Mortality Gap Widens in Bipolar Disorder vs General Population

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Investigators found a significant increase in all-cause standardized mortality ratios over the study period.
Investigators found a significant increase in all-cause standardized mortality ratios over the study period.

Over the past 20 years, the gap in mortality rates have grown between patients with bipolar disorder and the general Danish population, according to a study published in Bipolar Disorders. In addition, while the mortality rate of patients with bipolar disorder was nearly triple that of the general population, a decrease in excess mortality was associated with an increase in patient age.

This study sought to assess whether the mortality rates of patients with bipolar disorder compared with mortality rates of the background population have increased over the past 20 years. Furthermore, the study investigated mortality trends according to age.

The study included patients under 65 years diagnosed with incident or prevalent bipolar disorder and who were registered in the Danish Psychiatric Research Registry from 1965 through 2014. Data on the death dates of these patients and the background population (all inhabitants of Denmark) were drawn from the Danish Civil Registration System. Standardized mortality ratios were calculated for each calendar year comparing the mortality rates of the general population and the bipolar disorder cohort. The study investigators further stratified the standardized mortality ratios by 5-year age intervals. Finally, time trends in all-cause mortality were assessed over the 20-year study period.

From 1995 to 2014, the total Danish population consisted of 6,176,414 individuals, including 27,281 patients with bipolar disorder. The study results showed that overall, patients with bipolar disorder had an elevated mortality rate relative to the general population with a standardized mortality ratio of 2.8 (95% CI, 2.8-2.9).

When the results were stratified by age, the youngest groups demonstrated the highest standardized mortality ratios: patients 15 to 29 years had a standardized mortality ratio of 8.13 (95% CI, 6.70-10.02) and patients 30 to 34 years had a standardized mortality ratio of 7.70 (95% CI, 6.37-9.30), whereas patients 55 to 59 years had a standardized mortality ratio of 2.71 (95% CI, 2.58-2.84) and patients 60 to 64 years had a standardized mortality ratio of 2.24 (95% CI, 2.10-2.34). The standardized mortality ratio calculated for each calendar year revealed a general increase of 0.03 (P<.01) annually for patients with bipolar disorder.

Limitations of the study included censoring patients at the age of 65, potentially increasing the overall standardized mortality ratio. Less severe cases of bipolar disorder treated by non-hospital based psychiatrists and general practitioners were not reported to the Danish Psychiatric Research Registry, resulting in possible selection bias toward a more severely ill cohort and thus increasing the standardized mortality ratio.

The overall mortality rate of patients with bipolar disorder was almost triple that of the general population, and excess mortality was more pronounced among the younger age groups. However, the most significant finding observed over the 20-year study period was the widening gap in mortality between patients with bipolar disorder and the general population. Further studies are needed to explore the reasons for increasing mortality in patients with bipolar disorder.

Reference                                                                                                                       

Hansen PS, Laursen MF, Grøntved S, Straszek SPV, Licht RW, Nielsen RE. Increasing mortality gap for patients diagnosed with bipolar disorder – A nationwide study with 20 years of follow-up [published online July 26, 2018]. Bipolar Disord. doi: 10.1111/bdi.12684

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