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What is fluoride?

Fluoride is a negatively charged ion (anion) of the chemical element fluorine. It naturally appears in water and certain foods; in some countries, it is added to water (water fluoridation) or salt (salt fluoridation). Fluoride is not considered an essential nutrient, but it can help prevent dental caries in children and adults [1].

The chemical symbol for fluoride is F.

Fluoride Functions in the Human Body

Fluoride that is absorbed into the tooth enamel changes some of the mineral hydroxyapatite into fluorapatite, which is more resistant to the acids produced by the mouth bacteria [33]. In children until 8 years of age, fluoride from the blood can be incorporated into the enamel of the primary teeth and of the permanent teeth before they erupt [1]. After age of 8, the fluoride that is absorbed and secreted into the saliva and fluoride from toothpaste stimulate the incorporation of calcium and phosphate into the surface of the tooth enamel of both primary and permanent teeth; small amounts of fluoride are also incorporated into the enamel [33].

Fluoride absorbed into the bones also forms fluorapatite. It is currently not clear if fluoride has any beneficial effect on the human bones [1].

How much fluoride do you need?

Fluoride is not an essential nutrient to human health, but low fluoride intakes have been associated with an increased risk of dental caries [33].

The Institute of Medicine in the U.S. has set the Adequate Intake (AI) for fluoride as the intake that helps to prevent dental caries.

Chart 1. Adequate Intake for Fluoride (mg/day)

0-6 months 0.01 (provided by breastfeeding) [7]
7-12 months 0.5
1-3 years 0.7
4-8 years 1
9-13 years 2
14-18 years 3
Men 18+ 4
Women 18+ (including pregnancy and lactation) 3

Chart 1 source: Linus Pauling Institute [1]

Fluoride Sources


Most foods naturally contain less than 0.3 mg of fluoride per serving [35].

Foods with fluoride image

Picture 1. Foods and beverages with fluoride
(copyright: nutrientsreview.com)


Chart 2. Foods High in Fluoride

FOOD Fluoride (mg)
Non-fluoridated water (US) (1 liter) 0-40, usually <0.3
Tea (1 cup, 237 mL) 0.3-1.5
Fluoridated water (US) (1 liter) 0.7-1.2
Fluoridated salt (5 g) 1
Fluoridated milk (200 mL) 0.5-1
Chicken (3 oz, 85 g) 0.05-0.9
Grape juice (1 cup, 237 mL) 0.05-0.7
Sardines, with bones (3 oz, 85 g) 0.2-0.3
Wine, table (5 oz, 150 mL) 0.2
Fish without bones (3 oz, 85 g) 0.01-0.15

Source: Linus Pauling Institute [1], USDA.gov [35]

Non-Fluoridated Water

In most parts of the United States, non-fluoridated tap water contains less than 0.4 mg fluoride/liter [13], but in certain parts of New Mexico, Nevada, Arizona, California, Utah, and other areas, it may contain more than 1.2 mg/liter, so even more than fluoridated water.

In certain parts of Africa, China, India, Middle East and Mexico, non-fluoridated water may contain more than 10 or even more than 40 mg fluoride/liter, which can, after regular drinking, cause severe dental or skeletal fluorosis.

  • The World Health Organization (WHO) has set the standard maximum fluoride concentration in drinking water to avoid dental fluorosis at 1.5 mg/liter [19].
  • The U.S. Environmental Protection Agency (EPA) has set the Maximum Contaminant Level (MCL) for fluoride upon prevention of crippling skeletal fluorosis at 4 mg/liter [16,17] and the Secondary Maximum Contaminant Level (SMCL) upon prevention of moderate and severe dental fluorosis at 2 mg/liter [27].

Fluoridated Water

In the United States, fluoridated water contains 0.7-1,2 mg fluoride/liter [33]. The U.S. Department of Health and Human Services has recently recommended the optimal concentration in drinking water 0.7 mg/liter in order to reduce the risk of dental fluorosis [37]. Water is also fluoridated in certain parts of Australia, Brazil, Canada, Chile, Colombia, Hong Kong, Ireland, Israel, Malaysia, New Zealand, Singapore, UK and in some other countries, but usually not in the continental Europe [33]. Fluoride in fluoridated water can be in the form of sodium fluoride (NaF), fluorosilicic acid (H2SiF6) or sodium fluorosilicate (Na2SiF6).

Fluoridated water has no specific smell, taste or appearance.

To find out if the drinking water you use is fluoridated or not, you can contact your water supplier. To test the concentration of fluoride in the tap or well water, you can contact the local health authorities or a private laboratory. Commercial kits for testing fluoride amount in water are also available.

