Effects of biochemically confirmed smoking cessation on white blood cell count

OBJECTIVES: To determine the relationship between white blood cell (WBC) indices and several baseline variables in a large cohort of healthy smokers and to assess whether these changed after biochemically confirmed smoking cessation. SUBJECTS AND METHODS: The study consisted of 784 healthy smokers enrolled in a trial of sustained-release bupropion, 300 mg/d, for relapse prevention after smoking cessation from 1995 to 1998. Both WBC counts and absolute neutrophil counts (ANCs) were measured at baseline, week 7, and week 52. Smoking status was assessed at weeks 7 and 52 by self-report and biochemically confirmed with expired air carbon monoxide levels. Multivariate analyses compared changes in WBC count and ANC between smokers who did and did not stop smoking, adjusting for treatment group, age, sex, and body mass index. RESULTS: Of 784 smokers enrolled, 461 had biochemically confirmed tobacco abstinence after 7 weeks of bupropion; 429 were randomly assigned to receive continued bupropion therapy or placebo until week 52. Between baseline and week 7, there was a significantly larger decrease in WBC count in continuously abstinent subjects compared with continuing smokers (adjusted P=.03). At 52 weeks, continuously abstinent subjects, compared with continuing smokers, had a greater decline from baseline in WBC count (1.2±1.9 × 10⁹/L vs 0.1±1.9 × 10⁹/L; P<.001) and ANC (1.0±1.6 × 10⁹/L vs 0.2±1.5 × 10⁹/L; P<.001). CONCLUSION: Biochemically confirmed tobacco abstinence leads to a rapid and sustained decrease in WBC and ANC, possibly reflecting a decrease in an underlying state of tobacco-induced inflammation.