Assessment of dietary intake and urinary excretion of sodium and potassium in adults

Background: Hypertension is associated with elevated sodium and low potassium intakes. The determination of sodium and potassium intake by dietary records is inaccurate, being its measurement from 24-h urine collection the reference method. Aim: To determine urinary sodium and potassium excretion in adults. To compare dietary sodium and potassium intake and their excretion from an isolated urine sample against the reference method. Material and Methods: Seventy healthy adults aged 35 +/- 8 years with a body mass index 25 +/- 2 kg/m(2) (36 women) were studied. Urine was collected over 24 h, including an isolated urine sample taken in fasting conditions. Additionally, three 24-h dietary records were performed. Results: Reported sodium and potassium intake was 2,720 +/- 567 and 1,068 +/- 433 mg/day, respectively. In turn, urinary excretion of sodium and potassium was 4,770 +/- 1,532 and 1,852 +/- 559 mg/day, respectively. These latter values were significantly higher than those obtained by dietary records. Furthermore, the urinary sodium and potassium excretion estimated from an isolated urine sample was 4,839 +/- 1,355 and 1,845 +/- 494 mg/day, respectively. These values were similar to those obtained with a 24 h urine collection. Conclusions: Dietary records underestimated electrolyte intake when compared with the reference method. Using an isolated urine sample to estimate electrolyte intake may be a reliable alternative.