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1. What are the beneficial effects of fluoride?

Fluoride has been shown to prevent tooth decay. This relationship was discovered in the early part of the 20th century when it was observed that residents of certain areas of the United States developed brown stains on their teeth. These stained teeth, though unsightly, were highly resistant to dental decay. In the 1930s, it was discovered that the prevalence and severity of this type of mottled enamel was directly related to the amount of fluoride in the water.

2. What are the adverse effects of fluoride?

Too much fluoride can cause a disease called "fluorosis." At high levels of exposure, the beneficial effects on tooth structure are negated, and the tooth actually becomes weaker. At still higher exposures, the skeletal system is affected, and chronic exposure can be crippling. Skeletal fluorosis is usually restricted to tropical and subtropical regions, and is frequently exacerbated by factors such as calcium deficiency or malnutrition. Fluorosis is widely prevalent in regions of China, India, the Middle East, and Africa. The high incidence of fluorosis in India is due to the fact that large areas of the country contain water supplies with some of the highest known levels of fluoride in the world.

3. How can I be exposed to fluoride?

Individuals can be exposed to fluoride through a wide variety of foods, drinks, and dental care products. Some foods, such as tea and seafood, have high levels of fluoride. Bottled water or beverages can contain fluoride from public water. Mineral water may also have high levels. In the case of natural waters, the variation in the fluoride content from region to region is dependent upon such factors as the source of water, type of geological formation and the amount of rainfall. (Dry regions tend to have higher fluoride.) Surface waters generally have low fluoride while ground waters typically contain more. Certain dental care products have fluoride added, and your dentist can advise you on which formulation may be beneficial to you or your child.

4. What amount of fluoride is optimal?

The estimated range of safe and beneficial intake of fluorides from all sources for adults is 1.5 to 4.0 milligrams per day (mg/day), and less for children and those with renal disease. In contrast, the daily intake of fluoride in regions where fluorosis is most prevalent varies from 10 to 35 milligrams per day (mg/day) and can be even higher in summer months. The World Health Organization’s guideline value for fluoride in drinking water is 1.5 mg/L. Above 1.5 mg/L, mottling of teeth may occur to an objectionable degree. Concentrations between 3 and 6 mg/L may cause skeletal fluorosis. Continued consumption of water with fluoride levels in excess of 10 mg/L can result in crippling fluorosis.

5. What should I do if my well water contains too much fluoride?

If fluoride is present above 1.5 mg/l you should consult your dentist for advice on developing a plan to optimize fluoride intake. This is especially important if you have young children. The simplest and most reliable plan may be to purchase bottled water. Be sure that the bottled water is low in fluoride, as some products may contain more fluoride than your well water.

Other "point of use" treatment options include installing a reverse osmosis or distillation system. For more information on these systems, see the relevant fact sheets in this series. Regardless of the quality of the equipment purchased, it will not perform satisfactorily unless maintained according to the manufacturer's recommendations.