Researchers studied 400 children hospitalized with respiratory infections to understand how vitamin D levels affect their recovery. They found that children with low vitamin D stayed in the hospital almost twice as long as those with healthy vitamin D levels. Kids with low vitamin D also showed more severe symptoms, higher fevers, and needed more oxygen help. While this doesn’t prove vitamin D deficiency causes worse infections, it suggests that maintaining healthy vitamin D levels might be important for children’s immune systems, especially during cold and flu season.

The Quick Take

  • What they studied: Whether children with low vitamin D levels get sicker and stay in the hospital longer when they have respiratory infections like bronchitis or pneumonia
  • Who participated: 400 children admitted to hospitals in Eastern Europe between October 2020 and December 2024 with acute respiratory infections. They were divided into two groups: those with normal vitamin D levels and those with low or deficient levels.
  • Key finding: Children with low vitamin D stayed hospitalized for an average of 4.7 days compared to 2.9 days for children with normal vitamin D—about 60% longer. They also had higher fevers, worse symptom scores, and were more likely to need oxygen support (69.5% vs. 21%).
  • What it means for you: If your child has low vitamin D, they may be at higher risk for more severe respiratory infections. This suggests maintaining adequate vitamin D through sunlight, diet, or supplements might help protect children’s immune systems. However, this study shows an association, not proof that low vitamin D causes worse infections. Talk to your pediatrician about your child’s vitamin D levels.

The Research Details

Researchers looked back at medical records of 400 children who were hospitalized with respiratory infections over a 4-year period. They measured each child’s vitamin D level from a blood test and compared two groups: children with healthy vitamin D levels and children with low or deficient levels. They then compared how sick each group got, how long they stayed in the hospital, and what treatments they needed.

This type of study is called a retrospective comparison study. The researchers didn’t randomly assign children to have low or high vitamin D—they simply looked at what vitamin D levels the children naturally had and compared their health outcomes. This approach is useful for identifying patterns and associations between vitamin D and illness severity.

Understanding the connection between vitamin D and respiratory infection severity is important because vitamin D plays a key role in how our immune system fights infections. Many children around the world have low vitamin D levels, especially in regions with less sunlight. If low vitamin D truly contributes to worse infections, it could be a modifiable risk factor—something parents and doctors could address through supplementation or dietary changes.

This study has several strengths: it included a reasonably large sample of 400 children, measured actual vitamin D blood levels rather than relying on estimates, and looked at multiple markers of disease severity (fever, oxygen needs, inflammation markers). However, the study was conducted in Eastern Europe, so results may not apply equally to all populations. The study shows association but cannot prove that low vitamin D causes worse infections—other factors could explain the connection. The researchers used appropriate statistical methods for comparing groups.

What the Results Show

Children with low vitamin D levels had significantly longer hospital stays. Those with insufficient or deficient vitamin D stayed an average of 4.68 days, while children with normal vitamin D stayed only 2.89 days—a difference of nearly 2 days or about 60% longer.

The vitamin D levels themselves were dramatically different between groups. Children with low vitamin D had an average level of 21.63 ng/mL, while those with normal levels averaged 47.60 ng/mL—more than double. This confirms the groups were truly different in their vitamin D status.

Disease severity markers were consistently worse in the low vitamin D group. Children with low vitamin D had higher clinical severity scores (3.77 vs. 1.62), meaning doctors rated their illness as more serious. They also had higher inflammation markers in their blood (CRP levels of 3.50 vs. 1.64), indicating their bodies were fighting harder against infection.

Fever was significantly more common in children with low vitamin D—61% experienced fever compared to only 32% in the normal vitamin D group. Oxygen therapy requirement was dramatically higher in the low vitamin D group: 69.5% needed supplemental oxygen compared to just 21% in the normal vitamin D group. This suggests children with low vitamin D had more difficulty breathing and more severe lung involvement. Importantly, all cases of vitamin D deficiency occurred in the low vitamin D group, while no cases of deficiency were found in the normal vitamin D group, confirming the clear separation between the two groups.

This research aligns with previous studies showing that vitamin D plays an important role in immune function and controlling inflammation. Earlier research has suggested vitamin D deficiency may increase susceptibility to respiratory infections, but studies specifically looking at hospitalization outcomes in children with respiratory infections have been limited, particularly in Eastern European populations. This study adds to the growing body of evidence that vitamin D status may influence how severe respiratory infections become in children.

This study shows association but cannot prove cause-and-effect. It’s possible that children who get sicker from infections develop low vitamin D as a result of their illness, rather than low vitamin D causing the illness to be worse. The study only included children who were sick enough to be hospitalized, so it doesn’t tell us about children with respiratory infections who stayed home. The research was conducted in Eastern Europe, so results may differ in other geographic regions with different sunlight exposure and dietary patterns. The study didn’t account for other factors that might affect both vitamin D levels and infection severity, such as nutrition, socioeconomic status, or underlying health conditions.

The Bottom Line

Based on this research, maintaining adequate vitamin D levels in children appears important for immune health (moderate confidence). The CDC and pediatric organizations recommend vitamin D supplementation for children, especially those with limited sun exposure. Consider having your child’s vitamin D level checked if they have frequent respiratory infections. Encourage outdoor time when weather permits, include vitamin D-rich foods (fatty fish, fortified milk, egg yolks), and discuss supplementation with your pediatrician if your child has risk factors for deficiency.

Parents of children with frequent respiratory infections should pay attention to this research. Children living in northern climates with limited winter sunlight, those with darker skin tones (which reduces vitamin D production from sun exposure), children with dietary restrictions, and those with certain medical conditions affecting nutrient absorption should be especially mindful of vitamin D status. This research is less directly applicable to children living in sunny climates with adequate sun exposure and good dietary vitamin D intake.

If vitamin D deficiency is contributing to infection severity, correcting it would likely take several weeks to months to build up adequate levels in the body. You wouldn’t expect immediate changes, but over time, maintaining healthy vitamin D levels may help reduce the severity and duration of respiratory infections. Benefits would likely be most noticeable during cold and flu season.

Want to Apply This Research?

  • Track your child’s respiratory infection episodes (date, duration, severity on a 1-10 scale, whether hospitalization was needed) alongside vitamin D supplementation or sun exposure. Note any changes in infection frequency or severity over 3-6 months.
  • If your child has low vitamin D, set a daily reminder to take a vitamin D supplement as recommended by your pediatrician. Log the supplement intake in your health app. Also track outdoor time during daylight hours, aiming for 10-30 minutes of midday sun exposure several times per week (depending on skin tone and location).
  • Schedule annual vitamin D blood tests with your pediatrician, especially before winter months. Use the app to track patterns between vitamin D levels, supplementation consistency, sun exposure, and respiratory infection occurrences. Share this data with your doctor to optimize your child’s vitamin D management.

This research shows an association between low vitamin D and more severe respiratory infections in hospitalized children, but does not prove that vitamin D deficiency causes worse infections. This information is for educational purposes and should not replace professional medical advice. Do not start, stop, or change your child’s vitamin D supplementation without consulting your pediatrician. If your child has a respiratory infection or you’re concerned about their vitamin D levels, contact your healthcare provider for personalized guidance. This study was conducted in Eastern Europe and may not apply equally to all populations.