By Kathleen Doheny Experts say healthy blood levels of vitamin D may give people with COVID-19 a survival advantage by helping them avoid cytokine storm, when the immune system overreacts and attacks your body's own cells and tissues. How Did Researchers Start Looking at Vitamin D? Vitamin D, produced when the sun hits your skin, has many other benefits, such as bone health. Itís also found in some foods and supplements. Among recent studies finding a link between vitamin D levels and how severe COVID-19 is: Researchers from the U.K. evaluated the average vitamin D levels and the number of COVID-19 cases, as well as the death rates, across 20 European countries. Countries with low average vitamin D blood levels in the population had higher numbers of COVID-19 cases and deaths, says study leader Petre Cristian Ilie, MD, PhD, research and innovation director at the Queen Elizabeth Hospital Foundation Trust in King's Lynn, U.K. At Northwestern University, researchers used modeling to estimate that 17% of those deficient in vitamin D would develop a severe COVID-19 infection, but only about 14% of those with healthy vitamin D levels. They estimated the association between vitamin D and severe COVID-19 based on a potential link between vitamin D deficiency and C-reactive proteins, or CRP, a surrogate marker for severe COVID-19 In a small study, Louisiana and Texas researchers evaluated 20 patients hospitalized with COVID-19, finding that 11 of the patients admitted to the ICU were vitamin D deficient, but only four of those not needing the ICU. Indonesian researchers evaluated 780 documented cases of COVID-19 and found that most patients who died had vitamin D levels below normal. Irish researchers analyzed European population studies and vitamin D levels, finding countries with high rates of vitamin D deficiency also had higher death rates from COVID-19. Those researchers asked the government to raise the vitamin D recommendations.