FLUORIDES IN HUMAN NUTRITION

 

Fluoride in Human Nutrition

Abstract

The fundamental determinants of oral health are related to the consumption of non-milk sugars and the effective control of plaques in the mouth. Other factors that influence oral health include optimal exposure of fluoride and the appropriate use of good-quality dental care. Although all these factors can be modified at an individual level to promote oral health, they are clearly also influenced by complex socio-political factors which are outside the control of many individuals. Over the past 60 years fluoride has made enormous contributions to declines in dental caries (Murray & Taylor, 1996). This articles is a brief overview of the history of fluoride. It provides a brief summary of the mode of action of fluoride, including safety and methods of its delivery, together with the controversies associated with its use.

History

In 1901, Frederick McKay, a dentist in Colorado, USA, noticed that many patient, who had spent all their lives in the area, had a distinctive strain on their teeth known locally as ‘Colorado stain’.
Puzzled, McKay sought the assistants of a dental researcher, G.V. Black. They found that other communities in the USA had the characteristics. Histological examination of their affected teeth showed that the enamel was imperfectly calcified, but that the decay in the mottled teeth was no higher than in the normal teeth.

McKay suspected that something in the water was producing the brown stain, and more evidence came from Bauxite, a community formed to house workers of a subsidiary of ALCOA (Aluminium Company of America). A local dentist noticed that children in Bauxite had mottled teeth whereas children in nearby Benton did not. McKay investigated the problem but was unable to find a cause for the staining when the water supply was tested. In 1933, Mr H.V. Churchill, Chief chemist for ALCOA, anxious that aluminium would not be the blamed for the mottling, analysed the water and found that the fluoride ion concentration in the waters of the Bauxite was abnormally high (13.7μ/mg). He then tested other communities affected by mottling which had been previously identified by McKay and found that they too had high level of fluoride present in the water supplies.

In 1938, after an extensive survey of all communities affected by mottling in the US by Dr H. Trendley Dean, a public health scientist, summarised the knowledge in relation to tooth mottling and the presence of fluoride in the water. He showed that a level of fluoride ion concentration below 1μg/ml, mottling disappeared or was minimal. Further studies in America showed that, at a fluoride ion concentration of 1µg/ml, there was a reduction in caries, with the associated mottling of the teeth. All these findings had occurred in naturally fluoridated water supplies.

In 1944 Dean and his co-workers began to test the safety of artificially fluoridated water at 1µg/ml, and in 1945 the water supply of Grand Rapids, Michigan, was artificially fluoridated at this level. The town of Muskegon, Michigan, was used as a control (i.e., not fluoridated) and the town Aurora, Illinois, which was naturally fluoridated, was also included in the study for comparative purposes. After 6 years of the study, E.A. Arnold, a co-worker of Dean, reported that the decay experience of children in Grand Rapids had declined by almost half compared to Muskegon and had similar levels to those seen in Aurora. Fluoridation then came to be defined as ‘controlled adjustment of a fluoride compound to a public water supply in order to bring the fluoride ion concentration up to a level which effectively prevents caries’ (Burt & Eklund, 1997).

Recognizing dental caries as a major public health problem and seeking some effective means to control it, the United States Public Health Service in 1945 initiated a study to determine wether the addition of sufficient fluoride to the water supply to raise the natural content to above 1μg/ml would afford the same degree of protection against tooth decay as would a natural fluoride level of 1μ/ml. New Burgh, in the Hudson River in New York, was chosen as the experimental city. The second city was Kingston across the river, with a population of similar economic, racial and
cultural background and a low-fluoride water supply. Careful records were kept of the incidence of tooth decay in both cites. After 10 years, a report showed that children under 10 years of age had received the greatest protection having DMF (decayed, missing and filled permanent teeth) index of 60 to 65% below those of their counterparts in Kingston. Children 12 to 14 year years old who consumed fluoridated water from early childhood but not since birth had a 48% reduction in tooth decay, and 16-year-old who had consumed fluoridated water for an even shorter time had only a 4% reduction. A 15-year report on the same communities showed a similar degree of protection with no degree with no detectable effects. A comparison of 6-year-old children in the 2 communities in 1962 showed that 33.9% of those in Newburgh were caries-free compared with 16.4% in Kingston. These findings showed that the earlier a child is exposed to an available source of fluorine the greater the protection it will provide. The findings have since been confirmed and reconfirmed in fluoridation studies in many other communities in the USA and Canada.

