Heavy cigarette smokers (more than 15 cigarettes daily) who decrease their smoking by half can reduce their risk for lung cancer, according to an article in the September 28 issue of the Journal of the American Medical Association.

In the current study, Nina S. Godtfredsen, MD, PhD, 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 years 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 (1 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 10 was associated with a 27 percent reduction in lung cancer risk compared with unchanged heavy smoking," the authors reported.

"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 continued. "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 pointed 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 concluded.

In an accompanying editorial, Lawrence J. Dacey, MD, MS, and David W. Johnstone, MD, of Dartmouth-Hitchcock Medical Center, Lebanon, N.H., wrote that it is important to inform patients who smoke that the more they can reduce the number of cigarettes they smoke, the more they will decrease their risk of lung cancer.

"Physicians and other health professionals should do all they can to help their patients who smoke reduce their risk of getting lung cancer. Total discontinuation of smoking, no matter the age of the patient, will provide the greatest benefit," they noted. "The most effective interventions to achieve permanent smoking cessation combine pharmacological therapy and referral for intensive behavioral support from a trained counselor. Those patients who cannot quit smoking despite all efforts should be strongly encouraged to cut down on their cigarette consumption as much as possible, since doing so will significantly decrease their risk of lung cancer."