Intraindividual correlations between nocturnal urination frequency and sleep blood pressure: the Nagahama Study

Nocturnal urination frequency is associated with sleep blood pressure (BP). However, it was uncertain to what extent the sleep BP increases within individuals with each increase in the number of nocturnal urination. We calculated intraindividual differences in sleep BP between nights with different urination frequencies to clarify their relationship. We enrolled 2418 community residents (mean age, 61.1 years). Participants wore a cuff on the upper arm when sleeping that automatically measured BP at fixed times during a 1-week period. The frequency of nocturnal urination was recorded in a sleep diary by the study participants. Sleep systolic BP increased with increased nocturnal urination frequency (0 time vs. 1 time, Δ2.1 mmHg, P < 0.001; 1 time vs. 2 times, Δ1.8 mmHg, P < 0.001; 2 times vs. ≥3 times, Δ1.4 mmHg, P = 0.012), and a similar association was observed for sleep diastolic BP. These associations were independent of age, the use of antihypertensive drugs reduced renal function, and the presence of sleep-disordered breathing. Sleep BP in participants who experienced nocturnal urination 0, 1, and 2 times during the 1-week measurement period showed a linear increase with the frequency of urination (0 time vs. 2 times: systolic BP, Δ4.7 mmHg; diastolic BP, Δ3.1 mmHg; P < 0.001). There was an intraindividual correlation between nocturnal urination frequency and sleep BP. These correlations were independent of baseline BP and participants' clinical backgrounds. Nocturnal urination frequency may be an indicator of individuals who require detailed ambulatory BP measurement.