London, Aug. 14 (Reuters): Smoking is to blame for half the tuberculosis deaths among Indian men, according to a new research to be published tomorrow, highlighting a neglected link between tobacco and the killer lung disease.
Most big studies into smoking and health until now have been conducted in developed countries where tuberculosis (TB) has been uncommon for more than half a century.
As a result, the connection with TB — which is still endemic across much of Asia and Africa — has been greatly underestimated, according to the authors of the first major study on how smoking causes death in India.
“This is something that causes at least a few hundred thousand deaths a year worldwide... but the relationship had been forgotten and ignored,” Richard Peto of the University of Oxford, co-author of the study, said.
The study also predicted the number of men dying from smoking related illnesses in India could double to over a million a year by 2025.
Three quarters of male Indian smokers who become ill with TB would not have done so if they had not smoked, Peto and colleagues said in a paper in a medical journal, The Lancet.
Their findings suggest that in some parts of the world the main way smoking kills is not via cancer and heart disease, but by damaging the lung’s defences against chronic TB infection.
About a billion people worldwide are carrying live TB infection in their lungs, but if they do not smoke then most will never become seriously ill. Smoking increases the danger that any infection will get out of control and cause clinical TB, which spreads easily and can kill a person.
TB causes about 1.6 million deaths worldwide each year, including more than a million in Asia and 400,000 in Africa. India has more TB deaths than any other country.
The study by the Epidemiological Research Center in Chennai — with funding from the UK’s Medical Research Council and Cancer Research — compared the smoking habits of 43,000 men who had died of various diseases in the late 1990s with the habits of 35,000 living men.
It found that smokers were about four times as likely to become ill with TB as non-smokers, and consequently four times as likely to die from the disease.
Vendhan Gajalakshmi of the Epidemiological Research Center, who led the research, estimates almost 200,000 Indians die each year from TB because of smoking — half of them are still only in their 30s, 40s or early 50s.
Smokers of both cigarettes and bidis are similarly at risk.
Overall, smoking currently causes some 700,000 deaths a year in India, 550,000 among men aged 25 to 69. The number of deaths could double by 2025 if current smoking patterns persist, the authors conclude.