Insomnia and the risk of depression: a meta-analysis of prospective cohort studies.
BACKGROUND
Observational studies suggest that insomnia might be associated with an increased risk of depression with inconsistent results. This study aimed at conducting a meta-analysis of prospective cohort studies to evaluate the association between insomnia and the risk of depression.


METHODS
Relevant cohort studies were comprehensively searched from the PubMed, Embase, Web of Science, and China National Knowledge Infrastructure databases (up to October 2014) and from the reference lists of retrieved articles. A random-effects model was used to calculate the pooled risk estimates and 95 % confidence intervals (CIs). The I2statistic was used to assess the heterogeneity and potential sources of heterogeneity were assessed with meta-regression. The potential publication bias was explored by using funnel plots, Egger's test, and Duval and Tweedie trim-and-fill methods.


RESULTS
Thirty-four cohort studies involving 172,077 participants were included in this meta-analysis with an average follow-up period of 60.4 months (ranging from 3.5 to 408). Statistical analysis suggested a positive relationship between insomnia and depression, the pooled RR was 2.27 (95 % CI: 1.89-2.71), and a high heterogeneity was observed (I2= 92.6 %, P < 0.001). Visual inspection of the funnel plot revealed some asymmetry. The Egger's test identified evidence of substantial publication bias (P <0.05), but correction for this bias using trim-and-fill method did not alter the combined risk estimates.


CONCLUSIONS
This meta-analysis indicates that insomnia is significantly associated with an increased risk of depression, which has implications for the prevention of depression in non-depressed individuals with insomnia symptoms.
School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, No. 13 Hangkong Road, Wuhan, Hubei, 430030, China.|School of Economics and Management, Jiangxi Science and Technology Normal University, Nanchang, Jiangxi, China.
Liqing
L
Li
School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, No. 13 Hangkong Road, Wuhan, Hubei, 430030, China.|School of Basic Medicine, Gannan Medical University, Ganzhou, Jiangxi, China.
Chunmei
C
Wu
School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, No. 13 Hangkong Road, Wuhan, Hubei, 430030, China.
Yong
Y
Gan
School of Health Management, Hangzhou Normal University, Hangzhou, Zhejiang, China.
Xianguo
X
Qu
School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, No. 13 Hangkong Road, Wuhan, Hubei, 430030, China. zuxunlu@yahoo.com.
Zuxun
Z
Lu
D003863:Depression / Q000209:etiology*; D003866:Depressive Disorder / Q000209:etiology*; D006801:Humans; D011446:Prospective Studies; D012307:Risk Factors; D007319:Sleep Initiation and Maintenance Disorders / Q000150:complications*
Depression; Epidemiology; Insomnia; Meta-analysis; Sleep disorders