PS-C07-5: ASSOCIATION OF OVERNIGHT URINARY INDICATORS AND BMI WITH NIGHT TIME AND DAYTIME BLOOD PRESSURE IN ELDERLY

Abstract

Reportedly, the mean nighttime blood pressure (BP) is the sensitive predictor of cardiovascular diseases and the associated mortality. In this study, we investigated the effect of overnight urinary indicators (levels of sodium, potassium, and sodium to potassium ratio) on daytime and nighttime BP. A total of 108 volunteers (56 males, 52 females) aged between 51 and 76 years (mean age: 65.7 ± 4.9 years) who were not taking any antihypertensive medication participated in the study. Their 24-hour (24-h) BP was measured every 30 minutes with an ambulatory BP monitoring, four times (spring, summer, autumn, and winter) in a year. Overnight urine samples (after the last urination before sleeping and until the first urination on waking up the next day) were easily collected at home using a proportional urine-sampling device, Urine mate P. The ion electrode method was used to measure the sodium and potassium levels excreted in urine. The average values of daytime and nighttime BP were calculated. Multiple regression and simple linear regression analyses were used to evaluate the association of daytime and nighttime BP with the above-mentioned overnight urinary indicators, age, sex, and BMI. There were a total of 353 participants over the four seasons. The average values of daytime SBP and DBP were 130.4 ± 20.2 and 83.4 ± 12.7 mmHg, respectively; nighttime SBP and DBP were 113.7 ± 15.8 and 69.8 ± 9.4 mmHg, respectively. Multiple regression analysis of the six factors revealed that none of the variables were linearly combined. For nighttime SBP, the adjusted standard regression coefficients was 0.219 (p < 0.01) for the urinary Na/K ratio, 0.142 (p < 0.05) for age, and 0.119 (p < 0.05) for BMI. However, for daytime SBP it was 0.124 (p < .0.05) for age, -0.232(p < 0.01) for sex, and 0.175 (p < 0.01) for BMI. Simple linear regular regression analysis showed that nighttime SBP was significantly related to the Na/K ratio, Na, age, and BMI; daytime SBP to sex, BMI, and age. This demonstrates that overnight urinary Na/K ratio has greater effect on nighttime SBP than BMI and age; therefore, its optimal level should be achieved to control nighttime SBP in the elderly.