DEPRESSION AND ANXIETY 32:664–670 (2015)
Review SLEEP DURATION AND DEPRESSION AMONG ADULTS: A META-ANALYSIS OF PROSPECTIVE STUDIES Long Zhai,1,† Hua Zhang,2,† and Dongfeng Zhang, M.D.1 ∗
Background: Results from longitudinal studies on sleep duration and incidence of depression remain controversial. Methods: PubMed and Web of Science updated on October 22, 2014 were searched for eligible publications. Pooled relative risks (RRs) with 95% confidence interval (CI) were calculated using a randomeffects model. Results: Seven prospective studies were included, involving 25,271 participants for short sleep duration and 23,663 participants for long sleep duration. Compared with the normal sleep duration, the pooled RR for depression was 1.31 (95% CI, 1.04–1.64; I2 = 0%) for the short sleep duration overall. For long sleep duration, the pooled RR was 1.42 (95% CI, 1.04–1.92; I2 = 0%). The associations between short or long sleep duration and risk of depression did not substantially change in sensitivity and subgroup analyses. No evidence of publication bias was found. Conclusion: This meta-analysis indicates that short and long sleep duration was significantly associated with increased risk of depression C 2015 Wiley Periodicals, in adults. Depression and Anxiety 32:664–670, 2015. Inc.
Key words: depressive symptom; epidemiology; long sleep; meta-analysis; short sleep
INTRODUCTION
D
epression is a common cause of substantial disability and morbidity in the general population. By 2020, depression is predicted to be the second leading cause of disability, immediately behind cardiovascular diseases.[1]
1 Department
of Epidemiology and Health Statistics, Qingdao University Medical College, Qingdao, China 2 Department of Chronic Noncommunicable Diseases, Qingdao Municipal Centers for Disease Control and Prevention, Qingdao University, Qingdao, China † These
authors contributed equally to this work.
∗ Correspondence
to: Dongfeng Zhang, Department of Epidemiology And Health Statistics, Qingdao University Medical College, No. 38 Dengzhou Road, Qingdao 266021, China. E-mail: [email protected]; [email protected] Received for publication 21 November 2014; Revised 5 May 2015; Accepted 7 May 2015 DOI 10.1002/da.22386 Published online 5 June 2015 in Wiley Online Library (wileyonlinelibrary.com).
C 2015 Wiley Periodicals, Inc.
Being a complex mental disorder, depression is supposed to be affected by genetic,[2] lifestyle factors,[3] and their interactions.[4] Several epidemiology studies have found an association between sleep duration and health-related conditions, such as cardiovascular events,[5, 6] mental disorders,[7, 8] and mortality.[9] To date, many prospective studies have been carried out to investigate the role of the sleep duration in the development of depression. However, the results of these studies are controversial.[10–15] For example, one cohort study[13] showed a significant association between short sleep duration and depression; while another prospective study[12] indicated no relation between short sleep and depression. And the sample sizes of these studies are generally limited. Meta-analysis is the use of statistical methods to summarize the results of independent studies.[16] By combining information from relevant studies, metaanalyses can provide more precise estimates of the effects than those derived from the individual studies. Metaanalyses also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies.[17] Therefore, we conducted a meta-analysis of prospective studies to assess risk of depression for the short sleep duration versus normal sleep duration as well as the long sleep duration versus normal
Review: Sleep Duration and Depression
sleep duration, based on the postulation that the sleep duration would predict the incidence of depression in a U-shape fashion.
METHODS LITERATURE SEARCH AND SELECTION We followed the PRISMA guidelines.[18] A search of the literature up to October 22, 2014 was performed using the databases of PubMed and Web of Science with the following free text terms: sleep combined with depression. The search was limited to studies in humans. Moreover, we reviewed the reference lists from retrieved articles to search for further relevant studies. No language restrictions were imposed. Two investigators independently reviewed all identified studies, and studies were included if they met the following criteria: (1) a prospective design among adults; (2) the exposure of interest was sleeping duration categories assessed by questionnaires or objective measures across multiple consecutive occasions; (3) the outcome of interest was depression ascertained by rating scales or physician’s diagnosis; (4) the minimum time span of assessments was 6 months; (5) multivariateadjusted relative risk (RR) with 95% confidence interval (CI) was provided; (6) the most recent and complete article was chosen if a study had been published more than once.
