More than 5,000 people are being sought to join the research project, which will examine whether the so-called "sunshine" vitamin offers Covid-fighting benefits.
Researchers from Queen Mary University of London, funded by Barts Charity, aim to discover whether the risks from the virus can be reduced by correcting people’s vitamin D deficiencies over the winter months.
Volunteers will participate in the study from their homes with no need for face-to-face visits since all tests and supplements will be sent via post.
Any UK resident aged 16 or over can take part if they are not already taking high-dose vitamin D.
Lead researcher Professor Adrian Martineau, of Queen Mary University of London, said: “There is mounting evidence that vitamin D might reduce the risk of respiratory infections, with some recent studies suggesting that people with lower vitamin D levels may be more susceptible to coronavirus.
“Many people in the UK have low vitamin D levels, particularly in the winter and spring, when respiratory infections are most common.
“Vitamin D deficiency is more common in older people, in people who are overweight, and in black and Asian people – all of the groups who are at increased risk of becoming very ill with Covid-19.
“The UK Government already recommends that people take a low-dose vitamin D supplement over the winter to protect their bone health, but we do not know if this will have an effect on Covid-19 or if higher doses might be able to provide protection against the virus.
“The Coronavit trial will test whether higher doses of vitamin D might offer protection against winter respiratory infections, including Covid-19.”
Vitamin D is often referred to as the "sunshine" vitamin because the body creates it when the skin is exposed to direct sunlight.
However, a lack of sunshine between October and early March means many people often do not absorb sufficient amounts of the compound.
Official guidance urges adults and children aged over four to consider taking a daily supplement containing 10 micrograms of vitamin D during the autumn and winter.
Vitamin D helps maintain calcium and phosphate levels in the body, which assist with the health of bones, teeth and muscles.
The launch of the trial comes after officials said in June that there was not enough evidence to support taking vitamin D supplements to prevent or treat Covid-19.
Officials from the National Institute for Health and Care Excellence (Nice) examined five studies on the novel coronavirus and the vitamin.
They concluded that there is currently no evidence to support taking vitamin D supplements to reduce the risk or severity of Covid-19.
Principal investigator of the Queen Mary University of London study Dr David Jolliffe said: “(This) trial has the potential to give a definitive answer to the question of whether vitamin D offers protection against Covid-19.
“Vitamin D supplements are low in cost, low in risk and widely accessible; if proven effective, they could significantly aid our global fight against the virus.”
To register an interest in participating in the Queen Mary University of London study email email@example.com