Sister-chromatid exchanges and their distribution in human lymphocytes in relation to age, sex and smoking.

The effects of age, sex and smoking on sister-chromatid exchange (SCE) frequency and distribution in human lymphocytes were assessed by means of multiple linear regression. Differences in SCE scores were associated with all above variables: SCE increased with age and cigarette smoking intensity, and higher SCE frequencies were observed in females. Changes in SCE distribution were associated with age and smoking: the ratio of sample variance to sample mean (heterogeneity index) increased with age and smoking intensity. Cell proliferation kinetics, as measured by replication index, inversely correlated with age. Monte Carlo methods were used to show that in the occupational study, analysis of 20-50 persons per group and 25 cells per person may be recommended.