Association between urinary sodium-to-potassium ratio and home blood pressure and ambulatory blood pressure: the Ohasama study

Objective: No studies have demonstrated the association between urinary sodium-to-potassium (Na/K) ratio and all out-of-office blood pressure (BP) [home morning and evening BP (self-measured at home), and 24-h, daytime, and night-time ambulatory BP] in the same cohort. We aimed to assess, which type of out-of-office BP is more strongly associated with urinary Na/K ratio in the general population. Methods: This cross-sectional study was conducted in the general population of Ohasama, Japan. Home and ambulatory BP levels were measured, and 24-h urine samples were obtained from 875 participants (men, 25.5%; mean age, 60.1 years). The urinary Na/K ratio in the 24-h urine samples was calculated. Results: The median (interquartile range) urinary Na/K ratio was 4.19 (3.36-5.26). Significant positive trends of home morning, home evening, 24-h, and daytime SBP were observed across quartiles of urinary Na/K ratio (trend P < 0.041; adjusted mean values between Q1 and Q4 of urinary Na/K ratio: 121.0-125.5 mmHg for home morning, 120.1-123.8mmhg for home evening, 121.6-123.4mmHg for 24-h, 127.5-129.5 mmHg for daytime). Urinary Na/K ratio was not significantly associated with office or night-time SBP and nocturnal BP fall (trend P > 0.13). In the model with both home morning or evening SBP and daytime SBP, only home SBP was significantly associated with urinary Na/K ratio (P < 0.048 for home SBP). Conclusion: These findings suggest that urinary Na/K ratio might be more strongly associated with home BP than with 24-h and daytime BP but was not associated with night-time BP.