Study by Doll et Peto
of tobacco consumption by British physicians

First published in October 1984 (Br Med J 1994, 309, 937-939), this study concerns a group of physicians followed for a period of over 40 years. An update of the study in 2004 has not changed the results presented below.

In 1948, in order to evaluate the potential ravages of smoking, Austin Bradford HILL et Richard DOLL enrolled 35,000 British male physicians to answer a questionnaire about their smoking habits. New questionnaires were sent in 1957, 1966, 1972, 1978 and 1990. Almost forty years after the first questionnaire, 95% of the physicians still alive (around 11,000 doctors) continued to answer them.

The first publication showed that after 20 years, there was a very significant difference in life span between smokers (blue line on the graph) and non smokers (red line on the graph).

First study	Second study

Twenty years later, a tripling of mortality due to tobacco is observed: the life span of smokers remains identical to that previously observed, whereas medical progress has allowed a significant increase in life span (more than 80% of the non-smoking doctors over 70 were alive, around 35% were over 85). The median survival had increased by 3 years.

By grouping these two studies, Doll and Peto demonstrate that life expectancy is conversely proportional to the tobacco consumption.

Life expectancy of the British doctors

What was the cause of death among the smoking doctors?

They are very similar to the causes analysed by a prospective study of the American Cancer Society between 1984 and 1988.

Their are three times more deaths between the age of 35 and 69 among smokers, compared to non-smokers. Young men are the most affected by smoking.

Optimism

The study by Doll and Peto brings an optimistic point of view: stopping smoking is very profitable and the earlier it happens, the longer life expectancy will be. Thus a prevention policy is very useful.

Usefulness of quitting smoking before 35 years. (blue: non smokers, red: still smoking, green: quitting doctors)	Usefulness of quitting smoking before 45 years. (blue: non smokers, red: still smoking, green: quitting doctors)
Usefulness of quitting smoking before 55 years. (blue: non smokers, red: still smoking, green: quitting doctors)	Usefulness of quitting smoking after 55 years. (blue: non smokers, red: still smoking, green: quitting doctors)

Up to 45 - 50 years, it is still useful to quit smoking.

These impressive studies by Doll and Peto concerning 35,000 British physicians followed during 40 years, therefore brings major scientific breakthroughs:

• tobacco genuinely diminishes life expectancy,
  
• this diminution begins at middle-age (as early as 40 years),
  
• there are three times more deaths among smoking doctors compared to non-smoking doctors between 35 and 69 years,
  
• stopping smoking is very efficient and reduces the difference of mortality between smokers and non-smokers,
  
• the sooner one stops smoking, the better.

All of this data constitutes the most realistic and scientific approach for the prevention of smoking.