China and India are the world's biggest tobacco users, according to new research which highlights concerns about increasing death rates in developing countries and smoking by women.
Statistics compiled by the American Cancer Society and the World Lung Foundation for the third edition of their "Tobacco Atlas" found that some 311 million men in China and 229 million in India use tobacco in some form.
For women the figures were 14 million and 12 million, respectively, putting the two Asian giants far ahead as the world's biggest smokers.
There were 24 million female tobacco users in the United States, said the study, which was released in Mumbai at the 14th World Conference on Tobacco or Health.
Worldwide nearly one billion men and 250 million women use tobacco every day, said the study, released on Monday.
Some six million people will die from tobacco use next year, rising to seven million by the end of next decade and eight million in 2030, it estimated.
But death rates are rising faster in developing countries. Next year, nearly 72 percent of global tobacco-related deaths will be in what researchers called "low- and middle-income countries".
In 2030 that figure will rise to 83 percent, equivalent to some 135.1 million people, they added.
Of particular concern among health professionals is the increased take-up of smoking by poorer-educated men and women in developing countries, where female smoking has largely been considered socially unacceptable.
"If the women of the world begin smoking at the same rate as men, it will be an unmitigated global public health disaster," the study said.
"Preventing increases in smoking prevalence among women, especially in low- and middle-income resourced countries, will have a greater impact on global health than any other single intervention."