307Association between patterns of comorbid mental disorders and mortality-related estimates. A Danish register-based cohort study

Background Comorbidity within mental disorders is common, and people with two or more types of mental disorders have shorter life expectancy compared to those with exactly one type. The aims of this study were to: (a) describe the prevalence of combinations of mental disorders; and (b) estimate the excess mortality for each of these combinations. Methods We conducted a population-based cohort study including all 7,505,576 persons living in Denmark in 1995-2016. Using national registers, we described the most common combinations of mental disorders and investigated excess mortality by means of mortality rate ratios (MRRs) and differences in life expectancy. Results At the end of the 22-year observation, 6.2% individuals were diagnosed with exactly one disorder, and 5.3% with two or more types. People with any combination of disorders had higher mortality rates than those without any diagnosis (MRRs ranging from 1.10 [95% CI 0.67 – 1.84] to 5.97 [95% CI 5.52 – 6.45]) and shorter life expectancies compared to the general population (estimates ranging from 5.06 years [95% CI 5.01 – 5.11] to 17.46 years [95% CI 16.86 – 18.03]). Conclusions Mood disorders and neurotic disorders commonly co-occur, and contribute to many different sets of comorbid mental disorders. The association between mental disorders comorbidity and mortality revealed the prominent role of substance use disorders. Key messages Our study provides prevalence estimates of the most common sets of mental disorders. In light of the substantial contribution of substance use disorders to premature mortality, efforts related to the ‘primary prevention of secondary comorbidity’ warrant added scrutiny.