Dr Emberson said: "Despite recent declines in the numbers of people smoking and tar yields of cigarettes, smoking remains the leading preventable cause of death in Europe."
He added: "Previous studies had demonstrated that prolonged cigarette smoking from early adult life was associated with about 10 years loss of life expectancy, with about one quarter of smokers killed by their habit before the age of 70. Stopping at ages 60, 50, 40 or 30 years gained back about 3, 6, 9 or the full 10 years. However, the hazards of continuing to smoke and the benefits of stopping in older people had not been widely studied."
In the current study, scientists tracked the health of 7,000 older men (mean age 77 years, range 66 to 97) from 1997 to 2012 who took part in the Whitehall study of London civil servants. Hazard ratios (HRs) for overall mortality and various causes of death in relation to smoking habits were calculated after adjustment for age, last known employment grade and previous diagnoses of vascular disease or cancer.
During the 15-year study 5,000 of the 7,000 men died. Deaths in current smokers were about 50% higher than in never smokers (HR=1.50), due chiefly to vascular disease (HR=1.34), cancer (HR=1.74) and respiratory disease (HR=2.39).
Deaths in former smokers were 15% higher than in never smokers (HR=1.15), due chiefly to cancer (HR=1.24) and respiratory disease (HR=1.58). Compared with never smokers, men who had quit smoking within the previous 25 years (median 14 years) had a 28% higher mortality rate (HR=1.28) while men who quit >25 years ago (median 35 years) had no significant excess risk (HR=1.05).
Dr Emberson said: "Our results clearly show that active smoking continues to increase the risk of death in old age. Risk in former smokers decreases as the time since quitting gets longer and, if one survives long enough, eventually reaches levels of never smokers."
Average life expectancy from age 70 was about 18 years in men who had never regularly smoked, 16 years for men who gave up smoking before age 70 but only about 14 years in men still smoking at age 70. Two-thirds of never smokers (65%), but only half of current smokers (48%), survived from age 70 to age 85.
Dr Emberson said: "This study shows that even if you were to ignore all the deaths caused by smoking before the age of 70, older smokers still do considerably worse than older non-smokers, losing a considerable amount of subsequent lifespan."
Dr Robert Clarke (UK), coordinator of the study, concluded: "We have shown that even if a smoker is fortunate enough to survive to age 70 they still lose, on average, about 4 years of subsequent lifespan compared with men who do not smoke. Quitting is beneficial at any age and it really is never too late to stop."