According to Gram Research analysis, babies hospitalized with severe bronchiolitis have significantly lower vitamin D levels than those with milder cases. A 2026 cross-sectional study of 75 infants in Myanmar found that babies with severe bronchiolitis averaged 35.31 nmol/L of vitamin D compared to 44.29 nmol/L in non-severe cases, with none of the severely ill babies having sufficient vitamin D levels. However, researchers cannot yet prove that low vitamin D causes worse bronchiolitis—only that the two appear strongly connected.
Researchers in Myanmar studied 75 babies with bronchiolitis, a common lung infection in infants, to understand the connection between vitamin D levels and how sick the babies got. They found that babies with severe bronchiolitis had significantly lower vitamin D levels than those with milder cases. The study suggests that vitamin D deficiency may be linked to more serious bronchiolitis symptoms, though researchers note the findings are preliminary and more research is needed to prove vitamin D directly causes the difference.
Key Statistics
A 2026 cross-sectional study of 75 infants hospitalized with bronchiolitis in Myanmar found that babies with severe bronchiolitis had a mean vitamin D level of 35.31 nmol/L compared to 44.29 nmol/L in non-severe cases.
Among 75 infants with bronchiolitis studied in 2023, 64% had severe disease, and none of the 48 severely ill babies had sufficient vitamin D levels, while only 1 of the 27 non-severely ill babies was vitamin D deficient.
A 2026 analysis of 75 hospitalized infants found that each one-point increase in bronchiolitis severity score was independently associated with a 2.95 nmol/L decrease in serum vitamin D concentration.
Among 54 vitamin D insufficient infants in a 2026 study, 59.3% had severe bronchiolitis while 40.7% had non-severe bronchiolitis, demonstrating a clear pattern linking lower vitamin D to greater disease severity.
The Quick Take
- What they studied: Whether babies with lower vitamin D levels get sicker when they have bronchiolitis, a common breathing infection in infants.
- Who participated: 75 babies aged 1 to 12 months old hospitalized with bronchiolitis in Myanmar between August 2022 and July 2023. Most (86%) were between 1 and 6 months old.
- Key finding: Babies with severe bronchiolitis had vitamin D levels averaging 35.31 nmol/L, compared to 44.29 nmol/L in babies with milder cases—a meaningful difference that showed a clear pattern.
- What it means for you: If your baby has bronchiolitis, vitamin D status may play a role in how severe the illness becomes. However, this study cannot prove vitamin D deficiency causes worse bronchiolitis, only that they appear connected. Talk to your pediatrician about vitamin D screening and supplementation.
The Research Details
This was a cross-sectional study, which means researchers looked at a group of babies at one point in time rather than following them over months or years. They enrolled 75 babies hospitalized with bronchiolitis at Yankin Children’s Hospital in Myanmar from August 2022 to July 2023. For each baby, doctors measured their vitamin D blood levels and rated how severe their bronchiolitis was using a scoring system called the Wang clinical severity score. The researchers then compared vitamin D levels between babies with severe versus non-severe bronchiolitis to see if there was a connection.
The Wang severity score evaluates symptoms like how fast the baby is breathing, how much effort it takes to breathe, and oxygen levels in the blood. Vitamin D levels were measured in blood samples and categorized as deficient (very low), insufficient (low-normal), or sufficient (adequate). The researchers used statistical tests to determine whether the differences they observed were likely real or just due to chance.
This study design is useful for identifying patterns and associations between vitamin D levels and bronchiolitis severity, which can guide future research. However, because it’s cross-sectional (a snapshot in time), it cannot prove that low vitamin D causes worse bronchiolitis—only that they tend to occur together. Understanding these connections is important because if vitamin D truly plays a role, it could lead to new ways to prevent or treat severe bronchiolitis in infants.
The study has several limitations that readers should understand. The sample size is small (75 babies), which means the findings may not apply to all babies everywhere. The researchers did not control for other factors that might affect both vitamin D and bronchiolitis severity, such as nutrition, sun exposure, or season of the year. The study was conducted in one hospital in Myanmar, so results may differ in other regions or countries. Most importantly, this is a cross-sectional study, which cannot establish cause-and-effect relationships. The authors themselves note that ‘causal inference cannot be made’ from their findings.
What the Results Show
Among the 75 babies studied, 64% had severe bronchiolitis and 36% had non-severe bronchiolitis. Babies with severe bronchiolitis had a mean vitamin D level of 35.31 nmol/L, while babies with non-severe bronchiolitis had a mean level of 44.29 nmol/L—a difference of about 9 nmol/L.
The researchers found a clear pattern: 16 of the babies with severe bronchiolitis were vitamin D deficient, compared to only 1 baby with non-severe bronchiolitis who was deficient. Among 54 babies with insufficient vitamin D levels, 59.3% had severe bronchiolitis while 40.7% had non-severe bronchiolitis. Notably, none of the 48 babies with severe bronchiolitis had sufficient vitamin D levels.
Statistical analysis showed a moderate inverse correlation (meaning as one goes down, the other goes up) between vitamin D levels and bronchiolitis severity. For every one-point increase in the severity score, vitamin D levels dropped by approximately 2.95 nmol/L. This relationship was statistically significant, meaning it’s unlikely to have occurred by chance alone.