In 1953, the UK Government despatched an expert committee to visit the North America study sites (Report of the United Kingdom Mission, 1953). On the basis of their report, the government established schemes in Anglesey, Watford and Kilmarnock, publishing report after 5 and 11 years (Reports on Public Health and Medical Subjects, 1962 & Department of Health and Social Security,  Sottish Office, Welsh Office and Ministry of Housing Local  Government, 1969). The Kilmarnock study was particularly interesting. The level of the dental caries in 4-year-old children fell sharply after the initiation of fluoridation in 1956 but returned to a base-line value after cessation in 1962. In the control, non-fluoridated community of Ayr, dental caries remained high. During the 1960’s local authorities in Birmingham and Newcastle established new fluoridation schemes and by 1974 around 10% of the UK population were benefitting.

Safety

There have been claims that fluoridation causes cancer, Dawn syndrome and is environmentally unsound. Numerous studies have investigated the safety of fluoridation and found no evidence to support claims of harmful effects (Daly et al, 2002). Any possibility of fluorine toxicity has been thoroughly investigated by the Unites State’s Public Health Service, which has been unable to find any evidence of detrimental effects from addition of fluorine at 1 μg/ml to the drinking water, no matter how large the water consumption. Based on the heath records of 2 million people in artificially fluoridated areas, no evidence exists of increased deposition of fluorine in soft tissues, such as kidneys or heart, no increase in mortality or morbidity rates, no growth depression or abnormalities, no increase in cancer or nephritis, and no increase birth rate of mongoloids, all of which have been claimed by the anti-fluoridation forces (Guthrie, 1983). Claims that fluorine interferes with cell grow and protein synthesis have been discredited by studies showing that cellular reproduction continues in the presence of an amount of fluorine far in excess of the amount that can be bought into circulating fluid by oral intakes of fluorine. Fluorine is toxic but only at levels well above that at which it is added to communal water supplies. Mottled enamel, or dental fluorosis, may occur at fluoride concentration, 2 to 8 µg/ml; osteoporosis at 8 to 20 µg/ml; growth deprivation at 5o or more μg/ml; and fatal poisoning at 2500 times the recommended level. As an added precaution, it is suggested that in the tropical areas, where water intake may be higher, the level of fluoridation should be adjusted downward to 0.5 to 0.7 µg/ml.

Water Fluoridation – A Controversial Issue

In spite of the evidence that the addition of fluorine to the water, to provide fluorine at 1 /μg/ml,  has no adverse effect; and despite the endorsement of fluoridation by every medical and dental group in US, US Public Health Service, and many Asian and European countries [Guthrie], fluoridation is still a controversial issue. The WHO, the British  Medical Association and the British Dental Association (BDA) all endorse the safety and benefit of fluoridation. In 1978 the Strathclyde Regional Council agreed to a major scheme of water fluoridation to cover Greater Glasgow. However, the local opponents took the issue to the High Court in 1983. It made legal history as one of the longest court cases in British history. The presiding judge, Lord Jauncey, found the evidence for the safety of fluoridation to be convincing. But the case for water fluoridation failed on the legal technicality. In essence, the law as it then stood , did not explicitly permit the fluoridation of public water supply. People who did not want to drink fluoridated water would not be able to have it removed from the water supply, thus their freedom to choose would be removed. As a result of this  ruling, the Government introduced the 1985 Water Fluoridation Act, which allows health authorities to consider fluoridation after widespread local publishing and consultation. Recently an amendment to the Water Bill has been tabled by the Government which would place decisions about water fluoridation clearly with health authorities after appropriate consultation. The House of Lords strongly supported the Government proposal and the Bill was proceeded through the House of Commons.

