Risk of mortality and complications in people with depressive disorder and diabetes mellitus: A 20-year population-based propensity score-matched cohort study

People with depression have increased premature mortality and elevated prevalence of diabetes-mellitus compared to general population. However, risk of mortality and diabetes-related complications among patients with depression and co-occurring diabetes is under-studied. This population-based propensity score-matched (1:10) cohort study identified 12,175 patients with pre-existing depression and incident-diabetes (depression-diabetes group) and 117,958 patients with incident-diabetes only (diabetes-only group) between 2002 and 2021 in Hong-Kong, using territory-wide medical-record database of public-healthcare services, to investigate whether depression increased the risk of overall mortality, complications and post-complication mortality in people with diabetes. Associations of depression with all-cause mortality, complication and post-complication all-cause mortality rates were examined by Cox proportional-hazards model. Complications were assessed by Diabetes-Complications-Severity-Index (DCSI). Associations of complications, in terms of DCSI scores (complication burden), specific types and two-way combinations of complications (complication patterns) with all-cause mortality rate in depression were also examined. Our results showed that depression-diabetes group exhibited increased all-cause mortality risk (adjusted hazards-ratio: 1.06 [95 %CI: 1.02-1.10]) relative to diabetes-only group, particularly among men and older age group, with significantly higher rate of experiencing neuropathy (1.44 [1.27-1.62]) and metabolic complications (1.30 [1.09-1.56]) and lower likelihood of peripheral-vascular complications, retinopathy and nephropathy, albeit comparable macrovascular and microvascular complication rates. The mortality-rate-ratio for patients with depression and diabetes was significantly higher than patients with diabetes-only at a low level of complication burden. In conclusion, depression patients with co-occurring diabetes are at increased risk of excess mortality. Further research is warranted to improve diabetes-related outcomes and reduce mortality gap in this vulnerable population.