Niklas Hammar1,2, J. Kaprio3,4, L. Alfredsson,1 M. Koskenvuo5, T. Rönnemaa6, T. Hammar7, U.Hagström1, & L. Viikari6
Migrant studies offer a naturalistic experiment to enhance our understanding of how changes in environment and life-style can affect health habits, disease-risks and behavioral outcomes. Long-term international migration may significantly alter environmental exposure to factors relevant to disease-risk and trait-development, and comparisons of migrants with non-migrants have a long history in medicine and psychiatry. But such comparisons are confounded with uncertain matching of migrants and non-migrants on genetic and familial background, and the most meaningful contrasts are of migrants and non-migrants within-sibships, even more so within pairs of twins. In an ongoing collaborative study, a postal questionnaire is distributed to all twin pairs of the older Finnish Twin Cohort Study in which one or both cotwins have migrated to Sweden. We project the sample will include 2,700 twins or 1,350 pairs. Data-collection began, early 1998, with questionnaire content including medical history and physical symptoms, alcohol and tobacco use, dietary and exercise habits, educational, employment, and residential history. A clinical examination will be made of the most resident-discordant twin pairs. Extensive baseline information on these migrant-discordant twins was collected in earlier postal surveys, and the matched analysis of migrant-discordant twins will offer unusual, if not unique, power in understanding how environmental changes affect behavioral development and disease outcomes.
Address: Niklas Hammar, Department of Epidemiology, Division of Public, Health,Karolinska Hospital, Norrbackabyggnaden, S- 171 76 Stockholm, Sweden. E-mail:, niklas.hammar@imm.ki.se
1Department of Epidemiology, Institute of Environmental Medicine, Karolinska Hospital, Stockholm 2Department of Epidemiology, Division of Public Health, Karolinska Hospital, Stockholm 3Department of Public Health, University of Helsinki 4Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki 5Department of Public Health, University of Turku 6Department of Internal Medicine, Turku University Hospital, Turku 7Centre for Migration Research, Stockholm University, Stockholm