Fluoride - Excess or inadequate intake

Primary reference(s)

NCBI, 2020. PubChem Fluoride Compound Summary for CID 19800730. National Center for Biotechnology Information (NCBI). Accessed 8 October 2020.

WHO, no date. Inadequate or excess fluoride. World Health Organization (WHO). Accessed 8 October 2020.

Additional scientific description

Fluoride can be released into the environment in several ways: (i) natural activities, such as volcanic emissions, weathering of minerals and dissolution, particularly into groundwater; (ii) human activities, such as the production and use of phosphate fertilisers; manufacture and use of hydrofluoric acid and production of aluminium, steel and oil; and (iii) remobilisation of historic sources, such as water flow and sediment movement from aluminium production plants.

It is estimated that caries of the permanent teeth is the most prevalent of all conditions assessed, with 2.4 billion people globally suffering from caries of permanent teeth and 486 million children from caries of primary teeth. Public health actions are needed to provide sufficient fluoride intake in areas where this is lacking, so as to minimise tooth decay. This can be done through drinking-water fluoridation or, when this is not possible, through salt or milk fluoridation or use of dental care products containing fluoride, and by advocating a low-sugar diet (WHO, no date).

Excessive fluoride intake usually occurs through the consumption of groundwater naturally rich in fluoride, particularly in warm climates where water consumption is greater, or where high-fluoride water is used in food preparation or crop irrigation. Such exposure may lead to dental fluorosis or crippling skeletal fluorosis, which is associated with osteosclerosis, calcification of tendons and ligaments, and bone deformities. While the global prevalence of dental and skeletal fluorosis is not entirely clear, it is estimated that excessive fluoride concentrations in drinking water have caused tens of millions of dental and skeletal fluorosis cases worldwide. Although removal of excessive fluoride from drinking water may be difficult and expensive, low-cost solutions that can be applied at a local level do exist (WHO, no date).

The range in intakes producing detrimental or beneficial effects are not far apart (WHO, no date). Public health actions are needed to provide sufficient fluoride intake in areas where this is lacking, so as to minimise tooth decay. This can be done through drinking-water fluoridation or, when this is not possible, through salt or milk fluoridation or use of dental care products containing fluoride. Excessive fluoride intake usually occurs through the consumption of groundwater naturally rich in fluoride, particularly in warm climates where water consumption is greater, or where high-fluoride water is used in food preparation or irrigation of crops such as rice. In these areas, means should be sought to manage intakes by providing drinking-water with a moderate (i.e., safe) fluoride level or using alternative sources of water for drinking, cooking or irrigation. Although removal of excessive fluoride from drinking-water may be difficult and expensive, low-cost solutions that can be applied at a local level do exist. The preparation of food using fluoride-rich coal also contributes to excessive fluoride intake via ingestion and inhalation (WHO, 2019).

Metrics and numeric limits

World Health Organization (WHO) fluoride guideline values (WHO, 2019):

Drinking-water: The guideline value for fluoride in drinking water is 1.5 mg/l, based on increasing risk of dental fluorosis at higher concentrations and that progressively higher levels of fluoride lead to increasing risk of skeletal fluorosis. This value is higher than that recommended for artificial fluoridation of water supplies for prevention of dental caries, which is usually 0.5–1.0 mg/l. The WHO recommends that, in setting a standard, Member States should take into account drinking-water consumption and fluoride intake from other sources.

Air: The guideline value is 1 μg/m3 (developed to prevent effects on livestock and plants, and is also considered sufficiently protective of human health).

Examples of drivers, outcomes and risk management

Two worldwide public health concerns related to fluoride need to be addressed: the need to reduce dental caries and the need to mitigate the effects of excessive fluoride intake. Thus, public health actions are required to provide sufficient fluoride intake where this is lacking, so as to minimise tooth decay, as well as to provide drinking-water with a moderate (i.e., safe) fluoride level in areas where groundwater contains high fluoride levels (WHO, 2019).

To provide guidance on the need to control population exposure to fluoride and establish the balance between caries prevention and protection against adverse effects of fluoride, community health programmes can estimate total exposure by measuring renal fluoride excretion and compare these levels with established optimal levels using methods published by the WHO. However, risk mitigation measures implemented should also take into consideration local contexts and sensitivities (WHO, 2019).

The WHO recommends (WHO, 2019) that the following actions are required to provide adequate fluoride or control excess fluoride:

Adequate fluoride

Reduce the incidence of dental caries by:

• Fluoridating low-fluoride drinking-water where practicable, as well as considering alternatives, such as salt or milk fluoridation.
• Developing effective and affordable fluoridated toothpastes for use in developing countries.
• Promoting optimal oral hygiene, based on the use of effective fluoridated toothpaste; guidance on the amount of fluoridated toothpaste to and exposure to other sources of fluoride in the community.
• Supporting the use of silver diamine fluoride and atraumatic restoration treatment, and other minimally invasive techniques, using glass ionomer cement to stabilise caries lesions.
• Irrespective of fluoride exposure, advocating a low-sugar diet in accordance with the WHO recommendation that free (added) sugars should not exceed 10% of total energy intake by both adults and children (strong recommendation); the WHO further suggests reduction to below 5% of total energy intake (conditional recommendation).

Excess fluoride

• Where practicable, monitor the prevalence of enamel fluorosis using scoring guidance systems such as those developed by the WHO.
• Provide drinking-water with fluoride levels that do not produce adverse health effects, by:
  • seeking alternative water sources in areas with fluoride-rich groundwater, particularly where water consumption is high due to elevated temperatures;
  • defluoridating water for drinking and cooking, where an alternative source is not an option, using methods such as bone
    charcoal adsorption, contact precipitation, coagulation–flocculation/ sedimentation using aluminium sulphate (Nalgonda
    process), activated alumina adsorption and clay taking into account local context. Research the appropriateness of community fluoridation schemes in view of natural fluoride levels in water.
• Monitor fluoride levels in the environment, especially in areas where there is exposure to elevated fluoride levels due to human activities, and determine the overall exposure to fluoride.
• Encourage mothers to breastfeed, even in areas with high fluoride intake because breast milk is optimal for infant health and usually low in fluoride.
• Discourage the use of fluoride-rich coal for cooking purposes.