The Interplay Between Depression and Insomnia

Humans have a circadian rhythm that influences everything from metabolic and hormonal processes to mood, emotion and behavior. The circadian rhythm is photo regulated by night and day and maintains a proper sleep-wake cycle. Defects in the circadian rhythm are thought to be paramount in psychological disturbances, such as major depressive disorder. Specifically, perturbation of a normal sleep-wake cycle is thought to contribute to depression, as insomnia is a common co-morbidity. It is unclear whether depression leads to insomnia or insomnia ultimately leads to depression. Recent scientific advancements have gleaned light upon this subject and will be discussed in this article.

Understanding whether insomnia is causative or consequential in depression has implications for properly treating clinically depressed individuals. For instance, would correcting poor sleep hygiene be beneficial in treating both insomnia and depression?

In a recent study, investigators followed 591 Swiss individuals for 20 years and interviewed them periodically (1). The authors found that those with insomnia episodes lasting longer than 2 weeks were at increased risk for subsequently developing major depressive disorder at a later time. This suggests that insomnia may play a causative role in depression.

Another recent study conducted with older individuals (older than 60) suggested that patients with insomnia were less likely to improve their symptoms with conventional treatment (2). This suggests that insomnia is a marker for depression that will ultimately be more difficult to treat. This raises the question of whether treating insomnia will have a therapeutic benefit in depressed patients.

One recent study demonstrated that insomnia can indeed be treated in patients with major depressive disorder more effectively than with depression therapy alone (3). This suggests, as a commentary written by an expert in this field points out (4), that insomnia can be separated from depression. That is, if standard depression therapy is less effective at targeting insomnia than treating just the insomnia, then depression may not be the causative agent of insomnia. Perhaps just the opposite is true; the insomnia may be influencing depression.

The same study found that depression was treated more effectively in the group receiving insomnia therapy in comparison to those obtaining depression therapy alone. However, no statistical significance was found in this difference and a lager clinical trial devoted specifically to this aspect of the previous study will need to be conducted to clear up this matter.

In conclusion, recent advances in the field of research pertaining to the interplay between insomnia and depression have yielded interesting results. While insomnia has been described as a consequence of depression, just the opposite may be true. Further insight into this area of research has important implications in the future treatment of depression.

References:

1. Buysse JD, Angst J, Gamma A, Ajdacic V, Eich D, Rössler W. Prevalence, course and comorbidity of insomnia and depression in young adults. Sleep 2008:31;473-80
2. Pigeon WF, Hegel M, Unützer J, et al. Is insomnia a perpetuating factor for late-life depression in the IMPACT cohort? Sleep 2008:31;481-8.
3. Manber R, Edinger JD, Gress JL, San Pedro-Salcedo MG, Kuo TF, Kalista Cognitive behavioral therapy for insomnia enhances depression outcome in patients with comorbid major depressive disorder and insomnia. Sleep 2008:31;489-95
4. Taylor, DJ. Commentary on Buysse et al. Prevalence, Course, and Comorbidity of Insomnia and Depression in Young Adults. SLEEP 2008;31:473-80; on Pigeon et al. Is insomnia a perpetuating factor for late-life depression in the IMPACT cohort? SLEEP 2008;31:481-8; and on Manber et al. Cognitive behavioral therapy for insomnia enhances depression outcome in patients with comorbid major depressive disorder and insomnia. SLEEP 2008;31:489-95. Sleep 2008: 31; 447-48