A topic in Clinical Evidence 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 , 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 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 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.
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