There is not enough evidence that vitamin D supplements protect people against Covid-19, an expert panel says.
Made up of the National Institute for Health and Care Excellence, Public Health England and the Scientific Advisory Committee on Nutrition, it said more research was needed.
But everyone is still advised to take a daily supplement this winter to keep bones and muscles healthy.
Free supplements are being offered to the most vulnerable in the UK.
Health officials carried out a rapid review of the evidence on links between vitamin D and Covid-19, after a small number of studies had suggested it might play a role in the body’s immune response to respiratory viruses.
However, they found there was “insufficient evidence” to recommend it for preventing or treating the disease.
Health experts who studied the evidence said more high-quality randomised controlled trials were needed before they could come to any conclusions.
Dr Paul Chrisp, director of the centre for guidelines at NICE, said: “We are continuing to monitor evidence as it is published and will review and update the guidance if necessary.”
Prof Adrian Martineau, clinical professor of respiratory infection and immunity at Queen Mary University of London, said there was a chance the vitamin “might reduce risk and/or severity of Covid-19” and clinical trials currently in progress would “hopefully shed light on this question”.
Taking vitamin D is particularly important this winter because of the amount of time people have spent indoors isolating and shielding from coronavirus. This means they may not be making enough vitamin D from sunlight – a key source.
Vitamin D can also be obtained from certain foods, such as oily fish and cereals, and supplements.
Some people are at risk of not having enough vitamin D even in spring and summer, including:
People in these groups are advised to take a vitamin D supplement all year round.
Dr Alison Tedstone, chief nutritionist at Public Health England, said: “We advise that everyone – particularly the elderly, those who don’t get outside and those with dark skin – takes a vitamin D supplement containing 10 micrograms (400IU) every day,” she said.
“This year, the advice is more important than ever with more people spending more time inside.”