The prevalence of nocturia and its effect on health-related quality of life and sleep in a community sample in the USA

Authors


Karin Coyne, Senior Research Scientist, MEDTAP International, 7101 Wisconsin Ave, Suite 600, Bethesda, MD 20814, USA.
e-mail: coyne@medtap.com

Abstract

OBJECTIVE

To evaluate the prevalence of nocturia and its effects, with and without concomitant overactive bladder (OAB, i.e. urgency, frequency, urge incontinence and nocturia), on health-related quality of life (HRQoL) and sleep.

SUBJECTS AND METHODS

A national survey was conducted in the USA to assess the prevalence of OAB and nocturia. A nested case-control study was conducted among respondents with OAB symptoms and age- and gender-matched controls, with participants completing a series of questionnaires on HRQoL (OAB-q, Short Form-36, and Medical Outcomes Study (MOS) sleep scale). Descriptive analyses, t-tests, analysis of variance with post hoc comparisons and multivariate regressions were used to analyse the data.

RESULTS

In all, 5204 people participated in the survey, with 919 in the nested case-control study. The sample population had a mean age of 45.8 years, was 52.6% female and 80% Caucasian. In the community sample, 31% reported > 1 void/night and 14.2% reported > 2 voids/night. The prevalence of nocturia increased with age, with no gender differences. For OAB cases, 66.8% reported > 1 void/night and 42.2% reported > 2. In the case-control cohort there were significant HRQoL differences (P < 0.01), with increasing episodes of nocturia in all OAB-q subscales except social interaction. The amount of sleep per night was significantly correlated with the sleep, concern and social interaction OABq subscale scores. The number of nocturia episodes/night was also significantly (P = 0.02) associated with the number of hours of sleep/night.

CONCLUSION

Nocturia is widely prevalent and increases with age, affecting men and women equally. Incremental increases in the number of voids/night have further negative effects on sleep, symptom bother, and HRQoL.

Abbreviations
OAB(-q)

overactive bladder (questionnaire)

HRQoL

health-related quality of life

SF-36

Short Form-36

MOS

Medical Outcomes Study.

INTRODUCTION

Although characterized as one of the most bothersome of all urological symptoms [1], there is little consensus when defining nocturia. The ICS Sub-Committee defined nocturia as ‘waking at night to void. This applies to any number of voids during the night . . .’[2], but this definition does not provide an indication as to when nocturia becomes bothersome. Nocturia is associated with ageing and can result from behavioural influences (e.g. late-night fluid intake, caffeine) or from several clinical conditions (e.g. diabetes, congestive heart failure, lower urinary tract obstruction, prostatic disease, overactive bladder, OAB) [1]. The definition of OAB (‘urinary urgency, with or without urge incontinence, and usually with urinary frequency and nocturia’) [3] includes nocturia as a symptom, but little research has examined the effect of nocturia in OAB, particularly on health-related quality of life (HRQoL). Indeed, previous research on the effects of nocturia has focused primarily on bother, troublesomeness, or general health status, but not on HRQoL from a multidimensional perspective [4]. Given that HRQoL is multidimensional and can be defined as the patient's perception of health impact (including disease and treatment) on physical, psychological and social functioning [5], such a perspective is important in understanding the effects of nocturia. The purpose of this study was to evaluate the prevalence and effect of nocturia, with or without OAB, on HRQoL and sleep in a USA national community sample of adults.

Previous prevalence studies have typically defined nocturia as ≥ 2 voids per night [6–12]. Using this criterion, overall prevalence rates for nocturia range from 10.8% and 11.8%[10] to 25% and 21%[8] in men and women, respectively, and increased with age in both. Importantly, estimates of the prevalence of nocturia varied depending on the definition of nocturia and age group surveyed. While the prevalence of OAB has been estimated to be 6–35% in Europe [13] and 16.6%, or ≈ 33 million men and women in the USA [14], the prevalence of nocturia in those with OAB is unknown.

