CAUSES OF NOCTURNAL URINARY FREQUENCY AND REASONS FORITS INCREASE WITH AGE IN HEALTHY OLDER MEN

AKIHIRO KAWAUCHI, YOSHIYUKI TANAKA, JINTETSU SOH, OSAMU UKIMURA,MUNEKADO KOJIMA AND TSUNEHARU MIKI

From the Department of Urology, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kyoto, Japan

ABSTRACT

Purpose: We investigate the causes of nocturnal urinary frequency and reasons for its increasewith age.

Materials and Methods: All voided volumes and times were recorded for 3 days in 188 healthyolder men without prostatic diseases during a mass screening program for prostatic diseases inJapan. Nocturnal urinary frequency for each night was defined as the frequency during sleep notcounting the morning void. Relationships between nocturnal urinary frequency and functionalbladder capacity, nocturnal bladder capacity, nocturnal urinary volume and sleep time wereanalyzed. Age related changes in functional and nocturnal bladder capacity, and nocturnal anddiurnal urinary volume were evaluated.

Results: Multiple regression analysis demonstrated nocturnal bladder capacity and urinaryvolume to be significant independent determinants of nocturnal frequency. In age relatedanalysis nocturnal bladder capacity and diurnal urinary volume decreased with age, whilenocturnal urinary volume did not change.

Conclusions: Nocturnal urinary volume and nocturnal bladder capacity were the significantdeterminants of nocturnal urinary frequency in healthy older men. The increase of nocturnalfrequency with age was thought to be due to a decrease in nocturnal bladder capacity, sinceurinary volume did not change. In older men a decrease in water intake might influence agerelated changes in urinary volume.

KEY WORDS: urination disorders, age factors

Urinary frequency is a common symptom in older peopleand in particular nocturnal urinary frequency is a majorcomplaint at urological outpatient clinics. Although prostaticdiseases are important factors of nocturnal urinary fre-quency in older men, those without such diseases also com-plain of it. Average nocturnal urinary frequency was reportedto be 1.46 times per night in 732 older participants with anormal prostate, as shown on ultrasonograms in a massscreening for prostatic diseases.1 Frequency was more thanonce in 55 to 74-year-old men and more than twice for thoseolder than 75 years. Thus, nocturnal urinary frequency wasa common symptom which increases with age even in oldermen with a normal prostate.

Many factors other than age correlate with this symptom.Nocturnal polyuria and a decrease in bladder capacity werereported to be the most important factors. Asplund andÅberg showed that nocturnal urinary volume was greaterin patients with than those without nocturnal urinary fre-quency.2 Girman et al in a community based study showedthat mean voided volume decreased with age.3 Althoughindividual relationships between nocturnal urinary fre-quency and each of these factors have been reported, to ourknowledge no study has focused only on healthy men with anormal prostate. Moreover, the cause of nocturnal urinaryfrequency in older people is still unclear. We examined diur-nal and nocturnal urinary volume and voided volume inhealthy older men without prostatic diseases to evaluate thecauses of and reason for increasing nocturnal urinary fre-quency with age.

MATERIALS AND METHODS

Since 1975 a mass screening program for prostatic diseasesin community based populations 55 years old or older inJapan has been performed.4 The program comprised digitalrectal examination, transrectal sonography of the prostateand since 1992 serum prostate specific antigen. In Octoberand November 1995 a total of 519 men in 3 rural towns inKyoto Prefecture underwent program mass screening exam-ination. After obtaining informed consent a history of dis-eases and medication was compiled. Examinees were askedto measure all voided volumes passed into a measuring cupfor 3 days, and to void just before bedtime every night andjust after awakening every morning. Urinary volumes, andtimes falling asleep at night and awakening in the morningwere recorded at home on a frequency volume chart duringthe 3 days. Nocturnal urinary frequency for each night wasdefined as the frequency during sleep not counting the morn-ing void.

