Sleep duration and sleep quality are often linked to increased risk of mortality and morbidity. However, national representative data on both sleep duration and sleep quality and their relationship with chronic health problems are rarely available from the same source. This current study aimed to examine the independent and combined associations of sleep duration and sleep quality with physical and mental disorders, using data from the Singapore Mental Health Study 2016. 6,126 residents aged �18years participated in this epidemiological, cross-sectional survey. Sleep measures were assessed using the Pittsburg Sleep Quality Index while lifetime or 12-month medical and psychiatric diagnoses were established using the Composite International Diagnostic Interview 3.0. Both short sleep (<6hrs compared to 7-8hrs) and poor sleep were found to be independently associated with chronic pain, obsessive compulsive disorder and any mental disorder while poor sleep was additionally associated with major depressive disorder, bipolar disorder, generalized anxiety disorder and any physical disorder, when adjusted for confounders. Poor sleep combined with short sleep (�6hrs/day vs 7-8hrs/day) was associated with the highest number of comorbidities among other sleep combinations. Sleep duration and sleep quality, when adjusted for each other, remained independently associated with both physical and mental disorders. Affective disorders may be more closely related to poor sleep quality compared to abnormal sleep duration. Our findings suggest sleep quality to be a more important indicator for psychological and overall health compared to sleep duration.

With the new calling from DSM-5, clinicians treating psychiatric patients should view insomnia less as a symptom of their mental illnesses and treat clinical insomnia as a primary disorder. Patients should also be educated on the importance of reporting and treating their sleep complaints. Nonmedical (cognitive and behavioral) interventions for insomnia need to be further explored given their proven clinical effectiveness.

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Our study provides evidence to support the notion that a good mental health state is not simply the absence of a mental disorder. Mentally ill patients can also have high levels of PMH that possibly have a moderating or mediating effect on the relationship between patients' clinical symptoms and life satisfaction or general functioning.