Researchers looked at seven high-quality studies to see if pregnant women taking vitamin D supplements could help prevent respiratory diseases and allergies in their children. They found that while vitamin D is important for health, taking extra supplements during pregnancy didn’t significantly reduce the chances of children developing respiratory infections, asthma, wheezing, eczema, or allergies. This doesn’t mean vitamin D isn’t important—it just means that for these specific health outcomes, the extra supplements didn’t show the protective benefits researchers had hoped to find.

The Quick Take

  • What they studied: Whether pregnant women taking vitamin D supplements could help prevent their children from getting respiratory infections, asthma, wheezing, and allergies
  • Who participated: Seven different research studies involving pregnant women and their children were analyzed together. The exact total number of participants wasn’t specified, but these were high-quality randomized controlled trials where some pregnant women received vitamin D supplements and others received a placebo (fake pill)
  • Key finding: Prenatal vitamin D supplementation did not significantly reduce respiratory infections (asthma, wheezing) or allergic conditions (eczema, allergies) in children compared to those whose mothers didn’t take supplements
  • What it means for you: If you’re pregnant or planning to become pregnant, this suggests that taking extra vitamin D supplements specifically to prevent your child’s respiratory or allergy problems may not be effective. However, this doesn’t mean you shouldn’t maintain adequate vitamin D levels—talk to your doctor about what’s right for you

The Research Details

This was a meta-analysis, which means researchers searched through major medical databases (PubMed, Scopus, Web of Science, and Cochrane Library) to find all high-quality studies about pregnant women taking vitamin D and their children’s respiratory health. They only included randomized controlled trials, which are considered the gold standard in medical research because they randomly assign people to either receive the supplement or a placebo, making the comparison fair.

The researchers carefully evaluated the quality of each study using established scientific methods (the GRADE method and Cochrane risk-of-bias tool) to make sure they were only looking at reliable evidence. They then combined the results from all seven studies to see if there was a clear pattern showing whether vitamin D supplements helped prevent respiratory problems and allergies in children.

This research approach is important because individual studies sometimes show different results due to chance or small sample sizes. By combining multiple high-quality studies together, researchers can get a clearer picture of whether something actually works. This meta-analysis approach helps doctors and pregnant women make better decisions based on the strongest available evidence rather than relying on just one study.

This study is considered reliable because it only included randomized controlled trials, which are the most trustworthy type of medical research. The researchers used established quality assessment tools to evaluate each study, and they were transparent about their methods. The fact that they found consistent results across multiple studies (low variation between studies) for most outcomes adds confidence to their findings.

What the Results Show

The main finding was that prenatal vitamin D supplementation did not significantly reduce respiratory tract infections in children. The research showed that children whose mothers took vitamin D supplements had essentially the same rate of respiratory infections as children whose mothers didn’t take supplements.

For asthma, the results were similar—vitamin D supplementation during pregnancy did not significantly reduce the risk of children developing asthma. The same pattern held true for wheezing, another common respiratory symptom in children.

The researchers also looked at allergy-related outcomes. Vitamin D supplementation did not significantly reduce eczema (a skin condition often related to allergies), general allergic conditions, or immunoglobulin E (IgE) levels, which are markers of allergic responses in the body.

All of the secondary outcomes—eczema, allergic conditions, and IgE levels—showed the same pattern: no significant difference between children whose mothers took vitamin D supplements and those whose mothers didn’t. This consistency across multiple different health outcomes strengthens the conclusion that prenatal vitamin D supplementation may not be effective for preventing these specific conditions.

Previous research had suggested that vitamin D might have immune-boosting and respiratory-protective effects, which led scientists to hypothesize that supplements during pregnancy could help children’s lungs and immune systems. However, this meta-analysis of the highest-quality studies suggests that theory doesn’t translate into real-world benefits for preventing respiratory infections, asthma, wheezing, or allergies. This doesn’t mean vitamin D isn’t important for overall health—it just means the extra supplementation during pregnancy doesn’t appear to prevent these specific conditions.

The researchers didn’t specify the total number of children studied across all seven trials, making it harder to understand the overall scope. Some of the studies showed different results from each other (particularly for asthma), which suggests there may be factors the researchers didn’t account for. The studies may not have followed children long enough to see long-term effects, and they may not have included diverse enough populations to apply the findings to everyone. Additionally, the studies may have used different doses of vitamin D, which could affect the results.

The Bottom Line

Based on this evidence, taking extra vitamin D supplements during pregnancy specifically to prevent respiratory infections, asthma, wheezing, or allergies in your child is not recommended as a proven strategy. However, maintaining adequate vitamin D levels through diet, sunlight exposure, or supplements as recommended by your healthcare provider for overall health remains important. Pregnant women should discuss their vitamin D needs with their doctor rather than self-supplementing based on these findings.

This research is most relevant to pregnant women considering vitamin D supplementation specifically for respiratory and allergy prevention, and to healthcare providers advising pregnant patients. It’s less relevant to people concerned about vitamin D’s other health benefits. If you have a family history of asthma or allergies, talk to your doctor about evidence-based prevention strategies beyond vitamin D supplementation.

Since this research shows vitamin D supplementation didn’t help prevent these conditions, there’s no timeline for expecting benefits from this approach. If you’re interested in other proven prevention strategies for respiratory health and allergies, discuss those with your healthcare provider.

Want to Apply This Research?

  • Track your vitamin D intake and serum levels (if tested) during pregnancy, along with any respiratory or allergy symptoms in your child after birth, to monitor your own health outcomes and discuss patterns with your healthcare provider
  • Rather than focusing on vitamin D supplementation for respiratory prevention, use the app to track overall prenatal nutrition, ensure you’re meeting general vitamin D recommendations from your doctor, and monitor your child’s respiratory health for early intervention if needed
  • Log your prenatal vitamin intake, any respiratory symptoms in your child (cough, wheezing, infections), and allergy-related symptoms (eczema, allergic reactions) to create a health record you can review with your pediatrician to identify patterns and discuss appropriate interventions

This research summary is for educational purposes only and should not replace professional medical advice. The findings suggest that prenatal vitamin D supplementation may not prevent respiratory infections or allergies in children, but this does not mean vitamin D is unimportant during pregnancy. All pregnant women should discuss their vitamin D needs and supplementation with their healthcare provider, as individual circumstances vary. Do not start, stop, or change any supplements during pregnancy without consulting your doctor. If your child develops respiratory symptoms or allergies, seek appropriate medical evaluation and treatment from a qualified healthcare provider.