Introduction

Community access to fluoride through water and salt has proven to be an effective public health measure to reduce the incidence of dental caries worldwide.¹ Salt fluoridation has increased, mainly in developing countries, where water fluoridation has proven to be inaccessible due to decentralized and inadequate water supply and distribution systems.^2-4

Community salt fluoridation has been available in Uruguay since 1991, reaching almost the entire population.⁵ Compared to water fluoridation, this alternative showed a similar reduction in caries prevalence while providing consumers the possibility to choose to buy the product.² The Uruguayan population has access to fluoridated household salt at a 250 mgF/kg concentration.⁶

Studies conducted in other Latin American countries analyzed the fluoride concentrations of household salts and found significant variations between salt brands.^7-12 In addition, most salt brands did not have the fluoride concentration reported on the product label, which goes against the country's legislation. However, no studies reporting the fluoride content of salt marketed in Uruguay were found. Therefore, this study aimed to evaluate the fluoride concentration of different brands of commercially available household salt in Montevideo, Uruguay.

Methodology

Results

Of the fourteen brands of fluoridated salt commercially available in Montevideo and analyzed in this study, only six were produced in Uruguay (samples 3, 4, 5, 6, 11, and 12). The other eight salt brands were imported from Argentina (samples 1, 2, 7, 8, 9, 10, and 13) and Brazil (sample 14).

Figure 1 shows the mean fluoride concentration values found in each salt sample analyzed. They ranged from 19.22 to 553.42 mgF/kg. Most commercial brands available in Uruguay had fluoride concentration values below 250 mgF/kg. Only two salt brands (samples 10 and 14) reached the mean fluoride concentration expected (250 mgF/kg), and three brands had very high values (samples 2,4,7, and 13). A significant difference was detected when comparing the fluoride concentration values in different lots of the same salt brand, reflecting a wide standard deviation (Figure 1).

Six of the salt brands analyzed were available in two different presentations: fine and coarse. The mean value of fluoride concentration in the fine salts was 115.56 ± 109.09 mgF/kg (mean ± SD), with a coefficient of variation (CV) = 94.4%. The mean value of fluoride concentration in coarse salts was 242.33 ± 128.35 mgF/kg (mean ± SD), with a CV = 53.0%. In all salt brands, coarse salt presented higher fluoride concentration values than the fine salt concentration of the same brand (p < 0.05).

Sodium fluoride (NaF) and potassium fluoride (KF) were the compounds included in the salt brands analyzed. Salt brands containing KF (samples 4, 9, 10, and 11) had higher fluoride concentrations compared to salt brands containing NaF (samples 1, 2, 3, 5, 6, 12) (p < 0.05). The fluoride concentration of the salts with NaF was 125.76 ± 150.77 mgF/kg (mean ± SD), with a CV = 120%, while the salt brands with KF had a 214.49 ± 97.89 mgF/kg (mean ± SD) concentration, with a CV = 45.6%.

Figure 1: Fluoride concentrations (mg/kg) found in every salt sample (identified by their code numbers) analyzed in this study 

Discussion

In 1991, Uruguay introduced the nationwide National Salt Fluoridation Program at a concentration of 250 mgF/kg. In many Latin American countries, all salt for human consumption is fluoridated, while only household salt is fluoridated in Uruguay. As a result, specific legislation has been developed, and now the Uruguayan government requires 60% of household salt to be iodized and fluoridated throughout the country.⁶

Choosing a population-based approach to fluoride use benefits the general population, including people from lower socioeconomic status who lack access to fluoride toothpaste and professional fluoride applications. Several Latin American countries such as Colombia, Costa Rica, Mexico, and Jamaica use fluoridated salt as a population-based method to distribute fluoride. Uruguay is one of the countries that covers almost the entire population.¹⁴

The fluoride content of most salt brands available in Uruguay and analyzed in this study differed from the value declared on the package and that recommended by law. Even though the label indicates that the salt marketed has 250 mgF/kg, the values found in this study contradict this information. The fluoride concentration values of the samples analyzed ranged from very low-19.22 mgF/kg-to very high -553.42 mgF/kg. Only two brands had a mean content value close to the declared 250 mgF/kg (samples 10 and 14).