In the USA the anti-fluoridation groups have been so vocal that, in  many cases in which fluoridation has come up for a public referendum, it had been defeated. In 1974 less than 50% of persons on public water systems were receiving fluoridated water; another 6% were on  naturally fluoridated water.  In 1965 Connecticut  became the 1st State  to require  fluoridation of water supply in all cities  with populations over 50,000; by 1967 this extended  to cities  70,000 or more.  By 1969  over 75% of the population of 15 States were drinking fluoridated water. In a few cases  fluoridation had been terminated  after a period of successful use. By 1983 in 32 of the 50 States, mostly in the central and eastern parts of USA, over 15%  the population were on public water supplied with natural or controlled fluoridation; with Illinois ranking highest, 99%, and Colorado the lowest, 2.7% [Guthrie].

Opposing Arguments

Opponents base their objections on ethical and human rights constraints on public medication; and drinking water fluoridated is unethical. However, proponents argue that prominent organization endorse the safety and benefits of fluoridation and that fluorides occur naturally in all drinking water. In Hartlepool, for example, the level of fluoride reaches the optimum for dental health, about 1μg/litre. Fluorine is also found in many foods and drinks, such as fish and tea. Water fluoridation is broadly equivalent to fortification of cereals with vitamin and iron or addition of calcium and other nutrients to flour. On ethics there is no fundamental right to fluoride-free drinking water. In considering public activity, individual preferences should be subsumed by the potential health benefits to the community as a whole, and in particular to children living in poverty (Lennon).

Souses of Fluorides

An adult person supplied with water containing fluoride at 1 µg/ml usually takes in 1.5 mg fluorine daily in addition to 0.25 mg from tea and food (Guthrie). Fish products, especially mackerel, are rich in fluorides (see Table below). There is increasing evidence that fluoride contained in foods is two or three-fold greater than in fresh foods if the water used is fluoridated. Fluoride contents of vegetables grown in areas with water fluoridation is greater than that of those in areas without fluoridation.

Table 1: Fluoride contents of some foods

Food Souses mg/litre
Breast Milk <0-01 mg/litre
Milk-bases infant Formulas 0.05-0.37 mg/liter
Soya-based Infant Formulas 0.17-0.38 mg/litre
Processed Beverages 0.03-6.80 mg/litre
Raw Tea Leaves 400.0 mg/kg
Tea infused with deionised water 0.1-4.2 mg/litre

Canned fish up to 40.0 mg/kg
Dried seafood up to 290 mg/kg
Chicken Products 0.6-10.6 mg/kg
[Souse: Kathy R Phipps (1996) Fluorides: In Present Knowledge in Nutrition 7th Edition: Editors E. E. Ziegler and L J Filer Jr., ILSI Press, Washington DC. PP 329-333.]

According to Phipps, daily fluoride intakes amount to 0.01- 0.29, 0.02-0.25 and 0.02-0.24 mg/body weight in infants up to 6 months old, 12 month old and for children 2 to 3 years old, respectively.

Methods of delivery fluorides

(a) Water fluoridation

The Water Industry Act of 1991 for water fluoridation in the UK permits two compound: hexafluorosilicic acid (H2SiF6) and sodium hexafluorosilicate (Na2SiF6).

Benefits
Life-long residency produces the greatest cario-protective effect, over 20 to 40% reductions in caries over lifetime. Over 250 million people drink fluoridated water world-wide [Daley et al.]. Fifteen percentage of the water in the United Kingdom is fluoridated and compliance not needed. Incidence of caries increases after cessation of fluoridation. Furthermore, the use of these compounds is safe, cost effective, consistent, good-population coverage and low-risk of overdose.

