Effects of fluoride on thyroid hormone biosynthesis. Studies in a highly sensitive test system

The increasing use of fluoride for prevention of dental caries poses the problem as to whether this halogen has antagonistic properties towards iodine, whereby it could hamper the success of iodine prophylaxis of endemic goitre. Review of the literature shows that some authors have found an inhibition by fluoride of various steps of thyroid hormone biosynthesis in animal experiments. By and large, the inhibition was only slight and it was elicited only with fluoride doses greatly in excess of those recommended for caries prevention. The inhibition was not consistently present and other authors could not confirm it in comparable experiments. There is no convincing evidence that fluoride produces true goitres with epithelial hyperplasia in experimental animals. There are some reports based on casual observations that fluoride is goitrogenic in man. On the other hand, several good studies with adequate exposed and control populations failed to detect any goitrogenic effect of fluoride in man. It is noteworthy in particular that fluoride does not potentiate the consequences of iodine deficiency in populations with a borderline or low iodine intake. Published data failed to support the view that fluoride, in doses recommended for caries prevention, adversely affects the thyroid.

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Fluorine and thyroid gland function: A review of the literature

Bürgi

Siebenhüner

Miloni

1984

Klin Wochenschr

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Opinion of the Scientific Panel on Dietetic Products, Nutrition and Allergies (NDA) on a request from the Commission related to the Tolerable Upper Intake Level of Fluoride

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2005

EFSA Journal

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SUMMARYFluoride is not essential for human growth and development but is beneficial in the prevention of dental caries (tooth decay) when ingested in amounts of about 0.05 mg/kg body weight per day and when applied topically with dental products such as toothpaste. Dental enamel which contains fluoride is less likely to develop caries, because of greater resistance to ingested acids or to acids generated from ingested sugars by the oral bacteria. In addition, fluoride inhibits sugar metabolism by oral bacteria.Fluoride content of the body is not under physiological control. Absorbed fluoride is partly retained in bone and partly excreted, predominantly via the kidney. In infants retention in bone can be as high as 90% of the absorbed amount, whereas in adults retention is 50% or less. Fluoride is also incorporated into dental enamel during tooth formation.Excessive intake of fluoride during enamel maturation before tooth eruption from birth to eight years of age, when enamel formation is complete, can lead to reduced mineral content of enamel and to dental fluorosis of deciduous but predominantly of permanent teeth. The incidence and severity of dental fluorosis is dose-dependent. Mild dental fluorosis is not readily apparent and is associated with increased resistance to caries. The Panel considered moderate dental fluorosis, which is characterised by staining and minute pitting of teeth, to be an adverse effect. On the basis that the prevalence of moderate dental fluorosis of permanent teeth is less than 5% in populations ingesting 0.08-0.12 mg fluoride/kg body weight/day, the Panel considered that the upper level (UL) for fluoride is 0.1 mg fluoride/kg/day in children aged 1-8 years. This is equivalent to 1.5 and 2.5 mg fluoride per day in children aged 1-3 years and 4-8 years, respectively.Fluoride accretion in bone increases bone density but excessive long term intake reduces bone strength and increases risk of fracture and skeletal fluorosis (stiffness of joints, skeletal deformities). Studies with therapeutic oral administration of fluoride in amounts of 0.6 mg/kg body weight/day in postmenopausal women over several years increased the risk for nonvertebral bone fractures significantly. The Panel applied an uncertainty factor of 5 to derive an UL of 0.12 mg/kg body weight/day. This is equivalent to an UL of 5 mg/day in children aged 9-14 years and 7 mg/day for age 15 years and older, including pregnant and lactating women.The UL for fluoride applies to intake from water, beverages, foodstuffs, including fluoridated salt, dental health products and fluoride tablets for caries prevention.Children aged 1-8 years have fluoride intakes from food and water well below the UL provided the fluoride content of their drinking water is not higher than 1.0 mg/L. An increase

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Effects of fluoride on thyroid hormone biosynthesis. Studies in a highly sensitive test system

Cited by 2 publications

References 6 publications

Fluorine and thyroid gland function: A review of the literature

Fluorine and thyroid gland function: A review of the literature

Opinion of the Scientific Panel on Dietetic Products, Nutrition and Allergies (NDA) on a request from the Commission related to the Tolerable Upper Intake Level of Fluoride

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