Objective: To determine the risk of dying from specified smoking-related diseases and from any cause in heavy smoking men and women (> or =15 cigarettes/day), who reduced their daily cigarette consumption by >50%.
Design: A prospective cohort study.
Setting: Three counties in Norway.
Participants: 24,959 men and 26,251 women, aged 20-49 years, screened for risk factors of cardiovascular disease in the mid-1970s, screened again after 3-13 years, and followed up throughout 2003.
Outcomes: Absolute mortality and relative risks adjusted for confounding variables, of dying from all causes, cardiovascular disease, ischaemic heart disease, all smoking-related cancer and lung cancer.
Results: With sustained heavy smokers as reference, the smokers of both sexes who reduced their daily consumption (reducers) had the following adjusted relative risks (95% confidence interval (CI)): of dying from any cause, 1.02 (0.84 to 1.22); cardiovascular disease, 1.02 (0.75 to 1.39); ischaemic heart disease, 0.96 (0.65 to 1.41); smoking-related cancer, 0.86 (0.57 to 1.29); and lung cancer, 0.66 (0.36 to 1.21). The difference in cigarette consumption between two examinations was not a significant predictor of death from any of the causes. A follow-up from a third screening of the subgroup who were reducers at both second and third examinations (sustained reducers) did not have a lower risk than those who were heavy smokers at all three examinations.
Conclusions: Long-term follow-up provides no evidence that heavy smokers who cut down their daily cigarette consumption by >50% reduce their risk of premature death significantly. In health education and patient counselling, it may give people false expectations to advise that reduction in consumption is associated with reduction in harm.