One such study done in November 2020 found that COVID-19 patients who had low levels of vitamin D had a higher chance of dying from the disease. The study published in Scientific Reports found that severe COVID-19 patients had "markedly low" vitamin D levels and high inflammatory responses. The Indian authors recommended "mass administration of vitamin D supplements" to populations at risk for COVID-19."
A later study from May 2021, also published in Scientific Reports, noted the positive effects of vitamin D on the immune system. It argued that vitamin D promotes the expression of anti-inflammatory cytokines and reduces pro-inflammatory cytokines. Many COVID-19 treatments focused on eliminating the virus in the body instead of regulating the hyper-inflammation caused by these cytokines.
Cytokines are proteins produced by the body to control inflammation. These cytokines are released in the case of infections, but there are times that excess cytokines than needed are produced. This resulting "cytokine storm" becomes dangerous – and has been linked to the deaths of COVID-19 patients.
The authors of the May 2021 study then looked at the effects of Pulse D therapy on COVID-19 patients' cytokine levels. Pulse D therapy involved daily high-dose supplementation with vitamin D – as much as 60,000 international units (IU) – for a period of eight to 10 days. The therapy was done alongside standard therapy that COVID-19 patients received.
The patients who underwent Pulse D therapy saw their vitamin D levels increase significantly. Meanwhile, their inflammatory markers significantly decreased without any side effects. Thus, the study authors concluded that Pulse D therapy could be safely added to COVID-19 treatment protocols for improved outcomes.
Another study from June 2021 noted the positive effects of a type of vitamin D on COVID-19 patients in Spain. The study published in the Journal of Clinical Endocrinology & Metabolism involved researchers giving vitamin D3, also called calcifediol, to patients in the COVID-19 ward of Hospital del Mar in Barcelona.
About half of the patients received 21,280 IU of vitamin D3 on the first day of the study, while the other half did not. The vitamin D3 group received an extra 10,640 IU of calcifediol on the third, seventh, 15th and 30th day of the study.
COVID-19 patients who received vitamin D3 fared significantly better, with only 4.5 percent requiring intensive care unit (ICU) admission. On the other hand, 21 percent of patients in the group that did not receive vitamin D3 required ICU admission. Treatment with vitamin D3 also reduced the COVID-19 fatality rate, with only 4.7 percent of the vitamin D3 group dying compared to the 15.9 percent death rate in the non-vitamin D3 group.
The authors of the June 2021 study concluded: "In patients hospitalized with COVID-19, calcifediol treatment significantly reduced ICU admission and mortality." Initially submitted in January 2021, it was only published in June.
British Member of Parliament David Davis welcomed the study's findings at the time of its submission. He tweeted back in February 2021: "This is a very important study on vitamin D and COVID-19. Its findings are incredibly clear." He further remarked that the study's conclusion "should result in this therapy being administered to every [COVID-19] patient in every hospital."
A May 2020 statement by the French National Academy of Medicine (ANM) also espoused vitamin D as a "simple and inexpensive measure" against COVID-19. It elaborated: "Vitamin D cannot be considered as a preventive or a curative treatment for [SARS-CoV-2] infection. However, by mitigating the inflammatory [cytokine] storm and its consequences, it could be considered as an adjunct to any form of therapy."
The ANM recommended that COVID-19 patients above 60 years old get tested for vitamin D levels. It advised that the same patients take 50,000 IU to 100,000 IU of vitamin D once the deficiency is confirmed to "help limit respiratory complications." Furthermore, the ANM suggested that people below 60 years old who test positive for COVID-19 take a daily dose of 800 IU to 1,000 IU of vitamin D.
But in spite of the positive effects of vitamin D on COVID-19 patients, the U.S. has refused to acknowledge its potential as a treatment. The U.S. National Institutes of Health noted that low vitamin D levels "have been associated with an increased risk of community-acquired pneumonia in older adults and children" in observational studies. However, its guidance from April 21 said: "There is insufficient evidence to recommend either for or against the use of vitamin D for the prevention or treatment of COVID-19."