Background
Nocturia is the most common among lower urinary tract symptoms [
1]. An epidemiological study conducted in the United States (US), the United Kingdom (UK) and Sweden found that among people aged ≥ 40 years, the prevalence of having ≥ 2 nocturia episodes per night was 28% for men and 34% for women [
2]. A study in Asia also found that the prevalence of having ≥2 nocturia episodes per night was 36% among people aged ≥ 40 years [
3].
The impact of nocturia is not trivial. Studies in the US [
4] and Sweden [
5] also found that nocturia negatively affects health-related quality of life (HRQOL) as measured by the Short Form-36 Health Survey (SF-36). Notwithstanding, poor sleep quality is a common complaint among people with nocturia [
6]. A study in the US reported that poor sleep quality can have a serious impact on the ability to function and daytime functioning, leading to impaired HRQOL [
6,
7].
Even though the negative impacts of nocturia on sleep quality and HRQOL have been documented in previous research [
6], their interrelationship has been poorly studied. In fact, a study of a Dutch population found that the impacts of nocturia on HRQOL became statistically insignificant after controlling for sleep quality. Besides, in a qualitative study in the US, respondents indicated that nocturia affected their functioning and wellbeing in daytime because of poor sleep quality [
8]. These studies imply that the relationship between nocturia and HRQOL could be mediated by sleep quality. A better understanding of their interrelationship could help clinicians better manage patients with nocturia by informing the development of interventions to address their multidimensional needs.
Therefore, the objective of the present study was to explore the interrelationship between nocturia, sleep quality and HRQOL. We hypothesized that sleep quality mediated the relationship between nocturia and HRQOL.
Discussion
In our study, we found that sleep quality was a mediator in the association between nocturia and HRQOL, suggesting that nocturia affects sleep quality, which in turn affects HRQOL. One possible mechanism is that nocturia affects slow-wave sleep (SWS), which is associated with daily process of recuperation [
19]. It was reported that adults who wake early to void during their first two sleep cycles spend 34% less time in SWS than adults who sleep undisturbed through two sleep cycles [
20]. Moreover, disruption in sleep continuity throughout the night can also reduce SWS. Despite equivalent total sleep times, people who experience repeated awakenings during the night spend less time in SWS than people with uninterrupted sleep [
20]. It was reported that interruption of SWS leads to fatigue, increased discomfort and a decreased pain threshold [
21]. The findings of this mediation analysis provide additional depth to previous research. For example, the respondents in a qualitative study reported that nocturia impaired sleep in terms of quantity and quality. The next day, the respondents would feel very tired due to a lack of sleep. As a result, they could not concentrate at work [
8]. An epidemiological study among a Dutch population found that the impacts of nocturia on HRQOL became statistically insignificant when sleep quality was put in a regression model [
22]. No doubt, the findings that nocturia affects sleep and HRQOL are certainly not new. However, previous studies only examined the negative impacts of nocturia on sleep and HRQOL in isolation [
4].
Given that nocturia itself is not life threatening, the treatment outcomes should aim to alleviate its negative impacts on daily life. Understanding the interrelationship between nocturia, sleep quality and HRQOL can therefore guide clinical practice. One important implication of our findings is that, to optimize the HRQOL of patients with nocturia, behavioural interventions for nocturia should also target sleep quality in these patients. For example, we might incorporate cognitive-behavioural theory to enhance sleep hygiene among patients suffering from nocturia.
Poor sleep quality was very common in our sample. Using the PSQI global score with > 5 as the cut-off, we found that 60% of our participants were suffering from poor sleep quality. Our prevalence was much higher than the prevalence reported in the population-based studies in Hong Kong (PSQI global score > 5: 39.4%) by Wong and Fielding [
23], Germany (PSQI global score > 5: 36%) by Hinz, Glaesmer [
24] and China (PSQI global score > 5: 26.6%) by Tang, Liao [
25]. The high prevalence found in the present study could be explained by the characteristics of our study population. Compared with community samples, our study population in primary care were likely to include participants with multi-morbidities [
26]. It was found that multi-morbidities were associated with insomnia [
27].
