Epidemiology of Nocturia
Acta Universitatis Tamperensis No. 1504


By Kari Tikkinen
June 2010
Tampere University Press
Distributed By Coronet Books
ISBN: 9789514480195
226 pages
$77.50 Paper original

Background: Nocturia (waking at night to urinate) is one of the most common and bothersome lower urinary tract symptoms. Nocturia is associated with impaired quality of life, and increased morbidity and even mortality. Given the poor state of knowledge about nocturia, treatment is frequently inadequte. Objectives: To describe the prevalence of nocturia and overactive bladder by age and sex, formulate a clinically meaningful definition for nocturia based on bother and quality of life impact of nocturia, and identify risk factors (conditions, medications, lifestyle and female reproductive factors) of nocturia and evaluate their impact at population level.

Material and methods: The Finnish National Nocturia and Overactive Bladder (FINNO) Study was initiated in early 2003. In 2003-2004, questionnaires were mailed to 6,000 subjects (aged 18-79 years) randomly identified from the Finnish Population Register Centre.

Questionnaires contained items on medical conditions, medications, lifestyle, sociodemographic and reproductive factors, health-related quality of life (HRQL), urinary symptoms, and sleep disorders using validated instruments. European standard population and Finnish population structure were used for agestandardisation.

HRQL and bother from nocturia were examined in relation to self-reported nocturia frequency (using the American Urological Association Symptom Index and the Danish Prostatic Symptom Score). Bother from nocturia was assessed on a four-point scale (none-small-moderate-major). HRQL was measured by the 15D instrument which can be used as a profile measure or for a single index score (15D Score). 15D Score is a 0-1 scale with a minimum clinically important difference of 0.03. To assess risk factors for nocturia, factors associated with nocturia in age-adjusted analyses were entered into a multivariate model. Backward elimination was used to select variables for the final model with adjustment for confounding. Furthermore, propensity scores were used for adjustment of confounding in some analyses. To assess the population-level impact, population fraction in the exposed, attributable fraction and attributable number were calculated. In addition, positive predictive value and sensitivity were calculated for the identified risk factors. Results: Of the 6,000 subjects, 3,727 participants (1,725 men and 2,002 women) returned the questionnaires. The response proportion was approximately 32% after the 1st round, 50% after the 2nd round, and finally 62.4% after the 3rd round. After age-standardisation (to the Finnish population structure), 26%, 9%, 2% and 1% of men and 32%, 10%, 2% and 1% of women reported one, two, three or at least four void(s)/night. Nocturia was more common among women at younger ages, but the sex differences disappeared by middle age. In the elderly, nocturia was more frequent among men. Nocturia increased at a constant rate with age. It increased twice as rapidly in men than women. Degree of bother increased with nocturia frequency (p<0.01). The most commonly reported degree of bother for those with 1, 2 and 3 nightly voids was no bother, “small” bother and “moderate” bother respectively. The mean age-adjusted 15D Score for men (women) without nocturia was 0.953 (0.950), 0.925 (0.927) with 1 void per night, 0.898 (0.890) with 2 voids per night, and 0.833 (0.840) with ?3 voids per night. Nocturia was associated with statistically significant decrease on 15D Score and all dimensions of 15D except eating.

While numerous risk factors for nocturia were identified, none affected ?50% of nocturia cases in both sexes. The factors with the greatest impact at the population level were overactive bladder/urinary urgency (attributable number/1,000 subjects, AN 24), benign prostatic hyperplasia (AN 19) and snoring (AN 16) for men; and overweight and obesity (AN 40), overactive bladder (AN 24) and snoring (AN 17) for women. Moreover, risk factors included prostate cancer and antidepressant use for men; coronary artery disease and diabetes for women; and restless legs syndrome and obesity for both sexes. Among women, parity, postpartum and postmenopausal periods were associated with increased nocturia (but not with overactive bladder).

The prevalence of overactive bladder was 6.5% for men and 9.3% for women, i.e. approximately half of that reported in earlier studies. Possible overestimation in the earlier literature could be due to numerous methodological reasons. Among subjects with overactive bladder, nocturia (defined as at least two voids per night) was reported by 56% of men and 40% of women. However, only 31% of subjects of both sexes with nocturia reported overactive bladder.

Limitations: The cross-sectional study design limits conclusions about causality. Although the response proportion was high, approximately one third of those contacted did not participate in the study. Regarding impact measures (which generally are context specific), these results from the Finnish population may not be directly generalisable to other ethnicities.

Conclusions: In the population-representative FINNO Study, approximately 28% of subjects reported one, 10% two, 2% three, and 1% four or more void(s)/night. Nocturia was more common among young women than young men, but more common among men than women in old age. Most subjects reported small bother from nocturia with two nocturia episodes, and moderate bother only from three nocturia episodes. Two nocturia episodes impaired HRQL compared to those with no nocturia. Numerous risk factors for nocturia were identified. However, none of them accounted for ?50% of the nocturia cases, highlighting its multifactorial etiology. The risk factors differed slightly by sex. At population level, overactive bladder, benign prostatic hyperplasia and snoring for men, and overweight/obesity, overactive bladder and snoring for women accounted for the largest proportion of nocturia. Among women, parity, postpartum year and postmenopausal period were associated with increased nocturia. Overall, the lower urinary tract, but also beyond it, should be considered when examining and treating nocturia.

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