Heavy smokers who halved their daily cigarette quota failed to reduce their risk of death or smoking related diseases, the 21-year study showed. Only smokers who quit had a reduced risk of dying from smoking-related diseases.
The study involved 51,210 men and women aged 20–49 who were first screened in the 1970s for smoking status and other cardiovascular risk factors.
When participants were reassessed three to 13 years later, 6,570 were still heavy smokers, smoking at least 15 cigarettes a day. A further 475 people who were heavy smokers at the first assessment had since cut down by 50 per cent or more.
Follow-up until 2003 showed no difference in the rate of all-cause mortality between heavy smokers and those who had cut back. Among 4,260 people who quit smoking during the study period, all-cause mortality risk was 63 per cent lower than in heavy smokers.
The risk of lung cancer was lower for people who reduced their cigarette consumption but this did not reach statistical significance. The risk of developing cardiovascular disease, ischaemic heart disease and smoking-related cancer was similar in both groups.
Lead researcher, Dr Kjell Bjartveit, from the Norwegian National Health Screening Service in Oslo, said: ‘One explanation may be that the risk of dying from ischaemic heart disease increases dramatically between 0 and 1–4 cigarettes per day.
‘GPs should be wary of telling smokers who cannot quit to cut down,’ he added.