Urinary sodium and potassium excretions in young adulthood and blood pressure by middle age: the Coronary Artery Risk Development in Young Adults (CARDIA) Study

OBJECTIVE: Data are sparse regarding the impact of sodium and potassium intakes on serial blood pressure (BP) levels during long-term follow-up. METHODS: Among 1007 Coronary Artery Risk Development in Young Adults participants (mean age, 30.2 years; 53% blacks; 57% women) who had at least two 24-h urine samples collected at year 5 (Y5) examination, we assessed associations of urinary sodium and potassium excretions with BP trends and incident hypertension in the subsequent 25 years. Participants were classified by sex-specific medians for averaged 24-h urinary excretions: lower sodium and higher potassium (Na-Lo-K-Hi); higher sodium and lower potassium (Na-Hi-K-Lo); and others. RESULTS: In the adjusted generalized estimating equation model, SBP and DBP greatly increased in the Na-Hi-K-Lo group (n = 185) compared with the Na-Lo-K-Hi group (n = 185), with statistically significant BP differences at Y20, Y25, and Y30 (mean SBP, 3.93, 4.94, and 4.88 mmHg, respectively; and mean DBP, 4.70, 4.95, and 4.59 mmHg, respectively). During 25-year follow-up, among 926 participants without prevalent hypertension by Y5, 381 (41.1%) developed hypertension. In the adjusted Cox proportional hazards model, the Na-Hi-K-Lo group had hazard ratio (95% confidence interval), 1.45 (1.00-2.10) for incident hypertension compared with the Na-Lo-K-Hi group. The association with incident hypertension was predominant in blacks and white women (race--sex interaction, P = 0.03). Sodium-to-potassium ratio and sodium excretion were positively, whereas potassium excretion was inversely, associated with incident hypertension (all P trend <0.05). CONCLUSION: Our findings highlight the importance of dietary sodium reduction and higher potassium intake for hypertension prevention among young adults.