Insomnia carries more than double the risk of depression, according to a meta-analysis of more than 2 dozen studies published in the journal BMC Psychiatry.
“The current meta-analysis showed that the increased risk was more pronounced for participants from the United States than for European participants,” reported Liqing Li, of the Tongji Medical College of the Huazhong University of Science and Technology in Wuhan, China, and colleagues. “In order to make the finding [generalizable] to other populations, more studies are warranted to be conducted in other populations from Asia, Africa, and South America.”
The researchers combed PubMed, Embase, Web of Science and China National Knowledge Structure databases through October 2014 to identify observational cohort studies investigating the association between insomnia and depression. From an initial 4802 studies found, 34 studies involving 172 077 participants, followed for a mean 5 years, met their criteria. Cohorts ranged from 147 to more than 44 000 participants and came from the US, Europe, Australia, and Asia.
Combined analysis of the results revealed that individuals with insomnia were 2.3 times more likely to develop depression, even after adjustment for publication bias. Overall, 26 of the 34 studies suggested a positive relationship between insomnia and depression, though the studies were highly heterogenous. The results held true regardless of age, sex, geographical location, the definition of insomnia or measurement of depression used in the study, length of follow-up, study quality, or year of the study’s publication.
“Sleep disturbance may play a key role in the development of depression,” the authors suggested regarding potential mechanisms. “Experimental studies showed that sleep loss may result in cognitive and affective alterations that lead to depression risk.”
Another potential explanation is that sleep difficulties impair emotional regulation and stability, thereby altering neural processes that can lead to depressive symptoms, the authors suggested.
The researchers also explored the possibility that sustained, chronic hyperactivity in the hypothalamic-pituitary-adrenal axis might play a role in development of depression since that axis is a major neuroendocrine mediator of stress response.
“Finally, other proposed mechanisms by which insomnia might increase the risk of depression included increasing levels of inflammatory markers, such as C-reactive protein and interleukin-6, which indicated low-level systemic inflammation was a predictor of depression development,” Li and colleagues wrote. “Considering the increasing prevalence of insomnia worldwide and the heavy burdens of depression, the results of our study provide practical and valuable clues for the prevention of depression and the study of its etiology.”
Li L, Wu C, Gan Y, Qu X, Lu Z. Insomnia and the risk of depression: a meta-analysis of prospective cohort studies. BMC Psychiatry. 2016;16:375. doi:10.1186/s12888-016-1075-3.