Understanding Optimum Fluoride Intake from Population-Level Evidence

Abstract

Policy on fluoride intake involves balancing caries against dental fluorosis in populations. The origin of this balance lies with Dean's research on fluoride concentration in water supplies, caries, and fluorosis. Dean identified cut points in the Index of Dental Fluorosis of 0.4 and 0.6 as critical. These equate to 1.3 and 1.6 mg fluoride (F)/L. However, 1.0 mg F/L, initially called a permissible level, was adopted for fluoridation programs. McClure, in 1943, derived an "optimum" fluoride intake based on this permissible concentration. It was not until 1944 that Dean referred to this concentration as the "optimal" concentration. These were critical steps that have informed health authorities through to today. Several countries have derived toxicological estimates of an adequate and an upper level of intake of fluoride as an important nutrient. The US Institute of Medicine (IOM) in 1997 estimated an Adequate Intake (AI) of 0.05 mg F/kg bodyweight (bw)/d and a Tolerable Upper Intake Level (UL) of 0.10 mg F/kg bw/d. These have been widely promulgated. However, a conundrum has existed with estimates of actual fluoride intake that exceed the UL without the expected adverse fluorosis effects being observed. Both the AI and UL need review. Fluoride intake at an individual level should be interpreted to inform more nuanced guidelines for individual behavior. An "optimum" intake should be based on community perceptions of caries and fluorosis, while the ultimate test for fluoride intake is monitoring caries and fluorosis in populations.

Guidelines for use of fluorides in Australia: update 2019

“…Eight critical reports were identified (1997-2010); a database search of 977 papers revealed further information from three studies that met the search criteria (GRADE assessment). 20 The critical reports all referred to the Dean studies in US cities during 1936-42 linking dental health and natural fluoride levels in water supplies. An Expert Working Group concluded there were no better data to use as a basis for establishing fluoride NRVs, as contemporary population studies were confounded by fluoridated toothpastes and/or products containing fluoride.…”

“…Two biomarkers were selected for the evidence review for infants and young children; dental caries and dental fluorosis, as measured by the dmf/DMF index and Dean’s index respectively. Eight critical reports were identified (1997–2010); a database search of 977 papers revealed further information from three studies that met the search criteria (GRADE assessment) . The critical reports all referred to the Dean studies in US cities during 1936–42 linking dental health and natural fluoride levels in water supplies.…”

Fluoride in Human Health and Nutrition

“…264 As a result, the appropriateness of current guidance was addressed, however, no firm conclusions were made. [265][266][267]…”

“…272 It is therefore not surprising that the guidelines on the AI of fluoride have been recently questioned 264 and addressed. [265][266][267] Based on the available literature, current recommendations on fluoride intake and the fact that the majority of fluoride benefits can be ascribed to its topical, rather than systemic, effects, it is hard to say whether the current AI is appropriate, i.e. too low or too high.…”

Spatial distribution of groundwater fluoride levels and population at risk for dental caries and dental fluorosis in Sri Lanka

“…Furthermore, studies conducted using naturally fluoridated water supplies showed that at a fluoride concentration of 0.5–1.5 mg/L there was a reduction in caries, with no associated dental fluorosis or only questionable mottling of the teeth if the fluoride concentration exceeded 1 mg/L. However, when the fluoride concentration exceeds 1.5 mg/L in drinking water, it can cause dental mottling and discoloration, commonly known as dental fluorosis. Skeletal deformities have also been reported in known fluoride belts in range of countries following ingestion of 4–10mg/L of fluoride via drinking water.…”