Daily salt intake is associated with leg edema and nocturnal urinary volume in elderly men

Aims: There is accumulating evidence that excessive salt intake contributes to nocturnal polyuria. We aimed to investigate the relationship between salt intake, leg edema, and nocturnal urine volume (NUV) to assess the etiology of nocturnal polyuria.

Methods: A total of 56 men aged ≥60 years who were hospitalized for benign prostatic hyperplasia or with suspected prostatic cancer were enrolled. Urine frequency-volume charts of the patients were maintained, and they underwent bioelectrical impedance analysis twice daily (at 5:00 pm and 6:00 am) and examination of blood (brain natriuretic peptide levels) and urine (sodium and creatinine levels and osmotic pressure) samples once daily (at 6:00 am). Free-water clearance, solute clearance, and sodium clearance at night were measured, and daily salt intake was estimated.

Results: The data of 52 patients were analyzed. Daily salt intake positively correlated with leg edema at 5:00 pm, differences in leg extracellular fluid levels between 5:00 pm and 6:00 am, and NUV, but not with diurnal urine volume. Partial correlation coefficients showed that salt intake was a factor of the correlation between NUV and change in extracellular volume in the legs between 5:00 pm and 6:00 am. A multivariate logistic model showed that sleep duration and sodium clearance were independent predictive factors for nocturnal polyuria.

Conclusions: Sodium intake correlates with diurnal leg edema and NUV in elderly men. These results provide evidence supporting sodium restriction as an effective treatment for nocturnal polyuria.

Keywords: edema; leg; nocturia; sodium; urine.