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/m(2)) 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.

FIGURE 1.

Derivation of study sample. DXA, dual-energy X-ray absorptiometry.

FIGURE 2.

Linear regression of U[Na⁺]/[K⁺] on TBPF and race interactions, adjusted for age, sex, diabetes mellitus, systolic blood pressure, diastolic blood pressure, and serum glucose and triglyceride concentrations (covariates from model 2). Values are plotted at the mean levels of the covariates. Lines denoted by different letters have a significantly different slope (P-interaction < 0.10) from that of the referent category of African Americans. TBPF, total-body percentage fat; U[Na⁺]/[K⁺], ratio of urinary Na⁺ to K⁺.