Cigarette smoking dose-response
In
Bandolier's infancy it looked at some of the facts about the negative
health effects of smoking (Bandolier 7), particularly the strong dose-response
for lung cancer. Now we have smoking bans, fewer people smoke, and more of
those who do smoke, smoke less.
With
the changes of the last decade, it is worth revisiting the issue of dose
response, particularly when we have good evidence at the lower end of the
dose-response curve [1], and for effects other than lung cancer.
Dose-response study
Inevitably
the evidence comes from an observational study. In this case [1] it stems from
screening examinations for cardiovascular disease in parts of urban and rural
Norway that began in the 1970s. The screening included questionnaires about
cardiovascular disease, demographic measures, blood tests and questions about
smoking habits.
Excluded
were people with a history of chronic disorders like heart disease, diabetes,
or hypertension, and ex-smokers or pipe smokers. That left about 19,000 women
and 24,000 men for whom death and cause of death could be determined by the end
of 2002.
Results
In
this sample, 42% of women and 65% of men smoked. Men who smoked mostly smoked
10 cigarettes a day or more, while women rarely smoked more than 15 cigarettes
per day. The lowest consumption, 1-4 cigarettes per day, involved 4% of women
and 3% of men (Figure 1).
Figure 1: Smoking habits of 23,500 men and 19,000 women in Norway in the mid 1970s
Across
the whole population, the average age at the screening event was about 42
years, and BMI about 24. In women who smoked, the duration of smoking averaged
12 years for the lightest smokers (1-4 cigarettes a day) to 20 years in the
heaviest (25+ a day). In men who smoked, duration ranged from 18 to 24 years.
Average total cholesterol was quite high, over 6.5 mmol/L.
Figures
2 to 5 show the actual number of events per 100,000 person years for men and
women, for all cancer, for lung cancer, for ischaemic heart disease, and for
all death. There was a strong dose response with cigarette consumption, with
more cancers, lung cancers, cases of ischaemic heart disease, and death with
more cigarettes smoked. Ischaemic heart disease affected women less than men
(Figure 4).
Figure 2: All cancer by cigarette consumption
Figure 3: Lung cancer by cigarette consumption
Figure 4: Ischaemic heart disease by cigarette consumption
Figure 5: All-cause mortality by cigarette consumption
Figure 6: Relative risk for lung cancer according to cigarette consumption
The
strongest dose response was for lung cancer (Figures 3 and 6), where smoking
10-15 cigarettes a day increased the risk by 17-fold, and 25 a day or more by
about 35-fold compared with not smoking. For all-cause deaths, all cancers, and
ischaemic heart disease there was higher relative risk with more cigarettes.
Even with 1-4 cigarettes a day there was a significantly increased risk of all
cause mortality, ischaemic heart disease, and lung cancer in both men and
women. Relative risks were about 1.5 for all cause mortality, 2.8 for ischaemic
heart disease, and 3-5 for lung cancer.
Comment
No
apologies for a revisit. In the UK parents can still take children into pubs
for a meal, into atmospheres with a high proportion of tobacco smoke. Smoking
bans in many parts of the world have been successfully implemented, and it is
only when you go somewhere without one that one realises just how much of an
imposition smoking can be.
Getting
down the dose response curve is good if you are at the top. Stopping people
being on the curve at all is so much better.
Reference:
- K Bjartveit, A Tverdal. Health consequences of smoking 1-4 cigarettes per day. Tobacco Control 2005 14: 315-320.