COVID-19: High-dose vitamin D supplements reduce hospitalization and mortality

Several studies have shown that optimizing your blood vitamin D levels with supplementation reduces the risk of contracting respiratory infections such as COVID-19. A new Hungarian study, published in Nutrients, has also found that very high doses of vitamin D given to hospitalized COVID-19 patients can reduce the risk of prolonged hospital stays and death due to severe complications.

Numerous studies and meta-analyses in recent years have examined the effects of vitamin D supplementation on COVID-19 infections and mortality, yet the results have been somewhat conflicting. This variation may in part be due to insufficient dosages that were unable to optimize blood levels of vitamin D and meet the body's needs. In the new Hungarian study, researchers aimed to determine the optimal dose of vitamin D as part of the treatment for complicated COVID-19 infections.
The researchers analyzed data from 148 COVID-19 patients admitted to Semmelweis University Hospital in Budapest between 2022 and 2023. From the first day of hospitalization, all patients received standard treatment and had their vitamin D levels measured. They were then divided into two similar groups with regard to disease severity and other relevant parameters. In addition to standard treatment, one group received extremely high doses of vitamin D—approximately 30,000 IU (750 mcg) daily for three days, totaling 90,000 IU (2,250 mcg). For comparison, the official recommendation for daily intake of vitamin D is only 5-20 mcg, meaning this supplementation aimed to provide a rapid and substantial boost.
The researchers then compared disease progression and mortality rates between the two groups. They also measured blood levels of the vitamin D metabolites 25(OH)D and 1,25(OH)₂D on days 0, 4, and 8. The effectiveness and safety of the high-dose vitamin D supplementation were also assessed, as excessive vitamin D intake can disrupt the body’s calcium balance.
The study found that these high doses restored vitamin D levels within four days in patients who were deficient. None of the patients experienced excessively high levels of 25(OH)D or 1,25(OH)₂D, suggesting that the body's vitamin D requirements increase significantly during periods with infection. Also, no disturbances were observed in the calcium balance.
Additionally, mortality was significantly lower in the group receiving vitamin D supplements. Their risk of dying from complications was 67% lower compared to the placebo group. Importantly, this significant difference was independent of the patients' vitamin D levels at baseline.
The researchers concluded that a daily dose of 30,000 IU of vitamin D for three days is an effective and safe treatment for reducing COVID-19-related mortality. They also suggested that continued vitamin D supplementation at lower doses might be beneficial.
According to the researchers, this is the first study to specifically investigate the effects of short-term, high-dose vitamin D supplementation on COVID-19 mortality. The study also highlights vitamin D's role in immune function and shows why high doses may be necessary when treating severe COVID-19 cases.

How does vitamin D protect against COVID-19 and other respiratory infections?

COVID-19 (SARS-CoV-2) is a virus that infects nasal cells and spreads to the lower respiratory tract. However, most people either fend off the virus or experience mild symptoms only. Severe cases often occur as a result of underlying health conditions and an impaired immune response, which can lead to acute respiratory distress syndrome (ARDS). This condition results from a cytokine storm and hyperinflammation in the lungs. Hyperinflammation can also damage blood vessels and other organs, potentially causing circulatory failure, organ failure, and death.
Thus, the greatest threat is not the virus itself but rather a weakened and dysregulated immune system.
Numerous studies have shown that vitamin D plays a crucial role in immune function. Vitamin D receptors have been identified in white blood cells such as monocytes, macrophages, dendritic cells, and activated T-cells. Monocytes, macrophages, and dendritic cells are part of the innate immune system, which combats most viruses and pathogens with little to no symptoms. T-cells, which belong to the adaptive immune system, have a unique ability to develop strong immunity against various viruses.
Vitamin D also helps control inflammation after an infection is cleared. Earlier studies have demonstrated vitamin D’s role in protecting against other viruses such as influenza, HIV, rotavirus, and hepatitis. Additionally, systemic hyperinflammation - one of the factors that make COVID-19 and other infections life-threatening - has been linked to low blood vitamin D levels. Adequate vitamin D intake can counteract this dangerous hyperinflammation by reducing T-cell secretion of pro-inflammatory cytokines such as IFNγ and TNFβ.
Therefore, maintaining optimal vitamin D levels throughout life and taking supplements to prevent deficiencies is essential.

References:

Liza Dalma Sümegi et al. Effect of Moderately High-Dose Vitamin D3 Supplementation on Mortality in Patients Hospitalized for COVID-19 Infection. Nutrients 2025

Muhammet Mesut Nezir Engin, Öner Özdemir. Role of vitamin D in COVID-19 and other viral infections. World Journal of Virology. 2024