While nocturia is considered to be part of normal ageing, there are no ‘normal’ values for the frequency of nocturia. Desgrandchamps et al.[15] suggested that nocturia of ≤ 2 voids/night is normal, but there is evidence suggesting otherwise. Several community surveys found ≥ 2 voids/night to be ‘troublesome’[10,12,16]. Middlekoop et al.[17] reported that 67.5% of their community sample claimed nocturia to be the most frequent cause of disturbed sleep. When considering nocturia in relation to other urinary symptoms in men with BPH, Eckhardt et al.[18] noted nocturia to be the second most bothersome symptom after urinary urgency. In the community sample of Asplund et al.[19], 20% of women with nocturia of ≥ 2 voids/night reported poor health; this increased to 39% for women with nocturia of ≥ 3 voids/night and was independent of other comorbid conditions. In addition to bothersomeness and sleep deficits, nocturia can be a risk factor for falling. Stewart et al.[11] reported a significantly greater risk of falls among elderly people reporting nocturia of ≥ 2 voids/night (odds ratio 1.8); this risk increased with increasing nocturia episodes.

While the effects of nocturia in OAB have not been documented, OAB significantly compromises HRQoL and symptom bother. Liberman et al.[20] found that community respondents with symptoms of OAB reported significantly lower HRQoL as measured by the Short Form (SF)-20 than in controls. Coyne et al.[21] found individual symptoms of OAB (i.e. urinary urgency, frequency, incontinence and nocturia) to significantly increase symptom bother and decrease HRQoL using a disease-specific HRQoL instrument, the OAB questionnaire (OAB-q). Given that nocturia and OAB have detrimental effects on HRQoL, the effects of nocturia with or without OAB warrant investigation.

SUBJECTS AND METHODS

To estimate the prevalence of OAB in the USA a national survey was conducted using a clinically validated computer-assisted telephone interview [14]. The interview included questions about nocturia, urinary frequency, urinary urgency and incontinence within the previous 4 weeks, as well as demographics, childbearing history, sleep habits, fluid intake, UTIs, prostate problems, current medication use and comorbid conditions. Respondents were classified as having OAB (cases) or not (controls) depending on their survey responses.

Quota sampling methods were used in the national survey to ensure a representative USA population for gender, age and geographical region. A nested case-control study was conducted as a follow-up to the national survey to evaluate the HRQoL and sleep of respondents meeting OAB case criteria, and of age- and gender-matched controls. Self-administered questionnaires related to HRQoL and sleep were sent to cases and selected controls. Institutional Review Board approval was obtained before the study started and all participants provided informed verbal consent before data collection.

OAB

Continent OAB criteria were as follows: the presence of urinary urgency four or more times in the past 4 weeks in addition to either more than eight voids/day or the use of at least one coping strategy (e.g. restricting fluid intake, defensive voiding). Incontinent OAB criteria included the continent OAB criteria plus three or more episodes of urinary leakage in the past 4 weeks that were not completely explained by stress incontinence symptoms. Controls did not meet either of the above criteria.

NOCTURIA

Night-time was defined for telephone respondents as the ‘time between going to sleep and waking’. Questions about nocturia were: ‘How many nights in the past 4 weeks, on average, did you go to the bathroom and urinate?’ and ‘On these nights, how many times, on average, did you go to the bathroom and urinate?’. Responses to these two questions were multiplied together and divided by 28 to obtain an average number of nocturia episodes/night over the previous 4-week period.

NESTED CASE-CONTROL STUDY QUESTIONNAIRES

Questionnaires pertaining to disease-specific HRQoL, generic health status and sleep were used in the nested case-control study [14]. The questionnaires, the OAB-q, the Medical Outcomes Study (MOS) SF-36, and the MOS Sleep Scale (MOS Sleep) were previously described in detail elsewhere [22]. Respondents were also asked to rate their need for medical care for their bladder symptoms on a scale of 0–10.

STATISTICAL ANALYSIS

Categorical data were compared using chi-square tests and continuous data using t-tests or anova; the latter with pairwise comparisons were controlled for age, gender and clinical conditions (i.e. diabetes, congestive heart failure, prostate problems, previous bladder surgeries, cancer, number of births, and use of diuretics). P values were adjusted for multiple comparisons using Scheffe's adjustment. In all analyses, a Type 1 error level of α < 0.05 was considered statistically significant.

