Objectives: Sleep problems are highly prevalent among kidney transplant recipients. In this bibliometric study, we aimed to map the global scientific output related to sleep problems in the context of kidney transplantation.
Materials and Methods: We conducted a comprehensive literature search on May 14, 2025, using the Web of Science Core Collection database. The search strategy included title-based key words (“sleep” OR “insomnia” OR “sleep-related” OR “hypoventilation” OR “hypersomn*” OR “narcolepsy” OR “Kleine-Levin syndrome” OR “sleep-wake” OR “jet lag” OR “nightmare” OR “parasomnia” OR “confusional arousals” OR “exploding head syndrome” OR “restless legs syndrome” OR “periodic limb movement disorder”). Only English-language publications were included, and no year restriction was applied. We retrieved 400 articles, with articles analyzed using VOSviewer software for bibliometric mapping and visualization.
Results: Co-authorship and co-citation analyses revealed collaborative networks and influential contributions in the field. Novak (2019) emerged as a key author with the strongest collaborative ties. Key word co-occurrence analysis highlighted significant thematic links, particularly between “renal transplantation” and “sleep quality” and between “kidney transplantation” and “sleep apnea.” The American Journal of Kidney Diseases received the highest number of citations (n = 1146), followed by Nephrology Dialysis Transplantation (n = 468). These 2 journals also demonstrated a strong co-citation relationship, underscoring their central role in disseminating research in this area. Highly cited studies included Eltzschig (2011) with 2611 citations and Younossi (2019) with 1506 citations. Bibliographic coupling revealed that Artom (2014) and Picerillo (2017) shared a significant degree of relatedness based on shared references.
Conclusions: Results indicated increasing scientific interest on sleep quality and sleep disorders. The results can inform future interdisciplinary research agendas, support clinical practice improvements, and guide health policy efforts aimed at enhancing the quality of life and outcomes of kidney transplant recipients.

Key words : Insomnia, Renal transplant, VOSviewer

Introduction
Kidney transplantation is currently accepted as the standard and most effective treatment option for patients with end-stage renal disease.¹ Advances in immunosuppressive therapies and immunosuppressive regimens have substantially improved transplant outcomes, leading to increased patient and graft survival rates. In line with these developments, the contemporary approach focuses not only on improving survival but also on enhancing the quality of life of kidney transplant recipients.¹ Nevertheless, both medical and surgical treatment processes may exert various advantages and disadvantages on patients’ physical, psychological, and social well-being.² Deterioration in physical and/or psychological health may contribute to impaired sleep quality; similarly, worsening sleep quality may adversely affect overall health and well-being.³ Sleep disturbances occurring in the postoperative period may hinder recovery and consequently lead to a decline in quality of life.⁴ Physical or psychological stressors may prolong sleep-onset latency, increase nocturnal awakenings, and cause early morning awakening, thereby reducing total sleep duration and impairing sleep quality.⁵ The literature indicates that sleep problems are highly prevalent among kidney transplant recipients. A recent systematic review reported that the prevalence of posttransplant sleep disturbances ranges between 8% and 80%.³ The prevalence of poor sleep quality has been reported to range from 30% to 62%,⁶ and work has indicated that approximately 67% of kidney transplant recipients are affected by sleep disorders.⁷ In addition, nearly one-half of female kidney transplant recipients and one-third of male kidney transplant recipients have been reported to experience poor sleep quality.⁴ Multiple logistic regression analyses have demonstrated that sex, education level, monthly household income, and comorbidity burden are independently associated with postoperative sleep-related anxiety.⁷ Considering the broad effects of poor sleep quality on physical, psychological, social, and cognitive functioning, insomnia is likely to have a detrimental effect on transplant outcomes.⁸ Although self-reported assessments have suggested a relative improvement in sleep quality from pretransplant to posttransplant, insomnia, sleep disorders, poor sleep quality, and sleep dissatisfaction remain prevalent both before and after transplant across solid-organ transplant populations.³ Poor sleep has been strongly associated with increased fatigue, reduced motivation and concentration, lower levels of physical activity, decreased social participation, and diminished overall quality of life.⁴ Moreover, a large-scale study demonstrated that short sleep duration is associated with a rapid decline in kidney function.⁹ The detrimental effects of sleep disorders on renal function have been confirmed by numerous studies,¹⁰ and this condition may negatively affect both graft and patient survival.⁸ Sleep quality in kidney transplant recipients is closely associated with fatigue and depressive symptoms. This finding highlights the importance of systematically assessing sleep quality in the posttransplant care process in order to reduce fatigue and prevent depression.¹¹ Subjective assessment tools such as the Pittsburgh Sleep Quality Index and the Richards–Campbell Sleep Questionnaire are widely used for this purpose.¹¹ Evidence from long-term follow-up studies have further underscored the determining role of sleep quality in clinical and psychosocial outcomes among kidney transplant recipients.^12,13 Given the increasing prevalence of insomnia and sleep deprivation in the general population, understanding their relationship with kidney health has become even more crucial.¹⁴ In this bibliometric study, we aimed to analyze the global scientific output on sleep problems in the context of kidney transplantation and to reveal the existing knowledge structure in the field.

