Variations of SCE frequencies in peripheral lymphocytes of ex-smokers.

We measured SCE frequencies over a period of 8 months in 14 smokers who stopped smoking at the start of the study. In a first group of 10 subjects, who did not resume smoking during the period of cytogenetic follow-up, a lowering of SCE frequencies was already evident after 18 days and this became statistically significant after 78 days. SCE decrease was related to the logarithm of the period (in days) for which smoking was interrupted (r = 0.98; p less than 0.001). In a second group of 4 subjects, who at various times resumed smoking, the decrease of SCE followed the same pattern as in the first group during the period of nonsmoking, but SCE frequencies rose even higher once smoking was resumed. Our study indicates that the decrease of SCE in ex-smokers is rather rapid during the first 78 days after stopping smoking, and much slower from the 78th to the 233rd day.