Fluoride Removal Systems

In some parts of the U.S., non-fluoridated municipal water may contain up to 4 mg of fluoride/L, and well water may contain even more, so you might want to remove the excessive fluoride to prevent dental and skeletal fluorosis. Fluoride removal systems based on reverse osmosis remove about 80% of fluoride from water [21]. Systems for one faucet or the whole house are available. Excessive fluoride needs to be removed only from drinking and cooking water; fluoride from bathing water does not cross the skin and causes no known harm to the body. Apart from fluoride, reverse osmosis removes some other minerals, such as arsenic, calcium, magnesium, phosphate, nitrate and sulfate from the water, which therefore has a bland taste.

Boiling or freezing does not reduce the amount of fluoride in the water. Water softeners intended to treat hard water, Brita-type filters, activated charcoal units and UV light exposure do not remove fluoride from water [1,33].

Sea water desalination removes most fluoride from water [29].

Bottled and Mineral Water, Soft Drinks and Fruit Juices

Most bottled waters in the United States are low in fluoride (<0.4 mg/L) [1] but certain mineral waters are naturally high in fluoride; the producers are not obligated to reveal the levels of fluoride in these waters. To find out the fluoride concentration in a certain brand of bottled water, you can contact the water producer. Fluoridated bottled waters are also available; fluoride levels in these waters should be revealed on the labels. Soft drinks and fruit juices may be prepared with fluoridated or non-fluoridated water; they often contain more than 0.6 mg fluoride/liter [6,33].

Fluoridated Milk

Fluoridated milk programs for children run in some kindergartens and schools in the areas with non-fluoridated water in UK, Bulgaria, Macedonia, Russia, China, Thailand and Chile [14]. Fluoridated yogurts are available in some schools. One study in China has found an association between drinking fluoridated milk and reduced occurrence of tooth decay in primary teeth [25], but insufficient studies have been made to conclude whether fluoridated milk helps to prevent dental caries or not [3,9].

Fluoridated Salt

In some countries, where water is not fluoridated (Austria, Czech Republic, France, Germany, Hungary, Japan, Slovakia, Spain, Switzerland and certain parts of India, Central and South America and Middle East), fluoride is added to table salt [26]. Usually, there is about 2 mg of fluoride in 10 grams of salt (a usual daily salt intake). There is insufficient evidence about effectiveness of fluoridated salt in prevention of dental caries [9].

Fluoride Absorption and Excretion

Over 80% of the ingested fluoride is absorbed in the stomach and small intestine [11]. About one half of the absorbed fluoride is excreted in the urine [7]; the rest of it is incorporated into the developing teeth (until 8 years of age) and bones. Fluoride is not irreversibly bond to bone, which means that at low intake, fluoride can be released from bone and excreted with the urine [29].

Fluoride Deficiency: Causes, Symptoms

The only negative effect of an inadequate fluoride intake clearly recognized so far is an increased risk of tooth decay in all age groups [1].

Fluoride Products for Topical Use

Fluoridated Toothpaste

Fluoridated toothpastes contain either sodium fluoride or monofluorophosphate. Fluoridated toothpaste reduces the harmful effect of bacteria on the tooth enamel and can even treat a mild tooth decay (white spots) by enhancing enamel remineralization [1]. Some doctors think children under 2 years of age should not use fluoridated toothpaste in order to avoid dental fluorosis [24]. Fluoride from the toothpaste applied to the teeth does not cause dental fluorosis, but when children younger than 8 years swallow it, the absorbed fluoride may be incorporated into their teeth and cause dental fluorosis. Children may ingest up to 1 mg of fluoride with each brushing, so parents should instruct them to use only a pea-sized amount of toothpaste.

  • A pea-sized application (1 gram) of over-the-counter (OTC) fluoridated toothpaste usually contains 1.0-1.5 mg of fluoride (1,000-1,500 ppm). According to the studies performed at The University of Manchester, fluoridated toothpastes are, in average, 24% more effective in preventing tooth decay than non-fluoridated toothpastes [23].
  • Low-fluoride toothpastes that contain less than 1000 ppm fluoride are probably no more effective than non-fluoridated toothpastes [23].
  • A pea-sized application of a prescription (medicinal) toothpaste may contain 1.5-5 mg of fluoride (1,000-5,000 ppm). It is intended for individuals older than 6 years of age with a strong personal or family history of tooth decay.

Fluoride Mouthrinse

One 2009 Cochrane review suggests that a regular use of fluoridated mouthrinse can reduce the risk of caries in children [42].

Fluoride mouth rinses are intended for individuals older than 6 years of age living in the areas with low fluoride levels in tap water who are at high risk of developing tooth decay .

