A dose of vitamin D may help ward off tuberculosis, research suggests.
TB rates have been rising in England, Wales and Northern Ireland
A study of 131 people found the vitamin helped to boost the ability of the body to inhibit the growth of bacteria that causes the respiratory disease.
Researchers from Queen Mary's School of Medicine and Imperial College said it could be used to target at-risk patients or added to drinks.
The study appeared in the American Journal of Respiratory and Critical Care Medicine.
Vitamin D was originally used to treat TB in sanatoriums before antibiotics came in to use.
But until now no study has evaluated the effect of vitamin D on the body's immunity to mycobacteria, the family of bacteria that cause TB.
During the study, blood was taken from all the participants and infected with mycobacteria.
The group was then split into two with 64 given a dummy pill and the rest a 2.5mg dose of vitamin D.
After six weeks, blood was taken again and infected with mycobacteria.
The samples of blood were analysed after 24 hours, and the growth of the samples taken from people given vitamin D was 20% less than the placebo group.
The researchers said clinical trials were now needed to fully prove the findings, but they added the vitamin had the potential to help ward off the respiratory disease.
They said it could be given to those deemed at risk - the bacteria can lie dormant waiting for the immune system to be weakened before striking - or added to drinks such as milk and orange juice.
It comes as TB rose by 2% last year to over 8,000 new cases in England, Wales and Northern Ireland.
London accounted for nearly half of the cases, with the migrant population identified as the primary source.
TB is also a major global problem, responsible for 2m deaths a year.
Lead researcher Dr Adrian Martineau added: "This shows that a simple, cheap supplement could make a significant impact on the health of people most at risk from the disease."
Professor Peter Davies, a chest specialist and secretary of the TB Alert campaign group, said: "We have known for a while vitamin D could help and it is good to see it being confirmed in such a study.
"What makes this potentially a very good intervention is that it is cheap and easy to administer. But we need to await the clinical trials."
The results add to a growing body of evidence about the health benefits of vitamin D - it has also been linked to reducing the risk of cancer and diabetes as well as strengthening the bones.