Several salt brands showed high standard deviations, reflecting the large difference in results found in different lots of the same brand (Figure 1). Therefore, it can be assumed that there is no adequate quality control in the salt fluoridation process that standardizes the amount to include in all the lots manufactured.

Also, fluoride is probably not added uniformly to the salt particles in each package. The size of the salt particles might affect the incorporation of fluoride. When comparing fine and coarse salt of the same brand, coarse salts had higher fluoride values than fine salts in all the analyzed samples.

The salt fluoridation method may also influence the results. The salt brands fluoridated with the wet method (samples 4, 9, 10, and 11), used KF as the fluorinated compound and had higher fluoride concentrations than those fluoridated with the dry method, using NaF (samples 1, 2, 3, 5, 6, 12). In addition, the salt brands treated with the wet method showed less variability in fluoride concentration than those treated with the dry method.

Two observational studies^15,16 and one clinical trial⁽¹⁸⁾ compared various methods of fluoride distribution at the population level (fluoridated salt and fluoridated water). The studies conducted by Mejia et al. (1976)¹⁷ and Sagheri et al. (2007)¹⁵ found no differences between fluoridation methods, which reinforces the critical role of fluoridated salt in areas where water fluoridation is not possible. Mejía et al. (1976)¹⁷ conducted their study in different Colombian communities, while Sagheri et al. (2007)¹⁵ conducted theirs in Dublin (fluoridated water) and Fribourg (fluoridated salt).

However, Fabruccini et al. (2016)¹⁶ reached different conclusions from the previous studies. They compared the effect of water fluoridation in Porto Alegre, Brazil, to salt fluoridation in Montevideo, Uruguay. The results showed that fluoridated salt provides less protection against dental caries in schoolchildren than fluoridated water. Additionally, children consuming fluoridated salt had a significantly higher DMFT than those exposed to fluoridated water, regardless of the criterion used (WHO or modified WHO). The authors attributed these results to the fact that the salt fluoridation program in Uruguay is limited to household salt and does not include eating facilities and restaurants, which may have reduced its impact on the population.¹⁶

This is the first study to analyze fluoride concentrations in the household salt brands available in Uruguay. This study showed that most Uruguayan fluoridated salt brands had fluoride concentrations lower than those recommended to be effective against dental caries. This may also help understand the results of Fabruccini et al. (2016),¹⁶ who found that the protective effect of fluoridated salt available in Uruguay was lower than that of fluoridated water from Brazil. The variability of fluoride concentration compared to package labels and recommendations suggests the need to improve the regulation of the manufacturing process. The Uruguayan population only has this community method to use fluoride as a public health measure to prevent dental caries. The results show that the population does not benefit from this method because it is exposed to either very low or very high fluoride levels.

Maupomé-Carvantes et al. (1995)⁸ also evaluated fluoride concentration in salt samples in Mexico City and found similar results. Of the 221 salt packages analyzed by the authors, the majority had a fluoride content below the official standard, as 50.2% of the samples had 1 to 50 mgF/kg of fluoride, while the package labels declared 250 mg F/kg.

For salt fluoridation in Uruguay to be effective at the population level and in controlling dental caries in epidemiological indices over the years, it is necessary to improve the salt manufacturing process with greater control during the household salt fluoridation stage. This would help all brands include the recommended fluoride values regardless of the lots manufactured, the type of fluoridation, and the salt size so consumers buy a quality product.

Although the results are based on the analysis of products marketed in 2016, they remain valid because the surveillance mechanisms of the National Salt Fluoridation Program have not changed.

Conclusion

There is significant variability in fluoride concentrations in commercially available brands of fluoridated household salt in Montevideo, Uruguay. Most of the salt brands analyzed do not include the concentration declared on the product label: the real contents range from very low to much higher than expected. The Uruguayan population might not be receiving the expected benefits from this method due to the lack of quality control, so it is necessary to better regulate the manufacturing process of fluoridated household salt.