A comprehensive analysis of age of onset and cumulative incidence of mental disorders: A Danish register study

BACKGROUND

The age of onset (AOO), incidence and cumulative incidence of mental disorders are critical epidemiological measures, providing essential insights into the development and course of these disorders across the lifespan. This study aims to provide up-to-date estimates of the AOO, age-specific incidence, and cumulative incidence for a comprehensive range of mental disorders using data from Danish registers.

METHODS

We conducted a follow-up study encompassing all Danish residents from January 1, 2004, to December 31, 2021, totaling 91,613,465 person-years. Data were sourced from the Danish Psychiatric Central Research Register, identifying individuals treated for various mental disorders in psychiatric hospitals, outpatient departments, and accident/emergency departments, that is, treated in secondary care settings. We investigated specific categories of mental disorders, including substance abuse disorders, schizophrenia, mood disorders, anxiety, eating disorders, borderline personality disorders, intellectual disabilities, pervasive developmental disorders, and behavioral and emotional disorders. Age-sex-specific incidence rates were estimated using Poisson generalized linear models, and cumulative incidence was calculated using Aalen-Johansen's competing risks model. The study provides estimates of AOO, incidence, and cumulative incidence for various mental disorders, including their age and sex distributions.

RESULTS

The cumulative incidence by age 80 years for any mental disorder was 30.72% (95% confidence interval: 30.62%-30.83%) for males and 34.46% (34.35%-34.57%) for females. The most common types of mental disorders were anxiety-related disorders 16.27% (16.19%-16.36%) for males and 23.39% (23.29%-23.50%) for females, and followed by mood disorder 10.34% (10.27%-10.41%) for males and 16.67% (16.58%-16.77%) for females. For those who develop mental disorder, half will have developed their disorder by approximately age 22 years (median and interquartile range: males 21.37 (11.85-36.00); females 22.55 (16.31-36.08)).

CONCLUSIONS

Approximately one in three individuals will seek treatment for at least one mental disorder in a secondary care setting by age 80. Given that half of these individuals develop mental disorders before age 22, it is crucial to tailor service planning to meet the specific needs of young individuals. Web-based interactive data-visualization tools are provided for clinical utility.

Cause-specific life years lost in individuals with treatment-resistant depression: A Danish nationwide register-based cohort study

BACKGROUND

Depression is associated with excess mortality, but it is not known how treatment-resistance influences life expectancy. We estimated cause-specific excess mortality and Life Years Lost (LYL) in patients with treatment-resistant depression (TRD).

METHODS

The population included all individuals born and living in Denmark who redeemed their first prescription for an antidepressant at age 18-69 years between 2005 and 2012, identified in the Danish National Prescription Registry. TRD was defined as at least two additional and different antidepressant trials within two years. Mortality rate ratios (MRRs) were estimated with Cox regression adjusted for age at first prescription, calendar year and comorbidity. Differences in life expectancy were estimated by the Life Years Lost (LYL) method.

RESULTS

The cohort included 154,513 first-time pharmacologically treated patients with depression, of whom 8,294 (5.4%) were identified as having TRD. Patients were followed for 1,032,245 person-years during which 9,795 deaths occurred. Men and women with TRD had significantly higher mortality than non-TRD (aMRR: 1.34, 95% CI 1.18-1.52 and aMRR: 1.39, 95% CI 1.19-1.63, respectively). Life expectancy for men and women with TRD was 1.21 (95% CI 0.36-2.44) and 1.24 (95% CI 0.35-2.34) years shorter than in all patients with depression. Suicide accounted for the majority of excess LYL, with 1.10 (95% CI 0.46-1.61) years in men and 0.82 (95% CI 0.44-1.27) years in women with TRD.

LIMITATIONS

Using redeemed prescriptions to define TRD may increase the risk of misclassification.

CONCLUSIONS

Patients not responding adequately to several treatment trials are at increased risk for premature death, particularly suicide.

Early labor force exits in patients with treatment-resistant depression: an assessment of work years lost in a Danish nationwide register-based cohort study

BACKGROUND

Depression is one of the leading causes of premature workforce exit in many Western countries, but little is known about the extent to which treatment-resistance reduces number of work-years. We compared the risk of premature workforce exit among patients with treatment-resistant depression (TRD) relative to non-TRD patients and estimated work years lost (WYL) before scheduled retirement age.

METHODS

The study population, identified in the Danish National Prescription Registry, included all individuals born and living in Denmark who redeemed their first antidepressant (AD) prescription for depression at age 18-60 years between 2005 and 2012. TRD was defined as failure to respond to at least two different treatment trials. Premature workforce exit was measured using disability pension records. We used Cox regression to estimate the hazard ratio (HR) for premature workforce exit in TRD relative to non-TRD patients, adjusting for calendar year, psychiatric and somatic comorbidity, and educational level. Differences in WYL in patients with TRD and all depression patients were estimated through a competing risks model.

RESULTS

Out of the total sample of patients with depression (N = 129,945), 7478 (5.75%) were classified as having TRD. During follow up, 17% of patients with TRD and 8% of non-TRD patients received disability pension, resulting in a greater than three-fold larger risk of premature workforce exit [adjusted HR (aHR) 3.23 95% confidence interval (CI) 3.05-3.43]. The TRD group lost on average six work-years (95% CI 5.64-6.47) more than the total sample due to early labor force exit. The association between TRD and age at premature workforce exit was inversely U-shaped; the hazard rate of premature workforce exit for patients with TRD compared with non-TRD patients was highest in the age groups 31-35, 36-40, and 41-45 years.

CONCLUSION

Patients with TRD constitute a small group within depression patients, but contribute disproportionally to societal costs due to premature workforce exit at a young age.