Scientists from Northwestern University (USA, Illinois) found a strong connection between high mortality from coronavirus and vitamin D deficiency.

The analysis of statistics from different hospitals in several continents showed that patients from countries with high mortality from COVID-19 - for example, Italy, Spain, and the UK - recorded a vitamin D deficiency compared with patients from countries less affected by the pandemic.

Other researchers previously came to the same conclusions - scientists from the Queen Elizabeth Hospital Foundation and the University of East Anglia. Their observations were based on a comparison of the average blood vitamin D levels in residents of 20 European countries.

The authors of the new scientific work are sure that the difference in mortality rates is not explained by the quality of the healthcare system, the age composition of the population, or the volume of testing.

 "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," Science Daily reported quoting Northwestern's Vadim Backman, who led the research.

By analyzing publicly available patient data from around the globe, the discovered a strong correlation between vitamin D levels and cytokine storm - a hyperinflammatory condition caused by an overactive immune system - as well as a correlation between vitamin D deficiency and mortality.

"Cytokine storm can severely damage lungs and lead to acute respiratory distress syndrome and death in patients," said Ali Daneshkhah, a postdoctoral research associate in Backman's laboratory. "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."

According to the study, children do not yet have a fully developed acquired immune system, which is the immune system's second line of defense and more likely to overreact.

"Children primarily rely on their innate immune system," Backman said. "This may explain why their mortality rate is lower."