DATA EXTRACTION AND QUALITY ASSESSMENT The following data were extracted from each study by two investigators: (1) name of the first author, (2) publication year, (3) study population, (4) origin of country, (5) follow-up years, (6) sample size and number of cases, (7) age range or mean age at baseline years, (8) gender, (9) methods to assess sleep duration and depression, (10) RR (adjusted for the largest number of confounders in the original study) with 95% CI for short sleep duration and long sleep duration as compared with the normal sleep duration, (11) sleep duration category, (12) adjustment for confounders, (13) study quality. The study quality was assessed using the Newcastle–Ottawa quality assessment scale (http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp). Maximum score on this scale is 9. “Good” was defined as a total score of 7–9; “fair,” a total score of 4–6; and “poor,” defined as a total score less than 4.
STATISTICAL ANALYSIS We weighted the study-specific log RRs by the inverse of their variance to calculate a summary estimate and its 95% CI. The DerSimonian and Laird random effects model was used to combine study-specific RRs (95% CIs), which considers both within-study and between-study variation.[19] I2 of Higgins and Thompson was used to assess heterogeneity among studies[20] and I2 values of 0%, 25%, 50%, and 75% represent no, low, moderate, and high heterogeneity,[19] respectively. Univariate metaregression analysis by study region, study quality, number of participants, and follow-up years were conducted to investigate the potential sources of heterogeneity. Publication bias was assessed with visual inspection of the funnel plots, Begg’s rank correlation test,[21] and Egger’s linear regression test.[22] We also conducted subgroup analyses by age (mean age of subjects ࣙ60 and
Review SLEEP DURATION AND DEPRESSION AMONG ADULTS: A META-ANALYSIS OF PROSPECTIVE STUDIES Long Zhai,1,† Hua Zhang,2,† and Dongfeng Zhang, M.D.1 ∗
Background: Results from longitudinal studies on sleep duration and incidence of depression remain controversial. Methods: PubMed and Web of Science updated on October 22, 2014 were searched for eligible publications. Pooled relative risks (RRs) with 95% confidence interval (CI) were calculated using a randomeffects model. Results: Seven prospective studies were included, involving 25,271 participants for short sleep duration and 23,663 participants for long sleep duration. Compared with the normal sleep duration, the pooled RR for depression was 1.31 (95% CI, 1.04–1.64; I2 = 0%) for the short sleep duration overall. For long sleep duration, the pooled RR was 1.42 (95% CI, 1.04–1.92; I2 = 0%). The associations between short or long sleep duration and risk of depression did not substantially change in sensitivity and subgroup analyses. No evidence of publication bias was found. Conclusion: This meta-analysis indicates that short and long sleep duration was significantly associated with increased risk of depression C 2015 Wiley Periodicals, in adults. Depression and Anxiety 32:664–670, 2015. Inc.
Key words: depressive symptom; epidemiology; long sleep; meta-analysis; short sleep
INTRODUCTION
D
epression is a common cause of substantial disability and morbidity in the general population. By 2020, depression is predicted to be the second leading cause of disability, immediately behind cardiovascular diseases.[1]
1 Department
of Epidemiology and Health Statistics, Qingdao University Medical College, Qingdao, China 2 Department of Chronic Noncommunicable Diseases, Qingdao Municipal Centers for Disease Control and Prevention, Qingdao University, Qingdao, China † These
authors contributed equally to this work.