Nocturia was examined using a categorical and incremental approach. The first defined nocturia as ≥ 2 voids/night with the data examined by comparing ‘No nocturia’ (<2 voids/night) to ‘nocturia’ (≥2 voids/night). For a more thorough examination of the effects of nocturia on HRQoL and sleep, voids/night were also grouped as: 0 to <1 , ≥1 to <2 and ≥ 2. The number of voids/night was also compared incrementally with a 1 void/night increase up to ≥ 4 voids/night. Contrast statements were included in the anova models to further ascertain the effect of nocturia on HRQoL. To evaluate the potential interaction between OAB and nocturia, an interaction term of OAB*nocturia was included in the anova model.

As the amount of sleep per night affects health and HRQoL [23], the effect of the number of hours of sleep per night was investigated using a series of multivariate regressions with each OAB-q subscale as the dependent variable. Each model included the following variables: urinary urge intensity, number of frequency, nocturia and incontinence episodes, age, gender and the above noted clinical conditions. In the regression models all urinary variables, hours of sleep and age were continuous; all others were dichotomous. Multi-colinearity was assessed using the variance inflation factor, following the general rule that it should be ≤10 [24].

RESULTS

The demographics of the community sample are presented in Table 1. The sample was primarily Caucasian (80.3%) with slightly more women (52.6%), and a mean age of 45.8 years. Respondents with nocturia were significantly older (56.9 vs 43.8, P < 0.001) than respondents without. This age difference was most likely reflected in marital status (significantly more ‘never married’ without nocturia and ‘widowed’ with nocturia).

Table 1.  The demographic characteristics of the USA community sample, the nested case-control sample, and the clinical characteristics of the latter
CharacteristicNo nocturiaNocturia*P
  • *

    Defined as > 2 voids/night;

  • Based on patient self-report and includes the following drugs: antibiotics, cranberry pills, Detrol, Ditropan, Flomax, herbals, Macrobid, oxybutynin and ‘not sure’.

Community
N4351720 
Mean (sd) age, years  43.8 (16.6) 56.9 (17.1)< 0.001
Gender, n (%) male2112 (48.5)308 (42.8)0.004
Race, n (%)  0.17
White3514 (80.8)567 (78.8) 
Black 372 (8.5) 77 (10.7) 
Other 420 (9.7) 67 (9.3) 
Missing  45 (1.0)  9 (1.2) 
Marital status, n (%)  < 0.001
Married/living together2443 (56.1)424 (58.9) 
Widowed 285 (6.5)114 (15.8) 
Divorced/separated 604 (13.9)100 (13.9) 
Never married 977 (22.5) 75 (10.4) 
Missing  42 (1.0)  7 (1.0) 
Education, n (%)  < 0.001
< high-school graduate 370 (8.5) 96 (13.3) 
High-school graduate1392 (32.0)249 (34.6) 
Some college1116 (25.6)199 (27.6) 
College degree1087 (25.0)112 (15.6) 
Graduate degree 371 (8.5) 60 (8.3) 
Missing  15 (0.3)  4 (0.6) 
Nested case-control
N 683216 
Mean (sd) age, years  52.0 (16.1) 60.8 (15.6)0.001
Gender, n (%) male 274 (40.1) 85 (39.4)0.84
Race, n (%)  0.58
White 586 (85.8)177 (81.9) 
Black/other  94 (13.7) 37 (17.1) 
Missing   3 (0.4)  2 (0.9) 
Marital status, n (%)  0.005
Married/living together 398 (58.3)123 (57.0) 
Widowed  71 (10.4) 43 (19.9) 
Divorced/separated  113 (16.5) 31 (14.3) 
Never married  98 (14.4) 19 (8.8) 
Missing   3 (0.4)  0 
Education, n (%)  0.007
< high-school graduate  59 (8.6) 33 (15.3) 
High-school graduate 235 (34.4) 76 (35.2) 
Some college 180 (26.4) 64 (29.6) 
College degree 157 (23.0) 29 (13.4) 
Graduate degree  52 (7.6) 14 (6.5) 
Clinical characteristics
Clinical condition, n (%) yes
Diabetes  51 (7.5) 37 (17.2)< 0.001
Chronic heart failure  29 (4.3) 18 (8.4)0.02
CNS disorder  18 (2.6) 10 (4.6)0.31
Interstitial cystitis   9 (1.3)  7 (3.2)0.12
History of bladder surgery  47 (6.9) 33 (15.3)< 0.001
Prostate problems  47 (6.9) 30 (14.0)< 0.01
History of cancer  54 (8.0) 31 (14.4)< 0.01
Use of bladder drugs  27 (4.0) 19 (8.8)0.02
Use of diuretics  87 (12.8) 51 (23.8)< 0.001

