The effects of too little—and too much—Fluoride

Fluoride is a desirable substance: it can prevent or reduce dental decay and strengthen bones, thus preventing bone fractures in older people. Where the fluoride level is naturally low, studies have shown higher levels of both dental caries (tooth decay) and fractures. Because of its positive effect, fluoride is added to water during treatment in some areas with low levels. But you can have too much of a good thing; and in the case of fluoride, water levels above 1.5mg/litre may have long-term undesirable effects (Table 1: see also fact file on fluorosis). Much depends on whether other sources, such as vegetables, also have high levels. The risk of toxic effect rises with the concentration. It only becomes obvious at much higher levels than 1.5mg/l. The natural level can be as high as 95mg/l in some waters, such as in Tanzania where the rocks are rich in fluoride-containing minerals. Severe effects of excess fluoride have recently been reported from the Assam state in India (Box).

 

Table 1. Fluoride effects

 

Level in water Effects
0.8–1.2 mg/l Prevention of tooth decay, strengthening of skeleton
Above 1.5 mg/l Fluorosis: pitting of tooth enamel and deposits in bones
Above about 10 mg/l Crippling skeletal fluorosis

 

 

Box: Too much natural fluoride in India

Nearly 100,000 villagers in the remote Karbi Anglong district in the north-eastern state of Assam were reported to be affected by excessive fluoride levels in groundwater in June 2000. Many people have been crippled for life. The victims suffer from severe anaemia, stiff joints, painful and restricted movement, mottled teeth and kidney failure. The first fluorosis cases were discovered in the middle of 1999 in the Tekelangiun area of Karbi Anglong. Fluoride levels in the area vary from 5-23 mg/L, while the permissible limit in India is 1.2 mg/L. Local authorities launched a scheme for the supply of fluoride-free water and painted polluted tube-wells red: they also put up notice boards warning people not to drink the water from these wells.
(Times of India / UNI, 2 Jun 2000)