Smoking cessation can save lives. Duration of smoking is the most important factor associated with risk of premature death. The sooner someone quits the better their chances of avoiding adverse health consequences.
For all the money poured into cancer research in recent decades, most of the progress in reducing cancer mortality has been due to deaths avoided through successful tobacco control, especially efforts to persuade smokers to quit.
The American Cancer Society recently examined how much the decline in smoking had contributed to the decline in deaths from all cancers in the US. It concluded: "Even our most conservative estimate indicates that reductions in lung cancer, resulting from reductions in tobacco smoking over the last half century, account for about 40% of the decrease in overall male cancer death rates ... A more realistic straight line projection of what lung cancer rates might have become suggests that, without reductions in smoking, there would have been virtually no reduction in overall cancer mortality in either men or women since the early 1990s. The payoff from past investments in tobacco control has only just begun."
If there was any doubts about the benefits of quitting sooner than later this question was erased by a recent report based on the 50-year follow-up of over 34,439 male British doctors. It found that prolonged smoking from early adult life tripled the risk of premature mortality, but cessation by age 50 nearly halved the risk and quitting by age 30 reduced the risk to approximately the same level of someone who never smoked. Even those quitting after 65 added three years to their life expectancy.
Doll R, Peto R, Boreham J, Sutherland I. Mortality in relation to smoking: 50 years' observations on male British doctors. British Medical Journal. 2004; 328:1519-28.
Thun MJ, Jemal A. How much of the decrease in cancer death rates in the United States is attributable to reductions in tobacco smoking? Tobacco Control 2006; 15:345-7.