Fluoride is routinely added to drinking water (~1 mg/L) to supposedly improve the teeth of children. However, a growing body of evidence suggests that intakes of fluoride in the amount added to drinking water can be potentially deleterious to the health. The controversy surrounding fluoride is reflected in the growing number of European countries who have ceased fluoridation of drinking water supplies. Concerns over the deleterious effects of fluoride on the central nervous system are well documented from toxicity studies in animals. However, fluoride may also be detrimental to muscular, digestive and skeletal health. Because fluoride is deposited in the skeleton, researchers are interested in the effects of raising fluoride intakes, in an attempt to improve skeletal strength, in those at risk of bone diseases such as osteoporosis. However, evidence suggests that increasing the fluoride content of skeletal tissue results in the formation of abnormal structure.
This abnormal skeletal growth caused by fluoride was reported in a study published in the New England Journal of Medicine in 19901. Researchers randomly assigned 202 postmenopausal women to receive either 75 mg sodium fluoride per day or a placebo, with both groups also receiving 1500 mg of calcium. The number of new fractures in the treatment and control groups was not significantly different, suggesting that fluoride did not improve skeletal strength. Interestingly the number of fractures of the non-vertebral area was actually higher in the treatment group, when compared to the control group. The number of subjects in the treatment group reporting side effects, which included lower extremity pain and gastrointestinal symptoms, known symptoms of fluoride toxicity, was over double the control group. The authors reported that the fluoride group also reported more severe side effects when compared to the placebo group.
As well as causing bone abnormalities, fluoride may negatively affect the structure of teeth. The possible negative effects of water fluoridation were highlighted in a paper published in the journal Caries Research in 19972. Researchers investigated the effects of a number of factors on the dental health of Saudi Arabian boys age 14 years. The boys resided in either Jeddah, Riyadh or Qassim and were exposed to water fluoridation of 0.22 mg/L, 0.78 mg/L or 2.66 mg/L, respectively. Rural communities adjacent to these areas with similar fluoride levels were selected to investigate socioeconomic and nutritional factors affecting dental health. The results showed that 83 % of the boys had at least one enamel defect. Multivariate analysis showed that religion, nutritional status and socioeconomic status were all associated with tooth enamel defects. However, prevalence was highest in the areas with the highest water fluoridation.
These results and others argue against high intakes of fluoride in drinking water. Fluoride is used medicinally to treat both bone and tooth health, but the weight of evidence suggests that fluoride is effective at neither. Fluoride may alter bone and tooth structure by increasing the metabolic turnover of the tissue and as a consequence decrease the structural strength. The absorption of sodium fluoride is very rapid, but is decreased in the presence of calcium (here). High calcium diets have been shown to be inversely associated with the fluoride contents of tissues and this may be the mechanisms by which dietary calcium is beneficial to bone health. This would explain the inconsistent results in trials investigating calcium in osteoporosis prevention. If the benefits of calcium were dependent on fluoride intakes that were not considered, variability would be found between subjects. as has been observed.
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