Time Trends in Lifetime Incidence Rates of First-Time Diagnosed Bipolar and Depressive Disorders Across 16 Years in Danish Psychiatric Hospitals: A Nationwide Study

OBJECTIVE: There is conflicting evidence as to whether or not the incidences of affective disorders are on the rise. The aim of the present study was to identify time trends across 16 years in the incidences of affective disorders in a nationwide sample.

METHODS: Using the Danish Psychiatric Central Research Registry, age- and sex-adjusted incidence rates of diagnosed affective disorders in Danish psychiatric hospitals using ICD-10 classification were calculated per 100,000 person-years for the population aged 4-65 years during the period 1995-2010.

RESULTS: Incidence rates of diagnosed bipolar disorder increased from 11.5 to 24.5, and there was an increase from 86.2 to 189.7 per 100,000 person-years for depression. Time trends were most pronounced for individuals up to 29 years of age. A sizeable part of the increase in incidence rates could be attributed to an increase in the total number of persons diagnosed in psychiatry.

CONCLUSIONS: Time trends in incidence rates showed an increase for bipolar disorder and depressive disorders across 16 years, but found that some of the observed increase in incidence rates was related to a more widespread trend in Danish society of seeking and receiving psychiatric assistance.