Researchers studied 123 children who had long-lasting symptoms after COVID-19 infection to understand why some kids struggled more than others. They found that children with lower vitamin D levels in their blood had more severe long-term symptoms. The study also discovered that certain genetic differences in how children’s bodies use vitamin D affected symptom severity. Kids with the lowest vitamin D levels and specific genetic patterns had the worst outcomes. This suggests that vitamin D plays an important role in how severely children experience long COVID, and it might be something doctors could monitor or treat in the future.

The Quick Take

  • What they studied: Whether vitamin D levels and genetic differences in how bodies process vitamin D affect how severe long COVID symptoms are in children
  • Who participated: 123 children from a hospital who had persistent symptoms lasting weeks or months after COVID-19 infection; 90 completed the symptom survey and 109 had blood tests done
  • Key finding: Children with lower vitamin D levels had significantly worse long COVID symptoms (p=0.0052), and kids with both low vitamin D AND certain genetic patterns had the most severe symptoms
  • What it means for you: If your child has long COVID, checking their vitamin D level might help explain symptom severity, though this research is early-stage and shouldn’t replace medical advice from your doctor

The Research Details

This was an observational study where researchers recruited children from a hospital who were experiencing long-lasting COVID symptoms. They asked the children detailed questions about their symptoms and collected blood samples to measure vitamin D levels. They also analyzed the children’s DNA to identify specific genetic variations related to how their bodies process vitamin D. The researchers then looked for patterns between vitamin D levels, genetic variations, and how severe each child’s symptoms were.

The study examined two main things: first, whether children with lower vitamin D had worse symptoms, and second, whether certain genetic patterns made a difference. They looked at blood markers like immune cells and liver enzymes to understand the biological connections.

Understanding why some children have worse long COVID symptoms is important because it could help doctors predict which kids might struggle more and potentially offer treatments. If vitamin D plays a real role, it’s something relatively simple to measure and potentially treat. The genetic information helps explain why different children might respond differently to the same infection.

This study has some strengths: it measured actual vitamin D blood levels rather than just asking about diet, and it looked at genetic information which is objective. However, the sample size of 123 is moderate, not all participants completed every test (90 out of 123 finished the symptom survey), and this is a single-center study from one hospital. The results suggest associations but don’t prove cause-and-effect. More research with larger groups is needed to confirm these findings.

What the Results Show

The main finding was that children with lower vitamin D levels had significantly more severe long COVID symptoms. The relationship was clear and statistically significant, meaning it’s unlikely to be due to chance. When researchers looked at genetic variations in the VDR gene (which controls how bodies use vitamin D), they found that children with the GG genetic pattern had less severe symptoms compared to those with AA or AG patterns.

The most important discovery was the combined effect: children who had BOTH low vitamin D levels (below 20 ng/ml, which is considered deficient) AND the AA or AG genetic patterns had the worst symptoms overall. This suggests that vitamin D and genetics work together to influence long COVID severity.

The study also found connections between vitamin D levels and various blood markers. Children with higher vitamin D had different patterns of immune cells and liver enzymes, suggesting vitamin D affects how the body responds to lingering COVID effects.

The research found that vitamin D levels were connected to several blood markers: children with higher vitamin D had higher levels of certain liver enzymes (LDH and AST), while having different patterns of immune cells like neutrophils, lymphocytes, and eosinophils. These findings suggest vitamin D influences how the immune system and other body systems respond during long COVID recovery.

Previous research has shown that vitamin D deficiency is linked to more severe acute COVID-19 infection. This study extends that finding to long COVID in children, suggesting vitamin D’s role continues even after the initial infection. The genetic component is newer research territory—while scientists knew VDR genetic variations existed, this appears to be one of the first studies examining their role in long COVID severity in children.

The study was relatively small with 123 participants, and not everyone completed all tests. It was conducted at a single hospital, so results might not apply to all children everywhere. The study shows associations (relationships) but cannot prove that low vitamin D causes worse symptoms—it’s possible other factors are involved. The study is observational, meaning researchers watched what happened rather than randomly assigning children to different vitamin D levels. More research with larger, more diverse groups is needed to confirm these findings and determine if treating vitamin D deficiency actually improves long COVID symptoms.

The Bottom Line

Based on this research, doctors might consider checking vitamin D levels in children with long COVID symptoms (moderate confidence level). If vitamin D is low, supplementation might be worth discussing with your child’s doctor, though this study doesn’t yet prove it will improve symptoms. General vitamin D recommendations for children should still be followed regardless of long COVID status. This research is preliminary and should not replace personalized medical advice.

Parents of children experiencing long COVID symptoms should be aware of this research. Children with confirmed long COVID and low vitamin D levels might benefit most from discussing supplementation with their doctor. This is less relevant for children who had mild COVID or recovered quickly. Healthcare providers treating long COVID in children should consider this information when evaluating patients.

If vitamin D supplementation were to help, improvements in symptoms would likely take weeks to months to become noticeable, not days. Vitamin D levels in the blood take time to build up, and long COVID symptoms typically improve gradually anyway. This is a long-term consideration, not a quick fix.

Want to Apply This Research?

  • Track your child’s vitamin D supplementation (if prescribed) and long COVID symptom severity weekly using a simple 1-10 scale, noting specific symptoms like fatigue, brain fog, or shortness of breath to see if patterns emerge over 8-12 weeks
  • If your child’s doctor recommends vitamin D supplementation, set up a daily reminder in the app to take it at the same time each day, and log when doses are taken to maintain consistency
  • Create a monthly check-in to review symptom trends alongside vitamin D supplementation adherence; share this data with your child’s healthcare provider at appointments to help them assess whether treatment is working

This research is preliminary and shows associations, not proven cause-and-effect relationships. It should not be used to diagnose or treat long COVID. Always consult with your child’s healthcare provider before starting any vitamin D supplementation or making changes to treatment. This study was conducted in a hospital setting with a specific group of children and may not apply to all children with long COVID. Individual responses to vitamin D supplementation vary, and medical supervision is important for proper dosing and monitoring.