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

Abstract

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 (scores ⩽ 60), 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: 51.0 years, 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.

Introduction

Sleep quality includes quantitative aspects of sleep, such as duration, latency, and number of arousals, as well as more purely subjective aspects, such as “depth” or “restfulness” [1]. Physical and cognitive symptoms of poor sleep quality include tiredness, loss of concentration, low pain threshold, anxiety, nervousness, irrational thoughts, hallucinations, loss of appetite, constipation, and being accident-prone. Sleep problems are a serious public concern because they affect quality of life [1] and well being [2]. In addition, they are costly, with direct economic costs for insomnia in the US in 1995 estimated at about $30 billion [3].

Several studies have shown an association between sleep problems and the presence of comorbid conditions, such as heart disease, diabetes, hypertension, stroke, cancer, or hip fracture [4]. Further, the presence of comorbid conditions has been associated with an increased risk of depression, which itself may cause sleep problems [5]. Importantly, however, comorbid conditions may cause sleep problems independently of depression. This finding highlights the importance of distinguishing low sleep quality caused by depression from that resulting from other causes because the appropriate treatment of depression in these patients may improve their prognosis [6], [7].

In spite of the apparent association between the presence of comorbid conditions and low sleep quality, it remains unclear whether the presence of two or more conditions results in lower sleep quality than the presence of only one or how depression contributes to poor sleep quality in those with multiple comorbidities. Here, based on a survey of a population-based sample of a rural Japanese town, we investigated the relationship between the number of comorbidities, depression, and sleep quality as assessed using quantitative and subjective aspects of sleep from the Pittsburgh Sleep Quality Index (PSQI).