Researchers studied over 3,300 American preschoolers to understand how vitamin D affects their chances of getting colds and respiratory infections. They found that children with low vitamin D levels were significantly more likely to catch respiratory infections compared to those with adequate vitamin D. The risk was especially high for certain groups, including older preschoolers, girls, children from lower-income families, and those exposed to secondhand smoke. These findings suggest that making sure preschoolers get enough vitamin D might help prevent common childhood illnesses.

The Quick Take

  • What they studied: Whether children with low vitamin D levels get more colds and respiratory infections than children with normal vitamin D levels
  • Who participated: 3,316 American children between ages 2 and 6 years old, representing a mix of different backgrounds, incomes, and living situations across the United States
  • Key finding: Children with vitamin D deficiency had 56% higher odds of getting respiratory infections compared to children with adequate vitamin D levels. About 8 out of every 100 children studied had vitamin D deficiency, and more than half had less-than-ideal vitamin D levels.
  • What it means for you: If your preschooler has low vitamin D, they may be at higher risk for catching colds and other respiratory infections. Getting enough vitamin D through diet, supplements, or safe sun exposure might help protect them. However, this study shows an association, not proof that low vitamin D causes infections, so talk to your pediatrician about your child’s vitamin D status.

The Research Details

This was a cross-sectional study, which means researchers looked at information collected from a large group of American children at one point in time (between 2007 and 2016). They used data from NHANES, a national health survey that regularly checks on the health of Americans. The researchers measured vitamin D levels in the children’s blood and asked parents whether their children had gotten colds or serious infections in the past month. They then looked at whether children with different vitamin D levels had different rates of infections.

The researchers divided children into three groups based on their vitamin D levels: deficient (very low), insufficient (somewhat low), and sufficient (adequate). They used statistical methods to account for other factors that might affect infection risk, such as family income, diet, exercise, and exposure to secondhand smoke. This helps them understand whether vitamin D itself was connected to infection risk, or whether other factors were responsible.

This research approach is important because it uses real-world data from a representative sample of American children, rather than just studying one group in a lab. By looking at many children with different backgrounds and circumstances, the researchers could see whether vitamin D’s effect on infections was consistent across different groups or whether some children were more affected than others. This helps doctors and parents understand who might benefit most from vitamin D supplementation.

This study has several strengths: it included a large, nationally representative sample of children, meaning the results likely apply to American preschoolers in general. The researchers carefully adjusted for many other factors that could affect infection risk. However, the study has limitations: it only shows association (that low vitamin D and infections occur together), not causation (that low vitamin D causes infections). Also, parents reported infections from memory, which might not be completely accurate. The study was conducted over several years, so practices and vitamin D recommendations may have changed since then.

What the Results Show

Children with vitamin D deficiency had 56% higher odds of getting any respiratory infection compared to children with adequate vitamin D. This means that if a child with adequate vitamin D had a certain chance of getting an infection, a child with deficient vitamin D would have a noticeably higher chance.

When researchers looked at different types of infections, they found stronger connections for common colds and chest colds (47% higher odds) than for serious infections like pneumonia or influenza (24% higher odds, though this difference wasn’t statistically significant). This suggests vitamin D may be more protective against everyday respiratory infections than against the most serious ones.

The study found that more than half of all preschoolers studied (52%) had vitamin D levels that were lower than ideal, even though only 8% had severe deficiency. This means that many American preschoolers might not have optimal vitamin D levels for protecting against infections.

The research revealed that certain groups of children faced even higher risks from vitamin D deficiency. Children aged 4-6 years had nearly double the infection risk when deficient compared to younger preschoolers. Girls with vitamin D deficiency had 81% higher odds of infection than girls with adequate vitamin D. Children from lower-income households and underweight children also showed significantly elevated risks. Children exposed to secondhand smoke had even higher infection risks when vitamin D deficient. Interestingly, children whose diets included adequate vitamin D (at least 6.7 micrograms daily) had reduced infection risk even if their blood vitamin D levels were low, suggesting that dietary vitamin D intake provides some protection.

Previous research has suggested a connection between vitamin D and respiratory infections, but results have been mixed, especially in preschool-aged children. This study provides clearer evidence in a large, representative US population. The findings align with studies showing vitamin D’s role in immune function, though the exact mechanisms remain under investigation. The study confirms that vitamin D deficiency is common in American children and supports growing evidence that this deficiency may have real health consequences.

This study shows that vitamin D deficiency and respiratory infections are connected, but it cannot prove that low vitamin D causes infections. Other unmeasured factors could explain the connection. The study relied on parents remembering whether their children had infections in the past month, which might not be completely accurate. The data was collected between 2007-2016, so current vitamin D status and infection rates in American children might be different. The study cannot determine whether giving vitamin D supplements to deficient children would actually reduce infections, since it only looked at existing vitamin D levels and infections that had already occurred.

The Bottom Line

Based on this research, pediatricians may want to consider screening for vitamin D deficiency in preschoolers, especially those in high-risk groups (older preschoolers, girls, low-income families, underweight children, or those exposed to secondhand smoke). If deficiency is found, vitamin D supplementation may be recommended. The American Academy of Pediatrics recommends 600 IU of vitamin D daily for children ages 1-18 years. However, individual needs may vary, so consult your pediatrician about appropriate vitamin D intake for your child. This evidence is moderate in strength—it shows a clear association but not definitive proof of cause and effect.

Parents of preschoolers should be aware of vitamin D’s potential role in respiratory health, especially if their child frequently gets colds or infections. Pediatricians should consider vitamin D status when evaluating children with recurrent respiratory infections. This is particularly important for families with limited sun exposure, dietary restrictions that limit vitamin D sources, or lower incomes that might limit access to vitamin D-rich foods. Children in high-risk groups (older preschoolers, girls, underweight children, or those exposed to secondhand smoke) may benefit most from vitamin D screening. However, this research should not replace personalized medical advice from your child’s doctor.

If a child with vitamin D deficiency receives supplementation, it typically takes several weeks to months to normalize blood vitamin D levels. Improvements in infection rates might take a similar timeframe or longer, as the immune system gradually strengthens. This is not a quick fix—think of it as building stronger immune defenses over time rather than an immediate protection.

Want to Apply This Research?

  • Track your child’s respiratory infections monthly (colds, coughs, ear infections) alongside vitamin D intake sources (fortified milk, supplements, sun exposure time). Record the date, type of infection, and duration to identify patterns over 2-3 months before and after any vitamin D changes.
  • Work with your pediatrician to ensure your child meets daily vitamin D recommendations (600 IU for ages 1-18). This can be achieved through fortified milk or plant-based alternatives (about 2-3 cups daily), vitamin D-rich foods like fatty fish or egg yolks, or a daily supplement. Log these sources in your app to track compliance.
  • Set monthly reminders to record any respiratory infections your child experiences. Track vitamin D intake sources daily. After 3 months, review the data with your pediatrician to see if infection frequency has changed. If your child has had blood work done, note the vitamin D level and retest after 2-3 months of supplementation to confirm levels are improving.

This research shows an association between low vitamin D and respiratory infections in preschoolers but does not prove that vitamin D deficiency causes 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. Individual vitamin D needs vary based on age, diet, sun exposure, and health status. If your child has frequent infections or health concerns, speak with your healthcare provider about appropriate evaluation and treatment. This study was conducted on US children and may not apply to all populations.