Cessation of smoking enhances sister chromatid exchanges in lymphocytes

SCEs in peripheral lymphocytes are higher in smokers than in nonsmokers, and it might be expected that the SCE rate would decrease if smoking was stopped. In order to investigate this, 19 persons were persuaded to stop smoking, and venous blood samples were drawn for SCE analyses before and up to 124 days after cessation of smoking. A total of 104 successful cultures were obtained, and in each specimen 30 cells were scored for SCEs. The mean SCE/cell before cessation of smoking was 9.54 SCE/cell, and this increased significantly within a week to 10.55 SCE/cell (P-0.0013). After cessation of smoking, the weighted mean of individual slopes of regression lines for the transformed variable, y-(sum SCE)1/2+(sum SCE + 1)1/2, on time was b-0.028±0.022, not significantly different from zero. This indicated that after cessation of smoking, SCE increased significantly and stayed on that increased level during the whole observation period of 54 days (mean). The mechanism underlying these changes is unknown.