The fractional urinary fluoride excretion of adults consuming naturally and artificially fluoridated water and the influence of water hardness: a randomized trial

AIMS

To assess whether there was any significant difference in the average fractional urinary fluoride excretion (FUFE) values among adults consuming (NaF) fluoridated Ca-free water (reference water), naturally fluoridated hard water and an artificially (H2SiF6) fluoridated soft water.

DESIGN

Sixty adult females (N=20 for each treatment) participated in this randomized, double-blind trial. The experimental design of this study provided an indirect estimation of the fluoride absorption in different types of water through the assessment of the fractional urinary fluoride excretion of volunteers.

RESULTS

Average daily FUFE values (daily amount of fluoride excreted in urine/daily total fluoride intake) were not significantly different between the three treatments (Kruskal-Wallis; p = 0.62). The average 24-hour FUFE value (n=60) was 0.69; 95% C.I. 0.65-0.73.

CONCLUSIONS

The results of this study suggest that the absorption of fluoride is not affected by water hardness.

Fractional urinary fluoride excretion of young female adults during the diurnal and nocturnal periods

OBJECTIVES

This study aimed to confirm a previously obtained value for the fractional urinary fluoride excretion (FUFE) over a 24-hour period in adults and to assess whether there are significant differences between FUFE measured during the diurnal (7 a.m. and 6 p.m.) and the subsequent nocturnal (6 p.m. until 7 a.m. of the following day) periods.

METHODS

Urine was collected over 24 h from 60 healthy female volunteers residing in Santiago, Chile. The individuals' fluoride intakes over the diurnal and nocturnal periods were calculated from their corresponding F ingestion, measured by dietary analysis. Separate urine collections during both periods were obtained from each volunteer. The fluoride concentrations were measured with a fluoride-ion-selective electrode either directly (urine, water and beverages) or after sample treatment with the microdiffusion technique (food).

RESULTS

The average 24-hour FUFE value was 0.69, with a 95% CI of 0.65-0.72, while the average FUFE for the diurnal period was 0.46 (95% CI: 0.42-0.50), and the corresponding result for the nocturnal period showed a significantly higher (paired t test, p < 0.0001) amount of 1.09 (95% CI: 0.97-1.22).

CONCLUSIONS

A recently published result for the daily FUFE value (0.71) in adults was confirmed. The diurnal average FUFE value is significantly lower than the average nocturnal one. Accepting that approximately 10% of the fluoride intake is not absorbed, the daily fluoride retention can be preliminarily estimated as 20% of the ingested fluoride.

The fractional urinary fluoride excretion of adolescents and adults under customary fluoride intake conditions, in a community with 0.6-mg F/L in its drinking water

AIMS

To assess the fractional urinary fluoride excretion (FUFE) relative to the customary daily fluoride (F) ingestion in adolescents and adults aged 11-75 years, and to explore the influence that some metabolic variables, such as the F-dose (mg F/kg body weight), rate of urinary fluoride excretion, age and body weight, might have on FUFE values.

DESIGN

The fluoride ingestion and urinary excretion of 92 volunteers aged 11-75 years, resident in Santiago, Chile, were measured. In Santiago, the water is fluoridated to a concentration of between 0.5 and 0.6 mg/l. Individual FUFE values were calculated as the ratio between the total amount of F excreted with the urine and the total amount of F ingested, over a 24-hour period.

RESULTS

The average FUFE values did not differ significantly among adults (ANOVA; p > 0.31). The average 24-hour FUFE value for adults was 0.75; 95% C.I. = 0.70-0.80, while the corresponding value for adolescents was 0.35; 95% C.I. = 0.30-0.40. Individual FUFE values were fitted by a multiple regression model using the rate of F urinary excretion and the inverse of the F dose as significant predictors (R2 = 0.79).

CONCLUSIONS

Results obtained suggest that among adults residing in an area with an intermediate F-exposure, FUFE values do not depend on age. A relatively simple multiple regression model appears to explain 79% of the variability of the individually measured FUFE values. Further studies in areas with different F exposures are needed to refine the proposed model.

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.

Estimation of the fraction of an ingested dose of fluoride excreted through urine in pre-school children

OBJECTIVE

To determine the fraction of an ingested fluoride dose of 1 mg in 50 mL orange juice that is excreted through the urine (FUEF) of children aged 3-5 years.

METHODS

Eighty-eight controlled determinations involving 24-hour urinary collections from a total of 48 children were carried out during consecutive control and test days. Net fluoride urinary excretion due to the ingested dose was calculated as the difference between the total amount of fluoride excreted by each child on test and control days.

RESULTS

Excretion of the fluoride ingested from the single fluoride dose presented an average value of 30.7% (95% CI: 28.9-32.5%). No significant associations were found between individual FUEF values with either anthropometrical variables or urinary pH values. The average FUEF value found in the present study lies between previously reported values for infants and young adults. The epidemiological usefulness of the FUEF values in estimating daily fluoride dose in pre-school children is discussed.

Dental fluorosis in Chilean children: evaluation of risk factors

The purpose of this case-control study was to determine the association between very-mild-to-moderate enamel fluorosis and exposure during early childhood to fluoridated water, mainly through ingestion of powdered milk. Analysis was performed on 136 residents of the optimally fluoridated community of San Felipe in the Chilean Fifth Region, who were categorised into one of three groups according to their age when water fluoridation was introduced in 1986: Group I was born after 1986; Group II was 16-24 months old in 1986; and Group III was >24 months of age. The case and control subjects were selected on the basis of a clinical examination given in July 1996. Dean's scoring system was used to determine fluorosis status. Risk factor exposure was ascertained by a questionnaire used in interviews with mothers of participating children. Logistic regression analysis, after adjustment for confounding variables, revealed that very-mild-to-moderate enamel fluorosis of permanent central maxillary incisors (CMI) was strongly associated both with the age of the subjects when water fluoridation began and with breast-feeding duration for children belonging to Group I. Subjects in Group I were 20.44 times more likely (95% CI: 5.00-93.48) to develop CMI fluorosis than children who were older than 24 months (Group III) when fluoridation began. Subjects who were between 16 and 24 months old when water fluoridation began were 4.15 times more likely (95% CI: 1.05-16.43) to have CMI fluorosis than children older than 24 months. An inverse association was found with breastfeeding duration (OR=0.86, 95% CI: 0.75-0.98) among Group I subjects but not in Groups II and III. Results obtained suggest that the current fluoride concentration in drinking water may be contributing to fluorosis. Further studies will be necessary to determine the relative competing risks of dental fluorosis and dental caries in Chilean children in order to establish the most appropriate water fluoridation level in Chile.