Disadvantage
The main one is the freedom of choice removal from the population. The other is that the method requires complex infrastructure and initial capital outlay, although the annual cost of £1.5/user  is low. [Guthree].

(b) Fluoride Tablets and Drops

Sodium fluoride is the compound of choice. Care should be required to minimise over-dose and fluorosis. There is 40 to 50% reduction in caries experience in adults and children. For children 3 years and over the dosage is 0.5 mg F/day. The method is effective and it offers the freedom of choice. However, compliance and consistency of delivery are needed; and there is also the risk of over-dose.

(c) Fluoride table salt

The use of fluoridated salt is cost-effective and caries-protective effect is as  good as water fluoridation. For adults and children, the dose is 250 µg/g. The advantages include cost-effectiveness, freedom of choice and consistency and regularity of use. Disadvantages are conflict with general health messages regarding salt reduction in salt intake and the prevention of coronary heart disease.

(d) Fluoride Milk

Well absorbed, although calcium diminishes topical effect. It is safe, effective, regular, consistent  and offers freedom of choice. Risk of overdose is small.

(e) Fluoride in fruits juices: Few studies exist to support this.

(f) Topical Fluoride

Examples include aqueous solution of sodium fluoride and stannous fluoride, and low-pH solutions such as the acidulated phosphate-fluoride system. Up to 20-30% reduction in caries can be achieved. Used usually in school-based mouth-rinsing programmes. Fluoride varnishes may be applied directly to the teeth in high concentration when required. Topical application is effective , useful in individuals at high risk for dental caries; it also offers freedom of choice. It needs  personal, time-consuming access to services.

(g) Flouride tooth pastes
This offers a simplest method of delivery. World-wide decline in caries experience is attributed to tooth pastes. Topical concetrations used is 1000-1100 mg flouride per g  tooth paste; a lesser dose for children.  It is easy to use, effective and offers freedom of choice. Toot brushes and toot pastes are expensive; and there are risks of over-dosage.

In 1999 the Uk gorverment announced in Saving Lives: our Healthier Nation (Department of Health 1999) that it was commissioning a systematic review of the evidence relating to the safty and effectiveness of water flouridation. Systematic reviews differ from other types of reviews in tha they adhere to strict scietific design in other to make them more comprehesive, to minimize the chace of bias and so to ensure their reliability. The review was commissioned from the University of York and its conclusions were:
1. Fluorides were associated with a reduction in levels of dental caries.
2. There was a dose-response between the amount of flouride in the water and the levels of fluorosis.
3. No other harmful effects were found.
4. Fluorides were still associated with reductions in caries, even in later years when fluoride tooth paste commonly use.
5. There was limited evidence to support the view that fluoridation redused inequatilies.
6. Ther was a link between fluoride intake and bone disease or cacer, but it did not increase the prevelence of dental fluorosis.

7. Fluorides in drinking water undoutatedly reduces the incidence of dental caries.

Other methods of administering fluorides used as alternatives to fluoridation of public water supplies

Topical Application

This is time-consuming. Work with stannous fluorides solutions has yielded more promising results, the staining of calclcified areas, apparently due to uptake of stanous fluorides ion, is possibe.

Fluoridated Bread, Milk and Sweets
There is little direct evidence that these substancess reduce detal caries, and individual variations in their consuption are probably  greater than in the case of water.

In Switzerland, owing to the lack of a general piped water, other methods providing fluorides supplements have been tried, such as, fluoridated table salt and fluoride-supplemented milk given to children at school and at home. In practice, it is illegal to add aqueous solution to milk.

Mode of action of fluoride
Rendes the enamel less solube in acid. Possesses anti-bacterial and anti-enzyme properties. Calcium and magnesion can reduced the solubility of fluorides, but their effect is negligible with the small concentrations present in natural water. However, warer used for cooking purposes, e.g., vegetables, may boil away, increasing the concentration of fluoriedes proportionately.

