Researchers Richard Doll and Bradford Hill said that, on average, cigarette smokers die about ten years younger than nonsmokers.

The main tobacco-related causes of death included lung cancer; heart disease; cancers of the mouth, pharynx, larynx and esophagus; and other respiratory diseases.

Here's the good news:

Those who stopped at the age of 60 gained three years of life, those who quit at 50 gained six years and those who stopped smoking at 40 gained nine years of life expectancy, the report said. For those who kick the habit at 30 the increased risk was avoided almost totally, the researchers said.

The study, funded by the Medical Research Council, Cancer Research U.K. and the British Heart Foundation, followed almost 35,000 male doctors born between 1900 and 1930.

In the group of men born around 1920, about two-thirds of those who continued to smoke were killed by tobacco, the study concluded.