Psychiatric comorbidity in couples: a longitudinal study of 202,959 married and cohabiting individuals

To examine whether partner's psychiatric and somatic disorders are risk factors for incidence of psychiatric disorders among non-psychiatric individuals at baseline. Register-based 6-year follow-up on Finns (106,935 men and 96,024 women aged 40 and over), living with a married or cohabiting partner at the end of 1997. The outcome measures included non-psychotic major depressive disorder (MDD), substance use disorder (SUD), and severe psychiatric disorder, evaluated using information on reimbursement for drug costs, purchases of prescription medication, and principal causes of hospitalization. Among persons whose partner had any psychiatric disorder, the incidence rate ratio (IRR) for own MDD, controlling for own age at baseline, was 1.58 (95% confidence interval 1.48-1.69) in men, and 1.58 (1.48-1.69) in women. Among persons whose partner had somatic hospitalization, the IRR for own MDD was 1.14 (1.08-1.20) in men and 1.20 (1.15-1.25) in women. Among both men and women, the highest risk for incidence of own MDD was among persons whose partner had both MDD and SUD (IRR 2.65, 1.67-4.21 and IRR 2.13, 1.62-2.80, respectively). Further adjustment for sociodemographic and union characteristics had little effect on the associations. In married and cohabiting couples, partner's somatic and particularly psychiatric morbidity associate with psychiatric disorders in non-psychiatric subjects, independent of sociodemographic and union characteristics. The healthy spouse's care burden is a potential point of intervention in order to prevent new psychiatric morbidity, but also to provide the mentally ill first partner a chance to recover in a supportive family environment.