M36 - SLEEP DISORDERS AND RISK OF INCIDENT DEPRESSION: A POPULATION CASE-CONTROL STUDY

Abstract

Background A number of studies have found that disturbed sleep can precede onset of a psychiatric disorder, and that there is substantial comorbidity between sleep disorders and psychiatric disorders, particularly major depression. However, some studies have not been able to establish the temporal relationship between sleep disorders and psychiatric disorders, have been performed in clinical samples, relied on self-report information or have conditioned on the outcome. We sought to investigate and estimate the risk of developing new-onset depression in those with sleep disorders in the entire population of Denmark. Methods Data were obtained by linking longitudinal Danish population-based registers. Information on sleep disorders and major depression was obtained from the Danish National Hospital Register and the Danish Psychiatric Central Research Register. The registers contain records of all hospital visits with a diagnosis given by ICD-10 codes. To account for variability in depression and sleep disorder risk over time, we used a nested case-control design. A total of 65,739 individuals who had first onset of depression between 1995 and 2013 were selected as cases. For each case, a set of 20 controls of the same sex, birth month and year and who had not had depression by the date that the case was diagnosed were selected at random form the population (n=1,307,580 in total). We examined whether there was an increased rate of prior sleep disorders in MDD cases compared to controls using conditional logistic regression. Results We found that there was an increased risk of incident depression in cases for all sleep disorders analysed. Highest incidence rate ratios were found for circadian rhythm disorders (IRR=7.06 (2.78–17.91)) and insomnia of inorganic origin (6.76 (4.37–10.46)). The lowest estimated IRR was for narcolepsy (IRR=2.00 (1.26–3.17)). We also estimated the incidence rate ratio based on time since a sleep disorder diagnosis. Those diagnosed with a sleep disorder in the last 6 months were at highest risk of developing depression compared to those with at least 1 year since diagnosis (3.10 vs 2.36). Discussion Using data from Danish population registers, we show that all categories of sleep disorder are risk factors for incident major depressive disorder. Insomnia and circadian rhythm disorders have the highest associated risk, while narcolepsy and sleep-disordered breathing disorders excluding obstructive sleep apnea have the lowest associated risk. We found differences in risk between men and women for insomnia, obstructive sleep apnea and sleep movement disorders. Furthermore, we found that there is a moderate decrease in risk of depression as the time since diagnosis of a sleep disorder decreases, but that most cases of depression were diagnosed more than a year after diagnosis of a sleep problem. Our results have implications for clinical practice. Depression screening should be considered for patients with sleep disorders, and where possible, long-term follow up for mental health problems is advisable. Differences in risks between genders should also be considered in clinical practice.