Fluoride

 

Fluoride is not classed as an essential nutrient but because of its strengthening effect on bones and teeth it is officially considered to be a beneficial element in humans. Fluoride is found in the teeth, bones, thyroid gland and skin. The average body contains about 2.6 g of fluoride.

What it does in the body

Teeth

Fluoride helps in the formation of strong teeth. It protects them from decay by forming compounds with calcium and phosphorus that are stronger and less soluble than other calcium salts. These compounds remain in bone as they are not as easily re-absorbed into circulation to supply calcium needs. Children whose mothers have sufficiently high fluoride intake during pregnancy seem to have fewer cavities than children of mothers whose diets are lacking in fluoride. A baby's first teeth start forming in the first few months of pregnancy and adult teeth in the last few months. Fluoride affects the strength and susceptibility to decay of these teeth.

Bones

Bones seem to be more stable and resistant to degeneration when the diet is adequate in fluoride.

Absorption and metabolism

Excretion of fluoride is mainly through the kidneys.

Deficiency

Low fluoride levels increase the risk of dental caries in children and possibly, of osteoporosis in adults. The incidence of dental caries is higher in areas where the water is not fluoridated.

Sources

Natural sources of fluoride include tea, meat, fish, cereals and fruit. The fluoride content of food depends on the fluoride content of the soil in which the food is grown. Drinking water contains appreciable amounts of fluoride. Some fluoride is absorbed from toothpaste and other oral solutions.

Tea 100g 1.41 mcg

Oatmeal, cooked 100g 10.6 mcg

Rice Krispies 100g 5.9 mcg

Cottage cheese 100g 5.0 mcg

Coffee 100g 5.0 mcg

Noodles 100g 4.6 mcg

Potatoes, mashed 100g 4.3 mcg

Minestrone soup 100g 4.1 mcg

Spinach, cooked 100g 3.7 mcg

Rice, cooked 100g 3.5 mcg

Spaghetti and sauce 100g 3.3 mcg

Cheerios 100g 3.3 mcg

Peas, cooked 100g 3.0 mcg

Toast 100g 2.7 mcg

Sausage 100g 2.5 mcg

Potatoes, boiled 100g 2.5 mcg

Veal 100g 2.3 mcg

Special K 100g 2.1 mcg

Pork, roast 100g 2.1 mcg

Whole wheat bread 100g 1.7 mcg

Ham, baked 100g 1.7 mcg

Greens, raw 100g 1.5 mcg

Chocolate cake 100g 1.3 mcg

Fish, fried 100g 1.0 mcg

Recommended dietary allowances

The adequate intake levels for fluoride were set in 1997. The amount necessary to protect against tooth decay without causing fluorosis is used as a basis for calculating these values.

USA

Men 3.8 mg

Women 3.1 mg

Children 6 to 12 months 0.5 mg

Children 4 to 8 years 1.1 mg

Children 9 to 13 2.0 mg

The daily tolerable upper intake levels for fluoride are:

Men 10 mg

Women 10 mg

Children 6 to 12 months 0.9 mg

Children 4 to 8 years 2.2 mg

Children 9 to 18 10 mg

In most developed countries, fluoride is added to drinking water at a concentration of one part per million. This supplies between 1 and 2 mg fluoride per day.

Supplements

Fluoride supplements may be useful if drinking water is not fluoridated.

Toxic effects of excess intake

Signs of fluoride toxicity include dermatitis and mottling of the teeth as the enamel becomes infiltrated by yellow-brown staining. This is known as enamel fluorosis. If large quantities (20 to 80 mg per day) are taken for long periods skeletal fluorosis may occur. Appetite is depressed, the joints become stiff and painful, the spine, pelvis and limb bones become denser and calcium can be deposited in the muscles and tendons. Fatal poisoning can occur if fluoride is taken in amounts greater than 2500 times the recommended dose.

There is some evidence linking fluoride in water to various types of cancer, although many studies have not found any connection. A study published in 1996 reported on the relationship between fluoride concentration in drinking water and deaths from uterine cancer in Okinawa, Japan. Fluoride was added to the water supplies in the region in the period from 1945 to 1972. The results showed significant links between the time of water fluoridation and deaths from uterine cancer.1

A study published in 1997 in the Journal of the American Dental Association suggest that some commercially available infant foods contain high levels of fluoride which may put babies at risk of fluorosis. Some foods, particularly those containing chicken, are processed in ways which lead to high fluoride concentrations. Adding water to dry baby food also increases fluoride content.2

Therapeutic uses of supplements

Fluoridation of water

Approximately half of the US water supply is fluoridated in an effort to reduce tooth decay. Studies have shown that one part per million of fluoride in drinking water can substantially reduce tooth decay. This effect is particularly noticeable if treatment is started during early childhood when teeth are still forming. However, water fluoridation is a controversial issue and many experts feel that the practice should be discontinued.

