In a new analysis of data from the UK Biobank, vitamin D deficiency was associated with an increased risk of COVID-19 hospitalization but showed only a weak association with infection risk.
Monroy-Iglesias et al. performed a nested case-control study within the UK biobank cohort, among all individuals with at least one serum vitamin D level measurement at baseline (2006-2010) and a COVID-19 polymerase chain reaction (PCR) results recorded, and individuals with previous cancer diagnosis.
The global impact of COVID-19 on healthcare services has been significant, fuelling extensive research interest in exploring potential pathophysiological mechanisms underlying the disease.
At the start of the pandemic, several studies were conducted looking at risk factors influencing COVID-19 infection rates, severity, and mortality.
These studies consistently identified age, male sex, smoking status, obesity, belonging to certain ethnic groups, and a compromised immune system, among others, as factors contributing to an increased likelihood of developing severe disease and increased mortality rates.
Vitamin D plays a crucial role in modulating both the innate and adaptative immune response.
Deficiency in vitamin D has been associated with increased susceptibility to respiratory tract infections and is recognised as a risk factor for the development of exaggerated and persistent inflammation, which acts as a precursor to acute respiratory distress syndrome.
Consequently, since the outset of the pandemic, several studies have investigated the relationship between vitamin D and risk of COVID-19.
There is growing evidence of the association between vitamin D deficiency and risk of COVID-19 infection and severity
“We aimed to investigate the association between vitamin D levels and both COVID-19 infection and hospitalisation using data from the prospective UK Biobank,” said Dr. Maria Monroy-Iglesias of King’s College London and her colleagues.
“Additionally, we examined these associations across the general population, a subgroup of cancer patients, and considered potential variations by ethnicity.”
The authors assessed more than 150,000 participants in the UK Biobank, undertaking analyses to determine whether the risk of COVID-19 was higher among people with vitamin D deficiency (
They also compared risk of being hospitalised due to COVID-19 across these three groups.
“The findings could identify vulnerable people and guide future public health advice,” said co-author Dr. Kerri Beckmann, a researcher at the University of South Australia.
“Vitamin D plays a key role in regulating the immune system, so it’s plausible that low levels may influence how the body responds to infections like COVID-19.”
“Our study found that people with a vitamin D deficiency or insufficiency were more likely to be hospitalised with COVID-19 than those with healthy levels of vitamin D — but they weren’t more likely to catch the virus in the first place.”
The scientists also explored associations between vitamin D and COVID-19 outcomes among cancer patients, as well as across different ethnic groups.
People of Asian or African/Afro-Caribbean heritage were found to have a slightly higher risk of infection if they had low vitamin D levels, though the association between low vitamin D and severe illness was only seen in people of Caucasian backgrounds.
No association was found between vitamin D and COVID-19 outcomes among people previously diagnosed with cancer, though researchers caution this may reflect the smaller sample size.
“While risk from COVID-19 has lessened over time, the virus remains a public health concern,” Dr. Beckmann said.
“COVID-19 may not be the threat it once was, but it still affects peoples’ well-being.”
“Understanding who is most at risk helps those individuals take extra precautions, including monitoring their vitamin D levels.”
“It could be that people who are in poor health to start with may also have low vitamin D levels.”
“So, at this stage, we don’t know whether vitamin D supplements in themselves could reduce the severity of COVID-19.
“It’s certainly an area worth exploring — especially as we continue to live with the virus.”
The findings appear online in the journal PLoS ONE.
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M.J. Monroy-Iglesias et al. 2025. Effects of vitamin D on COVID-19 risk and hospitalisation in the UK biobank. PLoS One 20 (7): e0328232; doi: 10.1371/journal.pone.0328232
