Heterogeneity in Cause-Specific Mortality According to Birthplace in Immigrant Men Residing in Madrid, Spain
Introduction
Studies of mortality in the immigrant population compared with mortality in the native population have found important differences, the magnitude and direction of which vary depending on the immigrants’ place of origin and the cause of death 1, 2, 3, 4. Various reasons have been put forth to explain these results: characteristics of the place or environment of origin, differences in genetic susceptibility, socioeconomic inequalities, differences in health-related behaviors, the healthy migrant effect, access to medical care, adoption of lifestyles in the host country, the unhealthy re-migrant effect, and racism 5, 6, 7, 8, 9.
Possible explanations for these differences depend on the timing of the study. For example, as time goes by, immigrants adopt health-related attitudes and behaviors of the host country, making it difficult to distinguish between the influence on mortality of the country of origin and of the destination country for many causes of death. For this reason, some authors have noted that studies of health and illness in migrants involve two different types of epidemiologic analysis (10). On the one hand, there are studies that investigate the health of immigrants at the time of their arrival in the place of destination, whose population of reference is the host country population. On the other hand are follow-up studies of immigrants, whose reference population may be the host population or a cohort of nonmigrants who live in the immigrants’ place of origin.
Spain is currently an ideal place to carry out these types of studies, since in the early years of the 21st century it was the country with the highest rate of immigration in the European Union (11). The immigration rate has been particularly high in some regions such as the region of Madrid, where the percentage of the population born outside Spain rose from 3.5% in 1996 to 15% in 2005 (12). Studying an immigrant population composed primarily of persons who are recent immigrants has the advantage of minimizing the influence of certain factors in explaining mortality differences between the immigrant and native population, such as the unhealthy re-migrant effect (11)—selective return to one's birthplace when sick—and the adoption of health-related attitudes and behaviors of the host country. However, one factor that cannot be eliminated is the healthy migrant effect, since those migrating to a country tend to be a much healthier group in many respects than those who remain in their countries of origin and than persons in the host country (9).
A methodological alternative not used to date that may decrease this selection bias is the use of persons who have migrated within the host country as the reference population, that is, the native population that resides in a place other than where they were born. This is the strategy followed in the present study, which investigates mortality in the population residing in the region of Madrid (Spain), by country of birth.
Section snippets
Methods
The study population consisted of men aged 20 to 64 years residing in the region of Madrid in the period 2000–2004 who were not born in this region. Approximately 80% of immigrants born outside of Spain and 71% of Spaniards residing in Madrid who were born in other parts of the country (“Spanish in-country migrants”) were in this age group. Women were excluded because of the small number of deaths observed in those who had been born outside of Spain. Data on deaths by specific cause of death
Results
Table 1 shows the characteristics of the study population. Residents who were born in the rest of Spain were the oldest, and those from sub-Saharan Africa and Eastern Europe were the youngest. The largest proportion of residents in the poorest neighborhoods was seen in immigrants from sub-Saharan Africa, and the smallest proportion in immigrants from the rest of Western countries and Asia. The three leading causes of death in all groups were cancer, cardiovascular diseases, and external causes,
Main Findings
Compared with Spanish in-country migrants, those from sub-Saharan Africa had the highest mortality rate ratio for all causes of death and for most diseases studied, whereas immigrants from South America had the lowest. The pattern in other groups of immigrants was less homogeneous. Immigrants from Central America and the Caribbean and those from Asia had a lower mortality rate ratio for cancer, but a higher mortality rate ratio for cerebrovascular diseases. A low mortality rate ratio for
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