  • Over-the counter (OTC) fluoride mouthrinses for home use contain 0.05% sodium fluoride (NaF) or stannous fluoride (SnF2).
  • Mouthrinses containing 0.2% sodium fluoride are sometimes used in school-based weekly rinsing programs.

Fluoride Gel and Foam

According to one 2015 Cochrane review, there is a moderate evidence that fluoride gel can help prevent caries in the permanent teeth [39].

Fluoride gel or foam containing phosphate, sodium or stannous fluoride at concentrations ranging from around 0.1 to 1% can be applied by a dentist for 1-4 minutes in 3-12 month intervals onto the teeth of children older than 6 years of age at high risk of developing tooth decay. Because of an infrequent use, fluoride gels and foams do not likely cause dental fluorosis [6].

Fluoride Varnish

According to one Cochrane review, there is a moderate quality evidence that applying fluoride varnish in children and adolescents can help prevent tooth decay in primary and permanent teeth [40].

A non-permanent fluoride varnish containing sodium fluoride (2.26%) or difluorsilane (0.1%) may be applied by a dentist directly onto the teeth twice a year. It is intended for children older than 6 years, living in areas with non-fluoridated water, who are at a high risk of developing tooth decay. Varnishes contain only small amount of fluoride, so they do not likely cause dental fluorosis [6].

Oral Fluoride Supplements

Fluoride supplements containing sodium fluoride or monofluorophosphate in the form of chewable tablets, lozenges or fluoride/vitamin preparations may be prescribed to children 6 months to 16 years of age who live in the areas with a low concentration of fluoride in the drinking water and are at high risk of developing dental caries [1]. Children who drink fluoridated water should not receive fluoride supplements, otherwise they may develop dental fluorosis.

Some researchers believe that fluoride supplements do not prevent tooth decay in the primary teeth and they should not be prescribed to children under 6 yeas of age [22].

Fluoride Supplements Benefits

Fluoride supplements can help prevent tooth decay in both children and adults [1,38]. Fluoride can also treat white spots–the initial phase of a tooth decay caused by bacteria–but cannot treat developed cavities [*].

The exact effect of fluoride on the bone strength is not yet clear; treatment of osteoporosis with fluoride supplements has not given satisfying results so far [1].

Preventative Effect of Fluoride On Dental Caries

Fluoride sources that can prevent caries in a high percent of people include [6]:

  • Fluoridated water or water naturally containing 0.5-1.5 mg of fluoride/L
  • Fluoridated toothpaste

Water Fluoridation and Dental Caries – Studies

1. The Child Dental Health Survey, Australia, 2002 [30]:

From 136,000 children 5–15 years of age included in the survey, those living in the areas with more than 0.7 mg of fluoride/liter of drinking water had less dental caries (6.9% in the primary teeth and 12.7% in the permanent teeth), than those living in the areas with less than 0.3 mg of fluoride/liter (65.3% in the primary teeth and 50.6% in the permanent teeth), regardless of whether they lived in metropolitan, rural or remote locations.

2. Effectiveness of Water Fluoridation in Caries Prevention [31]:

In a 2012 systematic review of studies published worldwide from 1990-2010, all 59 studies showed a significant reduction in tooth decay from water fluoridation, with most showing reductions of around 20-60%.

3. Effects of Fluoridated Drinking Water on Dental Caries in Australian Adults [32]:

According to one 2013 review of studies in Australian adults, caries-preventive effects of water fluoridation were at least as great in the adults born before 1960 (before widespread implementation of fluoridation) as in the adults born between 1960 and 1990 (after widespread implementation of fluoridation).

4. Water Fluoridation to Prevent Tooth Decay [41]:

According to the 2015 Cochrane systematic review of prospective studies, initiation of water fluoridation results in 35% decrease of caries in children and 26% decrease in adults [41]. Since majority of the reviewed studies was performed before 1975, that is before widespread use of fluoridated toothpaste, the reviewers cannot conclude what is the exact current effect of water fluoridation on tooth decay [41].

The Effect of Other Fluoride Sources on Teeth

Fluoride gel, varnish and mouthrinse by themselves may be effective in prevention of tooth decay, but do not appear to add a lot of benefit to those who already use fluoridated toothpaste [10].

Fluoride Side Effects

The only proven side effect of water fluoridation is dental fluorosis [34]. Water fluoridation at 1 mg/L is usually not associated with the level of dental fluorosis that would be of public concern [29].

