The analysis published in The British Medical Journal said South Asia with a population of 1.1 billion adults has about 170 million adult smokers - and mostly from India - and very low rates of cessation.
The analysis calls on the South Asian countries to implement the World Health Organisation's (WHO) global tobacco control treaty, including high tobacco taxes, smoke-free public spaces, warning labels, comprehensive advertising bans and support for smoking cessation services.
He said the study looked at 140 million current and future smokers, aged under 35 years (about 33 million of whom are current smokers, aged 25-34 years, and 107 million under 25 years who have not yet started) and 100 million current smokers over 35 years (out of 171 million smokers at 15 years or more).
"Unless large numbers of them stop smoking, at least half of the 140 million young and future smokers would die because of smoking. At least half of these 70 million deaths would occur before the age of 70. Not starting smoking or complete cessation before age 40 would avoid nearly all of these deaths.
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It said in India and Bangladesh, cigarettes have gradually displaced bidis, particularly among younger and illiterate males.
"South Asia has large and growing numbers of tobacco users and very low rates of cessation. Effective implementation of the Framework Convention on Tobacco Control, particularly its tax provisions, could reduce tobacco consumption by at least one-third and save about 35-45 million lives," it said.
"The benefits of a one-third reduction in the 100 million current smokers over 35 years depend on their age of cessation. Conservatively, such a reduction might avoid about 10-20 million deaths, most of which would be before 2050," Jha said.
"Indeed, the loss of life among Indian male cigarette smokers is as extreme as now observed in prolonged smokers in high-income countries," the study said.
It stated that annual increase in tobacco tax has mostly been below the rate of inflation and income growth, thus cigarettes remain affordable.
The analysis also quoted a report by the Asian Development Bank on five Asian countries, including India, which stated that increasing the price of cigarettes by 50 per cent through excise tax increases of 70-122 per cent would reduce the number of current and future smokers by nearly 67 million and reduce tobacco deaths by over 27 million in the five countries.
"Moreover, about USD 24 billion additional revenue would be generated annually," the analysis quoting the report said.
Jha added that the price of cigarettes, bidis and chewing tobacco is lower in South Asia than in high-income countries in the West because the excise taxes are so low.