Associations of urinary and dietary sodium-to-potassium ratios with albuminuria in community-dwelling Japanese adults: a cross-sectional study

Introduction: The urinary sodium-to-potassium ratio is an indicator of dietary sodium intake and has been associated with reduced kidney function. However, less is known about its association with albuminuria, the other key component of chronic kidney disease, in the community-dwelling adult population. We examined the association of the spot urinary sodium-to-potassium ratio with albuminuria and compared spot urinary and dietary sodium-to-potassium ratios. Methods: We quantified the association of the urinary sodium-to-potassium ratio with albuminuria in 6,274 Japanese adults (age, 40–97 years; 50.9% women) based on spot urine samples. We performed linear and logistic regression modeling to account for potential confounders. Elevated albuminuria was defined as a spot urinary albumin-to-creatinine ratio (ACR) ≥ 30 mg/g. We secondarily evaluated the dietary sodium-to-potassium ratio based on a food-frequency questionnaire. Results: The median spot urinary and dietary sodium-to-potassium ratios were 2.70 (interquartile interval, 1.87–3.83) and 1.50 (1.21–1.84), respectively. The median ACR was 11.0 (6.0–24.0) mg/g. In a multivariable linear regression model, the spot urinary sodium-to-potassium ratio (per increment) was significantly associated with the natural logarithm of the ACR (regression coefficient, 0.023 [95% confidence interval [95% CI], 0.007–0.038]). This result was consistent in a multivariable logistic regression model (adjusted odds ratio, 1.08 [95% CI, 1.04–1.12]). The corresponding estimates for the dietary sodium-to-potassium ratio were 0.139 (95% CI, 0.087–0.191) and 1.28 (95% CI, 1.14–1.45), respectively. Conclusions: Both spot urinary and dietary sodium-to-potassium ratios were associated with elevated albuminuria in community-dwelling Japanese adults. Our findings further support the potential usefulness of the spot urinary sodium-to-potassium ratio as an indicator of sodium intake and suggest a link between sodium intake and kidney damage.