Risk of schizophrenia and minority status: A comparison of the Swedish-speaking minority and the Finnish-speaking majority in Finland
Introduction
The epidemiology of schizophrenia in Finland has a number of unique features. The lifetime prevalence of DSM-IV schizophrenia in Finland is one percent (Perälä et al., 2007), a higher rate than is reported in most other countries (Saha et al., 2005). A three-fold difference in the prevalence of schizophrenia has been reported between Eastern and Northern Finland and Southwestern Finland (Perälä et al., 2008). Urban–rural differences have been negligible (Perälä et al., 2008), although a study analyzing birth cohorts from 1950 to 1969 found suggestive evidence that urban birth was starting to emerge as a risk factor in cohorts born in the 1960s (Haukka et al., 2001).
From the 13th century until 1809, Finland was a part of Sweden, and approximately five percent (5%) of the Finnish population are still Swedish-speaking, living principally in the Western and Southern coastal areas. Both Finnish and Swedish are official languages in Finland, and Swedish-speaking Finns are Finnish citizens born in Finland. Swedish-speaking Finns have higher socioeconomic position, education, income and wealth, are less often divorced or unemployed and have longer life expectancy than Finnish-speaking Finns (Sipilä and Martikainen, 2009). The difference in mortality risk between Swedish- and Finnish-speaking Finns is highest in alcohol-related causes, suicides, and accidents and violence, but less than half of this is attributable to socioeconomic and demographic factors (Sipilä and Martikainen, 2009). Reported differences in health may be partly explained by higher social participation and social capital in Swedish-speaking communities (Hyyppä and Mäki, 2003, Sipilä and Martikainen, 2009), but there are also differences in population genetics. While there is a substantial Scandinavian gene flow into the southwestern parts of Finland, this has not occurred in eastern Finland (Palo et al., 2009). Specifically, Swedish-speaking Finns living in the Western coastal areas are genetically close to Swedes (Salmela et al., 2011). However, in terms of both socioeconomic factors and health, the differences between Swedish-speaking and Finnish-speaking men are greater than the differences between Swedish-speaking and Finnish-speaking women (Saarela and Finnäs, 2004, Saarela, 2006, Sipilä and Martikainen, 2010). This gender difference is unlikely to be related to genetic factors.
Previous studies have not investigated whether the prevalence of schizophrenia differs between Finnish- and Swedish-speaking Finns, although in Sweden, Finnish first- and second-generation immigrants have over two-fold increased incidence of schizophrenia compared to the Swedish majority population (Leão et al., 2006). Therefore, we set out to investigate in a general population sample whether the Swedish-speaking Finns have lower risk of schizophrenia spectrum disorders (SSD) than the Finnish-speaking Finns.
Section snippets
Study population
The study population consisted of a large population-based comparison group for offspring of a cohort of male workers biologically monitored for occupational exposure to lead from 1973 through 1983 (Fig. 1). The cohort of biologically monitored men has been previously established by the Finnish Institute of Occupational Health (FIOH) (Anttila et al., 1995). We linked this cohort with The Population Information System (PIS) maintained by the Population Register Centre to identify the children of
Results
The characteristics of the study population are presented in Table 1. About five percent of all offspring were Swedish speaking, but the proportion of Swedish speaking SSD cases was only 2.5%. Schizophrenia spectrum disorder was more common in the offspring born or living in the Helsinki Capital area than in other parts of Finland. A parental history of psychosis was associated with an increased risk of SSD in the offspring.
The unadjusted and adjusted hazard ratios on the risk of schizophrenia
Discussion
We found that the Swedish-speaking minority in Finland has a lower risk of schizophrenia spectrum disorders (SSD) than the Finnish-speaking majority. This effect was especially evident among men. These results are in keeping with several previous studies demonstrating better health and socioeconomic status in the Swedish-speaking minority in Finland as compared to the Finnish-speaking majority (Sipilä and Martikainen, 2009). While previous studies have not investigated mental health, the
Funding
This study was funded by US NIH grant K01 MH080114 to Mark Opler (PI). Jaana Suvisaari was funded by the Sigrid Juselius Foundation. The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.
Contributions
Authors Jaana Suvisaari, Mark Opler, Marja-Liisa Lindbohm and Markku Sallmén designed the study and wrote the protocol. Jaana Suvisaari managed the literature searches and analyses. Markku Sallmén undertook the statistical analyses, and Jaana Suvisaari wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript.
Conflicts of interest
Jaana Suvisaari has served as a consultant for Janssen Cilag in a study that is not related to this manuscript and has received a lecturing fee from AstraZeneca. The other authors report no conflicts of interest.
Acknowledgements
We thank Ritva Luukkonen, Ph.D., for advice in the statistical analysis.
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