A report from the committee appointed by the Royal College of Physicians to review the effects of fluorides on teeth and health comcluded that fluorides in water added, or naturally present at a level 1 mg/litre, over the years of tooth formation, substantially reduced detal caries throughout life. The consuption of water containing about 1 mg/litre of fluoride in a tempertate climate in safe, irrespective of the hardness of water. In comparison with fluoridation, systematic fluoride supplements, such as tablets, drops and fluorine salts, are not as effective on a community basis. Fluoridation does not harm the environment.

Health Benefits of Fluorides

Prevention of dental caries.

Numerous studies have clearly established a causal relationship between fluoride and the prevention of dental caries(Phipps). Technology of the effect of fluoride in reducing caries has been a controversial topic, but a consensus has emerge in recent years about the most important mechanisms. Three mechanisms are proposed. (a)  The  topical effect of a constant infusion of low concentration of fluoride into the oral cavity is to enhance remineralization during  repeated cycles of demineralization and remineralization in the early stages of the carious process.  (b) Fluoride in plaque inhibits glycolysis, the process by which sugar is metabolised by bacteria to produce acid. (c) There is evidence that pre-erupted fluoride exerts some degree of caries inhibition; it acts via incorporation onto the developing enamel hydoxyapatite crystal, thus reducing enamel solubility.

References

1. Murray, J. J; Naylor, M. N. (1996. Fluorides and dental caries. In The prevention of oral diseases. (ed. J. J. Murray) pp. 32-67. Oxford, Oxford University Press.

2. Burt, B A; Eklund/ S. (1997). Community-based strategies for preventing dental caries.  In Community oral Health (ed. C. Pine) pp. 112-125. Oxford, Wright.

3. Department of Health for Scotland. Ministry of Housing and Local Government (1953): The fluoridation of domestic water supplies in North America as a means of controlling dental caries. Report of the United Kingdom Mission, London. HMSO.

4.  Ministry of Scottish of Office, Ministry of Housing and Local Government (1962): The conduct of the fluoridation studies in the United Kingdom and achieved after five years. Report on Public Health and Medical Subjects No. 105, London: HMSO.

5. Department of  Health and  Social Security, Scottish Office, Welsh Office, Ministry of Housing

and Local Government  (1969:  The fluoridisation studies in the United Kingdom and the results  achieved after eleven years.  Report on Public Health and Medical Subjects No. 122.

6. Daly, B.; Watt, R.; Batchelor, P.; Treasurer, E.(2002): Essential Dental Public Health. New York, Oxford.

7. Guthrie, H.A. (1985). Introductory Nutrition, 5th Ed, St Louis, the C.V. Mosoy Company.

8. Cross. D. (2003) Ethics and Science: Time for a critical review of water fluoridation, Biologist 50, 199.

9. Lemon, M.A.  (2003) Water fluoridation: the public health benefits. Biologist 50, 200.

10. Kathy, R. Phipps (1996) Fluoride In  Present Knowledge in Nutrition 7th Ed. Editors  E. E. Ziegler, C. L. J. Filer, Jr, ILSI Press, Washington DC, pp 329-335.

11. NHS Centre for Reviews and Dissemination (2000). A systematic review of public water fluoridation. York, NHS Centre for Review and Dissemination (Report 18).

12. British Dental Association (1969). Fluoridation of water supplies: questions and answers. London: British Dental Association.

13. Sutton, P. R. N. (1960) Fluoridation – Errors and Omissions in Experimental Trials. Melbourne: Melbourne University Press.

14. Royal College of Physicians of London (1976) Fluoride, teeth and health: a report and summary on fluoride and its effect on teeth and health. [Committee on fluoridation of water supplies]. Tunbridge Wells: Pitruan Medical.