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Dietary Fluoride Intake by Children Receiving Different Sources of Systemic Fluoride

¹ Department of Biological Sciences, Bauru Dental School, University of São Paulo, Al. Octávio Pinheiro Brisolla, 9-75, Bauru, SP, 17012-901, Brazil;
² Peruvian University Cayetano Heredia, Lima, Peru; and
³ Health Science Center, Federal University of Paraíba, João Pessoa, PB, Brazil

Correspondence: mbuzalaf{at}fob.usp.br

	ABSTRACT

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There has been no comparison of fluoride (F) intake by pre-school children receiving more traditional sources of systemic F. The aim of this study was to estimate the dietary F intake by children receiving F from artificially fluoridated water (AFW-Brazil, 0.6–0.8 mg F/L), naturally fluoridated water (NFW-Brazil, 0.6–0.9 mg F/L), fluoridated salt (FS-Peru, 180–200 mg F/Kg), and fluoridated milk (FM-Peru, 0.25 mg F). Children (n = 21–26) aged 4–6 yrs old participated in each community. A non-fluoridated community (NoF) was evaluated as the control population. Dietary F intake was monitored by the "duplicate plate" method, with different constituents (water, other beverages, and solids). F was analyzed with an ion-selective electrode. Data were tested by Kruskall-Wallis and Dunn’s tests (p < 0.05). Mean (± SD) F intake (mg/Kg b.w./day) was 0.04 ± 0.01^b, 0.06 ± 0.02^a,b, 0.05 ± 0.02^a,b, 0.06 ± 0.01^a, and 0.01 ± 0.00^c for AFW/NFW/FS/FM/NoF, respectively. The main dietary contributors for AFW/NFW and FS/FM/NoF were water and solids, respectively. The results indicate that the dietary F intake must be considered before a systemic method of fluoridation is implemented.

Key Words: exposure • fluoride • diet • children • fluorosis

	INTRODUCTION

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The prevalence and severity of dental caries in most industrialized countries have decreased dramatically over the last decades (Marthaler, 2004; Burt and Eklund, 2005). One of the main reasons for the caries prevalence decline is the widespread use of fluoride (F), including water fluoridation (Bratthall et al., 1996).

Water fluoridation reaches an entire population, including socially under-served groups with the highest levels of caries, and systematic reviews have acknowledged its benefits (McDonagh et al., 2000; National Health and Medical Research Council, 2007). It has been shown that this method reduces the DMFT by, on average, 2.25 teeth per child and increases the proportion of caries-free children by 15%. Moreover, there appears to be some evidence that it reduces the inequalities in dental caries across social classes in 5- and 12-year-olds (McDonagh et al., 2000). However, for political, geographical, and technical reasons, the benefits of water fluoridation are unavailable to a large proportion of the world’s population (Armfield, 2007). Therefore, other methods of community fluoridation have been suggested—for example, salt, sugar, and milk (Horowitz, 1990; Kumar and Moss, 2008).

Simultaneous with the caries decline, an increase in the prevalence of dental fluorosis has been observed in many countries (Khan et al., 2005). This implies that the sources of F intake by children at risk for dental fluorosis warrant investigation. Additionally, the literature correlating F intake and dental fluorosis is scarce (Martins et al., 2008), and the "optimum" daily F intake to avoid dental fluorosis has been empirically established (Burt, 1992; Guha-Chowdhury et al., 1996). In Latin American countries where different national fluoridation methods have been implemented for decades, only a few data on F intake are available (Paiva et al., 2003; Levy et al., 2004; Franco et al., 2005; Pessan et al., 2005; Almeida et al., 2007). Few surveys have been performed (for review, see Buzalaf and Kobayashi, 2007), but there is no comparison of F intake by preschool children with different sources of systemic F. The aim of this study was to estimate dietary F intake by children receiving systemic F from different sources, considering the different constituents of the diet (drinking water, other beverages, and solids).

	MATERIALS & METHODS

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Participants
Ethical approval was obtained from the Institutional Review Boards (IRB) of Bauru Dental School (no. 116/2004) and Peruvian University Cayetano Heredia, as well as from the Brazilian National Research Council (no. 11174). Parents signed an IRB-approved consent document.

