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The link between smoking and lung cancer was originally discovered by Sir Richard Doll in 1956. Co-director Sir Richard Peto has continued to study the impact of tobacco of global health (see video below). Smoking cigarettes is a leading cause of premature death worldwide. There were about 100 million deaths from tobacco in the 20th century, most in developed countries. If current smoking patterns persist, it is estimated that tobacco will kill about 1 billion people this century, mostly in low- and middle-income countries, and about half of these deaths will occur before age 70.

Large prospective studies are needed in many different populations around the world to monitor reliably the current and future effects of smoking. CTSU has been, and continues to be, a major source of evidence on the hazards of smoking and the benefits of quitting.

During the 1980s, CTSU conducted major epidemiological studies of smoking, first in developed countries (including long-term follow-up of the British Doctors’ Study). They showed tobacco was far more important than all other known causes of cancer combined. This affected UK, US and Chinese tobacco control strategies.

CTSU has since initiated a new generation of large prospective studies of smoking and death in many countries, specifically to study the emerging epidemic of tobacco-related mortality in low- and middle-income countries. In collaboration with local principal investigators, CTSU is conducting studies in China, Mexico, Russia, Cuba and India (Chennai and Trivandrum) (total: 1.7 million participants).

As well as assessing the full hazards of lifelong smoking among men and among women in many different populations, one of CTSU’s consistent objectives has been to assess the lifelong benefits of quitting at various different ages. CTSU’s British Doctors’ Study and the Cancer Epidemiology Unit’s Million Women Study have demonstrated that stopping before age 40, preferably well before 40, avoids over 90% of the excess risk among those who continued. Even stopping before age 50, avoids more than two-thirds of the risk. Our emphasis on effects of cessation at particular ages has widened worldwide efforts to include encouragement of cessation as well as discouragement of initiation; our new findings confirm (and we consistently emphasise) that widespread quitting is needed to affect substantially deaths before 2050.

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