Generally about half of the fluoride absorbed is deposited in bone. It was found in Finland (1) that the fluoridation of a water supply greatly increased the rate of fluoride accumulation in bone, from a mean of 11 ppm annually in low-fluoride areas to a mean of 44 ppm in the fluoridated people. In a warmer climate with a very ‘soft’ water supply the rate of increase may be more rapid. In a pilot study in Melbourne (2) the annual fluoride concentration increase in alveolar bone in young women was 50 ppm and 103 ppm in those who suffered from overuse injuries – variously described as: cervico-brachial disorder, tenosynovitis and, in Australia, where it is a major problem, repetition strain injury, RSI.

Fluoride does not normally accumulate in the bones of breast-fed infants. They have a negative fluoride balance (3), the excretion of fluoride mobilized from bone exceeding the amount absorbed. This is due to the presence of a physiological ‘barrier’ which protects the infant from fluoride by almost completely preventing the passage of fluoride from the mother’s blood into her breast milk (4). However, in bottle-fed infants in fluoridated areas, there is a positive fluoride balance. They ingest approximately 150 times as much fluoride as their breast-fed counterparts (3), 65 per cent of which is absorbed (5).

Rich and Feist (6) said that fluoride deposited in bone is located mainly in the walls of the canaliculi and of the lacunae containing the osteocytes. They postulated that, when the osteocytes resorb this high-fluoride bone they would be damaged. Krook and Maylin (7) found, in fluorosed cattle, that osteocytes and osteoblasts were ‘target’ cells for fluoride, the most affected being the osteocytes, which were inactivated or killed. In developing teeth, fluoride damaged the ameloblasts, odontoblasts, and the cells of the tooth pulp.

It is likely that, during its normal resorption by osteocytes, some of the fluoride released from the high-fluoride bone will pass through the canaliculi into the bone marrow. As fluoride affects bone and tooth cells: osteocytes, osteoblasts, ameloblasts, odontoblasts, and pulpal cells, it is postulated that fluoride reaching bone marrow will inactivate or kill some of the developing cells of the immune system.

To test the effect of fluoridating public water supplies, Greenburg (8) provided Swiss mice with fluoridated water and made cell counts bimonthly for eight months. He reported: ‘Basket cells (degenerating leucocytes) appeared after the first month; their number subsequently expanded. By the fourth month, cytoplasmic RNA … was often clumped or fragmented; sometimes it totally vanished.’ The leucocytes from control mice were unaffected. He said: ‘These data suggest that fluoride in drinking water may induce leucocytic degeneration accompanied by alterations in the RNA content of the affected cells.’

CONCLUSIONS

Theoretical considerations, supported by some published experimental evidence, suggest that fluoride released during the resorption of high-fluoride bone may produce detrimental effects not only on bone cells but on developing cells of the immune system.

References

1. Arnala I. Bone Fluoride, Histomorphometry and Incidence of Hip Fracture. University of Kuopio, Kuopio, 1983.

2. Smith GE. A simple method for obtaining bone biopsy specimens for fluoride analysis and some preliminary results. New Zealand Medical Journal 98: 454, 1985.

3. Ekstrand J, Hardell LI, Spak CJ. Fluoride balance studies on infants in a 1-ppm-water-fluoride area. Caries Research 18: 87, 1984.

4. Ekstrand J, Boreus LO, de Chateau P. No evidence of transfer of fluoride from plasma to breast milk. British Medical J. 283: 761, 1981.

5. Spak CJ, Ekstrand J, Zylberstein D. Bioavailability of fluoride added to baby formula and milk. Caries Research 16: 249, 1982.

6. Rich C, Feist E. The action of fluoride on bone. p 70 in Fluoride in Medicine (TL Vischer, ed) Hans Huber, Bern, 1970.

7. Krook L, Maylin GA. Industrial fluoride pollution. Cornell Vetinarian 69: Supp. 8, 4, 1979.

8. Greenburg SR. The response of murine leucocytes to extended fluoride exposure. Anatomical Record 196: 232A, 1980.

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