Global data from the COVID-19 pandemic has revealed a strong correlation between severe vitamin D deficiency and mortality.

The deficiency appears to trigger the cytokine storm (an over-reaction of the immune system) that has killed many COVID-19 patients.

Turning that around, the researchers from Northwestern University say that vitamin D strengthens innate immunity and prevents overactive immune responses.

The researchers suggest their findings “could explain several mysteries, including why children are unlikely to die from COVID-19.”

How did they reach this conclusion?

According to a statement from the university, the researchers were “inspired” to examine vitamin D levels after noticing unexplained differences in COVID-19 mortality rates from country to country.

Some people hypothesised that differences in healthcare quality, age distributions in population, testing rates or different strains of the coronavirus might be responsible.

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“None of these factors appears to play a significant role,” said Dr Vadim Backman, the Walter Dill Scott Professor of Biomedical Engineering at Northwestern’s McCormick School of Engineering.

“The healthcare system in northern Italy is one of the best in the world. Differences in mortality exist even if one looks across the same age group. And, while the restrictions on testing do indeed vary, the disparities in mortality still exist even when we looked at countries or populations for which similar testing rates apply.”

The researchers conducted a statistical analysis of data from hospitals and clinics across China, France, Germany, Italy, Iran, South Korea, Spain, Switzerland, the United Kingdom and the US.

They found patients from countries with high COVID-19 mortality rates, such as Italy, Spain and the UK, had lower levels of vitamin D compared to patients in countries that were not as severely affected.

Further, they discovered “a strong correlation between vitamin D levels and cytokine storm” – the hyper-inflammatory condition caused by an overactive immune system, where the body starts to attack its own cells and tissues rather than fighting off the virus.

Cytokine storms are known to happen in autoimmune diseases like juvenile arthritis. They also occur during certain kinds of cancer treatment, and can be triggered by infections like the flu.

“Cytokine storm can severely damage lungs and lead to acute respiratory distress syndrome and death in patients,” said Dr Ali Daneshkhah, a postdoctoral research associate in Dr Backman’s laboratory, and the paper’s first author.

“This is what seems to kill a majority of COVID-19 patients, not the destruction of the lungs by the virus itself. It is the complications from the misdirected fire from the immune system.”

Vitamin D may reduce COVID complications

Dr Backman said vitamin D not only enhances our innate immune systems, it also prevents our immune systems from becoming dangerously overactive.

This means that having healthy levels of vitamin D could protect patients against severe complications, including death, from COVID-19.

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“Our analysis shows that it might be as high as cutting the mortality rate in half,” Dr Backman said.

“It will not prevent a patient from contracting the virus, but it may reduce complications and prevent death in those who are infected.”

Dr Backman said this correlation might help explain why children are less likely to die.

Children do not yet have a fully developed acquired immune system, which is the immune system’s second line of defence and more likely to overreact.

“Children primarily rely on their innate immune system,” he said.
“This may explain why their mortality rate is lower.”

Don’t start hoarding vitamin D

This does not mean that everyone – especially those without a known deficiency – needs to start hoarding supplements, the researchers caution.

“While I think it is important for people to know that vitamin D deficiency might play a role in mortality, we don’t need to push vitamin D on everybody,” Dr Backman said.

“This needs further study, and I hope our work will stimulate interest in this area. The data also may illuminate the mechanism of mortality, which, if proven, could lead to new therapeutic targets.”

The research is available here.