Potassium and sodium intake and excretion in calcium stone forming patients.

OBJECTIVE: To determine mean potassium (K) intake and its correlation with urinary calcium (uCa) and citrate excretion, as well as uCa, sodium (Na), and K levels of calcium stone forming patients. We determined the K-rich foods most commonly consumed by these patients.

DESIGN: Case-control.

SETTING: University-affiliated outpatient renal Lithiasis Unit.

PATIENTS AND CONTROLS: One hundred hypercalciuric calcium stone forming patients (CSF, 54 men/46 women), 37 with associated hypocitraturia, were sequentially enrolled in the study that was performed before the initiation of any care for their renal stones. The control group consisted of 100 age-matched healthy subjects (HS, 47 men/53 women) who were laboratory employees with no history of renal stones.

INTERVENTION: The analyses consisted of a 3-day dietary record to determine the mean K and calcium (Ca) intakes, and a 24-hour urine sample with measurements of K, Ca, Na, and citrate.

MAIN OUTCOME MEASURE: K and Na intake determined by dietary record.

RESULTS: uCa and Na levels and the Na/K ratio were significantly higher for CSF versus HS (238 +/- 118 v 148 +/- 74 mg/24 hours, 238 +/- 100 v 181 +/- 68 mEq/24 hours, 6.6 +/- 3.5 v 5.1 +/- 2.3, respectively, P < .05). The mean citrate excretion was lower in CSF than in HS patients (410 +/- 265 v 530 +/- 240 mg/24 hours). Mean uCa did not differ between groups. CSF patients showed a higher sodium chloride intake compared with HS (14 +/- 4 vs 8 +/- 3 g/day). The mean Ca intake of CSF and HS were 559 +/- 327 and 457 +/- 363 mg/day, respectively. The mean K intake of CSF and HS were 58 +/- 17 and 51 +/- 27 mEq/day. A positive correlation was observed between uCa and urinary sodium (r = .40 and r = .65, P < .05), urinary potassium and urinary citrate (r = .25 and r = .53, P < .05), uCa and Na/K (r = .33 and r = .56, P < .05) respectively for CSF and HS. The following were the K-rich foods consumed at least once a day by these groups: beans (by 70% of CSF and 75% of HS), tomatoes (by 42% of CSF and 50% of HS), oranges (by 30% of CSF and 55% of HS), and bananas (by 42% of CSF and 23% of HS).

CONCLUSION: Despite the consumption of K-rich foods at least once a day, the mean K intake by CSF patients was 58 mEq/day. This intake can still be considered to be low, although it meets recommended daily dietary allowance requirements. Therefore, we describe herein a population of CSF with high-Na intake and normal- to low-K intake, which may contribute to stone formation.