Association of urinary sodium-to-potassium ratio with obesity in a multiethnic cohort

Abstract

Background: Previous studies that reported an association of dietary Na+ intake with metabolic syndrome were limited by the use of imprecise measures of obesity, Na+ intake, or exclusion of multiethnic populations. The effect of dietary K+ intake on obesity is less well described. Objective: We hypothesized that high dietary Na + and low K+, based on the ratio of urinary Na+ to K+ (U[Na+]/[K+]) in a first-void morning urinary sample, is independently associated with total body fat. Design: In a prospective population-based cohort, 2782 participants in the community-dwelling, probability-sampled, multiethnic Dallas Heart Study were analyzed. The primary outcome established a priori was total-body percentage fat (TBPF) measured by dual-energy X-ray absorptiometry. The main predictor was U[Na+]/[K+]. Robust linear regression was used to explore an independent association between U[Na+]/[K+] and TBPF. The analyses were stratified by sex and race after their effect modifications were analyzed. Results: Of the cohort, 55.4% were female, 49.8% African American, 30.8% white, 17.2% Hispanic, and 2.2% other races. The mean (±SD) age was 44 ± 10 y, BMI (in kg/m2) was 30 ± 7, TBPF was 32 ± 10%, and U[Na+]/[K+] was 4.2 ± 2.6; 12% had diabetes. In the unadjusted and adjusted models, TBPF increased by 0.75 (95% CI: 0.25, 1.25) and 0.43 (0.15, 0.72), respectively (P = 0.003 for both), for every 3-unit increase in U[Na+]/[K+]. A statistically significant interaction was found between race and U[Na +]/[K+], so that the non-African American races had a higher TBPF than did the African Americans per unit increase in U[Na +]/[K+] (P-interaction < 0.0001 for both). No interaction was found between sex and U[Na+]/[K+]. Conclusions: The ratio of dietary Na+ to K+ intake may be independently associated with TBPF, and this association may be more pronounced in non-African Americans. Future studies should explore whether easily measured spot U[Na+]/[K+] can be used to monitor dietary patterns and guide strategies for obesity management. © 2014 American Society for Nutrition.