Heavy smokers can reduce their risk of lung cancer if they decrease smoking by 50 percent

Heavy smokers (more than 15 cigarettes per day) can reduce their risk of lung cancer if they decrease smoking by 50 percent, according to a study in the September 28 issue of Journal of the American Medical Association (JAMA).

Lung cancer remains the leading cause of cancer death worldwide, and an estimated 90 percent of lung cancer cases are tobacco-related, according to background information in the article. Despite efforts to prevent people from beginning smoking and to encourage smoking cessation, the overall prevalence of cigarette smoking is still high and many smokers are unable or unwilling to completely quit.

Nina S. Godtfredsen, M.D., Ph.D., of Copenhagen University Hospital, Copenhagen, Denmark, and colleagues conducted an observational, population-based study with up to 31 years of follow-up, to assess the effects of smoking reduction on lung cancer incidence. The study participants included 11,151 men and 8,563 women, aged 20 to 93, who attended two consecutive examinations with a five- to ten-year interval between 1964 and 1988. Participants were divided into six groups, according to smoking habits: continued heavy smokers (15 or more cigarettes per day), reducers (reduced from 15 or more cigarettes per day by a minimum of 50 percent without quitting), continued light smokers (one to 14 cigarettes per day), quitters (stopped between first and second examination), stable ex-smokers, and never smokers. During follow-up, 864 participants were diagnosed with lung cancer. There were 360 lung cancer cases among women and 504 cases among men.

"Reducing tobacco consumption from approximately 20 cigarettes per day to less than ten was associated with a 27 percent reduction in lung cancer risk compared with unchanged heavy smoking," the authors report.

"Participants who were continued light smokers or who quit smoking between baseline and follow-up reduced their lung cancer risk by 56 percent and 50 percent, respectively, compared with persistent heavy smokers," they continue. "Risk of lung cancer among the stable ex-smokers was 83 percent lower than among the heavy smokers, but still significantly higher than among the never smokers."

The authors point out that their study results indicate risk reduction is disproportionately smaller than the corresponding smoking reduction. They suggest the discrepancy between reported amount of reduction and calculated risk reduction can be largely explained by "compensatory smoking" – getting the maximum number of puffs out of the limited number of cigarettes allowed.

"More data from long-term studies of smoking reduction are warranted, but for the present, smoking cessation and not smoking reduction should still be advocated as the ultimate method of reducing harm from smoking, especially since diseases such as COPD [chronic obstructive pulmonary disease] and [heart attack], which have a larger public health effect than lung cancer, have not shown any reductions in risks after smoking reduction," the authors conclude.