Association between number of comorbid conditions, depression, and sleep quality using the Pittsburgh Sleep Quality Index: results from a population-based survey.

Objectives: Although sleep problems are a serious public concern, it is not clear if the presence of depression or multiple comorbid conditions has an additive or multiplicative effect on sleep quality.

Methods: We conducted a population-based, cross-sectional survey in a rural town in Japan. Multivariable-adjusted linear regression models were used to explore the association between the number of comorbid conditions and the Pittsburgh Sleep Quality Index (PSQI) global score. The association between the number of comorbid conditions and presence of depression, as defined by the five-item Mental Health Inventory (scores60), in those with poor quality sleep (PSQI global score>5) was determined using a non-parametric trend test.

Results: Of 5107 respondents, 3403 (mean age: 51.0years, women: 52.6%) were used for the analysis after exclusion of missing PSQI data. The PSQI global score (mean: 4.9) increased as the number of comorbid conditions increased in a linear and statistically significant manner (p<0.0001). The PSQI global score increased by 0.374 for each additional comorbid condition (p<0.0001). Among those with poor sleep quality, the proportion with depression increased significantly and linearly (p<0.0001) as the number of comorbid conditions increased (37.5% for 0 vs. 59.9% for 4 comorbid conditions).

Conclusion: The number of comorbid conditions correlated positively with poor sleep quality, and as the number of comorbid conditions increased, the proportion of those also suffering from depression increased. Recognizing the signs of depression in patients with multiple comorbid conditions is important because of its exacerbation of poor sleep quality.