AJ Garvey, Harvard School of Dental Medicine; PS Vokonas, VA Medical Center, Boston; T Kinnunen, Harvard School of Dental Medicine; BL Nordstrom, Harvard School of Dental Medicine; Z Quiles, Harvard School of Dental Medicine

Objectives: The prevalence of cigarette smoking has declined over the past 35 years, but many smokers still are unable to quit. Most results on smoking prevalence rates have been based on cross-sectional surveys which are vulnerable to mis-classification errors. Also, many prospective studies on health effects of smoking have been able to provide only baseline smoking statuses. We used prospective information on smoking collected at multiple time points to provide more reliable information on smoking cessation patterns over the period 1962-1996, as well as information on the effects of reduced smoking on subsequent mortality.

Methods: Subjects were from the Normative Aging Study (NAS), a longitudinal study of the aging process in men supported by the Department of Veterans Affairs. The 2,280 members of the NAS represent a middle-class sample who reside in the greater-Boston area. Mean age at entry to the NAS was 40 years (range 21-80 years). We calculated yearly quit rates from 1962-1996, both for our total sample, and for subgroups classified by age, amount smoked, and education status. We also assessed all-cause mortality rates across a 20-year period for smokers who quit, reduced their daily intake of cigarettes, or maintained or increased their smoking intake.

Results: The majority of smokers (75%) quit smoking over the 35-year period of follow-up. Yearly rates of cessation increased in a linear fashion from the late 1960s to 1996 (p < .0001). The most striking sub-group differences were between light (< 15 cigarettes per day) and heavy smokers (> 25 cigarettes per day), with heavy smokers consistently less likely to quit. Older smokers were significantly more likely to quit than younger smokers.

Survival analysis indicated that reduced smoking was associated with lower risk both of all- cause mortality and smoking-related mortality than maintained or increased rate of smoking (p < .05). Men whose smoking rate remained the same or increased were at substantially greater risk for death compared to those who quit smoking (p < .01).

Conclusions: Results strongly suggest that the great majority of male smokers (75%) will quit smoking over a period of 35 years. Even the majority of heavily-dependent smokers quit over the follow- up period, though in significantly lower proportions than low-dependence smokers. Older smokers are more likely to quit than younger smokers in any given year. This may be related to cumulatively more severe effects on health for smokers as they age. A clear implication of our findings is that those smokers who cannot quit can at least reduce their mortality risk significantly by cutting down their daily cigarette intake.

Impact: Our study provides compelling evidence that the majority of smokers will quit as they progress from middle- to older-age. This finding may give encouragement to those providing care to patients who currently smoke. We have also provided the very first prospective information to our knowledge to support the belief that health-care providers should encourage patients who can't quit to decrease their cigarette-consumption levels. Such reduction: (1) significantly reduces smokers' mortality risk, and (2) does not make them any less likely to quit subsequently.