Fluoride is the ionic form of the abundant element fluorine. It occurs in soil, rocks, and water, and is naturally present in food and drink. About 99% of the fluoride in the body is bound to calcified tissues (bones and teeth), and the rest is in the blood. Despite its presence in the body, it’s debated whether fluoride is an “essential” mineral, and there are no set dietary guidelines for fluoride.^[1] Fluoride is also found in many toothpastes and in some dietary supplements. While inadequate fluoride intake leads to tooth decay (dental caries), excessive intake can damage tooth enamel and cause other side effects. To prevent tooth decay, fluoridation of community water has been a practice since the 1960s in the United States.^[1] Currently, about 30 Western countries have fluoridation policies, but less than half have active community water fluoridation.^[3]

Fluoride’s claim to fame is its ability to stop and reverse tooth decay: when topically applied to the teeth (e.g., in toothpaste or water), it’s integrated into the structure of the enamel. It simultaneously inhibits demineralization and promotes remineralization of the tooth, as well as blocking the activity of plaque-forming bacteria.^[4] Toothpaste containing 1000 to 1250 ppm of fluoride prevents caries to a greater degree than non-fluoride toothpaste.^[5] Fluoride also plays a role in bone formation and has been used for preventing osteoporosis.^[1]

Excessive intake of fluoride (>5-6 mg/daily) can be toxic, and most commonly presents as dental fluorosis (mottled enamel with white/brown spots and pitting). Higher daily doses (10-25 mg/day) of fluoride can lead to skeletal fluorosis, an accumulation of fluoride in bone, which increases bone density, reduces joint mobility, and can lead to fractures and pain; such high doses can sometimes even lead to cardiac complications. Some evidence suggests that the neurological development of children may be stunted by high fluoride exposure, but more research is needed to be sure. Fluoride toxicity most often occurs due to excessive ingestion of fluoridated dental products and in areas with naturally elevated levels of fluoride in the groundwater (e. g., parts of China and India). In cases of fluoride toxicity, calcium is often used to minimize further absorption of fluoride.^[1]

Fluoride (from drinking water, supplements, tea, or dental products) is absorbed by the small intestine, and about half is excreted via the kidneys. Absorbed fluoride in the blood can bind with apatite in bone and teeth, becoming fluorapatite. Blood and bone concentrations of fluoride are in equilibrium and are impacted by bone remodeling activity and age.^[1] Fluoride in toothpaste and mouthwash works locally in the mouth by getting integrated into the structure of the tooth, supporting remineralization of teeth (by speeding up uptake of minerals like calcium and phosphate from the saliva to make stronger crystals on the outer enamel), resisting demineralization by acidic substances in the mouth, and inhibiting the activity of plaque-forming bacteria.^[6][7] Fluoride can also be professionally applied as a gel or varnish, allowing fluoride to be released when the mouth becomes acidic, thereby providing longer-term protection to the enamel.^[5]