No prior studies have evaluated the prevalence of nocturnal polyuria in both men and women. NP is a cause of nocturia where excess urine production occurs during sleep. This large epidemiologic study evaluated the prevalence and burden of NP (The EpiNP Study) among a United States (US) population-representative sample of men and women ≥30 years using alternative definitions for calculating NP.

The EpiNP study was designed to examine the prevalence and burden of NP in the US. Participants were recruited via an online panel (YouGov). After providing informed consent, participants completed the baseline EpiNP survey online (consisting of the Lower Urinary Tract Symptoms (LUTS) Tool, comorbidities, and measures of burden and health-related quality of life). 
All respondents who reported ≥ 2 voids/night on the LUTS Tool and a random sample of 100 respondents each reporting 0 or 1 void/night were invited to participate in the bladder diary portion of the study. If a respondent was selected and agreed to complete the bladder diary portion, the respondent was asked to provide electronic consent to participate in this study phase, and was sent instructional materials, urine collection containers, tape measure, and asked to complete a web-based bladder diary for three consecutive days and the first void of the fourth day.
Two frequently utilized definitions for calculating nocturnal polyuria were used: 1) calculating the proportion of urine production that occurred during sleeping hours, using the Nocturnal Polyuria Index (NPI33) threshold of >0.33 [1]; and 2) nocturnal urine production of >90 mL/h (NUP90) [2,3]. Raw prevalence rates and extrapolations to the US general population were calculated based on the completed bladder diaries using data from participants who completed the bladder diary for all three days. Prevalence rates were calculated for the following subgroups by sex and age: Nocturnal Polyuria Syndrome (NPS, defined as NP in the absence of other causes), NP with symptoms suggestive of overactive bladder (NPOAB), NP with symptoms suggestive of bladder outlet obstruction (NPBOO; men only), NP due to other comorbidities (NPCom; diabetes, hypertension, heart disease, sleep apnea), and no NP (did not meet NUP90 or NPI33). Descriptive statistics, including mean/standard deviation, or frequency/percentage were used to evaluate responses on the bladder diary variables by subgroups where appropriate. The study received institutional review board (IRB) approval from Ethical & Independent Review Services (Independence, Missouri; E&I study number: 19089-01; NCT: 04125186).

A total of 10,190 participants completed the baseline survey (4,900 men/5,290 women); mean age (range) was 54.4 (30-95) years. Overall, 3,339 reported ≥2 nocturia voids and were invited to complete the bladder diary; another 614 participants reported 0 or 1 void per night and were randomized to participate. Of those invited, 1,766 participants (718 men/1,048 women) completed the bladder diary for 3 days and were included in the analysis sample. Overall extrapolated NP prevalence using NPI33 was 39.1% for men and 49.9% for women; when using NUP90, NP prevalence was 31.6% for men and 25.7% for women. Descriptive statistics for the demographic and bladder diary variables by NP definition and NP groups are found in the Table below.

When comparing NP definitions, the number of participants who had NPS was twice as high when using NPI33 versus NUP90 for both men (NPI33 n=34 versus NUP90 n=17) and women (NPI33 n=99 versus NUP90 n=44); prevalence of NPS was higher in women. When using either definition of NP, mean age was lowest for the NPS group versus all other NP groups for both men and women. The average number of nighttime urinations was similar between NP definitions; mean values were greatest for the NPOAB and NPBOO groups in men and NPOAB and NPCom in women. For both sexes and all NP groups (except the No NP group), the average max daytime, nighttime, and first undisturbed sleep period (FUSP) volume was consistently greater when using NUP90. Conversely, the time to first FUSP was greater for all NP groups/sexes when using NPI33. A rating of bother greater than “somewhat” due to nighttime urinations as measured by the LUTS Tool was greater in the NPBOO group for men and NPOAB group in women when measured by either definition of NP.

This study is the first population-based prevalence study of NP that has studied both men and women. Overall NP is highly prevalent in the US for both sexes. Prevalence rates differ depending on which definition of NP is utilized, with a greater number of individuals defined as having NP when NPI33 is utilized. NPS was more common in the younger cohort of both sexes, while with increasing age NP with symptoms of other urological or medical causes became more prevalent.

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van Doorn B, Blanker MH, Kok ET, et al. Prevalence, incidence, and resolution of nocturnal polyuria in a longitudinal community-based study in older men: the Krimpen study. Eur Urol. 2013;63(3):542-547. 10.1016/j.eururo.2012.10.004.
Blanker MH, Bernsen RM, Bosch JL, et al. Relation between nocturnal voiding frequency and nocturnal urine production in older men: a population-based study. Urology. 2002;60(4):612-616. 10.1016/s0090-4295(02)01818-6.