Background People with mental illness (MI) face issues of social integration such as finding a job and maintaining social relationships. In the past decades, many countries have developed specific social integration interventions and policies towards people with MI. Despite heterogeneous assessments of those specific interventions and policies, the social integration of people with MI and its improvement over time remains inconclusive. This study aimed to assess the evolution of the social integration of adults with moderate and severe MI in the general Belgian population between 1997 and 2013.

Methods Data on the general adult population were retrieved from the Belgian Health Interview Survey in five cross-sectional waves (1997, 2001, 2004, 2008 and 2013, n ≈ 10,000 per wave). Three degrees of MI severity were compared using the General Health Questionnaire (GHQ-12): no MI, moderate MI, and severe MI (score <4, 4–7, and >7). Indicators of social integration were the employment status, social contacts, and partnership situation. Age-and gender-adjusted prevalence of social integration indicators were estimated in the different periods. The evolution of prevalence was estimated with time-trend measures (absolute and relative change, and average annual percent chance). The association between social integration indicators and survey year was assessed with logistic regression models.

Results In 2013, the adjusted prevalence of social integration indicators of people without MI, with moderate MI, and with severe MI were respectively 46%, 56%, 69% for unemployment, 2%, 6%, 11% for low social contacts, and 20%, 25%, 30% for being single. For unemployment and low social contacts, the gap between people with severe MI and the other two groups increased over time. The probability of being unemployed decreased significantly in 2013 compared to 1997 for people without MI (AOR=0.59, CI95=0.53–0.65) and for people with moderate MI (AOR=0.69, CI95=0.51–0.97), but not for people with severe MI (AOR=1.08, CI95=0.78–1.49).

Conclusion The social exclusion gap between people with severe MI and people with moderate or without MI is widening over time. Employability and social support of people with more severe MI should be supported. Some sociodemographic determinants of people with severe MI may explain why their social integration has evolved differently over time.