Tobacco use prevalence in Swedish male population
Figure 1 shows the distribution of prevalence of tobacco use in Swedish males for the nine categories by year for the age-groups 30-79, 30-34, 50-54 and 70-74 years. Cigarette smoking prevalence, standardized to age 30-79 years, declined from 33% in the 1980s to 11% in the 2010s (red and brown areas). Over the same period, the prevalence of snus users including snus and cigarette dual use increased from 11% to 23% (green and brown areas). Fewer former smokers and former snus users are observed at younger ages, as expected. Nevertheless, the prevalence of former tobacco users also decreased during the observed period. Consequently, the subcategory of never tobacco users increased with time.
Figure 1. Distribution of tobacco use status in Swedish males by year and age
Figure 1 shows the distribution of the nine subcategories of tobacco use status in Swedish males by year from 1980-2009 for all ages (30-79 years), and for three selected age groups.
There were seven other European countries where, over the period 1980-2009, the mean absolute difference between their age-standardized prevalence of current smoking in males aged 30-79 years differed from the prevalence of current tobacco use for Sweden by less than 4%. These countries, with the mean absolute differences from Sweden shown in parentheses, were Spain (1.34%), Hungary (1.46%), Lithuania (2.16%), Czech Republic (2.95%), Poland (3.09%), Denmark (3.36%) and Slovakia (3.93%).
Figure 2 shows (blue lines) the number of deaths occurring each year in Swedish males aged 30-79 years from each of the four diseases individually, and also from all SRDs combined and from all NSRDs. Also shown are the hypothetical number of deaths that would have occurred if Swedish males had had the average rates seen in the eleven countries with similar rates of tobacco use, either with adjustment for rates of all NSRD being higher in Sweden (green lines) or without adjustment (red lines). The hypothetical rates are higher, except for IHD in the early years. These results are consistent with the beneficial effect of Swedish snus on population health shown in Table 1. Table 1 in Supplementary File 4 presents the detailed results for the four diseases summarized in Figure 1, expressed as the increase in deaths that would have been seen, if Sweden had the mortality rates of other countries.
Figure 2. Approach 1. Comparison of observed deaths in Sweden with unadjusted and adjusted hypothetical deaths
For the period 1980-2009, Figure 2 compares the numbers of deaths occurring in Swedish males aged 30-79 years (blue lines) with those that would have occurred had they the average mortality of seven other European countries with a prevalence of cigarette smoking similar to the prevalence of tobacco use seen in Sweden. Rates are shown with adjustment (green lines) or without (red lines). Adjustment is based on the lower mortality from all NSRD in Sweden.
In this approach, deaths actually occurring in Sweden are compared with those that would have occurred if current and former snus users had been current and former cigarette smokers, with a resultant increase in risk. As shown in Figure 3, we observe increased mortality rates in the hypothetical scenario for each disease. The elevation is clear for lung cancer and COPD, but still evident for IHD and stroke. Details of the increase in the number of deaths that would have occurred in Sweden in the absence of snus are shown in Table 2 in Supplementary File 4.
Figure 3. Approach 2. Comparison of observed deaths in Sweden with those in the hypothetical scenario
For the period 1980-2009, Figure 3 compares the number of deaths occurring in Swedish males aged 30-79 years (blue lines) compared with those that would have occurred if the current and former snus users had been current and former cigarette smokers (red lines).
Figure 4 (historical scenario) and Figure 5 (hypothetical scenario) compare the tobacco use prevalence estimates for Sweden derived as described in Supplementary File 2 with those estimated by the PHIM based on the initial prevalences and the TTPs. The correspondence between the pairs of estimates for current smokers, snus users, and dual users appears quite reasonable. However, the prevalence of former smokers is overestimated by the PHIM simulations.
Figure 4. Approach 3. Comparison of published and PHIM simulated tobacco prevalence where snus is used
For the period 1980-2009 and for three age groups, Figure 4 compares tobacco use prevalence in Swedish males based on published data with that estimated from PHIM simulations for the historical scenario, where snus is used.
Figure 5. Approach 3. Comparison of published and PHIM simulated smoking prevalence where snus is not used
For the period 1980-2009 and for three age groups, Figure 5 compares smoking prevalence in Swedish males based on published data with that estimated from PHIM simulations for the counterfactual scenario, where snus is not used.
Two sets of analyses comparing the historical and hypothetical scenarios were carried out.
In the first set, analyses were carried out with the g-factor (relative exposure for dual users) fixed at 1, but with the f-factor (relative exposure for snus only users) varying with values of 0, 0.1 and 0.2. Figure 6 compares the increases in deaths that would have occurred in the hypothetical scenario for these three Approach 3 analyses as well as showing the corresponding estimates using Approach 2. The estimates from Approach 3 with f = 0 are, somewhat lower over the whole follow-up period than those from Approach 2 for lung cancer, and somewhat higher for the other three diseases. As the f-factor increases the estimates from Approach 3 decline for all four diseases, so getting closer to those from Approach 2 for COPD, IHD and stroke and less close for lung cancer.
In the second set, analyses were carried out with the f-factor fixed at 0, but with the g-factor varying with values of 0.9, 0.8 and 0.5. Figure 7 compares the increase in deaths for these three Approach 3 analyses with those using Approach 2. As the g-factor decreases, the estimates from Approach 3 increase for all four diseases, so getting less close to those from Approach 2 for COPD, IHD and stroke. For lung cancer decreasing the g-factor leads to the increase rising to exceed that from Approach 2.
Table 3 (f-factor) and Table 4 (g-factor) of Supplementary File 4 provide further detail.
Figure 6. Increase in deaths had snus not been introduced compared in Approaches 2 and 3 (varying f-factor)
For the period 1980-2009, Figure 6 compares the increases in deaths that would have occurred in Swedish males had snus not been introduced, as estimated from Approach 2 and from PHIM simulations with the f-factor varying but the g-factor fixed at 1.0.
Figure 7. Increase in deaths had snus not been introduced compared in Approaches 2 and 3 (varying g-factor)
For the period 1980-2009, Figure 7 compares the increases in deaths that would have occurred in Swedish males had snus not been introduced, as estimated from Approach 2 and from PHIM simulations with the g-factor varying but the f-factor fixed at 0.
Comparisons of the increases in deaths associated with unavailability of snus from the different approaches are summarized in Table 3, based on the period 1980-2009. They indicate that for lung cancer and COPD the highest estimates are from Approach 1 and the lowest from Approach 3. For IHD, the adjusted result for Approach 1 is unreliable (the occurrence of IHD being extremely high in Sweden compared to other countries, mostly due to non-smoking attributable cases). Nevertheless, Approach 2 and Approach 3 provide consistent results. For stroke, Approach 1 shows a very large increase in deaths compared to the other approaches.
Table 3. Increase in deaths in Sweden if snus had not been introduced – summary of results