O79 DAILY URINARY POTASSIUM EXCRETION IS NOT A FIXED PERCENTAGE OF DAILY POTASSIUM INTAKE

Background and Objective: High potassium intake is associated with a lower blood pressure and lower incidence of cardiovascular events. For estimation of potassium intake, the World Health Organization advices to multiply the 24-hour renal potassium excretion by 1.3, considering the substantial fecal potassium loss. We examined the variation in the required conversion factor in healthy volunteers and evaluated the effect of factors associated with tissue cation storage on the renal potassium excretion. Methods: We performed a post-hoc analysis of the Mars long-term sodium balance studies. Healthy male participants consumed a fixed amount of salt (6, 9 and 12 grams/day for >29 days) and potassium (4 grams/day) for 105 (n=4) and 205 days (n=6). All urine was collected in 24-hour aliquots. We calculated the percentage of potassium intake that was excreted in the corresponding 24-hour urine collection during steady-state. A multivariable mixed-effects model was used to assess associations of this percentage with sodium intake, potassium intake, urinary aldosterone, urinary cortisol and urine volume. Results: The median renal potassium excretion was 80% of potassium intake (IQR 65-97%, range 24-304%), corresponding to a conversion factor of 1.25 (IQR 1.03-1.54). Within individual subjects we also observed a marked day-to-day variation in the percentage of renal potassium excretion: the average intraperson width of the IQR was 25%. Sodium intake (figure A), urinary aldosterone (figure B), urinary cortisol (figure C) and urine volume (figure D) were positively associated with the percentage of renal potassium excretion, whereas potassium intake showed a negative association (figure A). A significant positive interaction between the effects of sodium and potassium intake was present (P<0.001). Conclusions: The percentage of dietary potassium that is excreted via urine varies considerably. During steady-state, this percentage is independently affected by sodium intake, potassium intake, urinary aldosterone, urinary cortisol, and urine volume. Our results suggest that the WHO's fixed 1.3 conversion factor may lead to inaccurate estimations of potassium intake.