Tobacco and Public Health - TCSC Indonesia

30
THE GREAT STUDIES OF SMOKING AND DISEASE IN THE TWENTIETH CENTURY
Never smoked
regularly
80
Current cigarette 76%
Current cigarette
83%
smokers
smokers
60
58%
60%
5 years
8 years
40
35%
27%
20
1951–71
12%
1971–91
12%
0
40 55 70 85 100 40 55 70 85 100
Age (years) Age (years)
Fig. 2.2 Survival after age 35 among cigarette smokers and non-smokers in the first half (left)
and second half (right) of the British Doctors Study. For ages 35–44 years, rates for the whole
study are used in both halves, since little information on these is available from the second
half. (From Doll et al. 1994.)
% Alive
100
Never smoked
regularly
smokers and 76 per cent among lifelong non-smokers in the interval 1951–71, and 60
per cent and 83 per cent in the follow-up from 1971 to 1991. Furthermore, the median
difference in overall survival between smokers and non-smokers widened over time,
from 5 years in 1951–71, to 8 years in 1971–91. The difference widened largely because
improvements in survival affected never-smokers more than smokers.
Contributing to the increase in lung cancer mortality among female smokers, and to
the widening disparity in survival between smokers and non-smokers, was a generational
shift towards initiating cigarette smoking at younger ages. Successive birth
cohorts of both male and female smokers began smoking regularly earlier in adolescence
(Anderson et al. 2002). The relationship between an early age of initiation
and lung cancer risk is illustrated in Fig. 2.3, showing the lung cancer death rate
(per 100 000) among men aged 55–64 years in the US Veterans Study (Kahn 1966).
Men who began smoking at an earlier age have higher death rates from lung cancer at a
given level of smoking than men who initiated smoking later. The difference in risk is
seen for both ‘moderate’ (10–20 cigarettes per day) and ‘heavy’ smokers (21–39 cigarettes
per day). This analysis cannot differentiate whether the higher lung cancer rate in
persons who begin smoking early reflects a longer duration of smoking or greater vulnerability
of the immature lung to the carcinogenicity of smoke, since the two factors
are inseparably correlated in current smokers of the same age. However, Fig. 2.3 does
illustrate that earlier age of initiation is a strong predictor of higher lung cancer risk.
Finally, the cohort studies demonstrate the substantial benefit of smoking cessation in
preventing much of the increased mortality caused by continued smoking. Figure 2.4
illustrates the cumulative probability of death from lung cancer, conditional on
survival from other conditions, during 7 years of follow-up of CPS-II, in relation to