50-year tobacco study shows smokers lose a decade of life
On average cigarette smokers die ten years younger than non-smokers, according to a 50-year-long study of smoking and death among British doctors, published in the British Medical Journal1. But stopping at age 50 halves the risk, and stopping at 30 avoids almost all of it.
Sir Richard Doll, emeritus Professor of Medicine at the Clinical Trial Service Unit (CTSU), University of Oxford, launched the study in 1951 when he himself was in his 30s. Now in his 90s, he reveals the final results. Among the doctors born between 1900 and 1930, about half of the cigarette smokers were killed by their habit. However, there is a unique group, born around 1920, among whom two-thirds of those who continue to smoke cigarettes are killed.
The study, funded by the Medical Research Council, Cancer Research UK and the British Heart Foundation, also demonstrates the benefits of quitting smoking at any age. Stopping smoking at ages 60, 50, 40 or 30 gains, respectively, about 3, 6, 9 or 10 years of life expectancy.
The initial results were published by Richard Doll in the BMJ on June 26, 1954, confirming that smoking tobacco caused lung cancer. The 50-year results are being published by him on the exact 50th anniversary (June 26, 2004) of those initial results, showing that the overall risks are much greater than originally suspected.
British men born in the first few decades of the 20th century are the first population in the world in which the full hazards of long-term cigarette smoking, and the corresponding benefits of stopping, can be assessed directly.
Doctors were chosen to be the subjects of the study because they were a relatively simple group to follow through the Medical Register held by the General Medical Council.
Sir Richard Peto, Professor of Medical Statistics and Epidemiology at Oxford, who has collaborated on the study for 30 years, says: "On average, those who continue to smoke lose 10 years of life but stopping smoking at ages 60, 50, 40 or 30 gains 3, 6, 9 or the full 10 years of life expectancy. Of those who continued to smoke, half were killed by their habit."
A unique group of men born around 1920 faced even worse odds. Smoking killed two-thirds of those who continued to smoke cigarettes. The study authors attribute the peculiarly high risk for this particular generation to conscription into the British army from 1939 onwards. The armed forces provided low cost cigarettes to conscripts, which established the addiction with an intense early exposure to smoking.
Sir Richard Doll says: "Over the past few decades prevention and better treatment of disease have halved non-smoker death rates in the elderly in Britain. But these improvements have been completely nullified by the rapidly increasing hazards of tobacco for those who continue to smoke cigarettes."
Sir Richard Peto adds: "Partly because of earlier results from this 50-year-long study many people in Britain gave up smoking, and this country now has the best decrease in tobacco deaths in the world. But, in many countries tobacco deaths are still going up. In Britain, tobacco has caused six million deaths over the last 50 years. But, worldwide, tobacco will soon be causing six million deaths each year."
Professor Sir Charles George, Medical Director of the British Heart Foundation and president elect of the British Medical Association, says: "We welcome the publication of this pivotal study. It provides a clear demonstration of the harmful effects of persistent cigarette smoking, which on average shortens life by around 10 years. Both for heart disease and for cancer the benefits of stopping smoking are clear cut and the earlier this occurs, the better."
Professor Alex Markham, Cancer Research UK's Chief Executive, says: "The tobacco epidemic is a global health catastrophe composed of millions of personal tragedies - the biggest tragedy being that it is preventable. Tobacco is responsible for a third of all UK cancer deaths. Since the study began in 1951, tobacco has killed around 100 million people globally."
Professor Colin Blakemore, Chief Executive of the Medical Research Council, says: "Fifty years ago, the findings of this unique study had a major impact on our understanding of the links between smoking and disease. These new findings complete the picture on smoking-related deaths and show the benefit of funding clinical research over a long period of time."
- British Medical Journal328 (7455) p1519-28
Notes to Editor
The full paper is available here: Mortality in relation to smoking: 50 years' observations on male British doctors
The study monitored 34,439 male doctors born between 1900-1930. They were monitored by questionnaires about their smoking habits in 1957, 1966, 1971, 1978, 1991 and 2001.
What was known already:
- About half of all persistent cigarette smokers are killed by their habit, a quarter while still in middle age (35-69 years).
- After a large increase in cigarette smoking by young people, the full effects on national mortality rates can take more than 50 years to mature.
- Because of early and intensive use of cigarettes, British men born in the first few decades of the 20th century could be the first population in the world in which the full long-term hazards of cigarette smoking, and the corresponding benefits of stopping, can be assessed directly.
What this study adds:
- Among the particular generation of men born around 1920, cigarette smoking tripled age-specific mortality rates.
- Among British men born 1900-1909, cigarette smoking approximately doubled age-specific mortality rates both in middle and in old age.
- Longevity has been improving rapidly for non-smokers, but not for men who continued smoking cigarettes.
- Cessation at age 50 halved the hazard; cessation at 30 avoided almost all of it.
- On average, cigarette smokers die about 10 years younger than non-smokers.
- Stopping at ages 60, 50, 40 or 30 gains, respectively, about 3, 6, 9 or 10 years of life expectancy.