Objectives: To estimate the risk of dying from all causes and from specified smoking-related diseases in people who were ex-smokers at two consecutive examinations, compared with never smokers and with people who were ex-smokers at the first examination but who had resumed smoking at the following examination.
Design: A prospective cohort study.
Setting: Three counties in Norway.
Participants: A total of 23 560 men and 25 122 women, aged 20–49, screened for cardiovascular disease risk factors in the mid 1970s, rescreened after 3–13 years and followed throughout 2005 participated in this study.
Outcomes: Absolute mortality and relative risks adjusted for confounding variables, of dying from all causes, cardiovascular disease, ischaemic heart disease, stroke, lung cancer and other smoking-related cancer.
Results: With sustained never smokers as reference, the sustained ex-smokers had adjusted relative risk (95% CI), of dying from any cause, for men 0.97 (0.80 to 1.18), for women 0.98 (0.65 to 1.48). Corresponding risk for ex-smokers who resumed smoking was for men 1.59 (1.32 to 1.91), for women 1.40 (1.08 to 1.81). For the specified smoking-related diseases, the risk in sustained ex-smokers was not significantly different from the risk in sustained never-smokers, except for lung cancer in men. For ex-smokers who resumed smoking, the corresponding risk was on the whole significantly higher.
Conclusions: A more valid and favourable picture of ex-smokers’ risk will be obtained if exposure is being based upon people with two consecutive examinations, years apart. The study confirms clearly the large health benefit of quitting smoking for good.
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Competing interests: KB has been involved in national and international tobacco control.