Scientists have found that vitamin D functions to reduce inflammation caused by immune cells that might be relevant to the responses during severe COVID-19.

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The study demonstrated a mechanism by which vitamin D reduces inflammation caused by T cells. These are important cells of the immune system and implicated as part of the immune response to the infection causing COVID-19.

The team led by Purdue University studied and analysed individual lung cells from eight people with COVID. They found that in the lung cells of people with COVID, part of the immune response was going into overdrive, exacerbating lung inflammation.

The team then examined how viruses affect lung cells in a previous study. Finding that viruses can trigger a biochemical pathway, known as the immune complement system, the researchers started looking for ways to disrupt that pathway and ameliorate the subsequent inflammation.

"In normal infections, Th1 cells, a subset of T cells, go through a pro-inflammatory phase," said Majid Kazemian, assistant professor in the departments of Computer Science and Biochemistry at Purdue University.

"The pro-inflammatory phase clears the infection, and then the system shuts down and goes to the anti-inflammatory phase. Vitamin D helps speed up this transition from pro-inflammatory to the anti-inflammatory phase of the T cells. We do not know definitively, but theorise that the vitamin could potentially help patients with severe inflammation caused by Th1 cells," Kazemian added.

In patients with COVID-19, the pro-inflammatory phase of the Th1 cells seems not switched off, possibly because the patients didn't have enough vitamin D in their system or because something about the cell's response to vitamin D was abnormal.

In that case, the researchers posit, adding vitamin D to existing treatments in the form of a prescribed highly concentrated intravenous metabolite may further help people recover from COVID infections, though they have not tested this theory.

"We found that vitamin D -- a specialised form of it, not the form you can get at the drugstore -- has the potential to reduce inflammation in the test tube, and we figured out how and why it does that," Kazemian said. "We do not recommend the use of normal vitamin D off the shelf at the pharmacy. No one should be taking more than the recommended doses of vitamin D in an attempt to prevent or combat COVID infections."

Further research, especially clinical trials, and testing in patients, are necessary before this can be adopted as a treatment option, Kazemian said.