Many smokers are unable or unwilling to completely quit smoking. A proposed
means of harm reduction is to reduce the number of cigarettes smoked per day.
However, it is not clear whether this strategy decreases the risk for tobacco-related
To assess the effects of smoking reduction on lung cancer incidence.
Design, Setting, and Participants
Observational population-based cohort study with up to 31 years of follow-up
from the Copenhagen Centre for Prospective Population Studies, which administrates
data from 3 longitudinal studies conducted in Copenhagen and suburbs, the
Copenhagen City Heart Study, the Copenhagen Male Study, and the Glostrup Population
Studies, Denmark. Participants were 11 151 men and 8563 women (N = 19 714)
aged 20 to 93 years, who attended 2 consecutive examinations with a 5- to
10-year interval between 1964 and 1988. Participants underwent a physical
examination and completed self-filled questionnaires about lifestyle habits.
The study population was divided into 6 groups according to smoking habits:
continued heavy smokers (≥15 cigarettes/d), reducers (reduced from ≥15
cigarettes/d by minimum of 50% without quitting), continued light smokers
(1-14 cigarettes/d), quitters (stopped between first and second examination),
stable ex-smokers, and never smokers.
Main Outcome Measure
Incident primary lung cancer cases assessed by record linkage with the
National Cancer Registry until December 31, 2003.
There were 864 incident lung cancers during follow-up. Using Cox regression,
the adjusted hazard ratio (HR) for lung cancer in reducers was 0.73 (95% confidence
interval [CI], 0.54-0.98) compared with persistent heavy smokers. The HR for
light smokers was 0.44 (95% CI, 0.35-0.56); for quitters, HR 0.50 (95% CI,
0.36-0.69), for stable ex-smokers, HR 0.17 (95% CI, 0.13-0.23), and for never
smokers, HR 0.09 (95% CI, 0.06-0.13).
Among individuals who smoke 15 or more cigarettes per day, smoking reduction
by 50% significantly reduces the risk of lung cancer.