Image caption The body makes vitamin D when it is out in the sun

Vitamin D could help the body fight infections of deadly tuberculosis, according to doctors in London.

Nearly 1.5 million people are killed by the infection every year and there are concerns some cases are becoming untreatable.

A study in Proceedings of the National Academy of Sciences showed patients recovered more quickly when given both the vitamin and antibiotics.

More tests would be needed before it could be given to patients routinely.

The idea of using vitamin D to treat tuberculosis (TB) harks back to some of the earliest treatments for the lung infection.

Before antibiotics were discovered, TB patients were prescribed "forced sunbathing", known as heliotherapy, which increased vitamin D production.

However, the treatment disappeared when antibiotics proved successful at treating the disease.

Drug resistance There is widespread concern about tuberculosis becoming resistant to antibiotics. The World Health Organization (WHO) says 3.4% of new cases of TB are resistant to the two main drug treatments - known as multiple drug resistant tuberculosis. That figure rises to nearly 20% for people who have been infected multiple times in their lives. One analysis said that in some countries about half of all cases were resistant. There is also concern about extensively drug resistant tuberculosis, which is resistant to the back-up drugs as well. The WHO says 9.4% of all drug-resistant TB is extensively drug resistant. In this study, patients all had non-resistant TB. The researchers said adding vitamin D to treatments may be even more valuable for patients when the drugs do not work as well. World Health Organization report on resistance

Heal faster

This study on 95 patients, conducted at hospitals across London, combined antibiotics with vitamin D pills.

It showed that recovery was almost two weeks faster when vitamin D was added. Patients who stuck to the regimen cleared the infection in 23 days on average, while it took patients 36 days if they were given antibiotics and a dummy sugar pill.

Dr Adrian Martineau, from Queen Mary University of London, told the BBC: "This isn't going to replace antibiotics, but it may be a useful extra weapon.

"It looks promising, but we need slightly stronger evidence."

Trials in more patients, as well as studies looking at the best dose and if different forms of vitamin D are better, will be needed before the vitamin could be used by doctors.

Vitamin D appears to work by calming inflammation during the infection. An inflammatory response is an important part of the body's response to infection.

During TB infection, it breaks down some of the scaffolding in the lungs letting more infection-fighting white blood cells in. However, this also creates tiny cavities in the lungs in which TB bacteria can camp out.

"If we can help these cavities to heal more quickly, then patients should be infectious for a shorter period of time, and they may also suffer less lung damage," Dr Martineau said.

The doctors suggested this might also help in other lung diseases such as pneumonia and sepsis.

Prof Peter Davies, the secretary of the charity TB Alert, said the findings were "excellent" and vitamin D could play "an important role in treating tuberculosis".

However, he thought there could be an even greater role in preventing the disease.

One in three people have low levels of tuberculosis bacteria in their lungs and have no symptoms, known as latent tuberculosis. However, this would turn to full blown TB in about 10% of people. Prof Davies's idea is that giving vitamin D supplements, for example in milk, could prevent latent TB developing.

"That would be a massive revolution if it was shown to work," he said.

Prof Alison Grant, from the London School of Hygiene and Tropical Medicine, said: "Drug-resistant TB is an increasing concern world-wide and so new treatments to reduce the length of TB treatment would be very welcome.

"Vitamin D supplements are often given to patients who are short of vitamin D and these low doses are generally very safe.

"In this study the researchers were giving higher doses of vitamin D, and I think we would need larger studies to be confident that there were no negative effects of this higher dose."