No other side effects, including asthma, allergic reactions or increased risk for birth defects, Alzheimer’s disease or Down syndrome, behavioral changes in children, cancer, including the bone cancer osteosarcoma, heart, kidney, liver or thyroid disease or skeletal fluorosis due to drinking fluoridated water have been confirmed so far [1,4,33,34].

The Institute of Medicine (IMO) in the United States has set the Tolerable Upper Intake Level (UL) for fluoride as the maximum intake that does not result in a moderate dental fluorosis or crippling skeletal fluorosis [1]:

Chart 3. Tolerable Upper Intake Limit for Fluoride (UL) (mg/day)

0-6 months 0.7
7-12 months 0.9
1-3 years 1.3
4-8 years 2.2
9-13 years 10
14-18 years 10
Men 18+ 10
Women 18+ (including pregnancy and lactation) 10

Chart 1 source: Linus Pauling Institute [1]

Dental Fluorosis: Causes, Symptoms

Individuals who were regularly consuming excessive amount of fluoride before the age of 8 may have dental fluorosis with discoloration of the permanent teeth [8,33]. The second and third year of life are the most critical period to develop dental fluorosis [8]. Susceptibility for dental fluorosis is genetically determined [*]. One study has shown that in the areas where water has contained about 1 mg of fluoride/liter, about 10% of population have had a mild dental fluorosis, and where it contained about 2 mg/liter, about 5% have had moderate fluorosis [20]. According to the National Health and Nutrition Examination Survey, 1999-2004, in the US, 23% of people aged 6-49 years had some degree of dental fluorosis [36].

Mild dental fluorosis with a slight whitish or brownish teeth discoloration may result from a long-term drinking of large amounts of water, tea or soft drinks containing as low as 1 mg of fluoride/liter, from adding fluoridated water to infant formula mixes, swallowing fluoridated toothpaste, or excessive use of fluoride supplements [33]. The teeth with mild fluorosis are more resistant to caries than the teeth without fluorosis [33].

Mild dental fluorosis image

Picture 1. Mild dental fluorosis
(source: Wikipedia, CC licence)

Moderate or severe dental fluorosis with an obvious brown discoloration, enamel pitting or loss may result from a long-term drinking of large amounts of water or tea containing as low as 2 mg of fluoride/liter, or regular consuming of jowar (a common Indian cereal). The teeth with severe fluorosis are more susceptible for caries than the teeth without fluorosis [33].

Severe dental fluorosis image

Picture 2. Severe dental fluorosis
(source: Wikipedia, CC licence)

Some pediatricians advise that children up to 8 years of age should not consume more than 0.05 to 0.07 mg of fluoride by kilogram of body weight per day in order to minimize the risk of dental fluorosis [33].

Fluoride Intake by Infants and Dental Fluorosis

An estimated daily fluoride intake by infants from various sources [13]:

  • Human breast milk: 0.01 mg/day
  • Cow’s milk: usually less than from human breast milk [12]
  • Ready-to-use infant formula (in the U.S. and Canada): 0.1-0.25 mg/day
  • Infant formula concentrates prepared with water: 0.1-1 mg/day. Concentrates mixed with fluoridated water or tap water containing more than 0.7 mg fluoride/L used on a regular basis may cause dental fluorosis, so you might want to mix them half-half with bottled, purified, demineralized, deionized or distilled water or water filtered by reverse osmosis, which are all low in fluoride [5].

Fluoride Toxicity

Acute Fluoride Toxicity

Fluoride supplements may be toxic when consumed in doses greater than 5 mg/kg body weight, and fatal in doses over 15 mg/kg body weight; symptoms of acute toxicity include vomiting, diarrhea, excessive tearing and salivation and weakness [1].

Chronic Toxicity: Skeletal Fluorosis

Skeletal fluorosis refers to accumulation of fluoride in bone that results in bone hardening (osteosclerosis) and eventual related symptoms.

In the preclinical stage, there are no symptoms, but an X-ray reveals dense bones [18]. One 1957 survey of radiographs of 170,000 individuals from Oklahoma and Texas, US, living in the areas with drinking water naturally containing 4-8 mg of fluoride/L revealed 23 cases of dense bones (osteosclerosis) [28].

Stage 1 skeletal fluorosis includes osteosclerosis, sporadic pain and joint stiffness [18]. In one case, a 54-year old woman who was consuming water containing 8 mg of fluoride/L for 7 years had osteosclerosis and stiffness in the knees and hips [15].

Stage 2 skeletal fluorosis can present with chronic joint pain, arthritic symptoms, slight calcification of ligaments and muscle tendons, osteosclerosis and eventual osteoporosis of long bones [18,33].

