Urinary excretion of iodide and fluoride from supplemented food grade salt

Iodide and fluoride supplemented food grade salt (NaCl) is a common source of these two micronutrients. In a pilot study, we investigated whether increased intake of NaCl supplemented with iodide (I-) and fluoride (F-) results in their higher bioavailability. Twelve healthy adult human volunteers ingested increasing quantities (1, 3, 6 and 9 g) of NaCl with usual diet over 8 days. Sodium (Na+), I- and F- were measured in 24 hour urine specimen. During the 4 day basal period when no additional NaCl was ingested, ingestion of NaCl calculated from urinary Na+ concentration and diuresis was 8.25 +/- 0.67 g/24 h. During the same period 0.11 +/- 0.01 and 0.61 +/- 0.04 mg of I- and F- respectively were excreted in the urine per 24 h. Increased ingestion of supplemented NaCl resulted in higher urinary excretion of sodium while urinary creatinine remained stable. 92% of I- and 40% of F- contained in the additional amount of NaCl ingested were excreted in the urine. These results indicate that with increased ingestion of supplemented (I- and F-) NaCl, almost the totality of I- is excreted in the urine while fluoride is either incompletely absorbed or retained by the body to a higher extent. I- and F- supplemented NaCl is, therefore, an effective vehicle to provide these micronutrients when ingested with diet.