Fluoridation

1. Introduction

Background

Fluoride is not considered to be essential for human growth and development but it is considered to be beneficial in the prevention of dental caries (tooth decay). As a result, intentional fluoridation of drinking water and the development of fluoride containing oral care products (toothpastes and mouth rinses), foods (fluoridated salts) and supplements (fluoride tablets) have been employed since the early 20th century in several parts of the world as a public health protective measure against tooth decay. Additional exposure to fluoride comes from naturally occurring water (tap and mineral), beverages, food, and to a lesser extent, from other environmental sources.

A body of scientific literature seems to suggest that fluoride intake may be associated with a number of adverse health effects. dental fluorosis and effects on bones (increased fragility and skeletal fluorosis) are two well documented adverse effects of fluoride intake. Systemic effects following prolonged and high exposure to fluoride have also been reported and more recently effects on the thyroid, developing brain and other tissues, and an association with certain types of osteosarcoma (bone cancer) have been reported.

Individual and population exposures to fluoride vary considerably and depend on the high variability in the levels of fluoride found in tap (be it natural or the result of intentional fluoridation of drinking water) and mineral waters, and on individual dietary and oral hygiene habits and practices. The emerging picture from all risk assessments conducted on fluoride is that there exists a narrow margin between the recommended intakes for the prevention of dental caries and the upper limits of exposure. Invariably, all assessments to-date call for continued monitoring of the exposure of humans to fluoride from all sources and an evaluation of new scientific developments on its hazard profile.

Exposure assessment was conducted in the most recent evaluations by the European Food Safety Authority (EFSA), setting upper tolerable intake levels (UL) related to concentration limits for fluoride in natural mineral waters (EFSA 2005) and on calcium fluoride and sodium monofluorophosphate as a source of fluoride (EFSA 2008a, EFSA 2008b), and by the Commission Scientific Committee on Consumer Products (fluoride in dental care products (SCCP 2009)). A similar approach was taken by the United States National Academies of Science in its 2006 review of the United States Environmental Protection Agency’s water standards for fluoride (NRC 2006).

There is a continuous controversy over the benefit of fluoride and, in particular, the practices of intentional water fluoridation in tooth decay prevention. This has led to several countries discontinuing drinking water fluoridation and others expanding it.

Besides questioning the practice of intentional water fluoridation itself as being unnecessary or superfluous in the light of the high exposure to fluoride from other sources, opponents of water fluoridation have pointed to reports showing that the health and environmental risks of the most commonly used fluoridating agents, silicofluorides (e.g. (hydro)fluorosilicic acid, sodium silicofluoride, disodium hexafluorosilicate or hexafluorosilicate or hexafluorosilicic acid), have not been properly assessed. Furthermore, they suggest that the presence of these chemicals in drinking water may cause adverse effects on the health of humans and exert possible exacerbating effects on fluoride disposition in bone.
The debate over water fluoridation has prompted several questions from the European Parliament, from Ireland and the United Kingdom where intentional water fluoridation is still practiced.

In order to obtain updated advice on the issue, the Commission considers it necessary to seek the advice of its Scientific Committee on Health and Environmental Risks (SCHER) who should work in close collaboration with the Scientific Committee on Consumer Products (SCCP), EFSA’s panel on dietetic products, nutrition and allergies (EFSA NDA) and EFSA’s panel on contaminants in the food chain (EFSA CONTAM) who have previously delivered opinions on fluoride.

In the preparation of this opinion, SCHER considered research articles and reviews published in peer-reviewed journals, reports from regulatory agencies and other organizations, as well as all papers submitted by different stakeholders following a public call on the internet for submission of relevant scientific information. The preliminary opinion was published for public consultation for a period of three months; it was discussed at a public hearing, and additional material was received. The scientific information available to the committee was evaluated using the weight-of-evidence approach developed by the EU Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR). In general, the health risks of fluoridation of drinking water have been investigated within different areas such as epidemiologic studies, experimental studies in humans, experimental studies in animals, and cell culture studies. A health risk assessment evaluates the evidence within each of these areas and then weighs together the evidence across the areas to produce a combined assessment. The general rules of the weight-of-evidence approach were used to evaluate the documents on which the opinion is based.

The Scientific Committee on Health and Environmental Risks (SCHER) is requested to:

1. Taking into consideration the SCCP opinion of 20.09.05(SCCP2005) on the safety of fluorine compounds in oral hygiene products, the EFSA NDA opinion of 22.2.05 on the Tolerable Upper Intake Level of Fluoride, and the EFSA CONTAM panel opinion of 22.06.05,

a. Critically review any information that is available in the public domain on the hazard profile and epidemiological evidence of adverse and/or beneficial health effects of fluoride. In particular the Committee should consider evidence that has become available after 2005, but also evidence produced before which was not considered by the SCCP and EFSA panels at the time.

b. Conduct an integrated exposure assessment for fluoride covering all known possible sources (both anthropogenic and natural). In doing so, and in the case of uncertainties or lack of actual exposure data, the SCHER is requested to conduct a sensitivity analysis that includes a range of possible exposure scenarios (e.g. sources, age group), and describe using appropriate quantitative or qualitative means the weight-of-evidence behind each scenario, the uncertainties surrounding each scenario, and the probability of it occurring in real life.

c. On the basis of its answers above, the SCHER is also asked:

c1 – To evaluate the evidence of the role of fluoride in tooth decay prevention and rank the various exposure situations as to their effectiveness in offering a potential tooth decay preventive action.

c2 – To make a pronouncement as to whether there may be reasons for concern arising from the exposure of humans to fluoride and if so identify exposure scenarios that may give rise to particular concern for any population subgroup.

d. Identify any additional investigative work that needs to be done in order to fill data gaps in the hazard profile, the health effects and the exposure assessment of fluoride.

