Prospective study on the effect of smoking and nicotine substitution on leucocyte blood counts and relation between blood leucocytes and lung function.

BACKGROUND: The influence of smoking and of nicotine substitution on the counts of total blood leucocytes and leucocyte subsets and the relations between the counts and lung function was investigated.
METHODS: The study was a combined cross sectional and prospective study of 298 smokers and 136 non-smokers. Forced expiratory volume in one second (FEV1) was measured in all participants at baseline and six months after quitting smoking in 160 ex-smokers (quitters) and 138 persons with smoking relapse. Blood samples were obtained from all participants at baseline and from 160 quitters and 30 continuing smokers two, six, 12, and 26 weeks after smoking cessation and from 92 quitters one year after the cessation of smoking.
RESULTS: Blood leucocyte counts and leucocyte subsets were all higher in smokers than in non-smokers. In cigarette smokers total leucocyte, neutrophil, and lymphocyte blood counts showed a dose dependent relationship with the daily cigarette consumption and pack years consumption. In smokers the neutrophil blood count was independently associated negatively with FEV1 residuals. After quitting smoking total leucocyte, neutrophil, and lymphocyte blood counts decreased during the first 26 weeks and after one year lymphocyte blood counts were higher than in non-smokers. In quitters substituted with nicotine chewing gum (2 mg) the accumulated number of pieces of chewing gum used in the 12 weeks had an inverse relationship with the decrease in the total lymphocyte blood count at 12 weeks after smoking cessation.
CONCLUSIONS: Leucocyte blood counts are raised in smokers and decrease after smoking cessation. Neutrophil blood counts had an inverse relationship with lung function and nicotine may increase lymphocyte blood counts in smokers.