NEWS

Smoking shortens life by a decade, concludes 50-year study

Sharon Kingman

London

Up to two-thirds of those who smoke cigarettes will eventually be killed by their habit, but those who give up by the age of 30 will avoid almost all the risk, according to a study of British doctors which has now been running for 50 years.

The study, Mortality in relation to smoking: 50 years' observations on male British doctors, published in the BMJ (2004;328:1519-28) shows that, on average, cigarette smokers die about 10 years younger than non-smokers. While the life expectancy of non-smokers has been increasing steadily since 1900, that of smokers has been progressively decreasing due to earlier and more intensive use of cigarettes.

Quitting works, however: stopping at age 60, 50, 40 or 30 adds, respectively, about 3, 6, 9 or 10 years to a person's life expectancy.

Sir Richard Doll, lead author of the study and emeritus professor of medicine at the University of Oxford told the Bulletin: "For countries where smoking has yet to take hold, the most important thing to do is to stop it doing so, and have the governments prevent the promotion of tobacco. But in countries where many people smoke but have not been smoking for very long, the message is that the way to save lives in the first half of this century will be by getting people to stop, rather than by stopping people from starting."

"This new report provides critical new information and convincingly shows that the risks for persistent cigarette smoking are actually substantially larger than had previously been suspected," wrote Meir Stampfer of the Department of Epidemiology at Harvard School of Public Health in Boston, US, in an editorial accompanying the paper in the BMJ.

Stampfer describes the study, which was led by Doll, along with Sir Richard Peto of the Clinical Trial Service Unit and Epidemiological Studies Unit at the Radcliffe Infirmary, Oxford, England, and co-authors Jillian Boreham and Isabelle Sutherland, as a "stunning achievement".

Doll, now 91, set out in 1951, with Bradford Hill and other colleagues, to recruit British doctors to the study. They chose doctors because they thought doctors would describe their own smoking habits accurately, and because they would be easy to trace through the UK medical register, so long as they continued to practise. In addition, they thought that as doctors would be likely to have access to good medical care, their causes of death would be relatively accurately documented.

Doll said: "We planned it to last five years, which would give us enough data on lung cancer, but after that we began to see one or two other diseases associated with smoking, most notably coronary thrombosis. So we decided to continue and the longer it went on, the more it was clear that there were yet other diseases due to smoking."

By 1954, the initial findings had pinned down the link between smoking and lung cancer. The papers that followed, after 4, 10, 20 and 40 years of follow-up, showed that smoking was associated with mortality from many different diseases, but that lung cancer accounted for less than half of the excess mortality among smokers.

The 2004 paper adds even more detail about the health risks of smoking. Its findings show that someone aged 70 who had never smoked had, between 1951 and 1961, a 12% chance of living to the age of 90. Between 1991 and 2001, this probability rose to 33% demonstrating improved health care. But for someone who was a cigarette smoker, this figure declined from 10% between 1951 and 1961 to 7% in the decade up to 2001 when the ill-effects of smoking began to take their toll on long-term smokers.

Dr Vera da Costa e Silva, Director of WHO's Tobacco Free Initiative said that the quality of the research and its time frame — it is the longest-ever study of smoking and health — adds much weight to the findings. "This study is an important contribution to the overwhelming body of evidence regarding the harmful effects of tobacco," said da Costa e Silva. "Being able to quantify not only the dramatic difference in average life expectancy between smokers and non-smokers but also the benefits of smoking cessation at every age, has a positive impact on public debate and on the decisions of individuals."

Governments and nongovernmental organizations in several countries have already been using earlier data from the Doll study in health education and anti-smoking campaigns. "We can expect the publication of the 50-year results to reinforce the global move towards implementation of comprehensive tobacco control measures, as laid down by the WHO Framework Convention on Tobacco Control," said da Costa e Silva. (See related news article, WHO tobacco convention set to become law by year's end, on p. 635.)