New Delhi, May 21: Vitamin C can kill tuberculosis bacteria in the laboratory, scientists announced today, describing their findings as “striking and totally unexpected,” but also cautioned that this new strategy is yet to be tested in humans.

The researchers in the US have shown that vitamin C has strong bactericidal activity against TB bacteria through a study that suggests that it might be worthwhile to explore the addition of vitamin C to standard anti-TB treatment.

The results of the study were published today in the journal, Nature Communications.

“Vitamin C has never been shown to kill TB bacilli,” William Jacobs Jr, professor of microbiologist at the Albert Einstein College of Medicine in New York and principal investigator of the study, told The Telegraph.

“The observation that vitamin C can sterilise (laboratory) cultures of drug-susceptible, multi-drug resistant and extreme-drug resistant strains of TB bacilli is striking and totally unexpected,” Jacobs said in a telephone interview.

Three years ago, microbiologists at the All India Institute of Medical Sciences, New Delhi, had observed that vitamin C can arrest the growth of TB bacilli and drive them into what is known as a dormant state.

Jaya Sivaswamy Tyagi and her colleagues at the AIIMS had also speculated about the possible “protective role” of vitamin C against TB through mechanisms that go beyond the role of this vitamin in bolstering immunity.

Jacobs and his colleagues have now shown that vitamin C used at an unusually high concentration in the presence of iron can selectively kill the TB germs. Their study suggests that the bactericidal activity of vitamin C is dependent on iron.

The iron in the experiments came from the culture medium — the broth of nutrients in which the TB bacilli are grown. Vitamin C reduces ferric ion into ferrous ion, producing molecules called reactive oxygen species that play a role in killing the bacteria. “We’re hoping this study will spur interest in testing the addition of vitamin C to current TB treatment regimen,” Jacobs said.

But medical researchers point out that it is still unclear whether the effect of vitamin C observed on TB bacteria maintained in laboratory culture will also be seen in germs growing in human patients.

“I would call this a proof-of-concept study,” said Madhukar Pai, an associate professor who leads a Tuberculosis Research Group at the McGill University in Canada. “The question is whether we'll see this effect of oxidative burst occur exactly at the sites of infection when vitamin C is adminstered orally,” Pai, who was not associated with either the US or the AIIMS study, told this newspaper.

Tyagi said there have been suggestions in the past that TB patients who had a vitamin C rich diet appeared to become free of their symptoms faster than those with relatively poorer vitamin C intake. The AIIMS study, published in the journal PLOS One, showing that vitamin C arrests growth of TB bacteria and sends them into a dormancy could explain such historical observations, Tyagi told this newspaper.

The US researchers said their observations would justify more studies to evaluate vitamin C in combination with standard anti-TB drugs or a high vitamin C diet in TB patients.