The participants in this multicentric study were 4- to 6-year-old children receiving systemic F from different sources: artificially fluoridated water (Bauru, Brazil, 316,000 inhabitants, Human Development Index-HDI 0.825, 0.6–0.8 mg F/L, n = 25), naturally fluoridated water (Brejo dos Santos, Brazil, 6000 inhabitants, HDI 0.613, 0.6–0.9 mg F/L, n = 21), fluoridated salt (Lima, Peru, 8,400,000 inhabitants, HDI 0.767, 180–200 mg F/Kg, n = 26), and fluoridated milk (Trujillo, Peru, 747,000 inhabitants, HDI 0.673, 250 mL of milk containing 1.0 mg F/L, n = 25). The fluoridation schemes were implemented in 1975, 1986, and 1999 in Bauru, Lima, and Trujillo, respectively. A non-fluoridated community (Pirajuí, Brazil, 20,000 inhabitants, HDI 0.779, n = 24) was included as a negative control population. All children enrolled were lifelong residents of their respective communities and drank water from the public supply only. They had good oral health, were not using medicines or topical fluorides, and had no gastrointestinal, bone, or health problems. Children who participated were not chosen randomly, since parental permission had been granted, and the source of systemic F intake had been previously checked. Sample size was calculated based on a previous study (Levy et al., 2004), to ensure and β errors of 5% when fluoridated and non-fluoridated communities were compared.

Collection of Duplicate Diets
The daily dietary F intake of the children was estimated by the "duplicate plate" method, as described previously (Almeida et al., 2007), with a slight modification that consisted of collecting water samples separately from milk samples, which were collected together with other beverages in the diet, since Trujillo has fluoridated milk. Thus, the constituents of the diet were collected separately (solids, water, and other beverages) in plastic vials (1000 mL), on two consecutive days, simultaneously in all communities. Parents were instructed to maintain the usual dietary habits of their children and to duplicate the diet as precisely as possible (for details, see Guha-Chowdhury et al., 1996). Diets were immediately homogenized with a known volume of de-ionized water. The total volume (or total weight for solids) was measured, and a 50-mL aliquot was taken and frozen (–20°C). Samples were kept frozen while shipped to the analytical laboratory. Children were weighed (± 0.1 Kg) on calibrated electronic scales (model HS301, Tanita Corporation, Arlington Heights, IL, USA). Their weights were recorded for calculation of the F intake (mg/Kg body weight).

Tap Water Collections
Since fluctuations in public water F levels have been described in Bauru (Buzalaf et al., 2002a), two samples of tap water were collected at the children’s houses on the same day as diet collection. Water samples were frozen (–20°C) until F analysis.

Analytical Procedure
F concentrations in the diet (solids and other beverages, separately) samples were determined after overnight hexamethyldisiloxane (HMDS)-facilitated diffusion (Taves, 1968) as modified (Whitford, 1996), with a F-ion-specific electrode (model 9409, Orion Research, Cambridge, MA, USA) and a miniature calomel reference electrode (Accumet #13-620-79), both coupled to a potentiometer (Orion, model EA 940). F standards (0.019, 0.095, 0.190, 0.950, 1.900, and 4.750 µg F) were prepared by serial dilution of a stock standard containing 0.1 M F (Orion 940906) in triplicate and diffused as the samples. In addition, non-diffused F standards were prepared with the same solution (0.05 M NaOH, 0.20 M acetic acid, plus NaF) for preparation of the diffused standards and samples. The non-diffused standards had exactly the same F concentration as the diffused standards. Comparison of the millivolt readings demonstrated that F in the diffused standards was completely trapped and analyzed (recovery > 99%). The millivoltage potentials were converted to µg F by a standard curve (r 0.99). All samples were analyzed in duplicate. The mean repeatability of the readings, based on duplicate samples, was 96.7% for solids and 96.8% for other beverages.

F analyses in the water samples were performed by means of an ion-specific electrode (Orion 9609), after sample buffering with an equal volume of TISAB II. Standards (containing 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 mgF/L) were prepared by serial dilution of 100 mgF/L NaF stock solution (Orion). The standard curves had a correlation coefficient 0.99. All samples were analyzed in duplicate. The mean repeatability of the readings, based on duplicate samples, was 98.5%.