2. Assess the health and environmental risks that may be associated with the use of the most common drinking water fluoridation agents, silicofluorides (e.g. (hydro)fluorosilicic acid, sodium silicofluoride, disodium hexafluorosilicate or hexafluorosilicate or hexafluorosilicic acid), taking into account their hazard profiles, their mode of use in water fluoridation, their physical chemical behaviour when diluted in water, and the possible adverse effects they may have in exacerbating fluoride health effects as reported in some studies.

Scientific Rationale

Fluoride, whether naturally present or intentionally added to water, food, consumer and medical products, is considered beneficial to prevent dental caries (tooth decay). However, the cause of dental caries is multi-factorial, and the causal factors include microorganisms in dental plaque, fermentable carbohydrates (particularly sucrose), time, the individual’s health status and level of oral hygiene, which depends on socioeconomic and educational status.

Fluorides are ubiquitous in air, water and the lithosphere. Fluorine as an element is seventh in the order of frequency of occurrence, accounting for 0.06-0.09% of the earth’s crust and occurs as fluoride, e.g. cryolite (Na3AlF6). Cryolite (used for the production of aluminium) and rock phosphates (used for the production of fertilizers) have fluoride contents up to 54%. Most of this fluoride is insoluble and not biologically available. Availability of fluoride from soil depends on the solubility of the compound, the acidity of the soil and the presence of water. Fluoride has been detected in the ash from the Icelandic volcano eruption, but EFSA has concluded that based upon available information, the potential risk posed by the fluoride for human and animal health through food and feed is not considered to be of concern in the EU.

The concentration of fluoride in ground water in the EU is generally low, but there are large regional differences due to different geological conditions. Surface water usually has lower fluoride contents than ground water (most often below 0.5 mg/L) and sea water (between 1.2 and 1.5 mg/L). There are no systematic data on the concentration of fluoride in natural drinking water in EU Member States, but rudimentary data show large variations between and within countries, e.g. Ireland 0.01-5.8 mg /L, Finland 0.1- 3.0 mg/L, and Germany 0.1-1.1 mg/L.

Bottled natural mineral water is increasingly being used as a major source of water for drinking. A large variation in the level of fluoride has been observed reaching up to 8 mg/L (EFSA 2005). Commission Directive 2003/40/EC of 16th May 2003 establishing the list, concentration limits and labelling requirements for the constituents of natural mineral waters and the conditions for using ozone-enriched air for the treatment of natural mineral waters and spring waters requires that waters which contain more than 1.5 mg/L must be labelled as not suitable for the regular consumption by infants and children under 7 years of age and that by 1st January 2008, natural mineral waters shall, at the time of packaging, comply with the maximum concentration limit set out in Annex I for fluorides of 5 mg/L.

WHO established a guidance value for naturally occurring fluoride in drinking water of 1.5 mg/L based on a consumption of 2 L water/day, and recommended that artificial fluoridation of water supplies should not exceed the optimal fluoride levels of 1.0 mg/L (WHO 2006). In Europe, only Ireland and selected regions in the UK and Spain currently fluoridate drinking water at concentrations ranging from 0.8 to 1.2 mg/L (Mullen 2005). The Council Directive 98/83/EC of 3rd November 1998 (Council Directive 98/83/EC) determined a fluoride level (both natural and as a result of fluoridation) for water intended for human consumption of less than 1.5 mg/L. Recently, the US Department of Health and Human Services recommended a fluoride level in water of 0.7 mg/L “to balance the benefit of preventing tooth decay while limiting any unwanted health effects” (http://www.hhs.gov/news/press/2011pres/01/20110107a.html).The parametric value refers to the residual monomer concentration in the water as calculated according to specifications of the maximum release from the corresponding polymer in contact with the water.

Fluoride intake from food is generally low, except when food is prepared with fluoridated water or salt. However, some teas (e.g. Camellia sinensis) represent a significant source of fluoride intake. Fruit and vegetables, milk and milk products, bread and cereals contain between 0.02-0.29 mg/kg (EFSA 2005). Recently, EFSA (2008a, 2008b) has permitted CaF2 and Na2PO3F as a source of fluoride in food supplements.

Dental products (toothpaste, mouthwashes and gels) contain fluoride at different concentrations up to 1,500 mg/kg (1,500 ppm). The mean annual usage of toothpaste in EU Member States in 2008 was 251 mL (range 130-405 mL) per capita. The extent of systemically available fluoride from toothpaste depends on the percentage of toothpaste swallowed per application.

Fluoride is widely distributed in the atmosphere, originating from the dust of fluoride containing soils, industry and mining activities, and the burning of coal. The fluoride content in the air in non-industrialized areas has been found to be low and is not considered to contribute more than 0.01 mg/day to the total intake.

An upper tolerable intake level (UL) of 0.1 mg/kg BW/day for fluoride has been derived by the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) (EFSA 2005) based on a prevalence of less than 5% of moderate dental fluorosis in children up to the age of 8 years as the critical endpoint, i.e. 1.5 mg/day for children 1-3 years of age, and 2.5 mg/day for children aged 4-8 years. For adults, an UL of 0.12 mg/kg BW/day was based on a risk of bone fracture, which converts on a body weight basis into 7 mg/day for populations aged 15 years and older, and 5 mg/day for children 9-14 years of age.

Tolerable upper intake levels for fluoride have not been established for infants. For infants up to 6 months old, the UK Department of Health (UK DoH 1994) concluded that 0.22 mg F/kg BW/day was safe.

Several pathologies have been linked to high levels of fluoride exposure but are mostly based upon circumstantial evidence. Thus, this opinion will focus on fluorosis of teeth and bones, osteosarcoma, neurotoxicity and reprotoxicity.