Acta Genet Med Gemellol 33:425-433 (1984) © 1984 by The Mendel Institute, Rome TWIN RESEARCH 4 - Part C: Clinical Studies Proceedings of the Fourth International Congress on Twin Studies (London 1983) Finnish Twins Reared Apart. IV: Smoking and Drinking Habits. A Preliminary Analysis of the Effect of Heredity and Environment J. Kaprio, M. Koskenvuo, H. Langinvainio Department of Public Health Science, University of Helsinki Abstract. Data on alcohol use and smoking habits was available from the 1975 ques- tionnaire of the entire cohort. Prior to pairwise analyses, the data of individuals was compared to that of age-sex matched groups of pairs reared together. The early sepa- rated twins had a higer alcohol consumption, while for smoking only slight differences were observed compared to twins reared together. Probandwise concordance rates were computed from smoking status (ever smoker/never smoker), alcohol use (user/nonuser) and "heavy" drinking (half-bottle of spirits on one occasion at least once a month). The following results were obtained in those pairs with the environmental dissimilarity score >15: Age at separation No. of cases Smoking Alcohol use "Heavy" drinking MZ DZ MZ DZ MZ DZ MZ DZ 0-5 18 61 0.67 0.65 0.89 0.81 0.67 0.38 0-10 30 95 0.67 0.68 0.80 0.81 0.67 0.33 Key words: Twins reared apart, Rearing environment, Adoption, Smoking, Alcohol use INTRODUCTION Health related behavior on a personal level encompasses many aspects of human behavior. Two major determinants of illness, alcohol use and smoking, are complex behavior patterns that are undoubtedly influenced by environmental, familial and genetic factors. The relative importance of these factors is not very well known. The purpose of this study is to analyse the effect of environmental and genetic fac- tors of smoking habits and alcohol use among Finnish twins reared apart in childhood before the age of eleven years. The results are compared to twins reared together but living apart at the time of study. In an earlier paper, the preliminary characterization of the rearing environment and causes of separation was given [18]. https://doi.org/10.1017/S0001566000005870 Published online by Cambridge University Press