Although a lack of fluoride can lead to childhood tooth decay, too much either in the diet or from other sources, such as swallowed toothpaste, tea, and fluoridated tap water, can cause fluorosis with its unsightly symptoms of mottled teeth with pitted enamel. Fluorosis may also cause excess bone formation, resulting in bones that are much denser than normal, but also less flexible, making them prone to fractures. Many health professionals believe that excess fluoride may be linked to forms of cancer.
Fluoride is not considered essential for life, but it does play a role in the maintenance of healthy bones: Fluoride combines with calcium to strengthen them. A deficiency, when associated with low intakes of calcium, may lead to osteoporosis.
Differing levels of fluoride occur naturally in soils and affect the amounts found in crops; most healthy organic vegetables grown in good soil contain fluoride. In many parts of the world, tea is the main source of dietary fluoride, as teal plants readily absorb the mineral from the soil.