Light Smoking Is Never Ideal

Godtfredsen NS, Prescott E, Osler M. Effects of smoking reduction on lung cancer risk. JAMA. 2005;294:1505-1510.

Bjartveit K, Tverdal A. Health consequences of smoking 1-4 cigarettes per day. Tob Control. 2005;14:315-320.

Two large studies ask the question: Is there any health advantage of light versus heavy tobacco use? According to researchers reporting in JAMA, reducing a smoking habit from 20 to 10 cigarettes a day cuts lung cancer risk by 27%--although they acknowledge that cessation, not reduction, should still be advocated. Bjartveit and Tverdal, reporting in the journal Tobacco Control, make the point that smoking as little as one to four cigarettes a day significantly increases all-cause mortality risk and death from ischemic heart disease and, particularly among women, lung cancer.

Pooled data for the analysis that appeared in JAMA were culled from several observational, population-based cohort studies conducted in Copenhagen and surrounding suburbs. Followed for as long as 31 years (mean, 18 years), 8,563 women and 11,151 men self-reported smoking status and changes in smoking habits during the study periods. Smoking reduction was defined as having sought and achieved a 50% decrease in tobacco use. Incidence of new-onset lung cancer was determined by linking subjects' records with those in the Danish National Cancer Registry.

Of the heavy smokers (ie, those who smoked 15 g/d or more of tobacco), older subjects, those who had smoked longer, and men were most likely to reduce their habit. The 27%-decreased lung cancer risk among smoking reducers was relative to risk in continued heavy smoking; the researchers note that "risk reduction is disproportionately smaller than the corresponding smoking reduction," perhaps due to compensatory behaviors (eg, increasing the puff volume per cigarette). Compared with continued heavy smokers, light smokers had 56% less lung cancer risk; and subjects who quit smoking between baseline and follow-up, 50% less risk.

A total of 23,521 men and 19,201 women in Oslo and three Norwegian counties were included in the analysis of the study outlined in Tobacco Control. All were screened in the mid-1970s for cardiovascular disease risk factors and, by means of a national death registry, followed through 2002 for the end point of deaths from ischemic heart disease, all cancer, lung cancer, and all causes.

The steepest increase in heart disease mortality risk from one tobacco consumption level to the next was from never smoking to light smoking (ie, one to four cigarettes per day). Compared with that of never smokers, the adjusted relative risk (RR) of dying of ischemic heart disease was 2.74 and 2.94 for men and women, respectively, who were light smokers. The RRs for lung cancer for men and women who were light smokers were 2.79 and 5.03, respectively.