Objective: Emerging evidence shows that evening chronotype is associated with mental health problems, especially mood disorders, but few studies have investigated its association with schizophrenia. Based on meta-analytic methods, we aimed to test whether eveningness is greater in individuals with schizophrenia compared with healthy controls and patients with bipolar I disorder.
Method: Medline/Pubmed, Google Scholar, and EBSCO databases were searched up to April 2021 for articles investigating chronotype in individuals with schizophrenia. Two meta-analyses were conducted: individuals with schizophrenia compared with healthy controls and individuals with bipolar I disorder. These meta-analyses were followed by a meta-regression controlling for potential confounders.
Results: Five studies comprising 386 individuals with schizophrenia (age 32.73 years; 67.4% male), 320 with bipolar I disorder (age 31.26 years; 38.3% male) and 638 healthy controls (age 32.19 years; 50.6% male) were included. Participants with schizophrenia were moderately higher on eveningness than healthy controls but they did not differ from those with bipolar I disorder. The difference was not affected by gender, age, and the type of scale used for assessing chronotype.
Conclusions: Individuals with schizophrenia are more evening oriented than healthy controls and have a similar chronotype to those with bipolar I disorder. The results supported the hypothesis that evening chronotype might be a marker of, or a risk factor for, mental health problems in general and not just limited to affective disorders.
Keywords: Chronotype; Circadian rhythms; Eveningness; Meta-analysis; Morningness; Schizophrenia.
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