In the community sample, the overall prevalence of ≥ 1 void/night was 31%; the prevalence for ≥ 2 voids/night was 14.2% and for ≥ 3, 5.4%. The prevalence of nocturia in the community sample by age and gender is shown in Fig. 1. The prevalence of nocturia increased with age and was similar among men and women. In women, the prevalence of nocturia doubled during the climacteric period, from 9.9% in those 35–44 years old to 18.6% in those aged 45–55. Prevalence rates of nocturia among only OAB cases in the community sample (862) were much higher than those in the overall community sample, with an overall prevalence of ≥ 1 void per night of 65.9%; the prevalence of ≥ 2 voids/night was 41.6% and of ≥ 3, 19.5%.

Figure 1.

Prevalence of nocturia (≥ two episodes/night) in a USA community sample of men (red) and women (green).

The remainder of the results focus solely on the case-control cohort for which HRQoL and sleep data were collected. Of the 1769 questionnaires sent to telephone respondents, 919 were returned (52% response rate). Overall, responders were more likely to be older, female and Caucasian, with 57% of incontinent OAB participants, 60% of continent OAB participants, and 53% of controls responding. Each group was representative of participants in the national survey. There were similar trends in the demographic characteristics of the nested case-control sample as in the national sample, except for gender differences (Table 1). There were significant differences in many clinical conditions between the groups with or with no nocturia (Table 1), with a higher prevalence rate of diabetes, chronic heart failure, history of bladder surgery, prostate problems, history of cancer, use of bladder medications or diuretics in the nocturia group. Consequently, all subsequent analyses controlled for these conditions as well as age and gender.

The effect of nocturia on HRQoL both incrementally (Fig. 2) and categorically (Table 2) gave similar findings. Figure 2 shows the effect of increasing episodes of nocturia on symptom bother and HRQoL. With increasing nocturia frequency, symptom bother scores increased significantly and the OAB-q subscale scores decreased significantly. On all subscales, the 0 to <1 group reported significantly lower symptom bother and higher HRQoL scores than all other nocturia groups, except in social interaction, where only the 0 to < 1 group was significantly higher than the ≥4 group.

Figure 2.

OAB-q subscales for nocturia episodes controlling for age, gender and clinical comorbidities. A higher score indicates better HRQoL and higher symptom bother scores indicate greater symptom bother. aP < 0.001 for all group comparisons; bP < 0.05 for all group comparisons; ns, not significant.

Table 2.  OAB-q, SF-36 and MOS Sleep subscale scores discriminated by number of voids/night and controlling for age, gender and clinical conditions
Mean (sem)No nocturia
(0 to < 1)
Nocturia ≥ 1, < 2Nocturia ≥ 2P
  • *

    Higher scores indicates better HRQoL and higher symptom bother scores indicate greater symptom bother. Scores for the OAB-q and SF-36 are 0–100.

  • For all subscales, except role-emotional, 0 to < 1 group vs ≥ 2 group, P < 0.04; for physical function, vitality and mental health P < 0.04 for ≥ 1 < 2 group vs ≥ 2 group.

  • ‡Higher scores indicate worse sleep function.

