Researchers reviewed studies about vitamin D and COVID-19 to understand if low vitamin D levels make the disease worse. They found that people with COVID-19 often have low vitamin D, and those with very low levels (below 20 ng/mL) may have worse outcomes and higher death rates. The review suggests that maintaining healthy vitamin D levels (above 30 ng/mL) through supplements might help reduce disease severity and improve survival chances. However, some studies show mixed results, so more research is needed to fully understand vitamin D’s role in COVID-19.

The Quick Take

  • What they studied: Whether low vitamin D levels make COVID-19 worse and if taking vitamin D supplements could help people with COVID-19 recover better
  • Who participated: This was a review of many different studies published between January 2020 and July 2022. The researchers looked at studies involving COVID-19 patients with different vitamin D levels
  • Key finding: People with COVID-19 who had very low vitamin D (below 20 ng/mL) were more likely to have serious complications and worse outcomes. Those with healthy vitamin D levels (above 30 ng/mL) appeared to have less severe disease
  • What it means for you: If you have COVID-19 or want to prepare your body to fight it, maintaining adequate vitamin D levels may be helpful. However, this shouldn’t replace vaccines or other proven treatments. Talk to your doctor about your vitamin D levels and whether supplements are right for you

The Research Details

This was a narrative review, which means researchers searched through published scientific studies to summarize what we know about vitamin D and COVID-19. They looked at articles published between January 2020 and July 2022 in the PubMed database, which is a large collection of medical research.

The researchers focused on four main areas: how vitamin D helps your immune system work, whether low vitamin D increases COVID-19 risk, whether low vitamin D makes COVID-19 more severe, and whether taking vitamin D supplements improves outcomes in COVID-19 patients.

A narrative review is like a comprehensive summary of what scientists have discovered on a topic, rather than a single experiment. It helps identify patterns and trends across many different studies.

This type of review is important because it brings together information from many different studies conducted around the world. Instead of relying on one study, researchers can see if findings are consistent across multiple research groups. This helps identify what we know for sure versus what still needs more investigation.

This is a narrative review, which means it summarizes existing research but doesn’t conduct new experiments. The strength of the conclusions depends on the quality of the studies reviewed. The researchers looked at published studies, which have been checked by other scientists, but some studies may have had limitations. The review covers a specific time period (2020-2022), so newer research isn’t included. Some studies showed mixed results, suggesting the relationship between vitamin D and COVID-19 is complex and not fully understood yet

What the Results Show

The review found that vitamin D plays an important role in helping your immune system fight infections. It does this by increasing special proteins in your body called cathelicidins and beta-defensins that help kill germs.

Many studies showed that people with COVID-19 often have low vitamin D levels. More importantly, people with very low vitamin D (below 20 ng/mL) had worse outcomes, including more serious lung problems and higher death rates.

The research suggests that maintaining vitamin D levels above 30 ng/mL appears to reduce how severe COVID-19 becomes and may lower the risk of death. This suggests that vitamin D supplementation could potentially help people with COVID-19 recover better.

However, the review also notes that some studies showed contradictory results, with some research finding no clear connection between vitamin D levels and COVID-19 infection risk.

The review identified that vitamin D deficiency is particularly linked to a serious breathing condition called acute respiratory distress syndrome (ARDS), which is one of the most dangerous complications of severe COVID-19. This connection suggests that vitamin D may be especially important for protecting your lungs during COVID-19 infection.

This review builds on growing evidence that vitamin D is important for immune health during respiratory infections. Previous research has shown vitamin D helps fight other respiratory viruses, so finding a similar pattern with COVID-19 makes sense. However, the mixed results in some studies mean scientists are still working to fully understand exactly how much vitamin D helps and for whom it works best

This review has several important limitations. First, it only looked at studies published through July 2022, so newer research isn’t included. Second, the studies reviewed had different methods and quality levels, making it hard to draw firm conclusions. Third, some studies showed contradictory results, suggesting the relationship between vitamin D and COVID-19 isn’t completely clear. Fourth, the review doesn’t tell us the exact right dose of vitamin D supplements or who would benefit most. Finally, this review summarizes other people’s work rather than conducting new experiments, so we can’t be as certain about the findings as we would be from a large, well-designed study

The Bottom Line

Based on this review, maintaining adequate vitamin D levels (above 30 ng/mL) appears to be beneficial, particularly if you have COVID-19 or are at risk for severe illness. However, confidence in these recommendations is moderate because some studies showed mixed results. Vitamin D supplementation should be considered as one part of overall health, not as a replacement for vaccines, treatments prescribed by doctors, or other proven prevention methods. Talk to your healthcare provider about whether vitamin D testing and supplementation are appropriate for you

This research is most relevant for people who have COVID-19, people at high risk for severe COVID-19 (older adults, people with chronic health conditions), and anyone interested in supporting their immune system. People living in areas with limited sunlight or those who spend most time indoors may particularly benefit from vitamin D attention. However, this research shouldn’t replace medical advice from your doctor or proven COVID-19 treatments

If you start taking vitamin D supplements, it typically takes several weeks to build up adequate levels in your body. If you already have COVID-19, vitamin D won’t provide immediate relief, but maintaining healthy levels may help your body fight the infection more effectively. For prevention, consistent vitamin D intake over months is more important than short-term supplementation

Want to Apply This Research?

  • Track your vitamin D supplementation daily (dose and type) and note any respiratory symptoms or illness episodes. If you’ve had COVID-19, record your recovery timeline and symptom severity to identify patterns
  • Set a daily reminder to take your vitamin D supplement at the same time each day. If you don’t take supplements, increase sun exposure to 10-30 minutes daily (depending on skin tone and location) or eat more vitamin D-rich foods like fatty fish, egg yolks, and fortified milk
  • Check in monthly on consistency with vitamin D intake. Consider getting your vitamin D level tested annually or before winter months. Track any respiratory infections or illness severity to see if maintaining adequate vitamin D correlates with better health outcomes for you personally

This review summarizes research about vitamin D and COVID-19 but should not replace medical advice from your healthcare provider. Vitamin D supplementation is not a substitute for COVID-19 vaccines, treatments prescribed by doctors, or other proven prevention methods. If you have COVID-19 or are considering vitamin D supplements, especially if you take other medications or have health conditions, consult your doctor first. The studies reviewed showed mixed results, meaning the relationship between vitamin D and COVID-19 is not completely understood. Always follow your healthcare provider’s recommendations for testing, supplementation, and treatment