Cognitive impairment (CI) is common in individuals with chronic kidney disease (CKD), especially in hemodialysis patients with end-stage renal disease (ESRD) (Murray et al., 2006). Previous studies including our own indicated that the prevalence of CI was ranged from 70 to 80%, which was significantly higher than those individuals with normal kidney function (Kurella Tamura et al., 2010; O’Lone et al., 2016; van Zwieten et al., 2018; Luo et al., 2020). Besides, CI was proved to be associated with adverse outcomes by means of influencing the compliance of hemodialysis patients regarding their dialysis schedules and medication regimens (Drew et al., 2015; Angermann et al., 2018). Facing such a great challenge, it seems critically important to make further exploration about the detection and prevention of CI among hemodialysis patients.

Sleep quality, another common public health issue, has been proved to be related to poor cognitive function in the general population (Ratcliff and Van Dongen, 2009). Researchers demonstrated that disturbed sleep, including sleep fragmentation, abnormal sleep duration, and sleep disorders, were independent risk factors for CI among those populations (Waters and Bucks, 2011; Gadie et al., 2017). Notably, sleep disorders are also shown to be highly prevalent in hemodialysis and peritoneal dialysis patients, the prevalence of sleep disorder was approximately 49.0 to 60.5% among those individuals (Kutner et al., 2007; Elder et al., 2008; Davison et al., 2015), and this deterioration generally covered a wide range of aspects including sleep satisfaction, timing, efficiency, and duration, etc (Buysse, 2014). Acting as two major problems which may have a negative influence on the quality of life among dialysis patients, the relationship between sleep disorder and CI has caused attention in recent years, however, the results of the relationship were inconsistent (Rodriguez et al., 2013; Zhao et al., 2019). A recent study in peritoneal dialysis patients noted that possible narcolepsy was associated with general cognitive dysfunction (Zhao et al., 2019), and another study concluded that sleep-disordered breathing was associated with CI, in patients with advanced CKD (Kang et al., 2012). In contrast with those studies, Rodriguez et al. (2013) reported no association between sleep disturbances and cognitive function in hemodialysis patients. These different results may be related to the difference in accessing methods of sleep and cognitive function and different individuals in those studies. Further exploration about the relationship between them is in great need in hemodialysis patients.

To clarify this important issue, we conducted a cross-sectional analysis to assess the features of sleep status in a group of middle age and older hemodialysis patients using the Pittsburgh Sleep Quality Index (PSQI) questionnaire and assess cognitive function by the Chinese Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) scale, then we evaluated the association between overall and specific sleep disorders with CI.

Our study showed that the prevalence of sleep disorders in this group of Chinese middle age and older adult hemodialysis patients was 77.0%, the prevalence of CI in those patients was 80.9%. Patients with CI were more inclined to have sleep disorders in specific aspects of sleep latency, habitual sleep efficiency, sleep disturbances, and daytime dysfunction. These results remained almost consistent in following multivariate adjustment, suggesting that poor sleep quality especially sleep disturbances, daytime dysfunction, and long sleep duration were associated with CI in middle age and older adult hemodialysis patients.

Currently, both sleep disorders and CI have become serious public health issues in aging and increase with advancing age (Gadie et al., 2017). Our study found the prevalence of sleep disorders was 77.0%, which was almost in agreement with previous data (45.6–88.5%) in hemodialysis patients (Iliescu et al., 2003; Bastos et al., 2007; Pai et al., 2007; Elder et al., 2008; Eryavuz et al., 2008; Cengic et al., 2012; Harris et al., 2012). The relatively wide range of reported prevalence may be related to different individuals and the difference in accessing methods of sleep quality in the studies. A study including 128 American hemodialysis patients reported the prevalence of sleep disorders was 45.6%, which was lower than that in our study, this might be related to the different regional characteristics and ages of the participants (the mean age was 57.3 ± 13.8 years in Harris’s study and 63.7 ± 7.8 years in our study) (Harris et al., 2012). Another study including 11,351 hemodialysis patients from 7 countries found nearly half (49%) of patients experienced sleep disorders, in which they accessed sleep quality through a patient self-reported scale while not the PSQI questionnaire (Elder et al., 2008). In recent years, the PSQI questionnaire has been widely used and recognized as a well-established instrument of self-reported sleep quality among older adults in different countries (Beaudreau et al., 2012; Hinz et al., 2017; Salahuddin et al., 2017). Therefore, it is vital to establish consistent methods for assessing sleep quality and we recommend using the PSQI questionnaire to improve the accuracy and reliability of the diagnosis of sleep disorders in hemodialysis patients.

