Researchers studied 19 hospitalized COVID-19 patients to understand whether vitamin D and a protein that carries it in the blood affect how sick people get. The patients were mostly older adults (average age 71) with serious illness—over half sadly did not survive. The study found that vitamin D levels were very low in this group, but surprisingly, the carrier protein didn’t seem to make a difference in how severe the disease was or what happened to patients. While this is an early finding from a small group, it suggests vitamin D may play a role in COVID-19 severity, though more research is needed to understand exactly how.

The Quick Take

  • What they studied: Whether vitamin D levels and a special protein that carries vitamin D in the blood are connected to how severe COVID-19 becomes and what happens to patients
  • Who participated: 19 hospitalized COVID-19 patients, mostly older adults (average age 71), with about 55% men. Most had serious or critical illness, and many had other health conditions like high blood pressure or diabetes
  • Key finding: Patients had very low vitamin D levels (average of 16.88, which is quite low). The carrier protein didn’t show clear differences between patients who got better and those who didn’t, but the extremely low vitamin D levels in such a sick group is noteworthy
  • What it means for you: This early research suggests low vitamin D may be connected to severe COVID-19, but this is a very small study with limited patients. Don’t make major changes based on this alone—talk to your doctor about your vitamin D levels, especially if you’re older or have other health conditions

The Research Details

This was a cross-sectional study, which means researchers looked at a group of hospitalized COVID-19 patients at one point in time and measured their vitamin D levels and a protein called DBP (vitamin D binding protein). They collected information about how sick each patient was, what symptoms they had, other health conditions they had, and what happened to them (whether they recovered, went home, or sadly passed away). They then looked for patterns between the vitamin D measurements and the patient outcomes.

The researchers measured two things: the actual vitamin D in the blood and the DBP protein that carries vitamin D around the body. They compared these measurements between patients with different disease severity levels and different outcomes.

Understanding whether vitamin D plays a role in COVID-19 severity is important because vitamin D is something people can potentially control through diet, supplements, or sun exposure. If vitamin D really does affect how sick someone gets with COVID-19, it could lead to new ways to help patients. This study looked at both the vitamin D itself and the protein that carries it, which is more complete than just checking vitamin D alone.

This study has some important limitations to understand: it only included 19 patients, which is a very small group. The patients were mostly older and very sick, so results might not apply to younger or less sick people. This was a snapshot study (cross-sectional), not a long-term follow-up, so we can’t prove that low vitamin D caused the severe illness. The study doesn’t tell us whether giving vitamin D supplements would have helped. These results are interesting but need confirmation with larger studies before drawing firm conclusions.

What the Results Show

The most striking finding was that vitamin D levels were extremely low in this group of hospitalized patients, with an average of just 16.88 (normal is usually above 30). This was true across all severity levels, suggesting that low vitamin D may be common in people sick enough to need hospitalization for COVID-19.

Interestingly, the DBP protein (the carrier protein) didn’t show significant differences between patients with different outcomes or disease severity levels. This was unexpected because some previous research suggested this protein might be important. The average DBP level was 5.51, which the researchers noted was exceptionally low.

The patient group was very sick overall: 41.77% had critical disease, 30.38% had severe disease, and only 3.80% had mild disease. Unfortunately, 53.16% of the patients died, 34.18% were discharged home, and 12.66% recovered. Most patients needed oxygen support, with over half needing a special mask that provides continuous pressure to help breathing.

The study found that common health conditions were very prevalent: 67% had high blood pressure, 38% had diabetes, and 25% had heart disease. The most common symptoms were shortness of breath (77%), cough (76%), and chest pain (61%). About 45% had persistent fever and 27% had high fever. Vaccination rates were low in this group (only 25% vaccinated), and most of those vaccinated had received two doses. The hospitalization length varied widely, with 38% staying 8-14 days and 23% staying longer than 14 days.

Previous research has shown mixed results about vitamin D’s role in COVID-19. Some studies suggested low vitamin D was linked to worse outcomes, while others found less clear connections. This study adds to that discussion by showing very low vitamin D in a severely ill group, but the finding that the carrier protein (DBP) didn’t differ between groups contradicts some earlier research that suggested this protein was important. The extremely low DBP values in this study are unusual and suggest this might be an important area for future research.

This study has several important limitations: Only 19 patients were studied, which is very small and makes it hard to draw firm conclusions. All patients were hospitalized and very sick, so we don’t know if these findings apply to people with milder COVID-19 or those who didn’t need hospitalization. The study was done at one point in time, so we can’t tell if low vitamin D caused the severe illness or if severe illness caused low vitamin D. The study doesn’t tell us whether giving vitamin D supplements would have helped patients. Different countries and regions may have different vitamin D levels in their populations, so results might not apply everywhere. The low vaccination rate in this group (25%) means results might not apply to more vaccinated populations.

The Bottom Line

Based on this early research, we cannot yet recommend specific vitamin D supplementation as a COVID-19 treatment. However, maintaining adequate vitamin D levels is generally good for overall health. If you’re concerned about your vitamin D level, especially if you’re older, have limited sun exposure, or have other health conditions, ask your doctor to check your level. If it’s low, your doctor can recommend appropriate supplementation. This should not replace vaccines, masks, or other proven COVID-19 prevention methods. Confidence level: Low—this is a very small preliminary study that needs larger confirmation.

This research is most relevant to: older adults (especially those over 60), people with chronic health conditions like diabetes or heart disease, people who are hospitalized with COVID-19, and healthcare providers caring for severely ill COVID-19 patients. People with mild COVID-19 or those who haven’t had COVID-19 should not assume these findings apply to them. This is not yet strong enough evidence to change treatment approaches for most people.

If vitamin D supplementation were to help, it would likely take weeks to months to see effects, as vitamin D builds up in the body gradually. This is not a quick-acting treatment. For people already hospitalized with severe COVID-19, vitamin D would be a supportive measure, not a primary treatment.

Want to Apply This Research?

  • If your doctor recommends vitamin D supplementation, track your daily intake (dose and type) and note any symptoms or health changes weekly. Record energy levels, respiratory symptoms, and overall wellness on a 1-10 scale to monitor trends over 8-12 weeks.
  • If recommended by your doctor, establish a daily vitamin D supplement routine (same time each day with food for better absorption). Set a phone reminder and log it in your health app. Also track sun exposure time when possible, as natural vitamin D production is free and effective.
  • Plan to recheck vitamin D blood levels every 8-12 weeks after starting supplementation to see if levels are improving. Track this in your app along with any changes in how you feel. Share results with your doctor to adjust supplementation if needed. For long-term monitoring, check levels seasonally since sun exposure varies by season.

This research is preliminary and based on a very small group of 19 patients. It should not be used to diagnose, treat, or prevent COVID-19 or any other disease. The findings are not yet strong enough to change medical treatment or supplementation recommendations. Always consult with your healthcare provider before starting any new supplements or making changes to your health routine, especially if you have existing health conditions or take medications. This study does not replace proven COVID-19 prevention methods like vaccination. If you have COVID-19 or suspect you do, seek immediate medical attention from a qualified healthcare provider.