical team.
  • Create a long-term tracking system that follows your baby’s growth and development milestones after hospital discharge. Note height, weight, and any bone-related health issues. Share this information with your pediatrician at regular check-ups to monitor whether the early vitamin D supplementation had lasting benefits.

This research applies specifically to very premature babies (under 1,500 grams birth weight) in hospital settings. Do not use this information to make decisions about vitamin D supplementation for your baby without consulting your pediatrician or neonatologist. This study was conducted at a single hospital and needs confirmation through larger, multi-center research before becoming standard practice. The long-term health benefits of higher vitamin D doses in premature infants remain unknown. Always follow your healthcare provider’s recommendations for your individual baby’s care.