N505178216 
OAB-q Subscales*
Symptom bother 15.1 (0.9) 23.1 (1.5) 32.5 (1.4)< 0.001
Coping 92.3 (0.9) 87.0 (1.4) 82.2 (1.3)< 0.05
Concern 92.3 (0.9) 87.7 (1.4) 81.2 (1.3)< 0.03
Sleep 89.0 (1.0) 79.1 (1.6) 67.9 (1.5)< 0.001
Social 97.3 (0.5) 94.8 (0.9) 93.0 (0.8)≥ 2 vs 0, < 0.001
HRQoL total 92.7 (0.7) 87.1 (1.2) 81.3 (1.1)< 0.003
SF-36 Subscales*
Physical function 80.5 (1.1) 74.8 (1.9) 72.5 (1.8) 
Role-physical 77.1 (1.6) 72.4 (2.7) 67.2 (2.5) 
Bodily pain 73.2 (1.1) 68.2 (1.8) 65.1 (1.7) 
General health 69.5 (0.9) 66.8 (1.6) 63.2 (1.5) 
Vitality 59.0 (0.9) 54.2 (1.5) 52.3 (1.4) 
Social functioning 84.4 (1.0) 80.6 (1.7) 78.9 (1.6) 
Role-emotional 78.8 (1.7) 75.3 (2.8) 71.6 (2.6) 
Mental health 74.5 (0.8) 72.3 (1.4) 70.5 (1.3) 
MOS Sleep Subscales
Hours sleep/night  7.0 (0.06)  6.9 (0.1)  6.7 (0.1)≥ 2 vs ≤ 1; < 0.02
Snoring  2.6 (0.8)  2.9 (0.1)  2.9 (0.1)NS
Shortness of breath  1.6 (0.05)  1.6 (0.08)  1.6 (0.08)NS
Adequacy of sleep  8.0 (0.1)  7.5 (0.2)  7.4 (0.2)≥ 2 vs ≤ 1; < 0.01
Somnolence  6.6 (0.1)  7.0 (0.2)  7.5 (0.2)≥ 2 vs ≤ 1; < 0.002
Sleep Index 1 13.7 (0.2) 14.8 (0.4) 15.7 (0.4)≥ 2 vs ≤ 1; < 0.001

When considering only voids/night irrespective of OAB status in a categorical analysis (0 to <1, ≥1 to <2, and ≥2), there were significant differences on all OAB-q subscales among each nocturia group (except for social interaction where nocturia ≥ 1 but <2 was not significantly different from either other group) (Table 2). The greatest differences were noted in the sleep subscale with significant declines (P < 0.001) with each increasing nocturia group. Importantly, neither the SF-36 nor the MOS Sleep subscale were as sensitive in detecting differences among the nocturia groups. There were significant differences (P < 0.03) on all SF-36 subscales, except role-emotional, between the 0 to <1 and ≥ 2 groups. Only three subscales (physical function, vitality, and mental health) had differences between the ≥ 1 to < 2 and ≥ 2 voids/night groups. In the MOS Sleep scale, significant differences among the nocturia groups varied among the other subscales.

To assess the effect of nocturia with and without OAB, the ‘no nocturia’ and ‘nocturia’ groups were compared among the controls and OAB cases (Table 3). Importantly, the interaction term of OAB and nocturia was not significant in any model, indicating that the effects of nocturia on HRQoL are independent of those of OAB. While both OAB groups had significant symptom burden and HRQoL impact, the OAB + nocturia group reported significantly higher symptom bother (P = 0.005) and decreased HRQoL in the OAB-q sleep subscale (P < 0.001) than the OAB group with no nocturia. Nocturia without OAB (i.e. controls with nocturia) had in significantly lower (P = 0.04) OAB-q sleep subscale scores. No significant differences were detected among the SF-36 subscales between controls with and without nocturia and OAB cases with and without nocturia. Respondent-rated need-for-care was also examined by nocturia group, with those with > 1 nocturia episode/night reporting a significantly higher need for care than those with ≤ 1 episode/night (all P < 0.05).

Table 3.  Impact of nocturia with and without OAB, controlling for age, gender, and clinical conditions
Mean (sem)
subscale score
ControlsOAB
no nocturia+ nocturiaPno nocturia+ nocturiaP
  • *

    Higher score indicates better HRQL; higher symptom bother scores indicative of greater symptom bother; Scores for the OAB-q and SF-36 are 0–100.