A total of 320 examinees (62%) returned completed charts.The response rate was nearly compatible with that of previ-ous studies.3, 5, 6 Of the examinees 25 (7.8%) with benignprostatic hyperplasia (BPH) and 2 (0.6%) with prostatic can-cer diagnosed histologically were excluded from study. Thediagnosis of BPH was based on transrectal ultrasonographiccriteria accepted by the Japanese Society of Ultrasonics inMedicine and the Japanese Urological Association.7 Briefly,since the prostate with advancing BPH appears rounder witha greater anteroposterior diameter, the shape is evaluated bythe presumed circle area ratio. A total of 105 examinees(32.8%) who had diabetes mellitus, renal, heart, cerebral,vascular or psychiatric diseases, or who used sleeping pills ordrugs which influenced voiding or diuretic conditions werealso excluded from study. Thus, 188 healthy older respon-

Accepted for publication July 30, 1999.Editor’s Note: This article is the second of 5 published in

this issue for which category 1 CME credits can be earned.Instructions for obtaining credits are given with the ques-tions on pages 288 and 289.

0022-5347/00/1631-0081/0THE JOURNAL OF UROLOGY® Vol. 163, 81–84, January 2000Copyright © 2000 by AMERICAN UROLOGICAL ASSOCIATION, INC.® Printed in U.S.A.

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dents (58.8%) were included in this study. Ages ranged from55 to 59 years in 17 men, 60 to 64 in 45, 65 to 69 in 67, 70 to74 in 35 and 75 to 80 in 24 (average age 67.1).

Patient age, bladder capacity, urinary volume and sleeptime were evaluated as relevant parameters. Since bladdercapacity is different in awake and sleep states,2 it was clas-sified into 2 categories. The largest voided volume in theawake state each day was the functional bladder capacityand the largest voided volume passed when awakened atnight or just after awakening each morning was the noctur-nal bladder capacity. Nocturnal urinary volume for eachnight was defined as the total of the voided volumes whenawakened at night and the morning void. Diurnal urinaryvolume was defined as the total of the voided volumes, notincluding nocturnal urinary volume. All values were aver-aged during the 3 days.

Single and multiple linear regression analyses were per-formed between nocturnal urinary frequency, and age, func-tional and nocturnal bladder capacity, nocturnal urinary vol-ume and sleep time. In addition, age related changes ofnocturnal bladder capacity and urinary volume were ob-served to evaluate the reason for increasing nocturnal fre-quency with age. Age related changes of functional bladdercapacity and diurnal urinary volume were also observed tocompare awake and sleep states. Single and multiple linearregression analyses were performed between age, and func-tional bladder capacity, nocturnal bladder capacity, diurnalurinary volume, nocturnal urinary volume and total dailyurinary volume. In simple linear regression analysis p ,0.05was considered significant. Multiple linear regression anal-ysis was performed by forward stepwise selection. Statisticalanalyses were performed using computer software.

RESULTS

Average nocturnal urinary frequency, functional bladdercapacity, nocturnal bladder capacity, diurnal urinary vol-ume, nocturnal urinary volume and sleep time for the entireseries are shown in table 1. Significant positive linear rela-tionships were noted between nocturnal urinary frequency,and age, nocturnal urinary volume and sleep time (fig. 1).Simple regression analysis demonstrated a significant nega-tive correlation between nocturnal urinary frequency, andfunctional and nocturnal bladder capacity (fig. 2). However,multiple regression analysis demonstrated only nocturnalurinary volume and bladder capacity to be significant inde-pendent determinants of nocturnal frequency (table 2).

In analyses of age related change of bladder capacitiessignificant negative linear relationships were noted betweenage and functional (r 5 20.334, p ,0.0001), as well as noc-turnal (r 5 20.281, p ,0.0001) bladder capacity. In linearanalyses of age related changes diurnal urinary volume de-creased significantly (r 5 20.334, p ,0.0001), while noctur-nal urinary volume did not change (r 5 0.040). Consequently,total daily urinary volume significantly decreased with age(r 5 20.269, p 5 0.0002). Nocturnal urinary frequency, func-tional and nocturnal bladder capacity, and diurnal and noc-turnal urinary volume in the 5 age groups are shown infigures 3 to 5.

