Fifty years' experience of reduced-tar cigarettes: what do we know about their health effects?

Since the 1950s, cigarettes sold in the United States have undergone a progressive modification, including the addition of filters and a reduction in the average machine-measured tar and nicotine yield per cigarette by over 60%. These, and other, temporal changes in manufactured cigarettes, coupled with the complexity of smoking behavior, make it difficult to assess the impact of the newer cigarettes on health. Recently, some researchers have suggested that the newer products, marketed as being less harmful, may in fact provide no benefit compared to the older, higher tar cigarettes. The primary purpose of this review is to critically evaluate the available epidemiologic evidence on the health effects of low-tar cigarettes. This body of data provides the only means of assessing the effects of long-term exposure to these products, as they are actually used. After identifying important methodological problems confronting research in this area, studies of lung cancer, coronary heart disease, chronic obstructive pulmonary disease, and total mortality are examined in terms of their strengths and weaknesses and their results. Thirty-five studies of lung cancer are suggestive that smokers of low tar cigarettes have a lower risk (by 20-30%) compared to smokers of higher tar cigarettes. Only a minority of studies of heart disease provide evidence of a reduction in risk, on the order of 10%. Studies concerning chronic obstructive pulmonary disease (COPD) are inconsistent, but the majority suggest decreased risk in smokers of lower tar cigarettes. Finally, studies that included total mortality indicate with a high degree of consistency that the total death rate is reduced in smokers of lower tar cigarettes, on the order of 10-20%. Because of the multiplicity of factors involved in smoking behavior, including compensation for reduced nicotine, and the modest magnitude of the apparent reduction in risk, the relative benefits of low tar cigarettes remain uncertain. Additional analyses of existing data sets could further clarify the impact of low-tar cigarettes.