In addition, our analysis and previous studies also indicated that CI was very common and related to poor outcomes in hemodialysis patients, the increased age, lower education level, cardiovascular and cerebrovascular diseases, and dialysis-related factors including hemodialysis vintage and single-pool Kt/V were shown to be the independent risk factors of CI (Kurella Tamura et al., 2010; Drew et al., 2015; O’Lone et al., 2016; Luo et al., 2020). As a major public health issue, sleep disorders are shown to be associated with CI in community individuals (Gadie et al., 2017). One of the largest studies including 3,151 Japanese community-dwelling older individuals revealed that both long sleep duration and excessive daytime sleepiness were independent risk factors for cognitive decline after 4 years of follow-up (Nakakubo et al., 2019). However, as we mentioned above, the association between sleep disorders and CI is still in controversy concerning hemodialysis patients. Kutner et al. (2007) investigated the relationship of sleep difficulty and cognitive function scores in a national cohort of 2,286 dialysis patients, the authors noted that patients with lower cognitive scores were more likely to report sleep difficulty, and the association also was significant in a subgroup analysis that was restricted to hemodialysis patients. While Rodriguez et al. (2013) reported no association between sleep disturbances and cognitive function in 168 hemodialysis patients, they applied the sleep subscale battery of the Choices for Healthy Outcomes in Caring for ESRD to assess sleep disturbances and a detailed battery of neurocognitive tests to assess cognitive function. The differences of the above mentioned results may be related to the possibility that both the sleep questionnaire and the cognitive function battery are not consistent and sensitive enough to appreciate this association accurately (Kurella et al., 2004; Rodriguez et al., 2013). In our study, sleep disorders were assessed through the PSQI questionnaire and cognitive function by the MoCA-BJ scale. Currently, the PSQI questionnaire has been recognized as an internally consistent and valid measure of self-reported sleep quality among older adults in a variety of languages and clinical circumstances (Beaudreau et al., 2012; Hinz et al., 2017; Salahuddin et al., 2017). The MoCA-BJ scale is a convenient assessing tool for cognitive function and we have validated its sensitivity and specificity with the fifth version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) recommended neuropsychological battery (Tian et al., 2020). Through these two widely accepted evaluation tools, we found that sleep disorders especially sleep disturbances, daytime dysfunction, and long sleep duration were significantly associated with CI in middle age and older adult hemodialysis patients. The association between them provided a useful hint that we should pay more attention to the evaluation of both sleep and cognitive function among hemodialysis patients in the clinical practice, and it seems that sleep function improvement might be benefitial in retarding the development of CI among those individuals.

Our study has several limitations. First, the study was a cross-sectional analysis, we could not determine the causal relationship between sleep disorders and CI. Second, the sleep scale in our study was self-reported and this might lead to a reporting bias. Even with the above-mentioned limitations, we still have several strengths concerning our study. First, we included a large cohort of 613 patients selected from 11 hemodialysis centers in Beijing which might have a good representative of hemodialysis patients in China. Second, sleep quality was assessed through the PSQI questionnaire and cognitive function by the MoCA-BJ scale, which might improve the sensitivity and accuracy of the diagnosis of sleep disorders and CI in hemodialysis patients.

In summary, our results indicate that sleep disorders are associated with cognitive impairment in Chinese middle age and older adult hemodialysis patients. Identifying one of these issues might be a hint for the existence of another issue in hemodialysis patients, the data may be helpful for the clinician in the detection and prevention of these two important diseases in those individuals. Future studies should evaluate this relationship in prospective cohort studies with more detailed and objective measurements of sleep quality.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Institutional Ethical Review Board of Beijing Shijitan Hospital, Capital Medical University (approval no. SJT2016-18). The patients/participants provided their written informed consent to participate in this study.

RT, YB, and YG collected data and contributed to the critical revision of the manuscript. RT, YG, and YL contributed to the hypothesis and study design and interpreted the result. RT and PY analyzed the data. RT wrote the manuscript. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer XL has declared a shared parent affiliation with the authors RT, YG, and YL at the time of the review.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.