Statistical Analysis
The software GraphPad Prism 4 version 4.0 for Windows (GraphPad, San Diego, CA, USA) was used. The assumptions of equality of variance and normal distribution of errors were checked for all the variables tested. Since the distribution of the errors was not homogeneous, data were tested by Kruskall-Wallis and Dunn’s tests for individual comparisons among the groups. A statistical significance level of 5% was selected a priori.

	RESULTS

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Data are expressed as mean (± SD). Mean F concentrations in tap water collected at the children’s houses were 0.70 ± 0.08, 0.66 ± 0.20, 0.04 ± 0.05, 0.49 ± 0.03, and 0.08 ± 0.01 mg/L for Bauru (Brazil, artificially fluoridated water), Brejo (Brazil, naturally fluoridated water), Lima (Peru, fluoridated salt), Trujillo (Peru, fluoridated milk), and Pirajuí (Brazil, non-fluoridated), respectively.

The Table shows the F intake from dietary components (solids, water, and other beverages) and total diet. There was a significant difference among the communities regarding the F intake from solids (KW = 87.49, p < 0.0001), and in Lima and Trujillo, the data were not significantly different, but were higher when compared with data from the other communities (p < 0.01). Despite the fact that Bauru had higher amounts of F intake from solids when compared with Brejo, this difference was not statistically significant. All the communities except Brejo had amounts of F intake from solids significantly higher than those from Pirajuí, the control community (p < 0.01).

Regarding the F intake from other beverages, there was also a statistically significant difference among the communities (KW = 71.93, p < 0.0001). The amounts found for Trujillo (0.39 ± 0.09 mg) were significantly higher when compared with those from all the other communities (p < 0.001). This reflected the consumption of fluoridated milk. If the F intake from milk alone is subtracted from the F intake from other beverages in Trujillo, the amounts found (0.14 ± 0.09 mg) were similar to those observed for the other communities. The amounts found for Bauru, Brejo, and Lima were not significantly different, but were significantly higher (p < 0.01) than those found for Pirajuí (0.04 ± 0.04 mg) (Table).

As for the total dietary F intake, a statistically significant difference could be observed among the communities (KW = 69.16, p < 0.0001). The highest concentrations were found for Trujillo (0.06 ± 0.01 mg/Kg b.w.) and Brejo (0.06 ± 0.02 mg/Kg b.w.), which did not differ significantly from each other. Intermediate values were found for Lima (0.05 ± 0.02 mg/Kg b.w.) and Bauru (0.04 ± 0.01 mg/Kg b.w.) The values found for Pirajuí (0.01 ± 0.00 mg/Kg b.w.) were significantly lower when compared with those from the other communities (p < 0.001) (Table). Seventeen children, most of them from Lima (n = 6) ingested more than 0.07 mg F/Kg b.w., a dose that has been regarded as the threshold for dental fluorosis (Burt, 1992).

	DISCUSSION

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Recent studies have analyzed dietary F intake as a whole (Murakami et al., 2002; Levy et al., 2004; Franco et al., 2005; Pessan et al., 2005). However, due to the high consumption of milk and water by Canadian children, Clovis and Hargreaves (1988) analyzed total F intake of solids and beverages, separating the latter into ‘water plus milk’ and ‘other beverages.’ This approach was successfully applied in Brazilian children (Almeida et al., 2007) and seems to be suitable for the identification of dietary risk factors for dental fluorosis. Therefore, it was regarded as appropriate for this study, where children of different countries and communities within a country are exposed to different F-delivery sources. In Trujillo, the data on F intake from milk as an isolated product were also included, due to the existence of a milk fluoridation program.

Surprisingly, Trujillo had water F concentration rates much higher than expected, considering the milk fluoridation program in this community. As a result, the mean dietary F intake in Trujillo was the highest value observed. It is also important to point out the large variation in water F levels in Brejo. Since this community has natural F in the drinking water, more constant F levels would be expected. This variation may be due to the fact that people in this community usually store the drinking water obtained from the wells for use in periods of drought. This storage may also have an impact on F intake, since it might increase water F levels due to evaporation.

