Researchers in Belgium have discovered a "clear link" between low levels of vitamin D and the severity of COVID-19 cases.  

Studies consistently show that at least 40 percent of the Belgian population has inadequate levels of vitamin D, known as the "sunshine vitamin." But scientist from AZ Delta hospital in West Flanders, who analyzed blood samples from 186 people during the first wave of the pandemic, found that severely ill COVID-19 patients admitted for care showed much higher rates of vitamin D deficiency.  

"Up to 75 percent of COVID-19 patients were vitamin D deficient on admission. That's a lot," said Dieter de Smet, director of the AZ Delta laboratory. "We also saw that the more severe the COVID-19 pneumonia was, the more pronounced vitamin D deficiency was." 
 

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De Smet said that independent of other risk factors, there was also a link to mortality. But he cautioned that the findings don't prove causality, meaning it's still unknown whether a lack of vitamin D causes serious cases of COVID-19, or if taking a supplement would reduce the risk.  

"At this moment it's a bridge too far to say that vitamin D is a therapeutic for COVID-19, but for sure it makes a call for maintaining your body at optimal form and making sure you're not vitamin D deficient," he said.   

People get vitamin D when their skin is exposed to the sun or by eating oily fish. It plays a key role in fortifying the immune system and preventing it from overreacting. Some health experts in Europe, including in Belgium and the UK, recommend the entire population be on vitamin D supplements.   

Governments recommend supplements 

Belgium is notoriously dreary, with many days blanketed in dark clouds and rain. In October, the sun shone for just 56 hours and 32 minutes in the municipality of Uccle, half the normal amount of light and the second darkest October on record.   

Health experts say people with little access to natural sunlight such as the elderly in care homes or people who work in offices should take vitamin D supplements. But if levels are normal, there's no evidence popping extra pills will do any good.  

Much more research is needed. In the past, a similar link was drawn between vitamin D deficiency and severe tuberculosis, only to be disproved during large-scale studies. 

"This is just to say that we know this in science, that it's not any association you find is a causal association. Things might just be linked without one causing the other," said Laura Cornelissen, from the department of epidemiology of infectious diseases at the Belgian health institute Sciensano.  

The best medicine, experts said, is a healthy lifestyle, which would help balance out any deficiency – sunshine or not.