Some UK intensive care units, including the Chelsea and Westminster and the Royal Surrey County Hospital, are already giving high-dose vitamin C supplements. The latest research, carried out in three hospitals across the central province of Hubei, concluded: "The addition of high-dose vitamin C may provide a protective clinical effect in critically ill patients with COVID-19."
Although not formally recognised as a treatment by the NHS, a global platform of drug trials involving 19 countries – known as Remap-Cap – has also launched a trial.
The head of Remap-Cap in the UK, Professor Tony Gordon, a consultant at St Mary's Hospital in London, said: "We don't yet have conclusive evidence of benefit and we need clarity."
According to the Remap-Cap report, vitamin C stimulates immune system cells and can also dampen down dangerous inflammation.
The head of the Chelsea and Westminster ICU Dr Marcela Vizcaychipi began adding the vitamin to the standard treatment package for Covid-19 at the start of the pandemic. She said: "It makes sense. It is vital for a healthy immune system."
She became aware of its benefits for infected patients while doing her medical training in Argentina.
"We gave them good nutrition plus mineral and vitamin supplements. I saw first-hand how effective vitamin C could be."
Official figures for ICU deaths puts Dr Vizcaychipi's unit about 25 percent below average. However, she said it is not clear if the use of vitamin C is the reason.
Separate research shows badly infected COVID patients have been found with almost no vitamin C in their blood.
A Barcelona intensive care unit found 17 out of 18 critical patients had undetectable levels. "It's as if they've got scurvy," said one researcher.
NHS emergency medicine expert Professor Iain Whitaker, from Swansea University, said: "Given its safety profile and relatively low cost, vitamin C should be considered based on emerging evidence from critical care groups worldwide."