Almost one third (31.2%) of our primary care patients were suffering from nocturia. This prevalence is similar to those reported in Korea [
28], the US, the UK and Sweden [
2]. These collective findings suggest that the burden of nocturia is common and universal across different populations. Moreover, the high prevalence of nocturia found in our primary care patients implies that the problems were likely overlooked and untreated.
In our study, having ≥2 nocturia episodes per night was associated with poorer HRQOL. It also appeared that nocturia had more negative impacts on the physical aspects of HRQOL than the mental aspects. However, our findings were different from those reported by Kupelian and colleagues [
29]. This US study found that nocturia affected both the physical and mental aspects of HRQOL as measured by the SF-12. In fact, HRQOL and symptom perception are culturally specific. A qualitative study in the UK found that patients with urinary problems had concerns about the aetiology of their symptoms as well as disease progression. In some cases, patients even thought that their urinary problems were related to the possibility of cancer [
30]. In contrast, a recent qualitative study in Hong Kong found that urinary problems had no psychological effects on the majority of Chinese patients. These patients indicated that urinary problems were just a consequence of normal ageing [
31]. Even though some people reported negative psychosocial impacts associated with urinary problems, the psychological burden was merely related to embarrassment, inconvenience and restrictions on social activities [
31]. These qualitative findings (i.e. urinary problems as a normal part of the ageing process and urinary problems affecting social and physical activities) by Suen and colleagues [
31] echoed our findings that nocturia among the participants in our study mainly affected their physical functioning, social functioning and general health, all to the detriment of the overall physical aspects of their HRQOL.
Poor sleep quality in our study was associated with poor HRQOL across all domains of the SF-12 v2. A study of an older population in the US also found that sleep problems negatively affected all 8 domains and the PCS and MCS of the SF-36 [
32]. In addition, another study found that insomnia and its associated daytime sleepiness impaired cognitive functioning such as concentration, memory, reasoning and problem solving, as well as the ability to perform ordinary daily tasks [
33]. Qualitative studies have also reported that sleep problems have a pervasive impact on daily life [
34], and the problems are unpleasant and worrying [
35]. In our study, we found that the participants who reported sleep disturbance had poorer mental aspects of HRQOL than those without, with a large effect size. It is suggested that sleep deprivation could induce dysphoria, increase irritability and lower frustration tolerance. Experimental studies have found that sleep deprivation can lead to a deterioration in mood and increased reactions to negative emotional information [
36]. Besides, based on the Cohen’s d effect sizes found in the present study, it appeared that poor sleep quality had more negative impacts on all aspects of HRQOL (except for the GH domain of the SF-12 v2) than nocturia did. For example, the effect size difference of the SF-12 v2 MCS between people with poor sleep quality than those without was 0.80 while it was 0.18 between people with nocturia than those without. The effect size difference of the SF-12 v2 PCS between people with poor sleep quality than those without was 0.42 while it was 0.38 between people with nocturia than those without. Our findings were in line with those found in Japan [
37].
Our study had some limitations. First, given its cross-sectional design, causality could not be provided in the present study. Longitudinal studies are needed to make causal inferences. In fact, it is possible that people with insomnia will go to the toilet just because they can’t sleep. Our findings should be therefore interpreted with caution. Second, all the study outcomes were self-reported and may therefore be susceptible to biases such as recall bias and social desirability bias. Third, our study was conducted in public sector primary care setting. Our study findings might therefore not be transferable to the general population. Fourth, we had a high non-response rate of our study. It might lead to a non-response bias. A common reason to refuse the study was that patients did not want to spend extra time to fill out the questionnaire. It implied that waiting room screening might not be an optimal way to recruit primary care patients. Future studies should consider other strategies such as telephone follow-up interview so that patients can finish the questionnaire at their convenience.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.