New research is putting a renewed spotlight on vitamin D, not for its usual association with bone health, but for its potential role in protecting people from the more serious effects of COVID-19. A major study led by the University of South Australia, in partnership with King’s College London and Guy’s and St Thomas’ NHS Foundation, has found that people with low vitamin D levels are more likely to end up in hospital if they contract the virus.
The findings come as Australia heads through another wave of COVID-19 infections, prompting health experts to look beyond vaccines and anti-viral treatments for additional ways to safeguard at-risk groups. While vitamin D won’t prevent someone from catching COVID-19, it may influence how their body copes with it.
The study, which looked at more than 150,000 people from the UK Biobank, found a marked increase in hospitalisation risk among those with vitamin D deficiency (less than 25 nmol/L) and insufficiency (25–49 nmol/L), compared to those with healthier levels (50+ nmol/L). This is not about a mild statistical fluctuation—the relationship was described as clear.
Dr Kerri Beckmann, an epidemiologist with UniSA and lead author of the Australian team, says the research could have practical applications for public health messaging.
“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,” she said.
The study found no link between vitamin D levels and the likelihood of catching the virus. The real difference came once someone had COVID—those with lower vitamin D were more likely to become seriously unwell and require hospital care.
This has particular relevance in Australia, where nearly one in four adults—roughly four million people—are vitamin D deficient. The problem is even more widespread globally, affecting around a billion people, with about half the world’s population showing some degree of vitamin D insufficiency.
The study also explored different outcomes among people with cancer and across various ethnic backgrounds. People of Asian or African/Afro-Caribbean heritage with low vitamin D levels showed a slightly higher risk of catching COVID-19. However, the connection between low vitamin D and severe illness was clearest among people of Caucasian background. Researchers noted that data on cancer patients was too limited to draw firm conclusions, though no pattern was evident in that group.
Dr Beckmann said, “COVID-19 may not be the threat it once was, but it still affects people’s well-being. Understanding who is most at risk helps those individuals take extra precautions, including monitoring their vitamin D levels.”
Whether supplementing with vitamin D could actively reduce COVID-19 severity remains an open question. The researchers stress that while the association is strong, it doesn’t prove causation. It may be that poorer general health contributes both to low vitamin D levels and worse COVID outcomes.
“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,” Dr Beckmann said. “It’s certainly an area worth exploring—especially as we continue to live with the virus.”
The study adds to a growing body of research that looks at the broader role of micronutrients in supporting immunity, especially during respiratory infections. And it arrives at a time when public interest in preventative health is growing, spurred on by the pandemic years.
The research also provides another angle to consider for Australia’s healthcare system, which is still managing the aftershocks of the pandemic and preparing for ongoing waves of the virus. With hospital capacity always a point of concern, any measure that could lower the risk of admission for vulnerable people is worth examining.
Dr Beckmann’s work comes amid broader changes in the university sector as well. The University of South Australia is preparing to merge with the University of Adelaide, with the new Adelaide University set to launch in January 2026. The new institution aims to bring together research and teaching strengths from both universities, with a focus on globally relevant health challenges among its priorities.
For now, the advice from experts is clear: while you can’t rely on vitamin D to keep COVID-19 at bay, it’s wise to know your levels—especially if you fall into a group at higher risk. And with winter sunlight often insufficient for generating enough vitamin D naturally, a check-up and a conversation with a GP might be more useful than most realise.
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