It has been reported that rat plasma fluoride (F) concentrations are higher by up to 100% when F is administered ig in coffee or a caffeine solution compared with when it is administered in water. It was hypothesized that the consumption of caffeinated beverages has contributed to the prevalence of dental fluorosis. The present studies were done to determine the physiological mechanism for these effects. For approximately 2 h after F was administered in coffee, plasma F concentrations were higher than when administered in water, decaffeinated coffee, or a caffeine solution (3 mg/kg), but the intergroup differences were small and generally not statistically significant. The 4-hour plasma AUC values did not differ with statistical significance. There were no differences among the groups in the renal or extrarenal (skeletal) clearances of F, which suggested that the higher plasma F concentrations in the coffee groups may have been due to a slight and transient increase in absorption rate. The possibility that caffeine per se might elevate endogenous plasma F and calcium concentrations was excluded after caffeine (25 mg/kg) ig without F was given. In addition, the renal excretion, clearance, and fractional renal clearance of calcium did not differ among the groups. The results indicated that decaffeinated coffee and caffeine had no effect on F metabolism, whereas caffeinated coffee appeared to increase the initial absorption rate but not the 4-hour bio-availability. The possibility that the ingestion of F with caffeinated coffee has contributed to the increased prevalence of dental fluorosis in the US is supported only weakly by the present findings. Long-term exposure studies are needed to clarify this relationship.
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