The researchers examined whether age or gender affected the relationship between vitamin D and bronchiolitis severity. Neither factor showed a statistically significant effect. This suggests that the vitamin D-severity connection appears similar across the age range studied (1-12 months) and between boys and girls.
This study aligns with numerous international research findings suggesting that low vitamin D levels are associated with increased bronchiolitis severity. The pattern observed in Myanmar mirrors what researchers have documented in other countries over the past three decades. However, most previous studies have also been limited by similar constraints—small sample sizes, lack of control for confounding factors, and cross-sectional designs that cannot prove causation.
The authors explicitly acknowledge several important limitations. The small sample size (75 babies) limits how much these findings can be generalized to all babies with bronchiolitis worldwide. The study lacks control for confounding variables—factors like overall nutrition, breastfeeding status, sun exposure, and season of diagnosis that could independently affect both vitamin D levels and bronchiolitis severity. The study provides no information about seasonality, which is important because vitamin D production varies by season and geographic location. Most critically, this cross-sectional design cannot establish whether low vitamin D causes worse bronchiolitis, whether severe bronchiolitis causes vitamin D depletion, or whether both are caused by a third factor. The authors conclude that ‘clinical significance is limited’ by these constraints.
The Bottom Line
Based on this research, pediatricians may consider screening vitamin D levels in infants hospitalized with bronchiolitis, particularly those with severe disease (moderate confidence). Vitamin D supplementation may be worth discussing with your child’s doctor, especially if your baby has risk factors for deficiency such as limited sun exposure or dietary restrictions (low to moderate confidence). However, this study alone cannot recommend vitamin D supplementation as a treatment for bronchiolitis—larger, controlled trials are needed to establish whether supplementation actually improves outcomes.
Parents of infants with bronchiolitis should be aware of this potential connection and discuss vitamin D status with their pediatrician. Healthcare providers caring for infants with respiratory infections may consider vitamin D assessment as part of comprehensive care. Researchers studying bronchiolitis should note this association as a direction for future investigation. People living in regions with limited sun exposure or those with dietary restrictions affecting vitamin D intake should be particularly attentive to infant vitamin D status.
If vitamin D deficiency is identified and supplementation is started, improvements in bronchiolitis severity would likely be observed over days to weeks as the infection resolves. However, this study does not provide data on how quickly vitamin D supplementation might improve symptoms. Any changes to your baby’s care should be discussed with your pediatrician and monitored closely.
Frequently Asked Questions
Does low vitamin D cause severe bronchiolitis in babies?
This study found a strong association between low vitamin D and severe bronchiolitis, but cannot prove causation. Babies with severe bronchiolitis had significantly lower vitamin D levels (35.31 vs 44.29 nmol/L), but researchers note that larger controlled trials are needed to establish whether vitamin D deficiency actually causes worse disease.
Should I give my baby vitamin D supplements to prevent bronchiolitis?
This study suggests vitamin D may play a role in bronchiolitis severity, but does not provide evidence that supplementation prevents the infection. Discuss vitamin D screening and supplementation with your pediatrician based on your baby’s individual risk factors and dietary intake, not solely based on this research.
What vitamin D level is considered deficient in infants?
This study measured vitamin D in nmol/L and found severe bronchiolitis cases averaged 35.31 nmol/L. Generally, pediatricians consider levels below 50 nmol/L (or 20 ng/mL) as deficient and 50-75 nmol/L as insufficient, though recommendations vary by region and age.
Can vitamin D supplementation help treat bronchiolitis?
This study does not test whether vitamin D supplementation treats bronchiolitis—it only measures vitamin D levels in babies who already have the infection. While the association is interesting, clinical trials would be needed to determine if supplementation improves outcomes in babies with active bronchiolitis.
Are all babies with bronchiolitis vitamin D deficient?
No. In this study of 75 infants, 64% had severe bronchiolitis and lower vitamin D levels, but 36% had non-severe bronchiolitis with higher average vitamin D levels. This shows vitamin D status varies among babies with bronchiolitis, and other factors also influence disease severity.
Want to Apply This Research?
- If your baby has been hospitalized with bronchiolitis, track their vitamin D levels at diagnosis and during follow-up visits. Record the specific values (in nmol/L or ng/mL) and note the date. Compare these to your pediatrician’s recommended targets for your baby’s age.
- Work with your pediatrician to establish a vitamin D supplementation plan if your baby is deficient or insufficient. Set reminders to give supplements consistently, and log each dose in your app. Track any changes in respiratory symptoms, feeding, and overall energy levels as you implement supplementation.
- Schedule vitamin D level rechecks 8-12 weeks after starting supplementation to confirm levels are improving. Create a long-term tracking system that records vitamin D levels seasonally, as levels naturally fluctuate. If your baby experiences another respiratory infection, note the vitamin D level at that time to identify any patterns.
This research describes an association between vitamin D levels and bronchiolitis severity in infants but cannot establish cause-and-effect relationships. The study is limited by small sample size, single-location design, and lack of control for confounding factors. These findings should not be used to diagnose, treat, or prevent bronchiolitis without consulting your pediatrician. Vitamin D supplementation decisions should be made in consultation with your child’s healthcare provider based on individual assessment. If your infant shows signs of respiratory distress, difficulty breathing, or severe illness, seek immediate medical attention.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.