A topic in Clinical Evidence summarizes the evidence on smoking and total mortality. The study on male British doctors found a strong association between smoking and increased mortality: smokers were about three times more likely to die in middle age (45 - 64 years) and twice as likely to die in older age (65 - 84 years) compared with lifelong non-smokers.
In a prospective study , 1.2 million UK women were asked at entry whether they were current or ex-smokers, and how many cigarettes they currently smoked and resurveyed postally about 3 and 8 years later. All were followed through national mortality records (mean 12 woman-years, SD 2). For 12-year mortality, those smoking at baseline had a mortality rate ratio of 2.76 (95% CI 2.71 to 2.81) compared with never-smokers, even though 44% of the baseline smokers who responded to the 8-year resurvey had by then stopped smoking. Mortality was tripled, largely irrespective of age, in those still smoking at the 3-year resurvey (RR 2.97, 95% CI 2.88 to 3.07).
In another prospective cohort study of 290 215 adults data were gathered with a questionnaire assessing lifetime cigarette smoking history. Hazard ratios (HRs) and 95% CIs were determined for all-cause mortality and cause-specific mortality through the end of 2011. 159 (9.1%) and 1493 (22.5%) of these individuals reported consistently smoking fewer than 1 or 1 to 10 cigarettes per day (CPD) in each age period that they smoked, respectively. Relative to never smokers, consistent smokers of fewer than 1 CPD (HR 1.64, 95% CI 1.07 to 2.51) and 1 to 10 CPD (HR 1.87, 95% CI 1.64 to 2.13) had a higher all-cause mortality risk. Associations were similar in women and men for all-cause mortality and were observed across a range of smoking-related causes of death, with an especially strong association with lung cancer (HR 9.12, 95% CI 2.92 to 28.47, and HR 11.61, 95% CI 8.25 to 16.35 for <1 and 1-10 CPD, respectively). Former smokers had progressively lower risks with younger age at cessation. For example, the HRs for consistent smokers of fewer than 1 and 1 to 10 CPD who quit at 50 years or older were 1.44 (95% CI 1.12 to 1.85) and 1.42 (95% CI 1.27 to -1.59), respectively.
A prospective study of 204 953 individuals aged ≥45 years assessed tobacco smoking to mortality in Australia. Overall, 5 593 deaths accrued during follow-up (874 120 person-years; mean: 4.26 years); 7.7% of participants were current smokers and 34.1% past smokers at baseline. Compared to never-smokers, the adjusted RR (95% CI) of mortality was 2.96 (2.69 to 3.25) in current smokers and was similar in men (RR 2.82, 95% CI (2.49 to 3.19) and women (RR 3.08, 95% CI 2.63 to 3.60) and according to birth cohort. Mortality RRs increased with increasing smoking intensity, with around two- and four-fold increases in mortality in current smokers of ≤14 (mean 10/day) and ≥25 cigarettes/day, respectively, compared to never-smokers. Among past smokers, mortality diminished gradually with increasing time since cessation and did not differ significantly from never-smokers in those quitting prior to age 45. Current smokers are estimated to die an average of 10 years earlier than non-smokers.
Comment: The quality of evidence is upgraded by large magnitude of effect and by a dose-response gradient.