How times have changed! Canadian smoking patterns in the 20th
century
In our last issue, we described the role of microsimulation modeling
in our research program Population Health Impact of Disease, Injury,
and Health Determinants in Canada. In 2002, HAMG initiated a unique
analysis to provide input for this initiative. We established a
profile over time for an important behavioral risk factor –
the use of cigarettes. Tobacco use is associated with cardiovascular
and respiratory diseases, a range of cancers, and numerous other
maladies. The age of smoking initiation, cumulative exposure, both
in years and amount smoked, and interaction of smoking with other
health determinants all contribute to the health risk of smokers.
In the past, trends in age of smoking initiation have been measured
using cross-sectional prevalence data; the youngest age group at
a given threshold of smoking prevalence reflected the approximate
age of the youngest cohort of smokers. This provided a limited measure
of smoking initiation because it did not measure average age (or
range) at initiation, although it could provide some sense of changes
over time.
The current analysis integrates data for age at smoking initiation,
smoking patterns (ever/never smokers), and number of cigarettes
smoked by age and gender from 13 Canadian population-based health
surveys (see Surveys used). Data for
cohorts of individuals born between 1910 and 1985 were combined
into a single dataset to analyze changes in smoking behaviour. The
availability of multiple datasets contributed to the stability of
estimates, particularly for the earlier cohorts.
Smokers are starting earlier
Fewer people are smoking, and the gender
gap is closing
Smoking peaks in the middle age groups
In summary
Methods and limitations
Surveys used
Smokers are starting earlier
The age of smoking initiation has decreased substantially in subsequent
birth cohorts over the past decades (Figure 1). The overall decrease
for males was modest compared to that for females. For those born
early in the century, males reported smoking at a much earlier age
than females. A look at the 1956 cohort shows that the mean age
of initiation for females converged with that of males at just over
16, and over the next 20 cohorts, the age of initiation continued
to decrease slightly for both males and females. For those born
in 1975, both females and males started to smoke, on average, at
just over age 15.
Notes
1. Based on nine surveys (1981, 1983, 1985, 1989, 1991, 1996, 1998,
1999, 2000)
2. Data for cohorts born 1910 through 1925 should be interpreted
with caution (see Methods and limitations).
Fewer people are smoking, and the gender gap is
closing
Cross-sectional data for ever/never smoking were available from
1977 on. From 1977 to 1998, the proportion of individuals stating
that they had never smoked declined from 45% to 38%; the proportion
who had smoked but quit (former smokers) increased from 15% to just
over 34% (data not shown). The proportion that were current smokers
thus declined from 45% and 35% for males and females, respectively,
in 1977 to 29% and 27% in 1998. The prevalence of smoking was higher
for males than females across the years (Figure 2).

Note: Based on 11 surveys (1977 through 1998)
Smoking peaks in the middle age groups
Among smokers, the pattern of cigarette use by age group was similar
across birth cohorts: the proportion of heavy smokers peaked in
the middle age groups. For example, in 1998, about 44% of smokers
aged 45 to 49 used more than 20 cigarettes per day, compared with
less than 29% of those in the youngest (15 to 39 years of age) and
oldest (70+) age groups (Figure 3). The youngest and oldest age
groups tended to be lighter smokers: over half smoked 15 cigarettes
or less per day compared with less than 37% of those aged 45 to
49 (data not shown).
Smoking trends were examined over time (according to the year the
survey was conducted). Recent surveys suggest that smokers are using
fewer cigarettes on a daily basis. In 1977, less than 43% of smokers
stated that they used 15 cigarettes or less per day, and just under
11% used more than 25. By 2000, almost 62% of smokers stated that
they used 15 cigarettes or less; just over 5% said they smoked more
than 25 per day (data not shown).
In summary: good news and bad news about smoking
patterns
This analysis provides a snapshot of changes in smoking behaviour
over the past century, using data amalgamated from 13 Canadian surveys.
The good news…the proportion of males and females who stated
that they were current smokers declined considerably over the years;
the proportion labelling themselves as former smokers has increased;
and recent birth cohorts are smoking fewer cigarettes than those
born earlier in the century. Although prevalence rates vary across
birth cohorts, the pattern of use within each cohort is fairly similar,
peaking during the middle years.
The bad news…females are now starting to smoke at a much
younger age than females born early in the twentieth century. Males
are starting at a slightly younger age than in earlier cohorts.
In every survey, more males than females stated that they were current
smokers, although this gap has closed over time. The most recent
survey data suggest that the gender gap for age at initiation and
smoking rates is now very modest.
Early initiation of smoking itself provides more opportunity for
exposure, and may combine with the effects of other health determinants
to increase risk of adverse health outcomes contributing to disability
and death. Given the 10 to 20 year latency for cancer, and the approaching
entry of baby boom cohorts into age brackets of high risk for cardiovascular
diseases and cancers, decreased age of smoking initiation could
place added pressure on health care resources over the next decades.
This analysis contributes information about smoking patterns over
time to a large integrative framework for population health: the
Population Health Impact of Disease, Injury, and Health Determinants
in Canada (PHI). The PHI incorporates epidemiologic data about diseases
and health determinants with Canadian health state preferences to
provide summary measures of population health for decision-makers.
Serge Tanguay, B. Phyllis Will, Karla Nobrega
Methods and limitations
The year of the survey and reported age were used to assign
individuals to birth cohorts. Each of the 13 surveys essentially
asked “Have you ever smoked?” and ten of them
asked “At what age did you start smoking?” For
age of initiation, the latest cohorts (1976 to 2000) were
excluded since some individuals might still start smoking.
Cross-sectional ever-smoker rates (the proportion who reported
having smoked at any time during their lifetime) were also
calculated for males and females within each birth cohort,
by five-year age group and survey year.
The strength of this analysis lies in the large, population-based
samples. These observations, however, should be considered
in the context of the study limitations. The smoking history
data are subjective, not externally validated, and are recollected
from the past. Information on the earliest cohorts (1910
to 1925) is relatively sparse and should be interpreted
with caution. If those who smoked earlier also died earlier,
estimated age at initiation would be biased upwards, implying
a more dramatic decrease than in reality. This would not,
however, account for the substantial gap between males and
females.
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Surveys used
Survey of
Smoking Habits 1977, 1979, 1981, 1983, 1986
General Social
Survey 1985, 1991
National Alcohol
and Drugs Survey 1989
National Population
Health Survey 1994, 1996, 1998
Canadian Tobacco
Use Monitoring Survey 1999, 2000
Serge Tanguay is a policy analyst in the Policy
Research Division of the Population and Public Health Branch, Health
Canada. Since obtaining his BSc in computer science from Université
du Québec à Hull, he has worked in the health field
for 13 years, ten of these at Health Canada. His research interests
are community health and environmental health.
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