Stage 3 or crippling skeletal fluorosis involves limitation of joint movement, calcification of ligaments, neck and vertebral column, crippling deformities of spine and major joints, muscle wasting, neurological defects or compression of spinal cord and, in children, bone deformities [18]. Crippling skeletal fluorosis may develop in individuals who were consuming more than 10 mg/day for at least 10 years [1,18]. It usually occurs only in people living in the areas with fluoride concentrations of natural drinking water exceeding 10 mg/L (east Africa, India, China, Mexico) [1].

NOTE: There are no known cases of skeletal fluorosis due to consumption of fluoridated water in the U.S. [33].

Crippling skeletal fluorosis picture

Picture 3. Crippling skeletal fluorosis
with bent lower legs
(source: Wikispaces, CC licence)

  1. Fluoride  Linus Pauling Institute
  2. Maguire A et al, 2005, Bioavailability of fluoride in drinking water: a human experimental study  PubMed
  3. Yeung A et al, 2008, Fluoridated milk for preventing dental caries  Cochrane
  4. Water fluoridation and cancer risk  Cancer.org
  5. Overview: Infant Formula and Fluorosis  Centers of Disease Control and Prevention
  6. Recommendations for Using Fluoride to Prevent and Control Dental Caries in the United States  Centers of Disease Control and Prevention
  7. Fluoride  Australian Government, Ministry of Health
  8. Adverse cosmetic effect: enamel fluorosis  National Academic Press
  9. Espelid I, 2009, Caries preventive effect of fluoride in milk, salt and tablets: a literature review  PubMed
  10. One topical fluoride (toothpastes, or mouthrinses, or gels, or varnishes) versus another for preventing dental caries in children and adolescents  Cochrane
  11. Fluoride: Physiology of absorption, metabolism and excretion  National Academic Press
  12. Fluoride adequate intake  National Academic Press
  13. Intake of Fluoride  National Academic Press
  14. 2009, Milk fluoridation for the prevention of dental caries  World Health Organization
  15. Liteplo R et al, 2002, Fluorides  World Health Organization
  16. 2006, Fluoride in Drinking Water: A Scientific Review of EPA’s Standards  The National Academics
  17. Drinking Water Contaminants  United States Environmental Protection Agency
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  19. AbuZeid K et al Impact of fluoride content in drinking water  Cedare.int
  20. Fluoride: Dose-response assessment  National Academic Press
  21. 2007, Fluoride in drinking water  New Hampshire Department of Environmental Services
  22. Ismail AI et al, 2008, Fluoride supplements, dental caries and fluorosis: a systematic review
  23. Studies advise on fluoridated toothpaste use in children  EurekAlert
  24. Fluoride and water  KidsHealth
  25. Bian JY et al, 2003, Effect of fluoridated milk on caries in primary teeth: 21-month results  PubMed
  26. Marthaler TM, 2013, Salt fluoridation and oral health  Acta Medica Academica
  27. Secondary Drinking Water Regulations: Guidance for Nuisance Chemicals  United States Environmental Protection Agency
  28. Adverse functional effect: skeletal fluorosis  National Academic Press
  29. Lennon MA, et al, Fluoride  World Health Organization
  30. Armfield JM et al, 2007, Water fluoridation and children’s dental health; The Child Dental Health Survey, Australia 2002  Malmö University
  31. Rugg-Gunn AJ et al, 2012, Effectiveness of water fluoridation in caries prevention  PubMed
  32. Slade GD et al, 2013, Effects of fluoridated drinking water on dental caries in Australian adults  PubMed
  33. Lewis CW, 2014, Fluoride and Dental Caries Prevention in Children   California Department of Public Health
  34. Campos-Outcalt D et al, 2012, Community water fluoridation: an evidence review  UA Zuckerman College of Public Health and UA College of Medicine-Phoenix
  35. List of foods and beverages high in fluoride  U.S. Department of Agriculture
  36. Beltran Aguilar ED et al, 2010, Prevalence and Severity of Dental Fluorosis in the United States, 1999–2004  Centers of Disease Control and Prevention
  37. 2015, U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries  Public Health Reports
  38. Tubert Jeannin S et al, 2011, Fluoride supplements (tablets, drops, lozenges or chewing gums) for preventing tooth decay in children  Cochrane
  39. Marinho VCC et al, 2015, Fluoride gels for preventing tooth decay in children and adolescents  Cochrane
  40. Marinho VCC et al, 2013, Fluoride varnishes for preventing dental caries in children and adolescents  Cochrane
  41. Iheozor-Ejiofor Z et al, 2015, Water fluoridation to prevent tooth decay  Cochrane
  42. Fluoride mouth rinses for preventing dental caries in children and adolescents  Cochrane

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