A topic in Clinical Evidence 1 summarizes the evidence on risk of cardiovascular death after stopping smoking. Observational studies found that, in both male and female ex-smokers, the risk of coronary events rapidly declined to a level comparable with that of people who had never smoked after 2 - 3 years and was independent of the number of cigarettes smoked before quitting. The US surgeon general´s review of observational studies found that the risk of stroke decreased but remained raised for 5 - 10 years after cessation compared with those who had never smoked. One recent study in 7735 middle aged British men found that 5 years after smoking cessation the risk of stroke in previously light smokers (< 20 cigarettes/day) was identical to that in life-long non-smokers, but the risk in previously heavy smokers was still raised compared to lifelong non-smokers.
In a prospective study 2, 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). Women who had stopped at ages 35-44 years also still had, 20 or 30 years later, higher overall mortality (RR 1.20, 95% CI 1.14 to 1.26) and lung cancer mortality (RR 3.34, 95% CI 2.76 to 4.03) than never-smokers. However, these ex-smokers did avoid about 90% of the excess lung cancer mortality and excess overall mortality among continuing smokers. Likewise, that for chronic lung disease, coronary heart disease, and stroke, about 90% of the excess risk was avoided by stopping at around age 40 years (and more by stopping earlier).
In another prospective cohort study 3 of 290 215 adults data were gathered with a questionnaire assessing lifetime cigarette smoking history. Relative to never smokers, consistent smokers of fewer than 1 cigeretter per day (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. 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 4 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.
A retrospective cohort study 5 included 2072 patients who experienced an initial MI at 50 years or younger. Smoking status at the time of presentation and at 1 year after MI was determined from electronic medical records. 1088 were smokers at the time of their index hospitalization. Over a median follow-up of 11.2 years (interquartile range, 7.3-14.2 years), individuals who quit smoking had a statistically significantly lower rate of all-cause mortality (hazard ratio [HR], 0.35, 95% CI 0.19 to 0.63; P < .001) and cardiovascular mortality (HR 0.29, 95% CI 0.11 to 0.79; P = .02). These values remained statistically significant after propensity score adjustment (HR 0.30 [95% CI 0.16 to 0.56; P < .001] for all-cause mortality and 0.19 [95% CI 0.06 to 0.56; P = .003] for cardiovascular mortality).
Retrospective analysis 6 of prospectively collected data from Framingham Heart Study participants without baseline CVD included 8770 individuals. Over 26.4 median follow-up years, 2435 first CVD events occurred. In the pooled cohort, compared with current smoking, quitting within 5 years was associated with significantly lower rates of incident CVD (incidence rates per 1000 person-years: current smoking, 11.56., 95% CI 10.30 to 12.98; quitting within 5 years, 6.94, 95% CI 5.61 to 8.59; difference, -4.51, 95% CI -5.90 to -2.77) and lower risk of incident CVD (hazard ratio [HR], 0.61; 95% CI 0.49 to 0.76). Compared with never smoking, quitting smoking ceased to be significantly associated with greater CVD risk between 10 and 15 years after cessation in the pooled cohort (incidence rates per 1000 person-years: never smoking, 5.09, 95% CI 4.52 to 5.74]; quitting within 10 to <15 years, 6.31, 95% CI 4.93 to 8.09; difference, 1.27, 95% CI -0.10 to 3.05; HR 1.25, 95% CI 0.98 to 1.60).
Comment: The quality of evidence is upgraded by large magnitude of effect.
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