Association of Urinary Sodium/Potassium Ratio with Blood Pressure: Sex and Racial Differences

Background and objectives Previous studies reporting an association between high BP and high sodium and low potassium intake or urinary sodium/potassium ratio (U[Na ⁺]/[K ⁺]) primarily included white men and did not control for cardiovascular risk factors. Design, setting, participants, & measurements This cross-sectional study investigated the association of U[Na ⁺]/ [K ⁺] with BP in 3303 participants using robust linear regression. Results Mean age was 43±10 years, 56% of participants were women, and 52% were African American. BP was higher in African Americans than in non-African Americans, 131/81±20/11 versus 120/76±16/9 mmHg (P<0.001). Mean U[Na ⁺]/[K ⁺] was 4.4±3.0 in African Americans and 4.1±2.5 in non-African Americans (P=0.002), with medians (interquartile ranges) of 3.7 (3.2) and 3.6 (2.8). Systolic BP increased by 1.6 mmHg (95% confidence interval, 1.0, 2.2) and diastolic BPby 1.0 mmHg (95% confidence interval, 0.6,1.4) for each 3-unit increase in U[Na ⁺]/[K ⁺] (P<0.001 for both). This association remained significant after adjusting for diabetes mellitus, smoking, body mass index, total cholesterol, GFR, and urine albumin/creatinine ratio. There was no interaction between African-American race and U[Na ⁺]/[K ⁺], but for any given value of U[Na ⁺]/[K ⁺], both systolic BP and diastolic BP were higher in African Americans than in non-African Americans. The diastolic BP increase was higher in men than in women per 3-unit increase in U[Na ⁺]/[K ⁺] (1.6 versus 0.9 mmHg, interaction P=0.03). Conclusions Dietary Na ⁺ excess and K ⁺ deficiency may play an important role in the pathogenesis of hypertension independent of cardiovascular risk factors. This association may be more pronounced in men than in women.