The influence of fluoride ingestion on urinary aluminum excretion in humans

Fluoride (F) and aluminum (Al) are both ingested daily in water, foods, and pharmaceuticals. Owing to the strong chemical affinity between F and Al, these elements can interact in biological systems. The purpose of the present study was to investigate the influence of F ingestion on Al excretion in humans. Six healthy volunteers ingested 100 ml of distilled water at 6:00 a.m. on day 1 (control period) and the same volume of sodium fluoride solution containing 5 mg of F at 6:00 a.m. on day 2 (test period). A schedule for meals and for blood and urine collection was followed for the two successive days. The concentration of F was measured with an F-electrode, and Al was determined by ion-pair RP-HPLC with its complexation with 8-quinolinol. The mean concentration of serum F peaked within 30 minutes after ingestion of F and rapidly decreased thereafter, reaching baseline 24 hours later. In control period, there was no increase of Al concentration in serum in 24 hours. In test period, Al concentration in serum did not increase significantly compared with those in control serum. Although some variation was observed among subjects, cumulative amounts of F and Al excreted in urine during the test period were significantly higher than those during the control period. The results suggest that absorbed F enhanced urinary Al excretion and that the Al in urine may be, at least in part, derived from endogenous tissues.