Adults who halve the number of cigarettes smoked daily do not reduce their risks for cancer and early mortality compared with heavy smokers whose habits do not change with time, according to an article in the December issue of Tobacco Control.

Norwegian researchers based their findings on more than 51,000 men and women, all of whom were age 20 to 34 years at the start of the study. Participants were initially assessed for cardiovascular risk factors, and then screened again twice at intervals of 3 to 10 years, adding up to an average follow-up period of over two decades.

Participants were classified as never smokers; ex smokers, quitters (those who gave up between the first and second check); moderate smokers (1 to 14 cigarettes daily); reducers (more than 15 cigarettes a day, cut by more than half at the second check); and heavy smokers (more than 15 cigarettes a day).

Among men, deaths from lung cancer and cancers associated with smoking were not significantly lower in those who had cut back compared with heavy smokers. But this was not true of women who cut back, where the reverse was true. Men who cut back only had slightly lower death rates from all causes combined than the heavy smokers during the first 15 years. After that, death rates were comparable.

There were no significant differences in death rates from specific causes, including early death from cardiovascular disease, among women who cut back their daily consumption, compared with those who continued to smoke heavily. Women who cut back actually had higher death rates from all causes combined than heavy smokers.

The authors concluded that long term monitoring provides no evidence that heavy smokers who halve their daily cigarette consumption significantly cut their risk of early death. They add that people may be misled if they are advised that cutting back will help them stave off disease.