N44649 220160 
OAB-q*
Symptom bother  9.9 (0.8)14.9 (2.5)0.31 31.2 (1.2) 38.9 (1.4)0.005
Coping 95.9 (0.9)96.6 (2.5)0.99 81.5 (1.2) 77.0 (1.4)0.13
Concern 96.9 (0.8)96.3 (2.5)0.99 75.9 (1.4) 75.6 (1.7)0.14
Sleep 91.8 (1.0)82.9 (2.9)0.04 75.9 (1.4) 62.6 (1.7)< 0.001
Social 98.9 (0.5)99.5 (1.6)0.98 92.5 (0.8) 90.7 (0.9)0.52
HRQoL total 95.9 (0.7)94.4 (2.1)0.92 82.0 (1.0) 76.5 (1.2)0.06
SF-36*
Physical function 82.4 (1.2)83.4 (3.6)1.0 72.3 (1.7) 68.8 (2.0)0.61
Role-physical 79.6 (1.7)83.9 (5.1)0.88 68.7 (2.4) 61.6 (2.9)0.31
Bodily pain 74.2 (1.1)74.5 (3.4)1.0 67.4 (1.6) 62.0 (1.9)0.19
General health 70.9 (1.0)67.1 (2.9)0.67 64.6 (1.4) 61.7 (1.7)0.64
Vitality 60.5 (1.0)56.2 (2.8)0.56 52.3 (1.4) 50.8 (1.6)0.92
Social function 86.6 (1.1)87.8 (3.2)0.99 77.2 (1.5) 75.7 (1.8)0.94
Role-emotional 82.2 (1.8)88.8 (5.2)0.70 69.4 (2.5) 65.8 (3.0)0.82
Mental health 75.9 (0.9)74.1 (2.6)0.92 70.0 (1.3) 69.1 (1.5)0.97

As nocturia can affect the number of hours of sleep/night, multivariate regressions were conducted to ascertain the effect of the amount of sleep per night on HRQoL and sleep, in conjunction with OAB symptoms and clinical conditions. The amount of sleep per night was not significant in the symptom bother and coping subscale models, but it was in the sleep, concern and social interaction models. The sleep subscale regression model parameters are shown in Table 4. In each regression model, the urinary variables had the highest F values compared with the other variables in the model, and the greatest association with decreases in HRQoL and increases in symptom bother, except in social interaction, where nocturia was not significant. Importantly, gender and age were not significant in any of the regression models, indicating that neither influenced symptom bother or HRQoL. The variance inflation factor was < 2.1 for all variables in each regression model, indicating no multi-colinearity.

Table 4.  Multivariate regression of the OAB-q Sleep subscale model
CharacteristicParameter estimatesemFP
Age0.000.05 0.020.88
Gender− 0.691.92 0.130.72
Hours sleep/night2.020.5413.8< 0.001
Urinary urge intensity− 1.90.2277.7< 0.001
Times voided/day (frequency)− 0.360.15 5.70.02
Times urinate/night (nocturia)− 5.30.6469.6< 0.001
Incontinence episodes− 0.100.0314.0< 0.001
Parity− 0.420.55 0.60.44
Diabetes− 2.32.45 0.90.34
Chronic heart failure− 2.093.32 0.40.53
History of bladder surgery− 14.22.6728.3< 0.001
History of cancer− 5.42.34 5.340.02
Prostate problems− 7.692.64 8.510.004
Diuretic use− 4.092.01 4.150.04

To further examine sleep, a regression was conducted with the number of hours of sleep/night as the dependent variable and age, gender, clinical conditions, and all urinary symptoms as covariates. The only variables significantly associated with number of hours of sleep/night were age (P < 0.001) and nocturia episodes/night (P = 0.02); no other variables were significant.

DISCUSSION

While nocturia has been shown to be ‘bothersome’, its true effect on the many dimensions of HRQoL has not been adequately assessed [4]. This study is the first to examine the effect of nocturia on HRQoL and sleep incrementally and to find that as little as one void/night is not only ‘bothersome’, but affects HRQoL and sleep. Additional increases in voids/night have further significant effects on symptom bother, sleep and HRQoL. Although nocturia is associated with ageing and, for many individuals, nightly nocturia is ‘normal’, people with ≥ 1 void every night report declines in sleep, increases in symptom bother and a greater need for medical care.

