Table 1 shows background characteristics of the participants at the start of follow‐up.
Table 1Background characteristics at the last examination of participants*, by category of smoking
In both sexes, never smokers, ex‐smokers and quitters had a lower mean cholesterol level and a higher degree of leisure physical activity than smokers from any category. Ex‐smokers had a shorter duration of smoking than present smokers; duration in quitters was between that in smokers and that in ex‐smokers. In all smoking categories, the duration of smoking was 3–5 years less in women than in men.
Comparing reducers with heavy smokers, reducers had a considerably lower stature and a higher frequency of disability pension (both sexes). Male reducers had a shorter duration of smoking, and female reducers had a higher frequency of sick leave.
Table 2 shows the mean number of cigarettes at the first and last examinations in heavy smokers, reducers and moderate smokers.
Table 2Mean number of cigarettes per day at first and last examinations in moderate smokers, reducers and heavy smokers, by sex
At the last examination, reducers had a daily cigarette consumption that was 58% lower in men and 56% lower in women compared with consumption at the first examination. In both sexes, moderate smokers had a slightly higher and heavy smokers had a slightly lower daily consumption at the last examination than at the first examination.
Table 3 shows the mean serum thiocyanate values at the time of the last examination in participants in whom thiocyanate was determined.
Table 3Determination of serum thiocyanate at the last examination, by category of smoking
In both sexes, there are clearly higher mean serum thiocyanate levels in the smokers than in never smokers and previous smokers. Both male and female reducers have mean values that are lower than in heavy smokers, the difference being statistically significant for men (p
0.001), but not for women (p
0.074). Male and female reducers have mean thiocyanate values that are slightly above those of the moderate smokers. They report a cigarette consumption, however, which on average is slightly below those of the moderate smokers (table 2).
Table 4 shows the age‐adjusted mortality from any cause, cardiovascular disease, ischaemic heart disease, smoking‐related cancer or lung cancer, by sex and smoking category.
In men, the mortality among reducers was lower than that among heavy smokers only for smoking‐related cancer and lung cancer. These differences were not beyond chance. Only a few cause‐specific deaths were seen in women. Mortality from any cause, however, was non‐significantly higher in reducers than in heavy smokers.
Figure 1 shows the cumulative proportions of deaths from all causes, cardiovascular disease and smoking‐related cancer, by time of death. For all causes in men, the reducers have slightly lower death rates than heavy smokers during the first 15 years, whereas afterwards the reducers catch up with the heavy smokers. For women, reducers have higher total mortality than heavy smokers during the whole period. For cardiovascular disease in both sexes, there is on the whole no distinct difference between reducers and heavy smokers. For smoking‐related cancer, a clear difference can be seen between the sexes. In men, the reducers have lower death rates than the heavy smokers, whereas the reverse picture is seen in women. For the remaining smoking categories, the mortality levels are as expected. For female ex‐smokers, however, the curve falls slightly below that for never smokers. Mortality due to cardiovascular disease among female heavy smokers is comparable with that in men who have quit smoking.
Figure 1Deaths from (A) all causes, (B) cardiovascular disease and (C) smoking‐related cancer, as cumulative proportions of male and female participants in each category, by time of death. Nelson–Aalen cumulative hazard estimates. (more ...)
Table 5 shows the adjusted relative risks of death with heavy smokers as reference. Adjustments are made for age, systolic and diastolic blood pressure, serum total cholesterol, serum triglycerides, physical activity during leisure, body mass index (kg/m2
), height, disability pension, sickness leave and recorded coronary heart disease in the family. Table 5 also gives the relative risk for men and women together, to make comparisons with the reports by Godtfredsen et al
Here adjustments are also made for sex.
Table 5Adjusted relative risk* (95% CI) of death from all causes, cardiovascular disease, ischaemic heart disease, smoking‐related cancer or lung cancer, by smoking category, sex individually and both sexes together, with (more ...)
For both sexes, reducers have almost the same adjusted relative risk for death from any cause as heavy smokers. For cardiovascular disease and ischaemic heart disease, the adjusted risk in reducers is not significantly different from that in heavy smokers (see table 5). For smoking‐related cancer, the adjusted relative risk is lower for male reducers but higher for female reducers compared with the heavy smokers, but neither difference is statistically significant. For both men and women, the adjusted relative risk for lung cancer is clearly lower than in heavy smokers (29% lower in men, 49% in women), but does not reach statistical significance. In both men and women, and in all cause groups, relative risks decrease regularly: from reducers, through moderate smokers, quitters and ex‐smokers, to never smokers. An exception is cardiovascular deaths in women, where we find a somewhat higher relative risk in never smokers than in ex‐smokers.
As mentioned earlier, a third screening was carried out in all three counties. In Finnmark (25% of the total study population), this screening took place 10 years after the second screening; in the other two counties, 5 years after the second. Of the 475 reducers at the second examination, 271 attended the third examination. The main reason for the lower number of participants was that only a 10% random sample of the oldest 5‐year age group was invited to the third examination.
We grouped these 271 participants by their status at the third examination:
- New quitters: Those who quit smoking entirely between the second and third examinations
- Sustained reducers: Those who were daily smokers at the third examination, and still reported a consumption of at least 50% less cigarettes per day compared with the first examination
- Increasers: Those who were daily smokers at the third examination, but reported to have a daily cigarette consumption that had increased so much from the second examination that they no longer fulfilled the criteria of reducers.
As a reference group, we introduced sustained heavy smokers—that is, smokers with a daily cigarette consumption of
15 cigarettes at all three examinations.
Table 6 shows the relative risk of death from all causes in the three groups mentioned, with sustained heavy smokers as reference (both sexes together, but adjusted for sex).
Table 6Relative risk* (95% CI) of death from all causes in reducers at the second examination who attended the third examination, by group at the third examination, with sustained heavy smokers as reference,in both sexes
Relative risks in none of the three groups differ significantly from the reference group. The tendency of new quitters to have the same relative risk as quitters at the second examination is clear. Sustained reducers have a relative risk in line with the sustained heavy smokers, whereas increasers have an even higher relative risk.
Table 6 gives also the mean daily cigarette consumption in all groups at all three examinations. At the second examination, this mean differed only slightly between the three groups. At the third examination, the mean remained at the same level in sustained reducers, nearly doubled in those who increased smoking, and went down to zero in new quitters. In sustained heavy smokers, the mean consumption was almost constant at all three examinations.
So far, we have concentrated on participants who were heavy smokers, who at the second examination reported a consumption of at least 50% less cigarettes per day. As a last approach, we present relative risk by degree of change in daily cigarette consumption between the first and the last examinations. This is done by running Cox's proportional hazards analyses among the daily smokers at both the first and last examinations, with sex, consumption level and consumption change as covariates. Consumption level was defined as the mean number of cigarettes at the first and last examinations; consumption change was defined as the difference between number of cigarettes at the first and last examinations.
Table 7 shows the relative risks of dying from any cause and from specified smoking‐related diseases associated with a per 10 cigarette decrease in cigarette consumption, adjusted for sex and consumption level, for heavy smokers and for all smokers at the first examination. None of the relative risks is significantly different from 1. The largest decrease in risk is somewhat unexpectedly seen for ischaemic heart disease.
Table 7Relative risk (95% CI)* of dying from all causes and from cardiovascular disease, ischaemic heart disease, smoking‐related cancer or lung cancer in daily smokers at both examinations, per 10 decrease in cigarette (more ...)
In all smokers, the maximum decrease was 80 cigarettes, the maximum percentage decrease being 90%. The maximum increase was 62 cigarettes and the maximum relative increase was 10‐fold.