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, and had resumed smoking at the following examination.
Design: A prospective cohort study.
Setting: Three counties in Norway.
Participants: 23 560 men and 25 122 women, aged 20-49, screened for cardiovascular disease risk factors in the mid 1970s, re-screened after 3-13 years, and followed throughout 2005.
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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