DISCUSSION

Recently several investigators have reported the preva-lence of urinary symptoms in many different communities. Inmost series nocturia was the prevalent symptom and in-creased with age.5, 6 This symptom was associated with aconsiderable number of sleep interruptions in older people.The most frequently reported cause of lack of sleep wasnocturia in 1,485 men and women 50 years old or older.8

Nocturia was an important risk factor for falls in ambulatory

TABLE 1. Average nocturnal frequency, functional and nocturnalbladder capacity, diurnal and nocturnal urinary volume, and sleep

time in the entire series

Av. SD

Nocturnal frequency/night 0.88 0.70Functional bladder capacity (ml.) 302 108Nocturnal bladder capacity (ml.) 312 109Diurnal urinary vol. (ml.) 997 375Nocturnal urinary vol. (ml.) 491 188Sleep time (hrs.) 8.5 1.2

FIG. 1. Relationship between nocturnal urinary frequency, andage, nocturnal urinary volume and sleep time.

CAUSES OF NOCTURNAL URINARY FREQUENCY IN HEALTHY OLDER MEN82

elderly persons. Subjects who reported nocturia at least twiceduring the night were at significantly greater risk of falling,and the risk increased in those reporting more than 3 noctu-ria events.9 Thus, nocturia also had a role in other aspects ofthe health and well-being of the elderly.

Although it is evident that prostatic diseases can be thecause of nocturia, average nocturnal frequency was morethan once per night even in men with a normal prostate.1, 10

Changes in kidney and bladder function with age make noc-turnal voiding much more common among older people.11

However, many other factors, such as diseases or medication,are associated with this symptom and, therefore, 132 men(41%) were excluded from study so we could focus on therelationship between changes in kidney and bladder functionwith age and nocturia.

In simple regression analysis nocturnal urinary frequencysignificantly increased with age as reported previously.

Functional and nocturnal bladder capacity, nocturnal uri-nary volume and sleep time also correlated with nocturnalfrequency. However, in multiple regression analysis only noc-turnal urinary volume and bladder capacity proved to beindependent determinants. It is particularly noteworthy thatage was not an independent determinant of nocturnal fre-quency. Therefore, we analyzed the age related change ofnocturnal urinary volume and nocturnal bladder capacity.Nocturnal bladder capacity decreased but nocturnal urinaryvolume did not change with age. Based on these results, theaging change of nocturnal frequency was thought to be due tothe change of nocturnal bladder capacity and not that of

FIG. 2. Relationship between nocturnal urinary frequency, andfunctional and nocturnal bladder capacity.

FIG. 3. Age related changes in nocturnal frequency

FIG. 4. Age related changes in bladder capacity. FBC, functionalbladder capacity. NBC, nocturnal bladder capacity.

TABLE 2. Simple and multiple regression analyses of nocturnal urinary frequency as a function of age, bladder capacities, nocturnalurinary volume and sleep time

Simple Regression Analysis Multiple Regression Analysis

CorrelationCoefficient p Value Correlation

CoefficientAdjusted

R2 p Value

Age 0.284 ,0.0001 Not significantFunctional bladder capacity 20.168 0.0214 Not significantNocturnal bladder capacity 20.302 ,0.0001 0.795 0.629 ,0.0001Nocturnal urinary vol. 0.525 ,0.0001 ,0.0001Sleep time 0.193 0.0079 Not significant

