Fluoride is a trace element.
There does not appear to be a physiological requirement for fluoride and, in the UK, no Reference Nutrient Intake has been set, but a safe and adequate intake, for infants only, is 0.05 mg/kg daily.
Fluoride has a marked affinity for hard tissues, and forms calcium fluorapatite in teeth and bone. It protects against dental caries and may have a role in bone mineralisation. It helps remineralisation of bone in pathological conditions of demineralisation.
Foods high in fluoride include seafoods and tea. Cereals and milk are poorer sources. An important source of fluoride is fluoridated drinking water. In the UK, tea provides 70% of the total intake; if the water is fluoridated, consumption of large volumes of tea can result in fluoride intakes of 4–12 mg daily.
Oral fluoride is rapidly absorbed by passive transport from the gastrointestinal tract; some is absorbed from the stomach, and some from the small intestine.
Fluoride is found principally in bones and teeth.
Elimination is mainly via the urine, with small amounts lost in sweat (especially in warm climates) and bile.
No essential function has been clearly established; low levels of fluoride in drinking water are associated with dental caries.
Fluoride is recommended for the prophylaxis of dental caries in infants and children (see Dose, below).
Evidence for a role of fluoride in osteoporosis and prevention of fracture is conflicting. In one study,1 there was a higher incidence of fractures in an area of Italy with a lower concentration of fluoride in the water than in another area. In another study,2 women with continuous exposure to fluoridated water for 20 years were compared with those with no exposure. In those with exposure, BMD was 2.6% higher at the femoral neck, 2.5% higher at the lumbar spine and 1.9% lower at the distal radius. In addition, the risk of hip fracture was slightly reduced, as was the risk of vertebral fracture. However, there was no difference in the risk of humerus fracture and a non-significant trend towards an increased risk of wrist fracture.
Table 1 Daily doses1 of fluoride (expressed as fluoride ion) in infants and children
|Fluoride content of water||Under 6 months||6 months–3 years||3–6 years||Over 6 years|
|<300 µg||none||250 µg||500 µg||1 mg|
|300–700 µg||none||none||250 µg||500 µg|
- Recommended by the British Dental Association, the British Society of Paediatric Dentistry and the British Association for the Study of Community Dentistry (Br Dent J 1997 ; 182: 6–7).
In an intervention study,3 sodium fluoride (75 mg daily) was no more effective than placebo in retarding progression of spinal osteoporosis. Another study in 202 post-menopausal women4 with vertebral fractures showed that sodium fluoride 75 mg daily was not an effective treatment. Yet another intervention study5 showed that fluoride (as sodium fluoride 50 mg daily or monofluorophosphate 200 mg or 150 mg daily) was no more effective than calcium and vitamin D in preventing new vertebral fractures in women with post-menopausal osteoporosis. A trial comparing etidronate with fluoride6 in the treatment of post-menopausal osteoporosis showed that although fluoride was more effective at increasing lumbar bone mass, there were no differences in fracture incidence.
The British Association for Community Dentistry advises that fluoride is unnecessary for infants under 6 months and that fluoride should not be given in areas where the drinking water contains fluoride levels that exceed 700 µg/L.
Chalky white patches on the surface of the teeth (may occur with recommended doses); yellow-brown staining of teeth, stiffness and aching of bones (with chronic excessive intake). Symptoms of acute overdose include diarrhoea, nausea, gastrointestinal cramp, bloody vomit, black stools, drowsiness, weakness, faintness, shallow breathing, tremors and increased watering of mouth and eyes.
Systemic fluoride supplements should not be prescribed without reference to the fluoride content of the local water supply (information available from the local Water Board). See Table 1 for daily fluoride doses in infants and children.
Fabiani L, Leoni V, Vitali M. Bone-fracture in-cidence rate in two Italian regions with different fluoride concentration levels in drinking water. J Trace Elem Med Biol 1999; 13: 232–237.
Phipps KR, Orwoll ES, Mason JD, Cauley JA. Com-munity water fluoridation, bone mineral density, and fractures: prospective study of effects in older women. BMJ 2000; 321: 860–864.
Kleerekoper M, Peterson EL, Nelson DA, et al. A randomized trial of sodium fluoride as a treatment for osteoporosis. Osteoporosis Int 1991; 1: 155–161.
Riggs BL, Hodgson SF, O’Fallon M, et al. Effect of fluoride treatment on the fracture rate in post-menopausal women with osteoporosis. N Engl J Med 1990; 322: 802–809.
Meunier PJ, Sebert JL, Reginster JY, et al. Fluoride salts are no better at preventing new vertebral fractures than calcium-vitamin D in postmenopausal osteoporosis; the FAVO study. Osteoporosis Int 1998; 8: 4–12.
Guanabens N, Farrerons J, Perez-Edo L, et al. Cycli-cal etidronate versus sodium fluoride in established postmenopausal osteoporosis: a randomized 3 year trial. Bone 2000; 27: 123–128.