GENETIC AND SOCIAL INFLUENCES ON STARTING TO SMOKE - A STUDY OF DUTCHADOLESCENT TWINS AND THEIR PARENTS

In a study of 1600 Dutch adolescent twin pairs we found that 59% of th e inter-individual variation in smoking behaviour could be attributed to shared environmental influences and 31% to genetic factors. The mag nitude of the genetic and environmental effects did not differ between boys and girls. However, environmental effects shaved by male twins a nd environmental effects shared by female twins were imperfectly corre lated in twins from opposite-sex pairs, indicating that different envi ronmental factors influence smoking in adolescent boys and girls. In t he parents of these twins, the correlation between husband and wife fo r 'currently smoking' (r = 0.43) was larger than for 'ever smoked' (r = 0.18). There was no evidence that smoking of parents (at present or in the past) encouraged smoking in their offspring. Resemblance betwee n parents and offspring was significant but rather low and could be ac counted for completely by their genetic relatedness. Moreover, the ass ociation between 'currently smoking' in the parents and smoking behavi our in their children was not larger than the association between 'eve r smoking' in parents and smoking in their children.