Materials and Methods
This study was designed as a descriptive bibliometric analysis to evaluate scientific investigations related to sleep problems in the context of kidney transplantation. We conducted a literature search on May 14, 2025, using the Web of Science Core Collection database. For the search, we included title-based keywords such as “sleep” OR “insomnia” OR “sleep-related” OR “hypoventilation” OR “hypersomn*” OR “narcolepsy” OR “Kleine-Levin syndrome” OR “sleep-wake” OR “jet lag” OR “nightmare” OR “parasomnia*” OR “confusional arousals” OR “exploding head syndrome” OR “restless legs syndrome” OR “periodic limb movement disorder.” Only English-language publications were included, and no year restriction was applied. The search yielded 400 articles, which we analyzed using VOSviewer software for bibliometric mapping and visualization. However, before analyses, the dataset was carefully screened and cleaned to eliminate spelling variations and duplicate records.

Ethical statement
Because the research data was based on published studies, ethical committee approval was not required.

Results
Publications mentioned in this study are shown in Table 1.

Co-authorship analysis
A co-authorship analysis was conducted to reveal the scientific collaboration networks in the field of kidney transplantation and sleep-related problems. The findings demonstrated a network structure centered around Novak (2019), who appeared to play a bridging role between different clusters. Novak (2019) established strong collaborative relationships, particularly with authors Mucsi, Szeifert, and Molnar (Figure 1).

Keyword co-occurrence analysis
Keyword co-occurrence analysis was performed to identify the dominant thematic areas and conceptual structure in the literature. The terms “kidney transplantation” and “chronic kidney disease” were positioned at the center of the network, forming the core conceptual framework. These key terms showed strong connections with sleep-related concepts, including “sleep quality,” “sleep disorders,” “sleep apnea,” and “insomnia” (Figure 2).

Journal co-citation analysis
At the journal level, co-citation analysis revealed that the American Journal of Kidney Diseases had the highest number of citations (n = 1146). This was followed by Nephrology Dialysis Transplantation (n = 468). A strong reciprocal co-citation relationship was observed between these 2 journals, represented by a prominent link in the network visualization. This finding indicated that both journals constituted core knowledge sources within the field. Examination of the overall network structure further demonstrated that nephrology- and transplant-focused journals were interconnected with journals in neurology and sleep medicine, reflecting the development of an interdisciplinary publication structure (Figure 3).

Bibliographic coupling analysis
Document-level bibliographic coupling analysis was conducted to examine relationships based on shared references among publications. The results indicated that Shamsunder (2005) and the surrounding publications occupied a central position in the network, forming a conceptual core within the literature. According to the bibliographic coupling analysis, a strong linkage was identified between Artom (2014) and Piccirillo (2017). The high link strength between these 2 publications suggested substantial shared references and indicated that they addressed similar research questions within comparable conceptual frameworks (Figure 4).

Document citation analysis
At the document level, citation analysis identified several highly influential publications that prominently shaped the literature. The study published by Eltzschig (2011) emerged as the most cited publication within the dataset, with 2611 citations. This was followed by the study by Younossi (2019), which received 1506 citations (Table 2). Document co-citation analysis was performed to reveal the intellectual structure formed by publications that are frequently cited together in the literature. The connections observed between the 2 main clusters indicated an increasing integration over time between kidney disease and sleep disorder literature (Figure 5).

