The review of 11 studies worldwide showed people who chewed tobacco and used snuff also had a 60 per cent higher risk of oesophagus and pancreatic cancer.

The researchers sought to quantify the risk of smokeless tobacco after a number of studies differed on just how dangerous the products were, said Paolo Boffetta, an epidemiologist at the WHO's International Agency for Research on Cancer.

"What we did was try to quantify the burden of smokeless cancer," he said in a telephone interview. "This has never been attempted in such a systematic way before."

The researchers, who published their findings in Lancet Oncology, did this by looking at population-wide studies and trials of both humans and animals.

They found frequency of use varies greatly both across and within countries, depending on sex, age, ethnic origin and economic background, and were highest in the United States, Sweden and India.

They also found that while snuff and chew were less dangerous than smoking because they were not linked to lung cancer, getting cigarette users to switch was not good public policy.