Pulmonary function in relation to cigarette smoking and smoking cessation. MRFIT Research Group

More than half of the subjects in the MRFIT smoked at baseline and 10% of the subjects stopped smoking permanently during the first year of the trial. In this report, rates of decline in forced expiratory volume in 1 sec (FEV1) are compared for early permanent quitters and smokers who continued to smoke throughout the trial.

Since pulmonary function testing was not standardized across all centers until the third annual visit cycle, change in FEV1 is examined over the latter half of the trial; the level of FEV1 is analyzed cross-sectionally at the midpoint of the trial. Analyses are limited to 4,926 subjects who never used beta-blockers or smoked cigars, cigarillos, or pipes during the trial and who had annual FEV1s measured over 2-4 years in the latter half of the trial.

Quitters during the first 12 months experienced smaller declines in FEV1 over the latter half of the trial than continuing smokers, with -50.7 ml/year versus -59.0 ml/year, respectively, adjusted for the level of FEV1 (P = 0.05). Cross-sectionally, those who had never smoked, former smokers, quitters, and continuing smokers showed a gradient of decreasing FEV1, and all four smoking groups were significantly different from each other (P less than 0.05).

These data suggest that if a middle-aged, healthy smoker stopped smoking permanently, he could expect his FEV1 to deteriorate at a more gradual rate 3-4 years after stopping smoking than a similar smoker who continued to smoke. No information was available for the complete MRFIT cohort on the pulmonary function effects immediately following smoking cessation.