Journal co-citation analysis
The analysis demonstrated that the American Journal of Kidney Diseases occupied a central position in the network and had the highest co-citation strength. This journal exhibited strong linkages particularly with Clinical Journal of the American Society of Nephrology, Nephrology Dialysis Transplantation, and American Journal of Transplantation, all of which are leading journals in nephrology and transplantation. The results of the journal co-citation analysis indicated that sleep problems after kidney transplant are addressed at the intersection of nephrology, transplantation, sleep medicine, and general medical literature (Figure 6).

Discussion
The high prevalence of sleep disorders after kidney transplantation has been clearly documented in the literature.^4,15 A substantial proportion of transplant recipients report poor sleep quality, insomnia, sleep dissatisfaction, and reduced sleep duration.^3,8 These disturbances represent not only subjective discomfort but also clinically significant conditions that may affect the cardiovascular system, immune response, hormonal regulation, and psychological well-being.¹⁶ Furthermore, insomnia and insufficient sleep duration have been reported to exert detrimental effects on kidney function and to be closely associated with metabolic risk factors.^14,17 This bibliometric analysis comprehensively revealed the intellectual structure, research collaborations, and thematic orientations of the literature on sleep problems following kidney transplantation. The co-authorship analysis demonstrated that research output is concentrated around specific centers and investigators, with Novak and colleagues (2019) occupying a central position within collaboration networks. This finding suggests that the field is largely driven by particular research groups and exhibits a clustered pattern of academic production. The keyword co-occurrence analysis showed that “kidney transplantation” and “chronic kidney disease” constituted the conceptual core of the literature. These terms were strongly linked to “sleep quality,” “sleep disorders,” and “sleep apnea,” indicating a progressively strengthening interdisciplinary interaction between clinical nephrology and sleep medicine. Indeed, comorbid sleep disorders such as obstructive sleep apnea and restless leg syndrome have been frequently reported among transplant recipients and have been shown to adversely affect quality of life.^4,8 The thematic cluster analysis further demonstrated that the literature predominantly focused on clinical outcomes, quality of life, psychosocial factors, inflammation, and sleep physiology. Variables such as fatigue, depressive symptoms, and inflammatory processes were frequently examined in conjunction with sleep disturbances.¹⁸ Citation and co-citation analyses revealed that the intellectual foundation of the field is shaped by high-impact journals and pioneering studies. American Journal of Kidney Diseases and Nephrology Dialysis Transplantation emerged as the journals with the highest citation counts and link strengths. At the document level, Eltzschig (2011) and Younossi (2019) were identified as the most highly cited publications, and a strong bibliographic coupling was observed between Artom (2014) and Piccirillo (2017). These findings indicated a substantial flow of knowledge and interdisciplinary integration among the nephrology, transplantation, and sleep medicine literatures. Furthermore, the increasing visibility of journals such as Sleep Medicine and Seminars in Nephrology, particularly in association with more recent publications, suggests a growing shift toward a sleep-centered perspective within the field. The existing literature consistently demonstrated that sleep disorders persist after kidney transplant and exert significant effects on long-term survival and quality of life.^11,13,15,18 Nevertheless, sleep deprivation is often insufficiently addressed as a treatable clinical condition. Early identification and intervention for sleep disorders are critical for improving both physical and psychosocial outcomes among transplant recipients.²

Strengths and limitations
The application of co-authorship, co-citation, bibliographic coupling, and key word co-occurrence analyses enabled a holistic understanding of the intellectual structure and research trends in the field. However, several limitations should be acknowledged. First, the analysis was limited to publications retrieved from a single database. Inclusion of additional databases could have provided a broader coverage of the literature and potentially yielded different network structures.

Conclusions
This bibliometric analysis demonstrated that research on sleep following kidney transplantation is a rapidly expanding and interdisciplinary field. Future studies with longitudinal designs are needed to evaluate sleep quality across different phases of the transplant trajectory and to investigate early intervention strategies, which could provide substantial contributions to clinical practice. In particular, incorporating sleep assessment into routine nursing practice is of critical importance for symptom management, patient education, and improvement of overall quality of life among transplant recipients.