Fluorine is a trace (micro) mineral.
    Fluorine is best known for its role as a catalyst for the mineralisation of developing tooth enamel prior to emergence and for its remineralisation of surface enamel.
    The average human male's bones contain 2.6 grams of fluorine.

In humans, the only clear effect of inadequate fluorine intake is an increased risk of dental caries (tooth decay) for individuals of all ages. Epidemiological investigations of patterns of water consumption and the prevalence of dental caries across various U.S. regions with different water fluoride concentrations led to the development of a recommended optimum range of fluoride concentration of 0.7-1.2 mg/liter or parts per million (ppm); the lower concentration was recommended for warmer climates where water consumption is higher, and the higher concentration was recommended for colder climates.

The Adequate Intake (AI) The Food and Nutrition Board (FNB) of the Institute of Medicine updated its recommendations for fluorine intake in 1997. The FNB felt there were inadequate data to set a Recommended Dietary Allowance (RDA); instead, Adequate Intake (AI) levels were set based on estimated intakes (0.05 mg/kg of body weight) that have been shown to reduce the occurrence of dental caries most effectively without causing the unwanted side effect of tooth enamel mottling known as dental fluorosis. See the section below on Safety for a discussion of dental fluorosis.

Intake:

Adequate Intake (AI) for Fluorine
Babies 0-6 months	0.01 mg/day
Babies 7-12 months	0.5 mg/day
Children 1 to 3 years	0.7 mg/day
Children 4 to 8 years	1.0 mg/day
Children 9 to 13 years	2.0 mg/day
Teenagers 14 to 18	3.0 mg/day
Adults men	4.0 mg/day
Adults women	3.0 mg/day
Pregnant women	3.0 mg/day
Breastfeeding	3.0 mg/day

The primary function of fluorine is that it strengthens tooth enamel. Ingestion of fluorine decreases the incidence of dental caries or tooth decay.
    Fluorine also increases the deposition of calcium, which strengthens bones.

The major source of dietary fluorine in the U.S. diet is drinking water. When water is fluoridated, it is adjusted to between 0.7 and 1.2 milligrams (mg) of fluoride per liter, which is 0.7-1.2 ppm. This concentration has been found to decrease the incidence of dental caries while minimizing the risk of dental fluorosis and other adverse effects (see Safety). Approximately 62% of the U.S. population consumes water with sufficient fluorine for the prevention of dental caries.
    The average fluorine intake for adults living in fluoridated communities ranges from 1.4 to 3.4 mg/day. Because well water can vary greatly in its fluorine content, people who consume water from wells should have the fluorine content of their water tested by their local water district or health department. Water fluorine testing may also be warranted in households that use home water treatment systems. While water softeners are not thought to change water fluorine levels, reverse osmosis systems, distillation units, and some water filters have been found to remove significant amounts of fluorine from water. However, Brita-type filters do not remove fluorine.