Risk of schizophrenia and minority status: A comparison of the Swedish-speaking minority and the Finnish-speaking majority in Finland

https://doi.org/10.1016/j.schres.2014.09.014Get rights and content

Abstract

Approximately five percent of the Finnish population are Swedish-speaking and have higher socioeconomic position and longer life expectancy than the Finnish-speaking majority. Previous studies have not investigated whether Swedish-speaking Finns have lower risk of schizophrenia spectrum disorders (SSD) than Finnish-speaking Finns. We investigated this in a representative sample of 47 445 Finns born in 1972–1984. Hazard ratios of SSD between language groups were assessed with conditional proportional hazards regression. Sex, parental ages at birth, paternal employment around conception, parental psychosis and place and residence in the capital area were used as other explanatory variables. The prevalence of SSD was 0.7% in the Swedish-speaking minority and 1.5% in the Finnish-speaking majority. In the adjusted regression model, belonging to the Swedish-speaking minority was associated with lower risk of SSD (hazard ratio (HR) 0.41, 95% confidence interval (CI) 0.24-0.69). In a subset analysis by gender, the protective effect was evident among Swedish-speaking males (HR 0.32, 95% CI 0.15-0.68) but marginal in females (HR 0.75, 95% CI 0.41-1.37). Parental psychosis and place of birth in the capital area were associated with higher risk of SSD, whereas paternal employment at the time of conception was associated with lower risk of SSD. Our results support the role of social factors in the etiology of schizophrenia. Belonging to a minority with high socioeconomic status and social capital may be protective against schizophrenia, especially for males.

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.

References (36)

  • M.T. Hyyppä et al.

    Social participation and health in a community rich in stock of social capital

    Health Educ. Res.

    (2003)
  • M. Kiviniemi et al.

    Five-year mortality in first-onset schizophrenia in Finland with special reference to regional differences

    Psychiatr. Serv.

    (2010)
  • G.E. Kulla et al.

    Differences in self-rated health among older immigrants - a comparison between older Finland-Swedes and Finns in Sweden

    Scand. J. Public Health

    (2010)
  • W. Kwok

    Is there evidence that social class at birth increases risk of psychosis? A systematic review

    Int. J. Soc. Psychiatry

    (2014)
  • A. Lammintausta et al.

    Stroke morbidity in Swedish- and Finnish-speaking populations of Turku, Finland

    Scand. Cardiovasc. J.

    (2009)
  • A. Lammintausta et al.

    Myocardial infarction events and cardiovascular risk factor levels in Finnish- and Swedish-speaking populations of Finland

    Ann. Med.

    (2011)
  • T.S. Leão et al.

    Incidence of schizophrenia or other psychoses in first- and second-generation immigrants: a national cohort study

    J. Nerv. Ment. Dis.

    (2006)
  • J.J. McGrath et al.

    A comprehensive assessment of parental age and psychiatric disorders

    JAMA Psychiatry

    (2014)
  • Cited by (16)

    • Psychotic-like experiences and correlation with childhood trauma and other socio-demographic factors: A cross-sectional survey in adolescence and early adulthood in China

      2017, Psychiatry Research
      Citation Excerpt :

      Our results suggest that the influence of the urban environment may start from an early age and last throughout adolescence. No stable source of family income was another risk factor for frequent PLEs as well as DEs, which is consistent with the suggestion by some authors that socioeconomic status is related to the development of psychotic symptoms (Suvisaari et al., 2014). “Left-behind” children in our sample were likely to have frequent PLEs and HEs.

    • Paternal occupational lead exposure and offspring risks for schizophrenia

      2016, Schizophrenia Research
      Citation Excerpt :

      In part, this shortcoming is covered by adjusting for the father's self-employment status and Swedish as a primary language. Swedish speaking Finns, on average, have higher socio-economic status than the Finnish speaking Finns (Suvisaari et al., 2014). In conclusion, father's occupational exposure to lead prior to conception was not a risk factor for schizophrenia spectrum disorders in Finns born between 1972 and 1984.

    • Incidence of psychotic disorders among first-generation immigrants and refugees in Ontario

      2015, CMAJ
      Citation Excerpt :

      However, the immigration period considered in the Israeli study brought many Jewish refugees from Europe after World War II, and people who had been minorities in their country of origin were now part of the ethnic and religious majority.33 Similarly, minority groups who are relatively advantaged with respect to socioeconomic factors have also been found to have similar rates of psychotic disorders as the majority population,34 most notably migrants from Western countries to the Netherlands.35,36 Indeed, Canada’s immigration policies, which favour economic migrants who are more educated and proficient in English or French, may help to explain our findings of a reduced rate of psychotic disorders among some migrant groups.

    View all citing articles on Scopus
    1

    3 Park Avenue, ProPhase LLC – 28th Floor, New York, NY 10016, USA.

    View full text