CAUSES OF NOCTURNAL URINARY FREQUENCY IN HEALTHY OLDER MEN 83

nocturnal urinary volume. This finding was contrary to thoseof previous studies in which increased nocturnal urinaryvolume was reported to be a cause of the aging change ofnocturnal frequency.12 Kirkland et al compared 24-hour uri-nary volume in 24 young (mean age 29.2 years) and 21elderly (mean age 66.5) healthy subjects.13 Urinary volumesin the 2 groups were similar, while the ratios of night-to-dayurinary volume were greater in elderly subjects. The reducedday-to-night ratios of excretion might have been caused by adelay in peak water and electrolyte excretion, greater vari-ability in the timing of these peaks or reduction in the am-plitudes of the rhythms of each subject. Kirkland et al con-cluded that reduced day-to-night ratios might be partlyresponsible for complaints of nocturia and sleep disturbance inelderly people. Our ratios of night-to-day urinary volume simi-larly increased with age, since nocturnal urinary volume did notchange and diurnal urinary volume decreased. These findingshave been explained by the reduction in glomerular filtrationwith aging,14 decrease in urine concentration ability,15 alteredcardiac function or changes in circadian rhythms which maycause the increase in nocturnal urinary volume. However, thedecrease in total urinary volume with age is not explicable onlyby these factors. Moreover, unchanged nocturnal urinary vol-ume with age was also an interesting finding. Although we werenot able to determine the causes since water intake was notevaluated, a possible explanation was that diurnal urinary vol-ume decreased with age as older people drank less water. Bythe aging changes in many organs and their functions thenight-to-day ratios of urinary volume increased with age. Con-sequently, diurnal urinary volume decreased and nocturnalurinary volume did not change. Phillips et al reported that after24 hours of water deprivation healthy older men were lessthirsty and drank less, so that plasma and urine were notdiluted to pre-deprivation levels.16 From this viewpoint healthyolder people might drink less water than younger people, sincethey are less thirsty. On the other hand, they might restrictwater intake because they are bothered by nocturia which in-creases with age. Causes of the decrease in nocturnal bladdercapacity with age were unclear. The accompanying decrease infunctional bladder capacity might cause reservoir function to

become less efficient with age. Residual urine after voiding wasreported to increase with age,11,17 and so functional capacity ofthe bladder might decrease with age.

CONCLUSIONS

Nocturnal urinary volume and nocturnal bladder capacitywere the significant determinants of nocturnal urinary fre-quency in healthy older men. Increased nocturnal frequencywith age was thought to be due to a decrease in nocturnalbladder capacity, since nocturnal urinary volume did notchange. In older men a decrease in water intake might influ-ence the age related changes in urinary volume.

REFERENCES

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2. Asplund, R. and Åberg, H. E.: Micturition habits of older people.Voiding frequency and urine volumes. Scand J Urol Nephrol,26: 345, 1992.

3. Girman, C. J., Panser, L. A., Chute, C. G. et al.: Natural historyof prostatism: urinary flow rates in a community-based study.J Urol, 150: 887, 1993.

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8. Middelkoop, H. A., Smilde-van den Doel, D. A., Neven, A. K. etal: Subjective sleep characteristics of 1,485 males and femalesaged 50–93: effects of sex and age, and factors related toself-evaluated quality of sleep. J Gerontol A Biol Sci Med Sci,51: M108, 1996.

9. Stewart, R. B., Moore, M. T., May, F. E. et al: Nocturia: A riskfactor for falls in the elderly. J Am Geriatr Soc, 40: 1217, 1992.

10. Kojima, M., Naya, Y., Inoue, W. et al.: The American UrologicalAssociation symptom index for benign prostatic hyperplasia asa function of age, volume and ultrasonic appearance of theprostate. J Urol, 157: 2160, 1997.

11. Resnick, N. M. and Yalla, S. V.: Geriatric incontinence andvoiding dysfunction. In: Campbell’s Urology, 7th ed. Edited byP. C. Walsh, A. B. Retik, E. D. Vaughan, Jr. et al. Philadelphia:W. B. Saunders, vol. 1, chapt. 31, pp. 1044–1058, 1998.

12. Barker, J. C. and Mitteness, L. S.: Nocturia in the elderly.Gerontologist, 28: 99, 1988.

13. Kirkland, J. L., Lye, M., Levy, D. W. et al: Patterns of urine flowand electrolyte excretion in healthy elderly people. Br Med J,287: 1665, 1983.

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16. Phillips, P. A., Rolls, B. J., Ledingham, J. G. et al: Reduced thirstafter water deprivation in healthy elderly men. N Engl J Med,311: 753, 1984.

17. Diokno, A. C., Brown, M. B., Brock, B. M. et al: Clinical andcystometric characteristics of continent and incontinent non-institutionalized elderly. J Urol, 140: 567, 1988.

FIG. 5. Age related changes in urinary volume. DUV, diurnal uri-nary volume. NUV, nocturnal urinary volume.

CAUSES OF NOCTURNAL URINARY FREQUENCY IN HEALTHY OLDER MEN84