Socioeconomic inequalities in mortality associated with mental disorders: a population-based cohort study

Mental disorders are associated with elevated mortality rates and reduced life expectancy. However, it is unclear whether these associations differ by socioeconomic position (SEP). The aim of this study was to explore comprehensively the role of individual-level SEP in the associations between specific types of mental disorders and mortality (due to all causes, and to natural or external causes), presenting both relative and absolute measures. This was a cohort study including all residents in Denmark on January 1, 2000, following them up until December 31, 2020. Information on mental disorders, SEP (income percentile, categorized into low, <20%; medium, 20-79%; and high, ≥80%), and mortality was obtained from nationwide registers. We computed the average reduction in life expectancy for those with mental disorders, relative and absolute differences in mortality rates, and proportional attributable fractions. Subgroup analyses by sex and age groups were performed. Overall, 5,316,626 individuals (2,689,749 females and 2,626,877 males) were followed up for 95.2 million person-years. People with mental disorders had a shorter average life expectancy than the general population regardless of SEP (70.9-77.0 vs. 77.2-85.1 years, depending on income percentile). Among individuals with a mental disorder, the subgroup in the top 3% of the income distribution had the longest average life expectancy (77.0 years), and this estimate was lower than the shortest life expectancy in the general Danish population (77.2 years for individuals in the bottom 6% income distribution). The mortality rate differences were larger in the low-income than the high-income group (19.6 vs. 13.3 per 1,000 person-years). For natural causes of death, a socioeconomic gradient for differences in life expectancy and mortality rates was observed across most diagnoses, both sexes, and all age groups. For external causes, no such gradient was observed. In the low-SEP group, 10.1% of all deaths and 23.7% of those related to external causes were attributable to mental disorders, compared with 3.5% and 8.7% in the high-SEP group. Thus, our data indicate that people with mental disorders have a shorter life expectancy even than people with the lowest SEP in the general population. The socioeconomic gradients in mortality rates due to natural causes highlight a greater need for coordinated care of physical diseases in people with mental disorders and low SEP.