Fluoride - Definition, Description, Functions, Benefits, Precautions, Risks

Definition :

Fluoride is a naturally occurring element found in water and food. It is important for the development of strong bones and teeth. 

Purpose :

In addition to occurring naturally in some water, fluoride is added to toothpastes, mouthwashes, and some public water supplies to prevent tooth decay (dental caries). 

Description :

Fluoride is found naturally in seawater and in some drinking water and is present in small amounts in almost all soil, plants, and animals. In water, fluoride dissolves to form a negatively charged ion (F- ). In the body, this ion is absorbed into the bloodstream from the small intestine. It then binds with calcium in bones and teeth. The adult body contains less than one-tenth of one ounce (about 2.5 g) of fluoride. Ninety-five percent of this is found in bones and teeth. 

The importance of fluoride for dental health has been recognized since the 1930s when an association between the fluoride content of drinking water and the prevalence of dental caries was first noted. Acids found in food or released by bacteria that feed on sugar in the mouth cause tooth erosion. These acids eat away at the enamel on the surface of the tooth. Fluoride prevents tooth decay two ways. First, the fluoride in saliva reacts with calcium and phosphate in teeth to repair damage to the tooth’s surface. The new surface formed when the tooth is repaired is stronger than the original enamel and is better able to resist decay. This process is called tooth remineralization. Second, fluoride interferes with the metabolic processes of bacteria in the mouth so that they produce less decay-causing acid. 

Since teeth containing fluoride become stronger, some researchers have suggested that fluoride might also make bones stronger and prevent or delay osteoporosis (age related thinning of the bones). These researchers have generally found that the amount of fluoride that prevents tooth decay does not affect the strength or density of bones. High doses of fluoride are potentially toxic, and very large doses (5–15 times the daily adequate intake) taken over time cause bones to become chalky and brittle. Consequently, researchers have concluded that fluoride supplements are not an appropriate way to prevent or treat osteoporosis. 

Normal fluoride requirements 

Fluoride, in the proper amount, can cut the level of tooth decay in half and substantially reduce the amount of money spent on dental care. Too much fluoride, especially in children, results in a condition called dental fluorosis. The surface of the teeth becomes discolored by chalky white splotches. This is a cosmetic problem only and does not affect the health of the teeth. 

High doses of fluoride can be toxic. Doses between 20–80 mg per day can result in changes in bone that can be crippling, as well as changes in kidney function, and possibly nerve and muscle function. Doses as high as 5–10 g per day can be fatal. 

The United States Institute of Medicine (IOM) of the National Academy of Sciences developed values called Dietary Reference Intakes (DRIs) for many vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97– 98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women. Similar recommendations have been defined elsewhere, e.g., Canada, the United Kingdom, and other European countries. 

Fluoride is not considered an essential nutrient so the IOM has not set RDAs for it. Instead, it has set AI and UL levels for all age groups. The daily AIs and ULs for fluoride for healthy individuals as established by the IOM are:

•  Children birth–6 months: AI 0.01 mg; UL 0.7 mg
•  Children 7–12 months: AI 0.5 mg; UL 0.9 mg
•  Children 1–3 years: RDA 0.7 mg; UL 1.2 mg
•  Children 4–8 years: RDA 1.0 mg; UL 2.2 mg
•  Children 9–13 years: RDA 2.0 mg; UL 10 mg
•  Adolescents 14–18 years: RDA 3.0 mg; UL 10 mg
•  Men age 19 and older: RDA 4.0 mg; UL 10 mg
•  Women age 19 and older: RDA 3.0 mg; UL 10 mg
•  Pregnant women of all ages: 3.0 RDA mg; 10 UL mg
•  Breastfeeding women of all ages: 3.0 RDA mg; 10 mg

Sources of fluoride in diet

The overwhelming source of fluoride for most people is water. In 1945, Grand Rapids, Michigan, was the first city to add fluoride to its public water supply. About two-thirds of Americans now drink fluoridated water. From the 1950s to the 1970s, the issue of fluoridating public water supplies caused heated debate. Some scientists claimed that fluoridation caused birth defects, cancer, and liver disease. Multiple independent, well-designed studies have conclusively demonstrated that this is false. Fluoridation of water at a level that prevents tooth decay does not increase health risks.

Critics of fluoridation still persist. Some reject existing scientific research and claim that fluoridation is ineffective and/or harmful. For others, fluoridation of public water raises moral issues about personal rights versus the government’s rights. The decision to fluoridate drinking water has generally rested with local governments and communities. The recommended rate of fluoride in water is between 0.7 and 1.2 parts per million (ppm). The fluoridation rate is usually at the low end of the range in warm places and at the high end of the range in cold places because people drink more water and thus get more fluoride where it is warm.

A few foods contain significant amounts of fluoride. Since it is found in seawater, ocean fish contain fluoride. It is also concentrated in tea leaves. The approximate fluoride content for some common foods:

•  Tea, 3.5 ounces (100 mL): 0.1–0.6 mg
•  Canned sardines with bones, 3.5 oz (100 g): 0.2–0.4 mg
•  Fish without bones, 3.5 oz (100 g): 0.01–0.17 mg
•  Chicken, 3.5 oz (100 g): 0.06–0.10 mg

Toothpaste and mouthwashes containing fluoride provide significant protection against tooth decay. For children who do not drink fluoridated water, the American Dental Association (ADA) and the American Academy of Pediatrics recommend prescription fluoride supplements from age six months onward. Supplements come as liquids and chewable tablets of varying strengths and are prescribed by a pediatrician, family physician, or dentist. In addition, dentists may apply fluoride pastes or varnishes directly to children’s teeth for additional protection. This is usually done at six-month intervals at regular dental check-ups.

Precautions :

The amount of fluoride occurring naturally in drinking water varies widely depending on location. People who use wells should have them tested for fluoride. People on public water supplies should call their local public health office to determine if their water is fluoridated. People who primarily use bottled water should consult their supplier about whether or not it contains fluoride. Some built-in home water softening systems may remove fluoride from water. Consult the manufacturer or installer for specific information.

Interactions:

Antacids containing aluminum hydroxide and calcium supplements can decrease the absorption of fluoride from the small intestine.

Complications :

No complications are expected for people who get daily doses of fluoride falling between the AI and UL limits. Too little fluoride results in increased tooth decay. 

Too much fluoride can cause illness or death. A 40 lb (18 kg) child would likely begin to show symptoms of fluoride poisoning after consuming about 55 mg of fluoride (3 mg/ kg of body weight), and a dose of 290 mg (16 mg/kg of body weight) would likely be fatal. In 2004, the American Association of Poison Control Centers reported 24,180 incidents involving toothpaste with fluoride, 440 of which required emergency room treatment. About 22,000 of these incidents were with children under age six who ate toothpaste. Symptoms of fluoride poisoning include nausea, vomiting, diarrhea, headaches, muscle spasms, irregular heart beat, coma, and death. Besides toothpaste and mouthwash, fluoride is also found in pesticides, rodent poisons, and chrome polish for automobiles. 

Parental concerns :

Children should be taught not to eat toothpaste, and an adult should supervise tooth brushing for children under age six. Mouthwash containing fluoride and prescription fluoride supplements should be kept out of reach of children. A child who eats fluoridated toothpaste or mouthwash should receive an immediate medical evaluation.