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Independent Associations Between Nocturia and Nighttime Blood Pressure/Dipping in Elderly Individuals: The HEIJO-KYO Cohort

K. Obayashi, K. Saeki, and N. Kurumatani

Journal of the American Geriatrics Society, Volume 63, Issue 4, 1 April 2015, Pages 733-738

Commented by Prof. Antonella Giannantoni:
Previous epidemiological studies have shown that nocturia (≥ 2 voids per night) occurs in more than 20% of the general elderly population. Cardiovascular and all-cause mortality has been detected in men and women affected by nocturia although the mechanisms underlying this association remain obscure. In the present article, the authors investigate the relationship between nocturia and ambulatory nighttime bladder pressure as well as dipping in a large-scale general elderly population in Japan. 867 community-dwelling elderly individuals (mean age 72.1 ± 7.1 years; 429 males and 438 females) completed a sleep diary, which included nocturnal void frequency, and underwent ambulatory nighttime bladder pressure monitoring with a validated ambulatory recorder.

Nocturnal void frequency was measured for one night; the mean values of two days’ data for daytime and nighttime systolic BP (SBP) and diastolic BP (DBP) measurements were used as parameters for ambulatory bladder pressure. For these patients, age, sex, BMI, current smoking status, alcohol consumption, hypertension, antihypertensive drug use, diabetes mellitus, sleep efficiency, endogenous melatonin levels, serum asymmetric dimethylarginine, estimated glomerular filtration rate, bedtime, length of time in bed as well as daytime and nighttime physical activity were compared with nocturnal void frequency. Averages of two consecutive days were used for the analysis of ambulatory blood pressure.

The authors found that elderly individuals with two or more nocturnal voids had significantly higher nighttime BP than those with no nocturnal voids. More frequent nocturnal voiding was significantly associated with older age, male sex, greater BMI, serum asymmetric dimethylarginine, nighttime physical activity, hypertension, calcium channel blocker use and diabetes mellitus. The authors hypothesized that several mechanisms may be the cause of higher nighttime bladder pressure: low nocturnal vasopressin and natriuretic peptide secretion, sleep architecture disturbances, disorders in melatonin secretion – all these may play a role in elderly individuals affected by nocturia.

What seems really important in the present article is the large sample size which allows to make conclusions independently of several confounding factors such as age, sex, metabolic abnormalities, physical activity and circadian rhythm parameters. In addition, the paper indicates future directions in order to exactly explore the mechanisms underlying nocturia in elderly people. 

Abstract
 

Objectives

To evaluate the association between nocturnal void frequency and ambulatory blood pressure (BP).

Design

Cross-sectional.

Setting

Nara, Japan.

Participants

Community-based elderly individuals (mean age 72.1, N = 867).

Measurements

Nocturnal void frequency and ambulatory BP.

Results

Two hundred twenty-four participants had no nocturnal void, 384 had one nocturnal void, and 259 had two or more nocturnal voids. Univariate comparisons showed that more-frequent nocturnal voiding was significantly associated with higher nighttime systolic BP (SBP) and lower dipping (nocturnal voids: ≥2, nighttime SBP 121.1 mmHg, dipping 11.8% vs 0, nighttime SBP 111.5 mmHg, dipping 15.8%,P < .001). Multivariate models revealed that two or more nocturnal voids was significantly associated with higher nighttime SBP and lower dipping than no nocturnal voids (adjusted mean difference for nighttime SBP (nocturnal voids ≥2 minus 0): 6.3 mmHg, 95% confidence interval (CI) = 2.6 to 10.1 mmHg, P < .001; adjusted mean difference for dipping (nocturnal voids ≥2 minus 0): −2.8%, 95% CI = −4.9% to −0.7%, P = .005) and that the associations were independent of potential confounding factors such as age, sex, body mass index, smoking status, antihypertensive use, diabetes mellitus, renal function, asymmetric dimethylarginine, bedtime, length of time in bed, daytime and nighttime physical activity, endogenous melatonin levels, and bedroom light levels. In contrast, one void per night was not significantly associated with nighttime SBP and dipping.

Conclusion

Nocturia is significantly associated with nighttime SBP and dipping in the general elderly population, independent of several confounding factors such as age, sex, metabolic abnormalities, physical activity, and circadian rhythm parameters.