Children living in areas were the water is fluoridated are at increased risk of dental fluorosis, in which teeth become mottled with yellow or brown spots. Bottle fed babies are at particular risk if formula is made with fluoridated tap water. Breast milk and ready-to-feed formula contain safe fluoride levels and experts recommend using low fluoride filtered or distilled water with formula. Fluoridation may also increase the risk of dermatitis in sensitive people.

Tooth decay

Fluoride is used in the treatment of dental caries. It is available in the form of fluoride toothpaste, oral fluoride tablets, fluoride gel and mouth rinses with fluoride solutions. It can help reduce sensitivity to external stimuli in gums which have receded to expose dentine. Fluoride supplements discourage the formation of dental caries in children by reducing the susceptibility to erosion of tooth minerals and by preventing the growth of acid-producing bacteria in the mouth.

Osteoporosis

Sodium fluoride, along with calcium, has also been used to treat osteoporosis as it appears to increase bone mass.3 Researchers involved in a 1998 study published in the Annals of Internal Medicine compared the vertebral fracture rates in 200 women over a four-year period. One group was given 20 mg of fluoride and 1000 mg of calcium daily, and the other group received only calcium. The rate of new fractures in the fluoride group was 2.4 per cent compared to 10 per cent in the calcium only group.4

Sustained release fluoride in doses of 23 mg per day appears to be more beneficial than forms which are quickly absorbed from the gut.5 However, a 1996 study done in Argentina suggests that the increases in bone mineral density are not maintained after sodium fluoride therapy is stopped.6

The treatment of osteoporosis with fluoride supplements is controversial as there is the possibility that fluoride bone is not always stronger than normal bone. There may be an increase in the number of hairline fractures in the hips, knees, feet and ankles. In 1983/1984, a study of bone mass and fractures was begun in 827 women aged 20-80 years in three rural Iowa communities selected for the fluoride and calcium content of their community water supplies. Residence in the higher-fluoride community was associated with a significantly lower radial bone mass in premenopausal and postmenopausal women, an increased rate of radial bone mass loss in premenopausal women, and significantly more fractures among postmenopausal women.7 Fluoride therapy may increase the requirement for calcium as more is needed for bone formation.

Fluoride therapy has also been used to prevent rheumatoid arthritis-induced bone loss.8

Other uses

Fluoride may also aid in wound-healing after dental surgery, possibly due to antibacterial action. Fluoride supplements have been used to treat Paget's disease, bone pain, and to stabilize loss of hearing in patients with otosclerosis, a disorder in which deposits in the ear lead to deafness.

Interactions with other nutrients

Fluoride works with calcium, phosphorus, magnesium and vitamin D in the formation of healthy bones and teeth. Magnesium and calcium salts may reduce absorption of fluoride supplements. High calcium intakes may increase fluoride excretion. Caffeine may improve fluoride absorption.

Cautions

Fluoride supplements should be used with caution in patients with joint pain or rheumatic disease. Fluoride supplements may exacerbate gastrointestinal disease and ulcers.

 


1 Tohyama E. Relationship between fluoride concentration in drinking water and mortality rate from uterine cancer in Okinawa prefecture, Japan. Epidemiol, 1996 Dec, 6:4, 184-91

2 Heilman JR; Kiritsy MC; Levy SM; Wefel JS Fluoride concentrations of infant foods. J Am Dent Assoc, 1997 Jul, 128:7, 857-63

3 Murray TM; Ste Marie LG Prevention and management of osteoporosis: consensus statements from the Scientific Advisory Board of the Osteoporosis Society of Canada. 7. Fluoride therapy for osteoporosis. CMAJ, 1996 Oct, 155:7, 949-54

4 Ann Int Med 1998;129:1-8

5 Pak CYC, et. al. Treatment of postmenopausal osteoporosis with slow-release sodium fluoride. Annals of Internal Medicine 1995 September 15;123(6):401-408.

6 Talbot JR; Fischer MM; Farley SM; Libanati C; Farley J; Tabuenca A; Baylink DJ. The increase in spinal bone density that occurs in response to fluoride therapy for osteoporosis is not maintained after the therapy is discontinued. Osteoporos Int, 1996, 6:6, 442-7

7 Sowers MF; Clark MK; Jannausch ML; Wallace RB A prospective study of bone mineral content and fracture in communities with differential fluoride exposure. Am J Epidemiol, 1991 Apr 1, 133:7, 649-60

8 Adachi JD et al. Fluoride therapy in prevention of rheumatoid arthritis induced bone loss. J Rheumatol, 1997 Dec, 24:12, 2308-13