∗ Correspondence
to: Dongfeng Zhang, Department of Epidemiology And Health Statistics, Qingdao University Medical College, No. 38 Dengzhou Road, Qingdao 266021, China. E-mail: [email protected]; [email protected] Received for publication 21 November 2014; Revised 5 May 2015; Accepted 7 May 2015 DOI 10.1002/da.22386 Published online 5 June 2015 in Wiley Online Library (wileyonlinelibrary.com).
C 2015 Wiley Periodicals, Inc.
Being a complex mental disorder, depression is supposed to be affected by genetic,[2] lifestyle factors,[3] and their interactions.[4] Several epidemiology studies have found an association between sleep duration and health-related conditions, such as cardiovascular events,[5, 6] mental disorders,[7, 8] and mortality.[9] To date, many prospective studies have been carried out to investigate the role of the sleep duration in the development of depression. However, the results of these studies are controversial.[10–15] For example, one cohort study[13] showed a significant association between short sleep duration and depression; while another prospective study[12] indicated no relation between short sleep and depression. And the sample sizes of these studies are generally limited. Meta-analysis is the use of statistical methods to summarize the results of independent studies.[16] By combining information from relevant studies, metaanalyses can provide more precise estimates of the effects than those derived from the individual studies. Metaanalyses also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies.[17] Therefore, we conducted a meta-analysis of prospective studies to assess risk of depression for the short sleep duration versus normal sleep duration as well as the long sleep duration versus normal
Review: Sleep Duration and Depression
sleep duration, based on the postulation that the sleep duration would predict the incidence of depression in a U-shape fashion.
METHODS LITERATURE SEARCH AND SELECTION We followed the PRISMA guidelines.[18] A search of the literature up to October 22, 2014 was performed using the databases of PubMed and Web of Science with the following free text terms: sleep combined with depression. The search was limited to studies in humans. Moreover, we reviewed the reference lists from retrieved articles to search for further relevant studies. No language restrictions were imposed. Two investigators independently reviewed all identified studies, and studies were included if they met the following criteria: (1) a prospective design among adults; (2) the exposure of interest was sleeping duration categories assessed by questionnaires or objective measures across multiple consecutive occasions; (3) the outcome of interest was depression ascertained by rating scales or physician’s diagnosis; (4) the minimum time span of assessments was 6 months; (5) multivariateadjusted relative risk (RR) with 95% confidence interval (CI) was provided; (6) the most recent and complete article was chosen if a study had been published more than once.
DATA EXTRACTION AND QUALITY ASSESSMENT The following data were extracted from each study by two investigators: (1) name of the first author, (2) publication year, (3) study population, (4) origin of country, (5) follow-up years, (6) sample size and number of cases, (7) age range or mean age at baseline years, (8) gender, (9) methods to assess sleep duration and depression, (10) RR (adjusted for the largest number of confounders in the original study) with 95% CI for short sleep duration and long sleep duration as compared with the normal sleep duration, (11) sleep duration category, (12) adjustment for confounders, (13) study quality. The study quality was assessed using the Newcastle–Ottawa quality assessment scale (http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp). Maximum score on this scale is 9. “Good” was defined as a total score of 7–9; “fair,” a total score of 4–6; and “poor,” defined as a total score less than 4.
STATISTICAL ANALYSIS We weighted the study-specific log RRs by the inverse of their variance to calculate a summary estimate and its 95% CI. The DerSimonian and Laird random effects model was used to combine study-specific RRs (95% CIs), which considers both within-study and between-study variation.[19] I2 of Higgins and Thompson was used to assess heterogeneity among studies[20] and I2 values of 0%, 25%, 50%, and 75% represent no, low, moderate, and high heterogeneity,[19] respectively. Univariate metaregression analysis by study region, study quality, number of participants, and follow-up years were conducted to investigate the potential sources of heterogeneity. Publication bias was assessed with visual inspection of the funnel plots, Begg’s rank correlation test,[21] and Egger’s linear regression test.[22] We also conducted subgroup analyses by age (mean age of subjects ࣙ60 and