In optimally fluoridated communities, water was the most contributory factor for Bauru (42.60%) and Brejo (62.90%). The higher levels for Brejo could be explained by the higher temperatures (mean annual temperature of 28°C, in contrast to 19–21°C for the other communities) and higher water intake than in Bauru. In fact, the mean volume of water ingested per day in Brejo was the highest among the communities. Additionally, Brejo is a rural community, where the consumption of industrialized foods, which may, in some cases, have high F content (Buzalaf et al., 2004b), is smaller compared with that in Bauru.

When F intake from solids alone was considered, the communities that showed high contributions of solids to total dietary F intake were Lima (84.30%), Trujillo (54.90%), and Pirajuí (44.80%). This result was expected for Lima, which has fluoridated salt, but not for Trujillo. This high F-intake value may be due to the diffusion effect of salt fluoridation in Trujillo (the distance between these communities is around 500 km). In Trujillo, two children had a high F concentration in the salt used at home. Thus, it is possible that children living in Trujillo and using non-fluoridated salt at home consumed food manufactured with fluoridated salt. Additionally, the distribution of fluoridated salt in Peru must be monitored.

Regarding the F intake from other beverages, the value found for Trujillo (0.39 ± 0.09 mg) was significantly higher when compared with those from all communities, due to the consumption of fluoridated milk. The higher F intake from other beverages in the fluoridated communities was anticipated and may be due to the use of fluoridated water to prepare other beverages, such as powdered milk (Buzalaf et al., 2001, 2004a), juices, and teas (Buzalaf et al., 2002b). In previous studies conducted in Bauru with 4- to 7-year-olds (Pessan et al., 2005), 2- to 6-year-olds (Levy et al., 2004), and 1- to 3-year-olds (Almeida et al., 2007), the dietary F intake was 0.02 ± 0.01, 0.03 ± 0.03, and 0.03 ± 0.01 mg/Kg b.w., respectively. These intakes are lower than those found for this community in the present study. A possible factor responsible for this difference may be the distinct age range when compared with that used in the present study. Regarding the non-fluoridated community (Pirajuí), the estimated dietary F intake was very close to levels reported previously (Levy et al., 2004) for 2- to 6-year-old children residing in another non-fluoridated Brazilian community (0.004 ± 0.003 mg/Kg b.w.).

The total dietary F intake found for Trujillo and Brejo was 0.06 ± 0.01 and 0.06 ± 0.02 mg/Kg b.w., respectively. In Trujillo, overlap of systemic fluoridation methods (naturally fluoridated water, salt fluoridation, and milk fluoridation) has probably occurred, whereas in Brejo the high F intake seemed to be related mainly to the high ingestion of naturally fluoridated water. For both communities, strategies for reducing F intake are necessary, since if F intake from dentifrices is added to the amounts obtained from the diet, it is probable that the upper limit of F intake (0.07 mg/Kg b.w./day) (Burt, 1992) is exceeded for many children. The overlap of systemic fluoridation methods, as found in Trujillo, indicates that decision-making for the boundaries of national programs of community water fluoridation cannot disregard political, cultural, and geographical differences within countries. Finally, the results of this study clearly indicate that: (a) the dietary F intake must be taken into account before a systemic method of fluoridation is implemented; and (b) F exposure monitoring of existing and newly developed fluoridation schemes must be conducted on a regular basis.

	ACKNOWLEDGMENTS

 
This study was supported by The Borrow Foundation. The authors thank CAPES for a PhD scholarship to the first author. This study was based on a thesis submitted to Bauru Dental School, University of São Paulo (Brazil), in partial fulfillment of the requirements for the PhD degree in Oral Biology.

Received for publication January 16, 2008. Revision received September 11, 2008. Accepted for publication October 15, 2008.

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Journal of Dental Research, Vol. 88, No. 2, 142-145 (2009)
DOI: 10.1177/0022034508328426


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This Article Abstract Free Full Text (Free PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Rodrigues, M.H.C. Articles by Buzalaf, M.A.R. Search for Related Content PubMed PubMed Citation Articles by Rodrigues, M.H.C. Articles by Buzalaf, M.A.R. Social Bookmarking                         What's this?