International migration and coronary heart disease : epidemiological studies of immigrants in Sweden

Abstract: In today's globalised world, with considerable international migration, knowledge about the health of immigrants is becoming increasingly important. In Sweden, about 13% of the population or over one million persons are born outside the country. Large groups have moved to Sweden from Finland, other Nordic countries, the Baltic States and other Eastern European countries, Western Europe, Turkey, Iran, Iraq, and Latin America. The aim of the thesis was to describe incidence of myocardial infarction (MI) among foreignborn persons compared to Sweden-born, taking into consideration gender, socio-economic status and time spent in Sweden and to evaluate if the long term trend of decreasing MI incidence in Sweden was present in immigrants to Sweden. In addition, the aim was to analyse survival after a first MI among immigrants and Sweden-born. Furthermore, the aim was to investigate to what extent migration from Finland to Sweden is related to the access to welfare components including education and socio-economic status as well as social support and coronary heart disease (CHD) prevalence. The association between country of birth and incident MI was studied by case control methods. The study base consisted of subjects 30-74 years of age in Stockholm County during the 20 year period 1977-96. Incident cases of first acute MI were identified using registers of hospital discharges and deaths and controls were selected randomly from the study base. In the sampling of controls, sampling fractions were known, which enabled estimates of person time at risk and incidence rates employed in the analyses of time trends. Information on country of birth was obtained from national censuses and from a register on immigration. The study of survival utilised all the cases in the case control study. Cases surviving 28 days were followed with regard to mortality during one year. In the studies of welfare components and CHD in Finnish twins, the study population consisted of twin pairs of the Finnish Twin Cohort Study where at least one twin had lived one year or more in Sweden. The study included 1,534 migrant or non-migrant subjects and 251 complete twin pairs discordant regarding residency in Sweden. Emigrant twins were compared to nonmigrant co-twins regarding welfare components and prevalence of CHD. Data on welfare components and CHD was assessed by an extensive questionnaire administered in 1998 including questions on social factors, health, life style factors and migration history. Immigrants to Sweden had a higher incidence of first MI including non-fatal as well as fatal cases compared to Sweden-born during the period 1977-96 after adjustment for age and socioeconomic group. Immigrant men had a decreasing time trend of MI incidence during the period 1977-96 of the same magnitude as Sweden-born but among women immigrants had a somewhat less pronounced decline compared to natives. Furthermore immigrants did not have an increased case fatality within 28 days after a first MI compared to Sweden-born persons when differences in socioeconomic group were accounted for. Subjects born in Finland however had an increased case fatality during the first ten years in Sweden among men and after 20 years in Sweden among women. These results suggest that differences in CHD mortality between foreign-born and Sweden-born are primarily due to a higher disease incidence rather than a lower survival. Migration from Finland to Sweden did not substantially improve access to central welfare components for the migrants but a reduced prevalence of CHD in emigrants compared to non-migrants was observed, taking genetic and early childhood factors into account. In conclusion the results of this thesis reinforce the impression that immigrants to Sweden, from a number of countries including Finland, are at increased risk of MI compared to native Swedes. Concerning immigrants from Finland this appears to be the case in spite of a certain reduction in CHD prevalence associated with migration to Sweden.