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3. What are the possible health effects of fluoride, and what is the latest evidence about them?

• 3.1 What is the evidence regarding dental fluorosis?
• 3.2 What is the evidence regarding skeletal fluorosis?
• 3.3 What is the evidence regarding osteosarcoma?
• 3.4 What is the evidence regarding neurological effects?
• 3.5 What is the evidence regarding effects on human reproduction?

3.1 What is the evidence regarding dental fluorosis?

dental fluorosis is produced by absorption of excessive fluoride when teeth are forming. The crucial period for the permanent (second) teeth starts at birth and goes on until the age of 12-14.

Absorbing too much fluoride can impair normal development of enamel in teeth before they erupt, and the effects may not be visible until 4-5 years after exposure. They include white streaks on the enamel surface and, in more severe cases, porous areas of enamel, pitting and discolouration of the tooth surface.

Development of fluorosis depends on the dose, duration and timing of fluoride exposure while tooth enamel is forming. It is not known exactly how fluoride affects mineralization of the enamel. No threshold has been detected for risk of dental fluorosis in children exposed to fluoride which enters the body. However, the EFSA panel considered that an intake of less than 0.1 mg of fluoride per kilogram of body weight, per day, led to no significant incidence of “moderate” fluorosis in permanent teeth.

Fluorosis can occur in areas with fluoridated water, and also in those without. Fluoride supplements and use of fluoridated toothpaste, in large amounts, also increase the risk.

3.2 What is the evidence regarding skeletal fluorosis?

Fluoride can be incorporated into the mineral structure of bones, and in large amounts leads to a weaker bone matrix. Skeletal fluorosis results from long-term exposure to high levels of fluoride, and can have crippling results. It has been found in some parts of India, China and Africa where fluoride intake is exceptionally high. This is due either to fluoride in drinking water reaching unusually high levels or to burning fluoride-rich coal in confined spaces.

In Europe, skeletal fluorosis has only been seen in workers in mineral processing industries. It has not been seen in the general population.

Children under a year old incorporate up to 90 per cent of ingested fluoride into bone, and the percentage slowly decreases to 50 per cent incorporation by the time they are 15. Epidemiological studies have revealed no clear association of bone fracture risk with water fluoridation. There may even be a slightly lower fracture risk at low levels of fluoridation (0.6 to 1.1 mg/L). SCHER concludes that there is not enough data to evaluate the risk of bone fracture at the fluoride levels seen in areas with fluoridated water.

3.3 What is the evidence regarding osteosarcoma?

Fluoride has been subjected to a wide range of tests of mutagenic and carcinogenic effects. There is little evidence of any mutagenic effects, and equivocal evidence of carcinogenic effects in rats.

Epidemiological studies have not produced any strong evidence of carcinogenic effects. Concerns about possible cancer-causing effects of fluoride have focused on bone cancer because fluoride accumulates in bone. However, bone cancer, or osteosarcoma, is rare, making epidemiological studies more difficult to do.

On reviewing the most recent studies, the SCHER concludes that epidemiological work does not indicate a clear link between fluoride in drinking water and any cancers. Nor is there evidence from animal studies to support such a link. Fluoride should therefore be classified as non-carcinogenic.

3.4 What is the evidence regarding neurological effects?

Animal studies show little or no effect of fluoride on brain or behaviour, even at very high doses, hundreds of times above those received by people drinking fluoridated water.

Human studies do not suggest adverse thyroid effects at realistic human exposures to fluoride.

Some studies of developmental effects of human fluoride consumption in China suggested that high fluoride intake was linked with lower mean IQs in schoolchildren. However, these studies were poorly controlled, and the results may be due to other factors affecting these populations, such as iodine or lead intake, diet or other social factors.

The SCHER concludes that there is no clear evidence that fluoride in drinking water at concentrations permitted in the EU may reduce children’s IQ, and that there is no biological basis for thinking that this would occur.

3.5 What is the evidence regarding effects on human reproduction?

Animal studies in this area are of limited quality, but multi-generation studies on mice show no reproductive toxicity of fluoride even at very high doses. There is no new evidence from human studies that fluoride in drinking water influences male or female reproduction. A few human studies have suggested that fluoride might affect reproductive hormones, but they are poorly designed for risk evaluation. SCHER concludes that fluoride in drinking water at concentrations permitted in the EU has no reproductive effects.