King's College London

The research, conducted in collaboration with Guy’s and St Thomas’s NHS Foundation Trust and the University of South Australia, explored whether vitamin D levels influence a person’s risk of catching COVID-19 and, if infected, whether they are more likely to become seriously ill. Vitamin D is known to support the immune system, so understanding its role could help identify people at greater risk from the virus.

The paper published in PLOS One found that people who had low levels of vitamin D in their blood were more likely to be hospitalised with COVID-19. However, low vitamin D levels did not make people more likely to catch the virus in the first place. These findings add to growing evidence that having enough vitamin D could reduce the severity of illnesses such as COVID-19.

To do this, the researchers analysed health data from more than 150,000 people who were part of the UK Biobank. They divided participants into three groups based on their vitamin D levels. People with less than 25 nanomoles per litre (nmol/L) of vitamin D were considered deficient. Those with levels between 25 and 49 nmol/L were classified as insufficient, and individuals with 50 nmol/L or more were considered to have normal or healthy levels. The researchers then compared these groups to see if the risk of infection and hospitalisation due to COVID-19 was higher among people with low vitamin D levels.

Professor Van Hemelrijck continued: "It’s this kind of translational research—rooted in collaboration and real-world relevance—that drives our work forward."

The study also explored associations between vitamin D and COVID-19 outcomes among cancer patients, as well as across different ethnic groups. Among people of Asian or African/Afro-Caribbean heritage, low vitamin D was linked to a slightly higher risk of infection. However, the link between vitamin D deficiency and serious illness was seen only in people of Caucasian backgrounds. There was no strong connection between vitamin D and COVID-19 outcomes in people who had previously been diagnosed with cancer, although further research with a larger sample size may be needed to confirm this result. 

Professor Karagiannis added: "Next steps could be to test whether boosting vitamin D levels, by perhaps a combination of dietary adjustments, supplementation and controlled sun exposure, it may be possible to mitigate severe effects of COVID-19 infection." 

While the study highlights an important link between vitamin D levels and the risk of hospitalisation, it remains unclear whether vitamin D supplements alone can reduce the severity of COVID-19. Therefore, further research is needed to better understand whether improving vitamin D status could help protect against more severe outcomes.