The fractional urinary fluoride excretion in young children under stable fluoride intake conditions.

The purpose of this study was to determine the fraction of the total daily fluoride intake that is excreted through the urine (FUEF) of children aged 3-5 years under usual intake conditions. Participating children were residents of an area with a fluoride (F) concentration of 0.5-0.6 mg/L in their drinking water. Assessments were made on two successive 24-h periods on 20 children, measuring the total amount of fluoride ingested through liquid and food consumption, and from ingestion of fluoridated toothpaste (500 microg F/g), together with the determination of the amount of fluoride excreted through urine. Fluoride retention was also estimated assuming a constant average F fraction of 10% excreted through faeces. It was found that the average proportion of liquids, solid foods, and toothpaste to the daily fluoride intake (1.02-mg F/day on average) were 40.8, 34.6, and 24.5%, respectively. The average FUEF value was 35.5% (95% C.I.=31.7-39.3%), and the estimated fractional F retention was 54.5%. The present data suggest a slight relationship between FUEF values and the inverse of the daily fluoride dose (1/dose) (r=0.513; P=0.021). When the present results are combined with those from previous studies on F-retention and urinary excretion, the correlation between both FUEF and fractional retention and 1/dose are very strong and highly significant (r=0.98, P<0.0001, and r=-0.986, P<0.0001, respectively). A possible mechanism is suggested in order to explain this latter finding. The potential usefulness of the current FUEF value for the estimation of daily F intake (or dose) from urinary F excretion data is also discussed.