Hypothesis / aims of study
Insomnia is not only prevalent in the elderly but also increases the incidence of falls and fractures. Worse, the risk is exacerbated by the sedative/hypnotic drugs used to treat insomnia. At the same time, nocturia is one of the most common causes of insomnia in the elderly. Clinically discerning whether nocturia is a cause or consequence of insomnia is difficult, especially in older adults in whom comorbidity and polypharmacy are common. Yet the role of nocturia in the etiology and management of insomnia among the elderly remains understudied as has the potential contribution of bladder dysfunction. This is particularly true for older adults with insomnia who lack lower urinary tract symptoms (LUTS). Hence we examined the factors associated with nocturia in healthy older women without LUTS as well as their impact on sleep.
Study design, materials and methods
We examined baseline participant data derived from two prospective studies of healthy and continent older women. One study examined normative voiding patterns in healthy older adults, and the other assessed brain responses to bladder filling in a similar group. All participants had completed a comprehensive baseline evaluation which included complete medical and voiding history, careful questioning about the presence of urgency, urinary incontinence, and nocturia, and a detailed physical examination. All participants also underwent comprehensive videourodynamic testing to exclude involuntary bladder contractions (detrusor overactivity) and other significant bladder dysfunction such as impaired compliance, outlet obstruction, and sphincter dysfunction.
The 3-day bladder diary completed by participants at baseline was used in this secondary analysis. Because intake had not been recorded, we used the 24-hour excretion volumes as a proxy for fluid intake. The first void after waking for the day was included in the nocturnal urine volume (NUV). The nocturnal polyuria index (NPi) was calculated by dividing NUV by 24-hour urine volume; nocturnal polyuria (NP) was defined by an NPi > 33%. Time in bed was defined as the interval between going to bed with the intent of sleeping and getting up for the day, and was obtained using times recorded in the bladder diary. We used the sleep restlessness question of the Center for Epidemiologic Studies Depression Scale (CES-D) as a proxy measure of sleep quality.
Since the analysis was performed on participant data from two studies, to standardize our cohort, we included only participants who met the following definition of “normal”: 1) denied precipitant urgency and incontinence on both detailed questioning and questionnaire, 2) had normal results on detailed videourodynamic testing, 3) had adequate but not excessive fluid intake (i.e. 1200- 2500 ml urine output/24 hours by 3-day voiding diary), and 4) had normal daytime frequency (≤7 voids).
A total of 39 subjects met our definition of “normal”. Age ranged from 60-87. More than half of these participants had nocturia (54%) which was attributable to NP in 90% of them.
Although daytime frequency was similar between those with and without nocturia, women with nocturia had significantly smaller functional bladder capacity (484±157 vs. 608±167 ml, p=.02), and their mean voided volume while awake was 41% less compared to women without nocturia. (Table 1)
Additionally, subjects with nocturia spent nearly an hour more in bed than those without nocturia; 60% spent >8 hours in bed per night. However, NP was not only related to time in bed at night but also to the duration of uninterrupted sleep before the first awakening to void; those with NP had an hour less of uninterrupted sleep before the first awakening to void than did those without NP (182±100 vs. 250±60 minutes, p=.03). Participants with a shorter duration of first uninterrupted sleep reported worse sleep quality and had a higher NPi although time in bed was not significantly different. (Figure 1)
Interpretation of results
Nocturia is extremely common among older women, even those without LUTS. Two factors contributed independently to nocturia: 1) a larger proportion of 24-hour urine output at night (43.4±7.4 vs. 25.4±5.5%. p=<.001) and 2) smaller bladder capacity (484±157 vs. 608±167 ml, p=.02). In addition, sleep quality is adversely impacted not only by the frequency of nighttime awakenings, but also by the duration of uninterrupted sleep before first awakening to void.