Hundreds of thousands of TB deaths in India can be directly linked to smoking, say expert researchers.
A dangerous habit: Smoker in Calcutta
Scientists from the Epidemiological Research Centre in Madras calculated that half the male tuberculosis deaths in India stemmed from tobacco.
If you have TB, it can lie dormant in your lungs - but smoking can encourage an active, and often fatal, infection.
Three-quarters of those diagnosed with TB in India would not have done so if they were not smokers.
TB remains a major killer in South Asia.
In India alone approximately 400,000 people a year die from the lung infection.
The Madras researchers, working in collaboration with the University of Oxford, found that half these deaths were caused by smoking, and were perhaps therefore preventable.
They compared 43,000 men who had died from various diseases in the late 1990s with the health habits of more than 35,000 living men.
More than 4,000 of the deaths were from TB - but if there had been no smoking involved, the researchers calculated that only 2,000 of these deaths would have happened.
Dr Vendhan Gajalakshmi, from the research centre in Madras, said: "Almost 200,000 people a year in India die from TB because they smoked - and half of these are still only in their 30s, 40s or early 50s when they die."
Sir Richard Peto, from Oxford University, said: "In some parts of the world the main way smoking kills people is by damaging the lung's defences against chronic TB infection.
"Our study indicates that in rural India about 12% of smokers, but only 3% of non-smokers, die prematurely from TB."
However, this is far from being a problem just for smokers.
If smoking leads to an active infection, that person also gains the ability to infect other people - regardless of whether they smoke or not.
Approximately a billion people worldwide are carrying the bacterium that causes TB in their lungs, but in most cases their natural defences suppress it.
It is only when a chink appears in that immune defence that the actual illness surfaces and a threat to life emerges.
That could either be caused by smoking, or by another infection such as HIV, which reduces immune defences.
This is why so many people with HIV eventually fall prey to TB.
The paper was published on Friday in the Lancet medical journal.