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 +/- 1-20/11 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 BP by 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. Clin J Am Soc Nephrol 7: 315-322, 2012. doi; 10.2215/CJN.02060311