These findings are consistent with previous research that asked overall questions related to the effect of nocturia (e.g. ‘How much of a problem is that for you . . . ?’) with increases in nocturia episodes leading to increases in the number of people for whom nocturia was a problem; however, using a multidimensional assessment of HRQoL provides much greater insight as to ‘how’ nocturia affects HRQoL. When examining nocturia by number of voids/night regardless of case-control status, increases in symptom bother and decreases in sleep are the primary effects, followed by coping and concern; social interaction was largely unaffected by nocturia. When examining nocturia (≥2 voids/night) by case-control status, respondents with OAB reported significantly higher symptom bother and lower HRQoL than the controls.

While it is difficult to compare the findings of the OAB-q against other conditions because of the specificity of the OAB-q to OAB, using population normalised data from the SF-36 [25] provides an insight into the effect of nocturia. For respondents with nocturia of ≥2 per night, the impact on HRQoL was similar to that of Type II diabetes and greater than that of hypertension. These findings are similar to those of Thom [26] when examining the effects of OAB. Respondents with two or more nocturia episodes per night also reported a greater need for care, providing additional support for the effects of nocturia.

Although the number of hours of sleep per night was significant in three of the OAB-q subscale models, the amount of sleep per night did not account for the greatest variance in the models. Certainly, sleep interruptions and deficits diminish HRQoL, but the greatest effect on HRQoL and symptom bother in this study was associated with symptoms of OAB, i.e. urinary urgency, nocturia, frequency and urge incontinence. While age was a significant predictor of nocturia and the amount of sleep per night, it was not associated with any HRQoL subscale. The finding that social interaction was not significantly affected by nocturia, but was significantly associated with the amount of sleep, is inherent in the symptom; nocturia would probably not affect daily social interactions unless it significantly affected sleep quality. In the present community sample this did not appear to be the case.

Given that the prevalence of nocturia varies by definition, the prevalence rates noted in this study are similar to those reported elsewhere. The nearly two-fold increase in nocturia among women in the climacteric period is noteworthy and merits further investigation, given the likely confounding effect of vasomotor instability resulting in night sweats. Prevalence rates of nocturia among patients with OAB have not been previously reported, but the rates of ≈ 67% for 1 void/night and 42% for 2 voids/night appear reasonable given the symptomatic presentation of OAB. The effect of nocturia in OAB is highlighted by the nearly 20% prevalence of 3 voids/night, which seriously compromises sleep, symptom bother and HRQoL. Nocturia with OAB has the greatest impact on sleep and symptoms, which is probably related to urinary urgency, the defining symptom of OAB, which can occur at any time, day or night.

The finding that nocturia affects sleep is certainly not new, nor is the finding that increasing voids/night cause further sleep disruption. However, the standardized assessment using the OAB-q sleep subscale provides a more quantitative assessment of the effects of nocturia. The OAB-q, and in particular the sleep subscale, discriminated well among nocturia groups and incremental increases in voids/night, indicating that it would probably be responsive to change in voids/night [27]. The MOS Sleep Index scale was not as sensitive as the OAB-q sleep subscale, probably because the question phrasing in the OAB-q specifically relates sleep difficulties to bladder problems.

As with all cross-sectional research, this study is limited in its findings. All data were collected by telephone survey and self-administered questionnaires for the case-control study. No clinical data were available to confirm the presence of OAB, but the survey was rigorously and clinically validated before data collection [14]. As with previous nocturia research, the reason for night-time awakening was unknown (i.e. whether the respondent awoke because of the urge to urinate, or for other reasons and decided to urinate). Despite these limitations, this descriptive research provides a valuable insight into the impact of nocturia on HRQoL and sleep.

Nocturia is not a benign symptom. Regardless of how it is defined, the prevalence of nocturia increases with age, affects men and women equally, and significantly compromises sleep, symptom bother and HRQoL. When nocturia occurs in OAB, this impact is further magnified.

ACKNOWLEDGEMENTS

This research was funded by Pharmacia Corporation.

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