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Newsletter of the Health Analysis and Measurement Group (HAMG)

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82-005-XIE

 

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.

Figure 1: Age of smoking initiation (weighted mean), Canada, cohorts born 1910 through 1975
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).

Figure 2: Prevalence of smoking by gender, Canada, 1977 to 1998
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).

Figure 3: Proportion smoking more than 20 cigarettes per day, by age group, Canada, 1998

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.


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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